DE2844498A1 - METHOD FOR DEGRADING SLUDGE - Google Patents

Description

L-11234-2-G

UNION CARBIDE CORPORATION 270 Park Avenue, New York, N.Y. 10017, V.St.A.

Process for breaking down sludge (addendum to patent 28 05 054.6)

The invention relates generally to a method for hot degradation of sludge under aerobic and anaerobic conditions. It represents a further development of the process according to patent 28 05 054.6.

With continued industrial growth and population increase the problems associated with wastewater disposal increase accordingly. Although physical, Chemical and biological treatment systems have been developed that allow wastewater to be used effectively to treat and to achieve a drain suitable for discharge into natural receiving waters, almost all walk currently used wastewater treatment systems that include clarification, chemical precipitation, biological filtration and Activated sludge treatment involves converting water pollutants into a concentrated form known as sludge. In particular with the activation process, which is one of the most widespread of the commonly used wastewater treatment processes heard, there is usually a

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ner significant resulting production of volatile Suspended solids (MLVSS), d. that is, the rate of cell synthesis exceeds the rate of cell breakdown. As a result, an increasing builds up Sludge supply on; the activated excess sludge must be removed from the process continuously or periodically.

With the increase in the total amount of wastewater, the one Requires treatment, especially under the influence of aer constantly stricter legal measures to contain it pollution, there is a corresponding increase in the wastewater treatment processes mentioned above generated blowdown volume. As a result, it is highly desirable to have this blowdown to process in such a way that it is easy and economical can be eliminated without further polluting the ecosphere. Although a great effort has been made have been to achieve improvements in sludge treatment technology and 'existing To refine sludge treatment processes there is still a great need for better and more efficient ones Sludge treatment systems.

The fundamental goal of all sludge treatment processes is to reduce sludge solids to economical and effective way to reduce and stabilize. The sludge treatment system should also be an end product

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deliver that for a final elimination without further ado physical or chemical treatment is fully suitable. Conventionally, the sludge is removed usually by bringing the sludge into the sea, by burning, landfilling, or by farming Sludge recovery (spreading of sludge). In many cases, sludge is disposed of on land; this is particularly attractive in view of the minimal long-term environmental impact. An agricultural one Sludge recovery can be highly beneficial in promoting soil renewal. An agricultural one Sludge recovery by spreading sludge on land as the final sludge disposal process however, requires a well pasteurized end product so that the concentration of pathogenic organisms is sufficiently low in the sludge to exclude potential damage to health when removing the sludge.

Traditionally used to treat sludge three different processes are used on a large scale, namely: oxidation ponds, anaerobic degradation and aerobic degradation.

Oxidation ponds are usually in the form of proportionate Shallow excavated earth basins provided, which extend over a land area and sewage hold back before it is finally eliminated. Such-

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day pools allow the biological oxidation of organic Substances through natural or artificially accelerated oxygen transfer from the surrounding air on the water. During the biological oxidation process, the solids in the wastewater are in biodegraded to some extent; they eventually settle at the bottom of the pond where they become anaerobic and can be further stabilized. The pond can be drained periodically to keep the settled Dredge the sludge and in this way the capacity of the pond for further wastewater treatment * restore. The withdrawn sludge is then for example used for land replenishment. In this way, oxidation ponds form a functionally simple system for wastewater and sludge treatment. Using Oxidation ponds are, however, limited in practice because the operation of such ponds involves considerable land areas requires. In addition, there is no significant degradation from this treatment and disposal process the amount of pathogens in the sludge achieved.

Anaerobic degradation is the most widespread Degradation process to stabilize concentrated organic solids, such as those from settling basins, biological filters and activated sludge systems. Conventionally, the excess sludge collected in large, vaulted mining areas where the

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Sludge is fermented anaerobically for 20 to 30 days. the The main reasons that anaerobic sludge degradation is economically acceptable are that large ones Volume of dilute organic sludge can be stabilized, little biological solids (biomass) are produced easily dewatered sludge is obtained and methane gas is produced. It has also been variously claims that the anaerobic degradation results in a pasteurized sludge. Although this pasteurizing ability of anaerobic degradation is in question, anaerobic degradation is widely used in practice because it converts the solid residue into a reasonably stable form that can be used for landfilling purposes, without causing major annoyance. The anaerobic degradation is characteristically in large tanks or Spaces carried out, the content of which is more or less thorough mixed by mechanical means or by circulating compressed degradation gas. One such Mixing quickly increases the sludge stabilization reactions by creating a large active decomposition zone will.

As noted above, anaerobic degradation was generally on the order of 20 with long residence times carried out for up to 30 days without adding heat to the system became. It has already been recognized earlier that elevated temperatures in the mesophilic range of 30 ° C to 40 ° C are a

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Reduction of the necessary length of stay to around 12 Allow up to 20 days. Such a shortened treatment time is due to the fact that the activity rate the organisms responsible for the degradation by the Temperature is strongly influenced and that in the temperature range from 30 ° C to 40 ° C highly active mesophilic microorganisms represent the dominant strain of microbes in the sludge being degraded. The best temperatures for you Mesophilic degradation is in the range of approximately 35 ° C to 38 ° C with minimal residence times of the order of magnitude from 12 to 15 days. Increase temperatures up to 35 C. the degradation rate and can allow shorter residence times, but this at the expense of the operational stability of the System works, while temperatures below 35 C make longer dwell times necessary.

Methane gas is generated during anaerobic degradation; it usually used in combustion heaters, to compensate for heat losses from the anaerobic degradation system operating at elevated temperatures. Seasonal temperature fluctuations however, fluctuations in the suspended matter concentration of the incoming sludge have one significant influence both on the methane gas production and on the amount of heat supply that is required is to keep the mining zone at the desired, elevated working temperature to keep. If therefore increased temperature conditions in the anaerobic degradation zone over the whole

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To be maintained throughout the year represents one
Auxiliary heat source usually constitutes an essential part of the sludge removal facility.

Because the anaerobic degradation rates and the resulting methane gas formation are strongly influenced by the suspended matter concentration of the treated sludge and the temperature prevailing in the degradation zone, it is generally desirable to keep the degradation zone as concentrated as possible
Feed sludge, thereby minimizing heat losses in the effluent stabilized sludge stream discharged from the anaerobic digestion zone while maximizing methane production in the digestion zone. Self
With such precautions, however, it is difficult to maintain elevated temperatures in an economical manner in the anaerobic
Maintain the mining zone, especially during the winter months. In addition, even comparatively small temperature fluctuations in the anaerobic degradation zone can, as is well known, lead to disproportionately strong disruptions to the process and to the content of the degradation zone becoming acidic.

In the anaerobic degradation process, the treated
Sludge solids are exposed in succession to essentially three separate treatment phases, namely first a period of solubilization, then a period of intensive acid production (acidification) and finally a

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28U498

a period of intensive degradation and stabilization (gasification). Each of these process stages is characterized by the production of various intermediate and end products in the mining zone. Under normal working conditions, all three phases occur simultaneously. The main gases generated during the final gasification phase are methane and carbon dioxide, which normally make up more than 95 % of the evolved gas, with 65 to 70 % methane present. The production of methane gas during anaerobic degradation is due to the breakdown of numerous compounds through many interdependent biochemical reactions that occur in an orderly and integrated manner. The complex organic components of the sludge are converted into volatile acids and alcohols by various bacteria known as acid generators without the formation of methane. These products of the acid formation phase are then converted into methane gas by other bacteria known as methane generators.

The optional acidifying agents used in anaerobic digestion Bacteria are robust and highly resistant to process changes in their environment. Methane-producing bacteria, on the other hand, require anaerobic conditions; they are opposed to process changes in theirs Environment extremely sensitive. For these reasons, no oxygen should be present in the anaerobic degradation zone.

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Unintentional introduction of air into the mining zone affects the methane fermentation and leads to Combining the flammable methane gas with oxygen may create a fire or explosion hazard. In addition, methane-forming bacteria are sensitive to process conditions such as fluctuations in the pH value and the presence of detergents, ammonia and sulfides. For these reasons, a temperature stabilization of the anaerobic degradation zone is of particular importance. The methane generators required within the degradation process are particularly sensitive to temperature fluctuations. Such fluctuations reduce their activity and viability j they lead to a relatively excessive Growth in acid formers. This in turn leads to an insufficiently stabilized sludge as well as a Sludge product that, without further treatment, cannot be used for landfilling or disposal in a similar manner suitable is. In addition, these methane generators have a relatively low growth rate, which is what the long ones Requires residence times that are intended for anaerobic degradation even at mesophilic temperatures will. Because of this low growth rate there is a risk that the methane-forming organisms from the breakdown zone be washed out when the sludge solids residence time is lowered below the above-mentioned lower dwell time limit. Because the anaerobic degradation zone is on in this way requires long dwell times in order to

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to ensure that there are sufficient methane generators, and because the amount of sludge flowing to the mining zone in the Is usually quite low, the capacity required for the mining zone is very large. Operation at increased Temperature is therefore difficult and requires a considerable amount of heat to be applied to the degradation zone in connection with tight regulation of the extraction zone temperature. As discussed above, one has in view of such considerations the methane produced by the anaerobic degradation process is used as heating gas for the degradation zone, even in extreme cases Outside temperature fluctuations maintain a constant elevated temperature. Such a use of Methane was found to be effective in minimizing the large amount of heating energy required by the process.

As an alternative to the above methods, biodegradable sludge can be degraded aerobically will. In practice, air was generally used as the oxidizing agent for this purpose. It is known, that the aerobic degradation proceeds more rapidly at elevated temperatures. When the temperature rises from 35 ° C, the population of mesophilic microorganisms decreases while the thermophilic forms increase. Of the Temperature range of 45 ° C to 75 ° C is often called the Thermophilic area denotes where thermophiles predominate and where most of the mesophiles are destroyed. Above in this area the thermophiles decrease. at

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90 ° C the system becomes essentially sterile. Because of the more rapid oxidation of the sludge will be within the same Degradation time means more complete removal of biodegradable volatile particulate matter than at ambient temperature achieved. A more stable residue is obtained which can be disposed of without inconvenience can. It was also found that a thermophilic degradation Effectively reduces or eliminates pathogenic bacteria in the sludge, thereby creating potential health hazards which may otherwise be associated with sludge disposal are avoided.

Are diffusion air systems used to convert the oxygen for the decomposition, the air being passed through the sludge mass in a decomposition tank and on the atmosphere is freely discharged, the loss tends to occur Heat from the sludge to that flowing through the digestion tank Air to take on a considerable size. When aerobic degradation using air occurred, it occurred as a result so far typically to a degradation with mesophilic microorganisms. Air systems are usually not used to perform thermophilic degradation, unless large amounts of heating energy are readily available to keep the temperature of the sludge in to keep the degradation zone in the thermophilic range. This can be the case, for example, when the mining system is located near a power station, the one

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large amount of waste heat generated, so that this thermal energy is practically freely available for use in the mining plant. Air contains only 21 % oxygen and only about 5 to 10 % of the oxygen content of the air is dissolved. As a result, a very large amount of air must be provided to meet the oxygen demand; the sensible heat of the "stale" air and the latent heat required to saturate the stale air with water vapor are significant. As a result of the heat losses described above during decomposition with air, autothermal heat effects are generally low; an uneconomically large amount of external heat is required to keep the temperatures at usable levels.

It is known that the heat losses during aerobic degradation can be reduced considerably if an oxygen-enriched gas is used instead of air. If the oxygen is used effectively, the amount of gas that is fed into the decomposition zone and leaves it is significantly lower than that of air, because nitrogen has been largely or completely removed beforehand. Heat losses due to the noticeable warming up of the gas and the evaporation of water into the gas are reduced. These reductions in heat losses are sufficient so that the autothermal heat alone keeps the temperature at values that are noticeably higher than the outside temperature.

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so that the degradation zone can operate effectively in the thermophilic temperature range with minimal or no supply of external heat to the process. Because the thermophilic stabilization takes place much faster than a mesophilic stabilization, the necessary residence time in the aerobic degradation zone is greatly reduced in thermophilic operation. This in turn allows smaller pools to be used, which further reduces heat losses to the environment. Because of the more rapid oxidation of the sludge, thermophilic aerobic degradation can achieve a usefully strong reduction in the biodegradable volatile suspended matter, for example a reduction of 80 to 90 %, with comparatively short sludge retention times of the order of 3 to 10 days.

Despite the considerable attractiveness, the thermophilic aerobic degradation is compared to an anaerobic degradation with associated several disadvantages. Because the thermophilic aerobic breakdown process is oxidizing in nature, created the process produces a bio-oxidation reaction product gas that contains carbon dioxide and water vapor that does not continue are usable, but are expediently discharged to the atmosphere. In contrast, it produces an anaerobic breakdown Methane gas as a reaction by-product that can be given off for other purposes and that also as Fuel gas can be used to cover the heating energy demand,

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associated with degradation at elevated temperatures is. In addition, the aerobic degradation zone requires a significantly greater amount of energy for mixing and that Bringing gas and sludge into contact, as is the case with the anaerobic digestion system, to mix the contents of the digestion zone necessary is.

The present invention is therefore based on the object to provide an improved method of breaking down sludge.

In the sludge degradation process according to the invention the sludge and containing at least 20% by volume of oxygen Aeration feed gas introduced into a first breakdown zone and mixed there in sufficient quantity and measure for an aerobic decomposition of the sludge, while a total suspended solids concentration (MLSS) des Sludge of at least 20,000 mg / l and a sludge temperature in the range of 35 C to 75 C in the first degradation zone be maintained.

The above aerobic degradation is for a Sludge retention time continued from 4 to 48 hours to maintain the level of the discharged into the first mining zone To partially reduce the amount of biodegradable volatile suspended matter in the sludge. Partially stabilized Sludge is discharged from the first mining zone. The-

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The partially stabilized sludge discharged is then decomposed anaerobically in a covered second decomposition zone, while the sludge temperature there is kept at 25 ° C to 60 ° C for a sludge retention time that is sufficient to keep the sludge's biodegradable, volatile suspended matter content below approximately 40 %. the content of biodegradable volatile suspended matter in the sludge introduced into the first degradation zone and to form methane gas. Further stabilized sludge and the methane gas are discharged from the second extraction zone.

In the present case, the term "sludge" means a solid-liquid mixture understood that has a solid phase and an associated liquid phase, the Solids are at least partially biodegradable, d. H. under the influence of living microorganisms can be disassembled. Biodegradable sludge is generally made biodegradable by its content degradable volatile suspended matter (BVSS) and its content of volatile suspended matter (VSS), the latter parameter being both biodegradable and non-biodegradable includes volatile particulate matter. In the present case, under "content of biodegradable volatile suspended matter" essentially understood the maximum reduction in solids caused by aerobic degradation of the sludge

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.mes can be achieved by treating the sludge with oxygenated Gas at outside temperature, for example 20 C, is ventilated. It is assumed that a maximum Reduction of the solids content is achieved after a period of fumigation of 30 days. Instructions for a such determination can be found in "Water Pollution Control", W. W. Eckenfelder and D. L. Ford, The Pemberton Press, 1970, page 152.By determining the VSS values on the fresh sludge and again after 30 days of fumigation, can be the biodegradable portion of the total existing volatile suspended matter can be calculated as follows:

VSS (fresh) - VSS (30 days) VSS (fresh)

In the present case, the "volatile suspended matter content of a sludge" means the volatile suspended matter content understood as described in experiments 224A and 224B in "Standard Methods for the Examination of Water and Wastewater ", 13th Edition (1971) published by the American Public Health Association, the American Water Works Association, and the Water Pollution Control Federation, Pages 535 to 536 is determined.

The term "stabilized sludge" means sludge with a reduced content of biodegradable volatile substances Suspended solids following a degradation treatment

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and understood on the basis of such treatment. Of the The term "sludge residence time" denotes the mean period of time during which the sludge is in a given Mining zone is present; it is calculated according to the following formula:

where T = sludge retention time (days or hours);

V. = Volume of the treated in the degradation zone d

Sludge (m); and

Q = volumetric flow rate of the sludge fed to the mining zone (m / day or m ³ / h).

The term "aerobic degradation" as used herein means the biological decomposition of sludge solids under the influence of aerobic microorganisms. Such a type of degradation requires that oxygen is dissolved in the liquid phase of the sludge in order to be accessible to microorganisms located in the sludge, namely in sufficient quantity and to a sufficient extent to meet the oxygen requirement for the biological decomposition. With the statement "Mixing of sludge and aeration feed gas in sufficient amount and in sufficient measure for an aerobic degradation of the sludge" an oxygen enrichment of the sludge to an extent which is at least equal to 10 % of the

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empirically determined value of the specific oxygen uptake rate (determined as set out below) or sludge oxygenation which the relative amounts of aeration feed gas and sludge and the aeration rate are sufficient to achieve exploitation of at least 0.03 kg of oxygen per kg of volatile To obtain suspended matter in the spoil introduced into the first mining zone, or any other suitable alternative quantitative definition of sludge / aeration feed gas contact level be understood, which is sufficient to an aerobic degradation in the first degradation zone according to the definition given above for aerobic degradation to ensure.

Expressed by the specific rate of oxygen uptake the oxygen enrichment necessary for aerobic degradation can be achieved of the sludge appropriately according to the following procedure, which is the procedure for determining the sludge oxygen demand on a laboratory scale well suited. The sludge to be treated is passed through a small experimental vessel with sufficient volumetric capacity Flow rate passed through to achieve the predetermined sludge retention time for the aerobic Degradation was selected and that for the aerobic degradation stage according to the present invention in the range from 4 to 48 Hours while the sludge is brought into contact with an aeration gas that is at least 50% by volume

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Contains oxygen. The ventilation is carried out in such a way that that a concentration of dissolved oxygen of at least 2 mg / 1 in the sludge (measured with the help of any appropriate dissolved oxygen sensor of conventional design) is maintained. During aeration, the one in the test vessel becomes Mud held at the selected for the aerobic degradation, predetermined temperature, the present is in the range of 35 ° C to 75 ° C. The aforementioned experimental treatment of the sludge, which is a dilution of the sludge flowing into the test vessel with tap water may require in order to obtain the required level of dissolved oxygen of at least 2 mg / l, is carried out, until steady-state operating behavior is achieved. This can make the test system work over require an extended period of time, for example on the order of 5 to 7 days.

After steady-state operation has been achieved in the test system, the test vessel becomes a measured sample volume taken on sludge and, while it was kept at the temperature previously prevailing in the test vessel is rapidly aerated, for example by intensive stirring, the sludge being brought into contact with aeration gas which contains at least 50% by volume of oxygen to increase the dissolved oxygen content of the aerated sludge increase to about 7.0 mg / l. If the salary is at

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dissolved oxygen of approximately 7.0 mg / L is reached, the aeration of the sample volume of the sludge is stopped. During the subsequent decrease in the dissolved oxygen content in the sludge from the value of approximately 7.0 mg / l at the end of the aeration down to an essentially negligible content of dissolved oxygen, the length of time during which the dissolved oxygen was then measured drops from a value of 6.0 mg / l to 1.5 mg / l. The oxygen uptake rate (OUR) of the sludge sample volume is then calculated by measuring the change of the content of dissolved oxygen during the measurement period, i.e., 4.5 mg / l (- 6.0 mg / l 1.5 mg / l) divided by the time that the dissolved oxygen content needed to drop from 6.0 mg / l to 1.5 mg / l. The specific oxygen uptake rate (SOUR) is calculated from the OUR value obtained by dividing the OUR value, which has the dimension mg / l / time, by the solids concentration of the sludge sample volume in mg / l. The SOUR value calculated in this way has the dimension mg oxygen / time / mg solids.

Based on the above calculation of the SOUR parameter for the sludge to be treated, the amount and degree of oxygen transfer from the oxygen-containing Aeration gas on the sludge in the aerobic breakdown phase of the present procedure. Around

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To cover the respiration requirement (oxygen consumption) of the sludge for aerobic decomposition with regard to a usable stabilization of the sludge in the aerobic decomposition phase before the subsequent anaerobic decomposition phase, the oxygen enrichment of the sludge in the first decomposition zone of the present process should be carried out to an extent that is at least equal to 10 % of the empirically calculated value for the specific oxygen uptake rate. Preferably, the oxygenation of the sludge should occur at a rate which is at least 50 % of the empirically calculated SOUR value.

Alternatively, based on considerations of the amount of oxygen necessary to biodegrade a unit of amount of volatile suspended matter in a given Mixing of sludge, intended for sludges of different properties, is required Sludge and oxygenated aeration feed gas in order to Carrying out aerobic degradation in the first degradation zone in the present process is carried out in such a way that that the relative amounts of aeration feed gas.and Mud as well as the amount or speed of aeration are sufficient to achieve an exploitation, i. H. an uptake by the sludge of at least 0.03 kg of oxygen per kg of volatile suspended matter in the aerobic degradation zone to achieve discharged sludge. The smallest value of this contact ratio is a limit value of the aerospace

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ben assigned to degradation, which is necessary to ensure adequate stabilization of the sludge in the first degradation phase of the present process, before the anaerobic degradation phase then takes place. In practice, it is usually appropriate to carry out the oxygen enrichment of the sludge with relative proportions of sludge and aeration feed gas as well as with an aeration rate which is sufficient to allow 0.1 to 0.35 kg of oxygen per kg of volatile oxygen to be utilized by the sludge To reach suspended solids in the sludge fed to the aerobic degradation zone. Such gas-to-sludge contact ratios generally allow the volatile suspended matter content of the sludge introduced into the first breakdown zone in the first breakdown zone to be reduced in an aerobic manner by 5 to 20%. In general, the volatile suspended matter content of the sludge flowing into the aerobic decomposition zone is suitably reduced there by at least 5% in order to produce a sufficiently partially stabilized sludge for the transfer to the subsequent anaerobic decomposition phase. Such a minimum value of the partial stabilization is particularly desirable in order to buffer the anaerobic decomposition phase sufficiently against process disturbances which result from changes in the type of sludge which is introduced into the overall process system. On the other hand, the reduction in the volatile particulate matter is brought into the

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aerobic degradation zone of incoming feed sludge in the course
the treatment taking place in this zone on one
Maintained value of about 20 % or less in order to take full advantage of the synergistic benefits of the present process. These advantages are discussed in more detail below. They include an unexpectedly high total production of methane gas in the anaerobic second breakdown phase compared to a conventional anaerobic breakdown process. In view of the above considerations, mixing
of aeration feed gas and sludge in the first degradation zone are preferably carried out with such relative amounts of aeration feed gas and sludge and such a ventilation rate that a utilization by the sludge of 0.15 to 0.25 kg of oxygen per kg of volatile matter in the first. Degradation zone introduced sludge is achieved.

In the present case, the term "anaerobic degradation" is used
understood biodegradation of sludge solids that occurs in the absence of free oxygen.

The invention is based on the surprising finding that an aerobic degradation zone operating in the thermophilic temperature range or close to this temperature range can be integrated with an anaerobic degradation zone located downstream in order to allow partial degradation of the sludge
to care in each of the successive zones, and that

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such integration leads to improvements in the process that go beyond those that are addressed Hand of considerations regarding the relevant degradation phases of the treatment process alone would be expected.

So far, for numerous reasons, no attempts have been made to aerobic and anaerobic processes at elevated temperatures Combine degradation of sludge in the presently proposed manner. First is the one with the anaerobic degradation process associated space requirements, as discussed above, extremely large, and it turned out to be necessary to use large amounts of methane to be generated as heating gas in order to ensure economical operation of the voluminous mining tanks. The combination an anaerobic degradation zone with an aerobic degradation stage therefore appears due to considerations regarding of the total tank capacity requirement for the combined Process as undesirable; one would expect the tank space required to be larger than for any of the degradation processes is alone. Such a combination seems to be common to each of the aerobic and anaerobic degradation processes only to double assigned functions with increased system expenditure without increasing the efficiency treatment is to be expected.

The combination of an anaerobic degradation zone with an aerobic degradation stage also appears undesirable because

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take is that the anaerobic degradation stage is unable is, within the combined system, only for to ensure a partial degradation of the sludge with sludge retention times that are below the long retention times that are characteristic of conventional anaerobic, stand-alone degradation zones. As discussed above, the anaerobic degradation stage long residence times required for effective methane production and sludge stabilization to care. Would the anaerobic residence time in a combined aerobic / anaerobic degradation process be below the Normal value for a full treatment lowered in order to ensure only a partial degradation within the anaerobic stage, one would cause an excessive exhaustion of the methane-forming agents in the short dwell time of the anaerobic stage expect losses of these slowly growing species in the runoff of the mining zone, so that under the combined A usable sludge stabilization is not to be expected in the process.

Besides the above reasons, the combined aerobic / anaerobic degradation system appears in view of the Operating stability is disadvantageous because both the aerobic and the anaerobic degradation stage alone require a tight operating temperature control, if at elevated temperature values is worked, so that a coupling of the two processes concerned apparently an even closer temperature control would make necessary and with possible

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increased adverse effects due to temperature instabilities and fluctuations are to be expected.

After all, you'd be doing a combined aerobic / anaerobic Abbat system drawbacks due to the consideration that there may be residual dissolved oxygen from the upstream aerobic stage to the downstream anaerobic part of the process. As stated above, there are existing in the anaerobic degradation zone Methane-producing bacteria are strictly anaerobic and extremely sensitive to changes in their environment. It it is known that any significant introduction of oxygen into the anaerobic degradation zone stabilizes the sludge adversely affected by methane formation and that there is a risk of oxygen from the liquid in the methane-containing gas phase passes and enters the degradation zone combustible gas mixture is formed.

Contrary to the behavior to be expected described above, it was surprisingly found that the use a thermophilic or near thermophilic aerobic Zone of degradation upstream of one with a mesophilic or anaerobic degradation zone working at a thermophilic temperature and the operation of these zones according to the process of present invention not just a workable one and economical sludge treatment system, but results in a degradation system that, due to synergistic

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shear effects between the aerobic and the anaerobic degradation part of the present process has decisive advantages compared to known processes. For example, the method according to the invention is able to ensure a thermal working stability within the entire sludge degradation system, which cannot be achieved in each of the individual degradation stages alone. Furthermore, the integrated degradation process of the invention provides a highly stabilized sludge, although the residence time within the overall process is significantly reduced from that which would be expected if the residence time requirements of each of the separate sub-degradation stages were taken into account together. Particularly surprising is the finding that the anaerobic degradation zone of this process is able to operate with sludge retention times which are considerably below those required for a full stabilization treatment of the sludge in conventional, stand-alone anaerobic degradation zones, and that such an operation is achieved without reducing the efficiency of the treatment , as would be expected. As an example of residence times suitable for the present process, it should be mentioned that a test plant designed for the present process worked satisfactorily with a sludge residence time in the first aerobic stage of 24 to 48 hours and a residence time in the anaerobic second stage of only 4 to 5 days. The previous

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The advantages mentioned are realized in connection with a substantial reduction in the capacity of the digestion zones compared to a conventional anaerobic digestion system, while an unexpectedly large part of the methane production capacity of the conventional anaerobic digestion device alone is retained, as will be shown in detail below. For example, the plant according to the invention can operate with only about 60% of the capacity that must be provided in a known anaerobic digestion zone, but have approximately 75 % of the methane production capacity of the known zone. The present process results in the production of a much larger amount of methane than is required for heating purposes within the process, so that a much larger amount of exhaust gas with a high methane content can be released from the sludge digestion plant for other purposes than is the case with the known anaerobic digestion system of FIG Case is. Finally, it was found that in the present process, oxygen is not transferred to any significant extent from the first decomposition zone into the gas phase of the second decomposition zone.

The reasons. For the unexpected benefits of the present Procedures are not fully clarified. It is likely, however, that the lack of a significant transition of oxygen from the first to the second degradation zone on the unexpectedly high rate of oxygen uptake in

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the first mining zone is due to each Dissolved oxygen content of the sludge passed from the first into the second degradation zone rapidly and thoroughly is degraded before dissolved oxygen enters the second degradation zone to a significant extent Gas phase can pass. The surprisingly short residence times of the present method, especially in the anaerobic degradation stage, together with the thermal stability of the process and the surprisingly high methane production capacity the anaerobic stage is the result of chemical or biological acclimatization of the Sludge and microorganisms in the aerobic degradation zone be necessary for improving the efficiency of the subsequent anaerobic treatment stage. Regardless of this, no commitment to a specific theoretical one is intended Explanation of this operating behavior. Only the method steps and features disclosed in the present case are essential.

The invention is illustrated below with reference to preferred ones Embodiments explained in more detail. In the accompanying drawings show:

Fig. 1 is a flow diagram of a degradation process according to an embodiment of the invention, with heat from the effluent streams of both the first and the second

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The mining zone is reclaimed,

Fig. 2 is a flow diagram of a modified embodiment of the invention, whereby from a covered first mining zone discharged, oxygen-depleted decomposition gas for the post-oxygenation treatment exploited by water containing BOD will,

3 shows a flow diagram of a further embodiment of the method according to the invention the sludge from the primary and secondary wastewater treatment stages to the sludge degradation zones is forwarded,

4 shows a graphic representation of the temperature of the entering the first degradation zone Sludge that is necessary to maintain a working temperature of 5O C in the first extraction zone plotted as a function of total suspended solids concentration (MLSS) of the sludge flowing into the first mining zone, and

Fig. 5. a flow sheet of a further embodiment of the invention in which a smaller

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Part of the sludge flowing into the process system is diverted to the second degradation zone will.

Fig. 1 shows a flow diagram of a first embodiment of the present process, which is suitable for a sludge treatment with a first thermophilic or near thermophilic aerobic degradation stage and subsequent mesophilic anaerobic degradation. Mud, for example from a primary settling basin, the clarification basin of a wastewater treatment plant that works according to the activated sludge process, a trickle filter or another sludge-generating system occurs via a line 8 and is successively heated in heat exchangers 22 and 15, for example to a temperature of 3O C to 35 ° C before it is introduced into the first mining zone 1O, the temperature in the zone in the range of 35 ° C to 75 ° C and preferably to be kept in the thermophilic range of 45 ° C to 75 ° C. The outside temperature showing sludge in the Line 8 is first heated in the heat exchanger 22 by the sludge in indirect heat exchange with the im Further stabilized sludge passed through countercurrent is brought to a second covered degradation zone 20 via a line 24 leaves. In this way, heat is recovered from the further stabilized sludge. Of the cooled, stabilized sludge obtained leaves the heat exchanger 22 and is removed from the system via a line

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device 25 for final disposal or other use. The further stabilized sludge entering the heat exchanger 22 via the line 24 can expediently have a temperature of 35 ° C. to 40 ° C., so that the inflowing sludge, which leaves the heat exchanger via a line 9, is at a temperature of 28 ° C. to 30 ° C is heated. Via line 9 flowing, partially heated slurry is further heated in heat exchanger 15 to a temperature of 3O ⁰ C to 35 C by being brought in countercurrent flow in indirect heat exchange with the partially stabilized sludge that from the first reduction zone 10 via a line 14 is discharged and reaches the second degradation zone 20 from the heat exchanger via a line 16.

As an alternative to the heat exchange described above with sludge product streams from the relevant mining zones can the inflowing sludge before it is introduced into the first degradation zone through indirect heat exchange an appropriate, externally supplied heating medium, for example steam or hot water, are heated, although a heat recovery from the warm mining zone product streams is preferred, as in this way the heat is effectively used within the process and the The heating energy requirement of the process is minimized. Although the heating of the incoming sludge before discharge in the first mining zone no essential part of the

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present process, it may be desirable in practice in order to maximize the thermal efficiency of the process taking place at elevated temperature. Whether such heating of the sludge is desired depends, as discussed in more detail below, on the solids content of the inflowing sludge, the sludge retention time in the aerobic degradation zone and other process parameters away.

The further heated sludge, which leaves the heat exchanger 15 via a line 11, is in the first degradation zone 1O introduced together with aeration feed gas from line 17, the sludge and aeration gas being the Form process fluids for the first stage of degradation. The aeration feed gas in line 17 contains at least 20, expediently at least 50 and preferably at least 8O vol.% oxygen in order for an appropriate high mass transfer driving force and oxygen dissolution rate in the mud at the high mud temperatures in the first degradation zone that is present are provided. Line 17 is to a source (not shown) of an oxygen-containing vent feed gas connected. This source can be, for example, a device for supplying compressed air, or when the aeration feed gas has a high oxygen content, as preferred, to provide a cryogenic oxygen system, a storage container or one with an adiabatic

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see pressure cycle adsorption air separation plant act, as it is often provided in the relevant technology, to be oxygenated Provide gas. As illustrated, the oxygen-containing Ventilation feed gas in line 17 can also be heated by means of a heating device 19 in order to do so to contribute that the temperature in the mining zone 10 is kept at the desired value. Generally can be present Air or other low aeration feed gas Oxygen content, i.e. 20 to 50% by volume oxygen, can be used when autothermal heating of the sludge in the aerobic degradation zone is not necessary to maintain the temperature of the sludge there in the required Maintain range of 35 ° C to 75 ° C. This ■ is the case, for example, when heating the A large source of externally supplied thermal energy is available in the sludge to maintain the necessary high temperature in the aerobic degradation zone. At. Air (or other low aeration feed gas Oxygen content), the heat losses are usually very large so that a vent feed gas with an oxygen content of at least 5O and expediently at least 80% by volume is preferably used to produce an autothermal Promote sludge heating in the aerobic breakdown zone and minimize the amount of oxygen depleted breakdown gas, which goes out of the degradation zone and which otherwise carries heat energy out of the process system. aside from that

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becomes a high oxygen aeration feed gas, i.e. with at least 50% by volume of oxygen, preferably by the amount of oxygen-mass transfer from the aeration feed gas to increase the sludge during the aerobic degradation and thereby a more intensive aerobic degradation effect than can be achieved with an aeration feed gas of low oxygen content can. Regardless of whether in the aerobic degradation zone of the present process with an aeration feed gas of high or low oxygen content (according to the definition above), it is usually It is expedient to provide the aerobic degradation zone with a cover in order to protect one lying above the sludge in this zone To form gas space from which the outgoing, oxygen-depleted degradation gas can be discharged. One Such training allows a controlled removal of exhaust gas, for example by means of a small, through the Cover extending vent line that connects the gas space with the external ambient gas. Through this there will be a retention of heat in the aerobic degradation zone promoted compared to an uncovered zone, in which oxygen-depleted ventilation gas in large Quantities of the treated volume of sludge release freely into the external surrounding gas, i.e. the outside atmosphere can. When in the aerobic degradation zone with an aeration feed gas If the work is carried out with a high oxygen content, it can also be expedient for the degradation zone

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to provide a cover in order to obtain a gas space from which the oxygen-containing ventilation gas is opposite the sludge can be circulated, for example by circulating gas from that located above the sludge Gas space to a gas distribution device immersed in the sludge. Instead, it is also possible to use the To circulate sludge against the aeration gas, for example with the help of a surface fumigation device. Allow such aeration gas or sludge circulation systems in the aerobic degradation stage a high utilization of the Oxygen content in the aeration feed gas entering the aerobic degradation zone is introduced.

In the aerobic degradation zone 10, the sludge and the be ^ - ventilation feed gas mixed. If the mining zone 10 with a cover is provided and a ventilation feed gas with a high oxygen concentration is used, it may furthermore, as stated above, be expedient to add the sludge or the aeration feed gas simultaneously with the mixing process in relation to the respective other fluid in the degradation zone in sufficient quantity and with sufficient Revolving speed to provide aerobic breakdown of the sludge while maintaining the total suspended solids concentration (MLSS) of the sludge is maintained at at least 20,000 mg / l. It is useful for mixing and circulating a contact device 12 is provided, which in practice a submerged turbine injector and a

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May have gas compressor, which is connected to the gas headspace in the mining zone and connected to the gas injection device is opposed to the oxygen-containing ventilation gas to stir the mud. Instead, a surface ventilation device can also be used be present, which the sludge against the aeration gas in the gas headspace of the Mining zone 10 circulates. The circulation of one of the fluids consisting of sludge and aeration gas over the other Fluid in the aerobic degradation zone may in practice be desirable when using high oxygen aeration feed gas work is being carried out to maintain a high level of dissolved oxygen and the oxygen in the sludge of the ventilation feed gas to a large extent. However, such a circulation is not a compulsory feature of the present procedure. In some cases it may be possible for adequate dissolved oxygen in the mud and high utilization of the oxygen in the aeration feed gas by adding aeration feed gas passed through the aerobic degradation zone only once will. The relative proportions of aeration feed gas and sludge that are in the first breakdown zone for a aerobic degradation taking place there in contact with one another are to be brought can expediently be determined in the manner described above, for example by hand an empirical determination of the specific oxygen uptake rate (SOUR) of the sludge to be treated, or based on the amount of oxygen required,

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284U98

by a unit of quantity of volatile suspended matter in the Biodegradation of sludge. In some systems it may be useful to have an intensive aerobic degradation action in to ensure the first degradation zone that in the sludge present there high levels of dissolved oxygen, for example at least 2 mg / 1, are maintained. In general, however, the rate of oxygen uptake is of the silt in the first mining zone of the present one Method = · sufficiently high so that the maintenance a significant amount of dissolved oxygen in the oxygenated sludge for an effective aerobic breakdown is not necessary.

The total suspended matter concentration is in the aerobic degradation zone (MLSS) of the sludge is kept to at least 2O CXDO mg / l in order to maintain a high sludge temperature in the first mining zone to enable what is necessary to achieve a satisfactory level of partial stabilization of the sludge in the aerobic degradation zone with short residence times.

Under the above process conditions, sludge in the first decomposition zone becomes decomposed at one temperature maintained in the range of 35 ° C to 75 ° C, and preferably in the thermophilic range of 45 ° C to 75 ° C, which is a ensures rapid biological decomposition of the volatile suspended matter content of the sludge. As part of the

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present process can be used for aerobic degradation in the almost thermophilic temperature range from 35 C to 45 ° C, whereby solids degradation rates are achieved that are not as high as those for the Thermophilic operation characteristic velocities are, however, sufficient for a sufficient sludge stabilization to achieve with the low sludge retention times required for the first degradation stage of the present process are typical.

The aerobic decomposition phase is continued in the first decomposition zone for a sludge retention time of 4 to 48 hours in order to partially reduce the biodegradable volatile suspended matter content of the sludge introduced into the first decomposition zone. The aerobic decomposition phase is preferably carried out in such a way that the volatile suspended matter content of the sludge introduced into the first decomposition zone is reduced by 5 to 20%. The reasons for this are explained above. The sludge retention time in the aerobic degradation stage should be at least 4 hours in order to achieve sufficient partial stabilization in the first degradation zone. If the residence time is less than 4 hours, the degree of sludge stabilization required in the subsequent anaerobic treatment stage becomes disproportionately large compared to the degree of stabilization in the first aerobic stage. The total system residence time and the tank capacity requirement begin to increase

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To approximate values of conventional "anaerobic degradation systems. The unexpected improvement of these process parameters, that means total system residence time and tank capacity requirement for operation with residence times of 4 to 48 hours are characteristic, is increasingly lost. For similar reasons, the sludge retention time should be do not exceed 48 hours in the aerobic degradation zone. Above this value, the extent of Excessive sludge stabilization of the aerobic decomposition zone large compared to the hen stabilization in the downstream anaerobic stage, so that methane production in the last-mentioned stage is severely impaired will. Again, the unexpected improvement is in overall system residence time and tank capacity requirements increasingly lost, with a sludge retention time in the aerobic degradation zone in the range of 4 to 48 Hours is achievable. Based on the above considerations, a dwell time in the range of 12 to 30 hours, and preferably from 12 to 24 hours, worked.

Following the aerobic degradation treatment explained above, partially stabilized sludge is produced from the aerobic Zone discharged via line 14, while oxygen-depleted degradation gas from the aerobic zone via a Line 18 is discharged separately. If a vent feed gas that contains at least 50 vol.Ji of oxygen,

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is introduced into the first mining zone, contains the oxygen-depleted degradation gas withdrawn from this zone at least 21 vol.% oxygen in order to achieve a suitably high utilization to achieve the oxygen contained in the ventilation feed gas and at the same time the energy expenditure for mutual contact of ventilation gas and To keep sludge at an economically low level. In order to ensure high oxygen utilization, in particular when a ventilation feed gas with high Oxygen content is used, the oxygen concentration can of the exhaust gas from the digestion zone in line 18 can easily be kept at a suitable value by the relative Flow rates of the gas supplied via line 17 and of the gas leaving via line 18 are appropriate be managed. For this purpose, for example, gas flow control valves in the gas inlet and / or gas outlet line can be provided, which is in a known manner from an oxygen concentration analyzer (not shown), the one in the outlet line 18 seated.

Because the sludge is in the aerobic degradation zone of the present Process is kept at a thermophilic temperature of at least about 50 to 52 ° C, can be, has been found to achieve substantially complete pasteurization of the sludge. Generally the outgoing from the aerobic zone 10 via the line 14,

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partially stabilized sludge in the present process has a temperature between 35 ° C and 75 ° C. Because with this one special embodiment a mesophilic anaerobic degradation is provided in the covered second mining zone 20, the partially stabilized sludge is in the line 14, heat is preferably withdrawn in order to ensure efficient operation of the anaerobic sludge treatment stage in a Ensure lower temperature than is provided in the first mining zone 1O. Accordingly, will the sludge in line 14 through the heat exchanger passed through and in indirect heat exchange with the brought partially heated, inflowing mud, which in the heat exchanger 15 enters via the line 9. The chilled, partially stabilized, aerobically treated sludge then flows via line 16 to the covered second Mining zone 2O. Alternatively, the partially stabilized Cool the sludge in the line 14 also by means of an externally supplied cooling medium, for example with the clarified runoff of a wastewater treatment plant. When operating in winter it may not be necessary to a heat exchange, as it is effected by the heat exchanger 15, for cooling the partially stabilized sludge flow to be provided because heat losses to the environment from the second mining zone and that from the first to the second mining zone flowing sludge stream can satisfactorily compensate for the lack of such a heat exchanger.

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- Oo ~ *

The partially stabilized sludge introduced into the second degradation zone via line 16 is kept there under anaerobic conditions at temperatures of 25 ° C to 45 ° C for a sufficiently long sludge retention time to keep the sludge's biodegradable volatile suspended matter content to less than about 40 % and preferably less than 20 % of the biodegradable volatile suspended matter content of the sludge introduced into the first degradation zone; in addition, methane gas is formed.

The temperature of the sludge in the covered second mining zone is kept in the range of 25 ° C to 60 ° C. This includes both operation in the mesophilic range of 25 ° C to 45 C as well as working in the thermophilic range of 45 C to 60 ° C. For operation with particularly high efficiency becomes the anaerobic zone during mesophilic work at a sludge treatment temperature between 35 C and 40 ° C and preferably between 37 ° C and 38 ° C. A preferred working temperature range for anaerobic thermophilic degradation is between 45 ° C and 50 ° C. A business in the above-mentioned preferred temperature ranges ensures a particularly rapid degradation of the biodegradable volatile substances by the relevant microbial strains.

When operating the anaerobic degradation zone 20, it is preferred

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the content of the mining zone by means of a stirring device 21 constantly mixed, creating a large zone for active degradation and the speed of stabilization reactions is increased significantly. The dwell time of the sludge in the second degradation zone can expediently be Range from 4 to 12 days and preferably in the range from 5 to 9 days. Sludge retention times in the second Mining zones of less than 4 days may be inappropriate; the length of stay is less and less sufficient to get a maintain a large viable population of methane generators in the anaerobic stage the overall sludge stabilization behavior the degradation system is adversely affected. On the other hand, with sludge retention times in In the anaerobic degradation stage of more than 12 days, the length of stay in the second degradation zone is unnecessarily long; it becomes increasingly difficult to take advantage of the synergistic advantages of the integrated process in terms of residence time and Realize tank space requirements that can be achieved within the residence time range of 4 to 12 days.

After the anaerobic treatment of the sludge in the second degradation zone 20 is completed, the on this Wise obtained, further stabilized sludge discharged from the second degradation zone via line 24 and for the purpose Recovery of the heat content with the inflowing feed sludge brought into heat exchanger 22 for heat exchange, before the sludge finally leaves the system via line 25

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tig leaves. That in the second mining zone 20 as a product of the biochemical reactions carried out there Methane gas leaves the anaerobic treatment stage via a line 23 in which a flow control valve 26 lies.

As discussed above, was more conventional in the implementation Process a continuous operation of a rapidly acting anaerobic degradation zone at an optimal temperature above the outside temperature lying temperature difficult to maintain from home. Cause outside temperature fluctuations typically fluctuations in both the temperature of the inflowing sludge and the heat loss of the digestion tank, which in turn leads to undesirable temperature fluctuations within the digestion tank. Such temperature changes affect, as discussed, the relative growth rates of the acid-forming and the methane-producing bacteria. The acid-producing bacteria are typically very robust; moderate temperature fluctuations do not change their metabolic activity to any significant extent. Against this are methane-producing bacteria extremely sensitive to environmental conditions. Will maintaining a constant temperature in the anaorobic degradation zone due to only minor temperature fluctuations disturbed, instabilities can easily arise with regard to the activity and growth of the methane generators. As a result, the activity of the acid

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sculptor; the acidic decomposition intermediates accumulate; the pH value in the mining zone drops. As the pH value falls, the activity of the methane generator increases further decreased; the process is significantly disrupted.

To the above-described process disturbances in the conventional To counteract anaerobic mining zone, large amounts of lime are usually introduced into the mining zone, to increase the buffering effect and thereby the pH value to increase in the mining zone. By raising the pH and lowering the inflow it is sometimes possible to bring such a disturbed mining zone back to normal work. The corrective action mentioned above however, it is usually only suitable for brief fluctuations or process disturbances; she offers usually no benefit if long-term fluctuations or disturbance conditions occur.

In the present process, increased working temperatures in the mining zone are achieved with minimal temperature fluctuations Realized and maintained regardless of climatic conditions by having a thermophile or almost thermophilic aerobic degradation stage with a subsequent anaerobic sludge treatment stage is integrated. In the case of the present process, the thermophile or near-thermophilic aerobic degradation stage usually contribute more than enough heat to cause the anaerobic

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Stage due to the heat content of the ^J : to thermally stabilize the stabilized sludge flow, which is passed from the aerobic decomposition zone to the anaerobic stage. As a result, temperature disturbances in the anaerobic zone can be practically eliminated in the present case by changing process parameters, which include the sludge residence time in the aerobic zone, the solids content of the sludge fed to the aerobic zone and the degree of heat exchange due to which the feed sludge before it is introduced into the aerobic zone is heated.

Another essential advantage of the integrated method according to the invention lies in addition to the advantages that are due to the working temperature stability, in the ability to deal with sporadic disorders, such as Shock loads to be absorbed without the efficiency of the process suffering. With a conventional anaerobic Degradation zone not only does the initial phase of solubilization occur rapidly within the degradation process, but also the microbial action by facultative acid-forming bacteria occurs at high speed. If the conventional anaerobic degradation system suddenly experiences a high level of solids, the solubilization takes place and acidifying at a faster rate than the methane-forming bacteria the acidic intermediates to be able to use. As a result, it occurs in the mining zone

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to an accumulation of acidic components. The pH falls in the mining zone. A souring of the contents of the The mining zone threatens to enter. In the present process, however, promotes the upstream thermophilic or almost thermophilic aerobic stage, a rapid solubilization of biodegradable material in the sludge, so that it leads to rapid solubilization in the aerobic degradation zone after the onset of a shock load in the aerobic zone as well to a stabilization of the most volatile sludge fractions, whereby the impact load is smoothed and their Effect on the downstream anaerobic zone is greatly reduced. In the further treatment stage, the anaerobic zone on a partially stabilized sludge, in which the acid-forming bacteria and the methane-forming Bacteria can grow in mutual equilibrium.

Insofar as the aerobic breakdown phase of the present one If a thermophilic degradation zone is preferably used in the sludge treatment process, this can be found in US Pat 3,926,794 known methods advantageously in connection with the method according to the invention for treating wastewater use to remove BOD in the activated sludge process and the resulting activated sludge by means of the present Procedure to deal with.

After-treatment of wastewater with activated sludge is known carried out as follows. Wastewater containing BOD,

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for example municipal sewage, can initially through a sand trap and a primary settling basin are conducted to separate a primary sludge from the wastewater, which contains biodegradable suspended matter, and in this way a primary runoff that is depleted in solids which is then introduced into the aftertreatment system. In the aftertreatment, the primary drain and return sludge mixed and aerated sufficiently and for a sufficient period of time to to form a mixed liquid with reduced BOD content. After that, the mixed liquid turns into purified liquid and revitalized mud separately. At least a larger part of the activated sludge is returned to to be mixed with the primary effluent as said return sludge. This sewage treatment system can appropriately used in conjunction with the present process, the primary sludge and not Revitalized sludge returned from the first mining zone of the present process are supplied as feed sludge.

According to the method of US Pat. No. 3,926,794, oxygen gas is used for thermophilic degradation of living Mud used in a warm covered mining zone; the exhaust gas of the degradation zone is considered to be at least the greater part of the aeration gas in a cooler, covered zone for wastewater post-treatment with activated sludge.

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det. The patent shows that an oxygen gas of relatively high purity should be used as aeration gas for the degradation stage in order to maintain the high mass transfer driving force to achieve that for an effective release. Oxygen in the at elevated temperature working aerobic degradation zone is necessary. At elevated temperatures, the stronger biochemical degradation effect A significant amount of carbon dioxide is generated as a gaseous reaction product on the sludge in the aerobic degradation zone. Because the solubility of carbon dioxide contributes that characteristic of aerobic thermophilic degradation When the temperature is comparatively low, a significant amount of the carbon dioxide goes into the aerobic degradation zone into the gas phase, thereby increasing the effective oxygen concentration is lowered in the ventilation gas of this zone. It is also used at high thermophilic temperatures the oxygen gas phase concentration in the degradation zone further reduced by the water vapor in the ventilation gas due to the relatively high vapor pressure of Water is present at such temperatures.

The above-mentioned effects are the driving force for an oxygen mass transfer from the gas phase to the Sludge in the thermophilic mining zone is considerably reduced. The driving force for oxygen mass transfer in the liquid sludge phase, due to the lower oxygen solubility with increased thermophilic

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- 16 -

len temperature values are reduced. Because of these reasons in US-P5,3,926,794 recommends that this be incorporated into the thermophile The oxygen-containing gas introduced into the decomposition zone has an oxygen concentration of at least 80% by volume. Under Such working conditions can the venting gas leaving the thermophilic degradation zone with advantage Oxidizing agent gas can be used in an aftertreatment with the aid of the activation process.

Fig. 2 shows a flow chart for another embodiment of the present method, which can recognize, may be such as that known from US-PS 3,926,794 Procedure with the process of this invention advantageously combined.

According to FIG. 2, water containing BOD, for example wastewater, enters a gassing zone 102 via a line 101. A first gas containing at least 40% by volume of oxygen is also fed to the gassing zone 1O2 via a line 118 (dashed) and activated return sludge fed via a line 1O8 in which a pump 1O9 is seated. Supernatant liquid from a sludge thickener 151 also passes via a line 150 into the covered aeration zone 1O2. In FIG. 2, lines carrying liquid and sludge are shown in solid lines, while lines carrying gas are shown in dashed lines. Valves are not shown for the sake of simplicity; the

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- ff -

Appropriate use of such valves is understood by those skilled in the art. The said currents are Thoroughly mixed in the aeration zone 1Ο2 by means of a mechanical stirrer 1Ο3. The stirring device can be motor-driven, seated near the surface of the liquid or immersed in the liquid Have impellers. The oxygen gas can through the pipe 118 supplied above or below the liquid level will. Devices of this type are known; they should be chosen so that there is a large contact area between the fluids is obtained with minimal expenditure of energy. The oxygen gas is blown into the liquid or caused to diffuse in, the bubbles should be so small that their total surface is large and their buoyancy is low. The dissolving of oxygen is also supported by the fact that the one provided for introducing the gas Arrangement immersed in the liquid so deep that the hydrostatic effect plays a role.

Means are preferably provided in order to keep one fluid in the aeration zone 1Ο2 in relation to the other fluids to overturn. For example, with the gas space in the gassing zone A compressor (not shown) can be connected to ventilation gas via an appropriate line arrangement to circulate to the lower part of the zone and in the form of small bubbles via an aerator more conventionally Kind of release. Alternatively, the said

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Mixing device can also be used to circulate the fluids, as is the case with surface gassing impellers. Fumigation devices are generally measured according to the so-called "normal air transition efficiency", which characterizes the ability of the device to dissolve oxygen from air in tap water that does not contain dissolved oxygen, is under a pressure of one atmosphere and has a temperature of 20 ° C. Suitable devices have a normal air transition efficiency of at least 0.92. kg Op / kVVh and preferably an efficiency of at least 1.85 kg CL / kV / h. For these purposes, the energy used for dimensioning the device is the total energy that is consumed both for stirring the liquid and for bringing gas and liquid into contact.

The above-mentioned oxygen is introduced and mixed with the mixed liquid in sufficient quantity and in brought into contact to a sufficient extent to reduce the dissolved oxygen content of the mixed liquid to at least Hold 0.5 mg / 1. The liquid temperature is also preferably maintained at at least 15 ° C so that at Cold weather agents may be needed to avoid a lower TcmpuruLur in the Dogasungszone 102. For example, the incoming wastewater in line 1O1 can be heated for this purpose. Structure and way of working the wastewater gassing zone 102 can be in the off

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known in U.S. Patents 3,547,811, 3,547,812 or 3,547,815 Wise so chose.

The mixed liquid enriched with oxygen is diverted from the covered gassing zone 102 and arrives via a line 104 in a clarifier 105, where it is separated into purified, supernatant liquid and activated sludge. Unused oxygen-containing gas leaves the gassing zone 1O2 via a line 119 and can, for example, be vented into the atmosphere. This gas is discharged from the gassing zone at a flow rate controlled so that its oxygen content does not exceed 40 % of the total oxygen introduced into the covered aerobic degradation zone (discussed below). Supernatant, purified liquid is drawn off from the clarifier 105 via a line 106, while activated sludge is discharged via a line 107. The activated sludge contains microorganisms in a concentrated form corresponding to a total suspended matter content (MLSS) of approximately 1,000 to 40,000 mg / l. The greater part of the activated sludge, for example at least 85%, is returned to the gassing zone via line 1O8 and pump 1O9, preferably in such a flow rate based on the BOD-containing wastewater that the volume ratio of return sludge to BOD-containing Wastewater is between 0.1 and 0.5. The flow rates

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the media introduced into the covered gassing zone 102 are preferably dimensioned so that the total suspended matter concentration there is between 400 and 12000 mg / l and the content of volatile suspended solids (MLVSS) 3OÜÖ to 1O 0OO mg / l. The liquid-solid contact time in the gassing zone 102 for the absorption and assimilation of organic substances lies between 30 minutes and 24 hours. This time varies depending on the strength (i.e. the BOD content) of the wastewater, the type of contaminants, the solids content in the aeration zone and the temperature, as this is appropriate for understands the skilled person.

Not all of it in the clarifier will be 1O5 for two reasons separated sludge is returned to the aeration zone 102. On the one hand, the activation process generates as a whole an excess of microorganisms, because the mass of the new synthesized from the impurities in the wastewater Cells is larger than the mass of cells that will self-oxidize during treatment. On the other hand The wastewater normally contains non-biodegradable solids that settle and together with the biomass accumulate. As a result, there must be a small proportion of the activated sludge to be excreted in order for a balance between the microorganism population and the supply of organic matter (BOD) as well as the accumulation of inert solids within

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-81-of the system. The sludge usually accounts for less than 3 % of the total separated sludge and rarely more than 15%.

The sludge represents a small proportion of the total solids separated in the clarifier; nevertheless, viewed in absolute terms, it often constitutes a large amount of substance. Regardless of the amount, the disposal of this sludge represents a significant part of the cost of wastewater treatment; in addition, the sludge is a significant ecological problem. The sludge is digestible and highly biologically active; it often contains pathogenic bacteria. The mud is potentially suitable as fertilizer and / or for landfilling. Before such an application, however, it must be well stabilized in order to avoid nuisance and health risks. Its high water content (e.g. 96 to 98 %) must be reduced.

The sludge is drawn off from the clarifier 105 via the sludge circulation loop in a line 111. It has a Gesamtschwebstoffkonzentration 10 0oo to 40,000 mg / l and initially about the same temperature as the waste water ₇ in the Begasungszone 102, ie 15 ° C to 25 ° C. The sludge is fed to the thickening tank 151. The thickening tank 151 concentrates the sludge to a total suspended matter concentration between 20,000 -

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. and 60 000 mg / l. The thickened one peeled off below Sludge is fed into the sludge removal system via a pipe 152 supplied.

In some cases, such as wastewater treatment at high outside temperatures and high solids concentrations in the stream drawn from the clarifier below, the sludge from the clarifier can thicken not be necessary; the sludge in the line 111 can then conveniently via a line 153 to the Thickening tank 151 are passed and then in line 152 to get to the 'sludge removal system to go. The overflow of the flame thickener (protruding Liquid) is, as described above, via the Line 150 is fed to the gassing zone 102.

The thickened sludge in line 152 can, if required before entering an aerobic degradation zone 110 can be heated by means of a methane boiler 130. Instead, the sludge can also be used with the stabilized sludge runoff from an anaerobic degradation zone 12Ob can be brought into heat exchange, similar to the above in connection with the embodiment according to FIG Fig. 1 is explained. Blowdown is covered in the first degradation zone 110 from line 152 either continuously or initiated intermittently. The aerobic degradation zone 110 is at a temperature of 35 ° C to

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/ L) ° C and preferably in the thermophilic range of 45 ° C held up to 75 ° C. In the case of autothermal operation in the aerobic degradation zone, preferably in the range from 55 ° C to 65 ° C worked. The elevated temperature in the covered first mining zone 110 can also be maintained, by adding external heat, for example by having an appropriate heated fluid in a heat exchanger, not shown, circulates in the degradation zone sits. Because of the tendency of the solids to form coatings and cause clogging, should be inside heat exchanger surfaces located in the mining zone are not complicated or closely spaced; advantageously they can be embedded in the wall of the tank or connected to it.

A second oxygen gas that contains at least 80% oxygen by volume is fed to the covered, first mining zone 110 via a line 117. As explained below is, the amount of this gas is sufficient to provide some of the first oxygen gas that is in the gassing zone 102 is introduced via the line 118.

Preferably, the elevated temperature is covered in the first degradation zone 110 achieved autothermally without the need for heat exchangers such as the device 130. The concentrated sludge, as it is in the oxygen gassing

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Solution process according to US Pat. No. 3,547,813 is customary accrues, is particularly suitable for an autothermal operation, as it has a biological effect compared to the content of degradable "fuel" has reduced water content. In addition, it is made with high solids concentrations the size of the digestion tank is smaller, as a result of which there is also heat conduction losses through the walls of the digestion tank be reduced. As previously mentioned, the total suspended solids content should of the sludge in the mining zone should be at least 20,000 mg / l on the basis of such considerations .

The upper limit values for the solids concentration in the aerobic degradation zone are essentially determined by two factors. In general, the maximum concentration depends on the ability of conventional settling and Eindickeinrichtungen to reduce the water content. Flotation devices, centrifugal separators and gravity thickeners often ensure total suspended matter concentrations of 60,000 mg / l. The solids content can also be increased by adding fresh sludge or concentrated waste from a source other than the wastewater. The second factor which limits the solids concentration is the increasing difficulty to mix in the degradation zone oxygen to Ibsen and the solids. An appropriate upper limit is 60,000 mg / l and preferably 80,000 mg / l to ensure

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len that a sufficient oxygenation of the
Mud can be done without using excessive energy for
the mixing of aeration gas and sludge was expended
needs to become.

The construction of the digestion tank also affects the maintenance of elevated temperatures. Concrete walls are because of the lower heat conduction losses
of concrete is preferable to metal walls. The heat loss can be further reduced in that the tank is embedded underground and earth is thrown against all exposed vertical tank walls. If necessary, thermal insulation, such as a low density concrete or foam, can be applied over a metallic cover,

Aerobic and anaerobic digestion tanks which have a surface / volume ratio of less than 2.62 m / m are also preferably used for the method according to the invention. The term "surface" includes the entire wall surface of the covered mining tank including the bottom, cover and side walls. Surfaces / volume ~

2 3

ratios of more than 2.62 m / m lead to large heat conduction losses through the walls, related
on the amount of heat to be maintained in the digestion tank. Such heat loss usually requires
thermal insulation on the outside atmosphere

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set walls.

The length of time the sludge remains in the aerobic degradation zone also affects the elevated temperature values, particularly the autothermal temperature values that are maintained can be. The relationship between length of stay and temperature is determined by numerous factors, among other things on the degradability and the strength (the solids content) of the sludge. In general should be worked with a sludge retention time in the first degradation zone of 4 to 48 hours. Appropriate the sludge residence time in the first degradation zone is 12 to 30 hours and preferably 12 to 24 hours Hours.

The first mining zone 110 is equipped with a mechanical agitator 112 which is of the same type as the Agitator 1O3 can be in the aeration zone 102. aside from that Means are provided to divert the second gas or the activated sludge from the other in the degradation zone Constantly circulating fluids.

The second gas containing at least 80 % oxygen is fed to the covered aerobic degradation zone 110 and mixed with the sludge located there in sufficient quantity and to a sufficient extent to bring about aerobic degradation "and the total suspended matter concentration

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The concentration of the sludge must be kept at "at least 20,000 mg / l .

An oxygen-depleted decomposition gas with an oxygen concentration of at least 40 % is withdrawn from the covered decomposition zone 110 via the line 118 in such a flow rate that its oxygen content is at least 35 % of the oxygen content of the oxygen feed gas flowing in via the line 117. The gas in the line 118 reaches the covered gassing zone 1O2 as at least a larger part of the mentioned first gas, which provides the oxygen that is required for the biochemical oxygenation of the wastewater. If necessary, additional oxygen-containing gas can be supplied from an external source to increase the oxygen-containing gas flow in line 118.

After the desired degree of aerobic degradation treatment is achieved in zone 110, it is partially stabilized Sludge discharged from the first covered degradation zone 110 via a line 114 and the anaerobic treatment part of the integrated system. In this embodiment, the second anaerobic degradation zone comprises one Acidification or acidification subzone 12Oa and the methanef Ermentation subzone 12Ob. The partially stabilized sludge coming from the first mining zone 110 in the pipe

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device 114 is introduced into the acid formation subzone 120α and held there for a sludge residence time of 24 to 60 hours in order to ensure the necessary acidification of the sludge. The contents of the subzone 120a are continuously mixed by an agitator 121a in order to break down carbohydrates, fats and proteins at a uniform rate to lower fatty acids. At the end of the necessary residence time in the sub-zone 120a, the acidified sludge is discharged from there via a line 126. If the temperature of the sludge leaving zone 120a is above the optimum methane formation values, the temperature of the acidified sludge is expediently lowered in order to ensure satisfactory operation of methane-forming subzone 120b. The sludge in line 126 is therefore passed through a heat exchanger 115 in countercurrent to a coolant flow which flows through the heat exchanger via a line 160. The partially cooled, partially stabilized sludge obtained, which leaves the heat exchanger 115, then flows via a line 127 to the methane fermentation subzone 120b. The heat exchange medium used for cooling in line 16O can appropriately be a flow of cooling water, for example part of the drain that leaves the secondary clarifier via line 106, or, as in the case of the previously explained embodiment, the incoming feed sludge flow flowing into the digestion system.

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The anaerobic degradation zone 120b represents the methane-forming degradation stage of the process. For optimal operation, the sludge in the methane fermentation zone is kept at a temperature between 35 ° C and 40 ° C and preferably between 37 ° C and 38 ° C. The contents of the zone 120b are constantly mixed by means of an agitator 121b, whereby a large active decomposition zone is provided and the speed of the stabilization reactions occurring there is significantly increased. The sludge retention time in the methane fermentation subzone is preferably between 4 days and 8 days based on the considerations discussed above with regard to the sludge retention time in the anaerobic second degradation zone. Methane gas, which is generated by the biochemical reactions taking place in the partial zone 12Ob, leaves this zone via a line 128 in which a flow control valve 129 is located. A portion of this discharged methane gas can be fed to the boiler 130 via a line 132, while the remainder is withdrawn from the process in a line 131 in order to undergo further treatment and / or to be fed to other end-use stages. The further stabilized sludge, which contains no more than 40 % and preferably no more than 20 % of the original biodegradable volatile solids content of the inflowing sludge, is discharged from the process via a line 133.

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Fig. 3 shows a flow diagram of a further AusfUhrungsforrn, in the sludge from wastewater pre- and post-treatment stages is fed to the sludge removal system. This embodiment represents a process sequence in the one thermophilic aerobic first degradation stage with a thermophilic anaerobic second degradation stage is integrated. So far, thermophilic anaerobic degradation has been in practice little used. This is due to the fact that related to the problems of known plants associated with mesophilic anaerobic operation discussed above thermal instability and extreme sensitivity to Changes in the process conditions in the case of thermophilic anaerobic degradation are even more pronounced. Because This sludge treatment process has the uncontrollable working stability of thermophilic anaerobic degradation heretofore received little attention in commercial sludge removal applications. The problems of operational instability and excessive sensitivity to process variability become apparent in the thermophilic aerobic / anaerobic embodiment of the invention is overcome in the same manner as that in connection with the embodiments of the invention which provide an anaerobic mesophilic second degradation stage.

In the arrangement according to FIG. 3, raw sewage, which consists for example of municipal sewage, industrial sewage and rainwater, flows via a line 24O into a

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ne primary settling zone 241. The settling zone 241 can appropriately consist of a conventional gravity clarifier Kind exist. The inflowing is in the settling zone Wastewater in a primary drain with reduced BOD content, which reaches a gassing zone 2O2 via a line 201, and a settled sludge underflow separated, which is discharged from the zone 241 via a line 242 will. The gassing zone 202 are also via a Line 218 an oxygen-containing ventilation gas, via a Line 250 supernatant sludge thickening liquid and fed in via a line 208 activated return sludge. A fluid mixing and circulating device 2O3 is located in the aeration zone 202 in order to mix the various fluids supplied to the aeration zone To form mixed liquid and at the same time the mixed liquid or the oxygen-containing ventilation gas opposite to constantly circulate the other fluids located there. As discussed above, the fluid mixing and circulation device immersed in the liquid Gas injection device in connection with a mixing impeller or a Surface ventilation impeller means include. To the required duration of fumigation, for example 2 to 6 Hours, become a mixed liquid depleted in BOD, and an oxygen-depleted ventilation gas with at least 21% by volume of oxygen from the gassing zone 202 via lines 2O4 and 219 respectively.

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The mixed liquid depleted in BOD and enriched with oxygen in the line 204 reaches the secondary settling zone 205, where activated sludge is separated from the purified liquid; the latter leaves the process via line 206. The settled activated sludge is discharged from the secondary settling zone via a line 2O7. A larger part of this withdrawn sludge is returned as return sludge to the gassing zone 2O2 via line 208, in which a circulating pump 2O9 is located. The remaining, non-recirculated part, which can make up 3% to 10 % of the sludge in the line 207, reaches a sludge thickener 251 via a line 252.

The Schlarr.rneindicker 251 has a further sludge settling and thickening zone which concentrates the sludge to a solids content between 2 % and 6 % , so that the total suspended matter concentration is between 20,000 and 60,000 mg / l. The thickened sludge underflow is discharged via a line 245 and combined with primary sludge in the line 242 from the primary settling zone 241, so that a combined sludge flow in a line 211 is formed. The supernatant liquid from the sludge thickener 251 is fed via the line 250 to the gassing zone 202 in the manner described above.

The combined sludge flow in line 211 can, if desired, by indirect heat exchange with the

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warm stabilized sludge from a second mining zone 22O are partially warmed up; he then arrives via a Line 248 to the first mining zone 210. Before discharge In the first degradation zone 210, the sludge in the line 248 can be heated further by means of a heating device 231 in which methane gas is burned that over a line 227 flows in.

If the outside temperature conditions make it unnecessary to heat the sludge fed to the digestion system the sludge bypasses heat exchanger 244 and heater 231 via bypass lines 261 and 263, respectively.

In the covered first degradation zone 210, the thermophile aerobic decomposition of the incoming sludge carried out. Aeration gas that contains at least 50% by volume of oxygen and preferably contains at least 80% by volume of oxygen, reaches the mining zone 210 via a line 217. A Mechanical agitator 212 mixes the inflowing sludge mixture and the oxygen-containing gas and constantly circulates one of these 'media versus the other around. The flow rate of aeration gas and that of the mechanical agitator 212 supplied energy are chosen so that in the sludge in the first degradation zone 210 oxygen is dissolved in sufficient quantity and in sufficient measure to meet the need for respiration the aerobic degradation in this zone.

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Sludge is in the first degradation zone 210 at a thermophile Maintained temperature of 45 ° C to 75 ° C for a period of 4 to 48 hours to reduce the content of the sludge to partially reduce biodegradable volatile suspended matter. Partially stabilized sludge becomes out discharged from the aerobic degradation zone 210 via a line 216; Degradation gas depleted of oxygen leaves the degradation zone separately via line 218.

The partially stabilized sludge arrives from the line 216 from the first mining zone into the covered second mining zone 220. - ■

The second degradation zone 220 is a thermophilic one anaerobic degradation zone. With a view to optimal working conditions, the sludge is raised in this mining zone a temperature in the anaerobic thermophilic temperature range between 40 C and 60 C and preferably between 45 ° C and 50 ° C held. Because in this embodiment both in the first and in the second mining zone a thermophilic operation takes place, the partially stabilized Sludge from the first mining zone as illustrated can be fed directly to the second mining zone. There is no heat exchange between the zones for heating or cooling purposes when the thermophilic temperatures are sufficiently closely coordinated in the relevant zones. Instead, in some cases

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len be desirable, in the second mining zone with sufficient higher or lower temperatures compared to the first to work aerobic degradation zone, so that a heating or cooling of the partially stabilized sludge from the aerobic Degradation stage is advantageous. The heating can be done with the help of a methane-fired heater similar to the Heating device 231 are carried out. A heat exchange of the partially stabilized sludge can be used for cooling from the first mining zone with the inflowing sludge supplied to the mining system, as described above in Connection with the embodiments according to FIGS. 1 and 2 is explained. Since there is also a thermophile Anaerobic degradation is even more critical than mesophilic anaerobic degradation, ensuring that in the degradation zone If there are no temperature fluctuations, it may be appropriate to use one for the thermophilic anaerobic degradation stage to provide a well-insulated tank, which offers security against strong climatic fluctuations.

In the second degradation zone 220, the sludge is continuously mixed by means of a mechanical agitator 221 in order to achieve a maintain high rate of stabilization. Methane gas that occurs due to the anaerobic degradation Biochemical reactions is generated, is discharged from the second degradation zone via a line 223. This Methane gas can be made from oxygen-containing gas, for example air, or the oxygen-depleted decomposition gas

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the aerobic degradation zone and burned as fuel to generate heat, with the help of which sludge is kept at an elevated temperature in one or both degradation zones. In the arrangement shown, part of the methane gas from line 223 is fed to methane heating device 231 via line 227 and burned in order to obtain the thermal energy with the aid of which the sludge in the first degradation zone is at a thermophilic temperature of 45 ° C to 75 ° C is held. The remaining part is discharged from the process via line 228. The further stabilized sludge from the anaerobic degradation zone, which has no more than 40 % and preferably no more than 20 % of the biodegradable volatile suspended matter content of the sludge flowing into the degradation system via line 248, is released from the second degradation zone via a line 225 carried out. It is passed through the heat exchanger 244 in order to recover the heat of the discharged sludge. The further stabilized sludge finally leaves the process system via a line 243 »

Due to the differences with regard to the sludge sources, the type of biological activity in the aerobic digestion zones of the embodiment according to FIG. 3 differs from the biological activity in the aerobic zone of the embodiment according to FIG. In the embodiment according to FIG. 2, the digestion system is used as feed sludge

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supplied sludge alone activated sludge from the secondary Wastewater treatment system, while in the case of the embodiment according to FIG. 3, the incoming sludge both Secondary sludge from * the activated sludge treatment stage as well as raw sludge from the raw sewage settling stage includes. Because the organic material of the secondary sludge composed primarily of viable microorganisms, the aerobic degradation of this sludge includes the various biochemical reaction stages of cell lysis, the assimilation of lysis products for the synthesis of new viable material, and respiration. Raw sludge, on the other hand, consists primarily of non-viable sludge organic material that the microorganisms present in the sludge can use as nutrients. Accordingly During the aerobic degradation of a raw sludge, the microbial population of the sludge experiences a considerable Cell synthesis phase in addition to cell lysis, assimilation of lysis products and respiration.-Hence the aerobic degradation of the raw sludge takes place with a greater degree of both cell synthesis and cell respiration than with the aerobic degradation of secondary sludge. In addition, the aerobic degradation of raw sludge leads to a smaller overall reduction in biodegradable volatile suspended matter than with a comparable one Sludge retention time is the case with aerobic decomposition of secondary sludge. The resulting decrease in biological degradable volatile suspended matter in the sludge

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rend of degradation represents a difference in terms of rival Represent degradation processes of cell synthesis and cell respiration.

The cellular respiration in the sludge breakdown process is exothermic; for the reasons discussed above, raw sludge has a higher arm production capacity per unit weight biodegradable volatile suspended matter that occurs during Degradation can be eliminated than is the case with secondary sludge. Accordingly, it is compared with primary sludge to secondary sludge a lower resultant reduction in volatile particulate matter required in order to to reach and maintain a certain temperature level in the aerobic degradation stage. So can the embodiment according to Fig. 3, in which the sludge fed to the digestion system includes both primary and secondary sludge comprises, at a given temperature, a lower degree of volatile matter reduction in the aerobic degradation zone are operated as the aerobic zone according to FIG. 2, which only processes secondary sludge. One lower reduction of degradable volatile suspended matter in the aerobic zone of the degradation system requires on your part, that the sludge residence time in the anaerobic degradation zone is extended accordingly by a given total disposal of volatile suspended matter. Because an increased proportion of the total removal of volatile particulate matter in such a case in the anaerobic

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beneath the degradation zone, the primary sludge processing system can therefore produce more methane in the anaerobic degradation zone generate than the mining system in which only secondary sludge is processed. The embodiment of FIG. 3 is therefore inherently capable of delivering greater quantities of methane than the system of FIG. 2; but this comes at a cost an increased sludge retention time in the anaerobic degradation zone of the embodiment according to FIG. 3.

In view of the above discussion, each of the exemplary embodiments described above provides the possibility to heat the sludge flowing into the digestion system before introducing the sludge into the aerobic digestion zone will. Such heating can be used in a given application be necessary or not; this depends on various factors, such as the sludge solids content, the outside temperature, the sludge retention time in the aerobic degradation zone and the type of treatment to be treated Mud. FIG. 4 shows a graphic representation of the temperature of the inflowing into the first degradation zone Sludge that is required to maintain a working temperature of 50 C in the first degradation zone at a Maintain sludge retention time of 24 hours as a function of the total suspended solids concentration of the sludge entering the first mining zone. This graph shows a biological secondary sludge flow in which the Ratio of the content of volatile suspended solids to

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suspended solids (VSS / TSS) is 0.79 and the biological V / arm content is
ge suspended matter lies.

gical V / arm capacity at 33 x 10 J / kg eliminated volatile

The graph according to FIG. 4 shows that thermophilic operation can be achieved without the need to heat the sludge going to the digestion system before it is introduced into the aerobic digestion zone if the inflowing sludge has a sufficient concentration of solids. If, for example, a sludge with a total solids concentration of 3% has to be broken down, the temperature of the

the imported sludge is only about 15 C, to maintain autothermal operation.

All of the above-described embodiments of the invention are able to provide a fully pasteurized product, since in all cases all of the sludge flowing into the digestion system is passed through an aerobic abcuzzone, in which high temperatures ir. Of the order of at least 50 up to 52 ° C can be provided in order to bring about a complete sludge plasticization. However, there may be application cases in which the final® sludge disposal does not require a completely pasteurized product or the sludge itself does not require pasteurization because no significant concentrations of pathogens.

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generi «are available. Fig. 5 shows a flow sheet of another Embodiment of the invention in which a smaller Part of the sludge flowing into the process system is diverted to the second degradation zone, which is suitable for applications that do not require full sludge pasteurization. In the embodiment of FIG. 5, a larger part of the in the process system Sludge entering via a line 311 of a covered first mining zone 31O via a line 331 supplied. Before being introduced into the first mining zone 310, the sludge in the line 331 can, if desired, be heated by means of a methane-heated kettle 33O.

Aeration gas containing oxygen, which is at least 50% by volume and preferably contains at least 80% by volume of oxygen, is fed to the aerobic degradation zone 310 via a line 317. The sludge flowing into this zone is appropriately mixed by means of a stirring device 312 and constantly circulated in relation to the oxygen-containing ventilation gas. The mixing of Sludge and aeration gas in for aerobic sludge removal in the zone of sufficient quantity and dimension. The sludge is in the aerobic degradation zone at a thermophilic temperature between 45 ° C and 75 ° C for a residence time between 4 and 48 hours. Oxygen-depleted mining gas is converted from the first mining zone discharged via a line 318. Mud that on

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Biodegradable suspended matter partially exhausted leaves the mining zone separately via a line 316.

The partially stabilized sludge in line 316 becomes then fed to a covered second degradation zone 320, which operates in the mesophilic temperature range. Because the The temperature of the sludge leaving the first degradation zone is between 45 C and 75 C, its temperature must be before being introduced into the second degradation zone, so that preferred mesophilic temperature conditions for the mesophilic anaerobic degradation process in the second Mining zone can be maintained. In the illustrated Embodiment, the smaller part of the inflowing sludge bypasses the methane boiler 330 and the aerobic Mining zone 310 in a line 329; it becomes immediate mixed with the warm mud in line 316. The flow rate of the diverted incoming sludge is adjusted so that the temperature of the combined sludge flow that goes to the anaerobic digestion zone 320, sufficient to maintain a working temperature between 35 ° C and 40 C in zone 320.

In the second mining zone, the sludge is circulated mixed by methane gas against the sludge located there, to the stabilization speed in the second Keep zone actively at high values. Me-

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thangas, which due to the in the second mining zone 320 occurring biochemical reactions is generated, leaves this zone via a line 323. A side stream of this Gas is diverted into a line loop 340, in which sits a compressor 326. The compressed methane gas obtained is added to the sludge in the second mining zone, for example Added via a blowing device, not shown, in order for the above-mentioned mixing and circulation to worry about the mud. A part of the methane gas can from the line 323 via a line 327 to the methane-heated gas Go boiler 330; the remaining part is discharged from the process system via line 328. Of the further stabilized sludge that is less than 4O% des original content of the sludge introduced into the system via line 331 of biodegradable contains volatile suspended matter, is made from the second Extraction zone discharged via line 325 for further treatment, e.g. B. drained and / or finally disposed of to become.

The advantages of the method explained can be made clear with the aid of the following examples:

Example I.

In this example, the performance is the embodiment according to FIG. 2, a conventional anaerobic

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High performance system juxtaposed. The further explanation is based on the treatment of the sludge of a wastewater treatment plant with a capacity of 3 _r 8x1O 1 / day based on the flow diagram according to FIG.

A mixture of 50 % primary sludge and 50 % secondary sludge, which initially has a temperature of 18 ° C., is introduced into the breakdown system of the arrangement according to FIG. 2 via line 111. The sludge, which has a total suspended solids concentration of 39,400 mg / L and a volatile suspended solids to total suspended solids ratio of 72 % , is introduced into the system at a flow rate of 3.4-1O L / day. In order to keep the sludge in the aerobic degradation zone 110 at a working temperature of 50 ° C. for a period of 24 hours, the inflowing sludge is heated to approximately 23 ° C. by means of the methane boiler 130. Assuming an efficiency of 50 % for the conversion of the calorific value of methane gas into heat, approximately 710 m / day of the methane gas generated in the anaerobic degradation zone are required to feed the heating boiler 130.

In the aerobic degradation zone, a reduction in the volatile suspended matter content of approximately 8 % is achieved (16% biodegradable volatile suspended matter; the biodegradable volatile suspended matter accounts for approximately 50 % of the total volatile matter content

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Suspended solids from), so that the acid-forming part zone via line 114 12Oa partially degraded sludge with a content of volatile suspended solids of 26 100 mg / l is fed. This sub-zone is at a 24 hour Sludge retention time operated at thermophilic temperature, In this stage there is a 10% reduction in the proportion of inflowing volatile suspended matter. A sludge with a volatile suspended matter content of 23,500 mg / l then comes on via line 126 the methane fermentation subzone 12Ob. From the discharged Sufficient heat is withdrawn in the heat exchanger 115 to produce a in the methane fermentation subzone 120b Ensure working temperature of 38 C.

The methane fermentation subzone will have a 5 day Sludge retention time operated, resulting in an overall reduction in volatile suspended matter for the integrated system of 4O% (reduction of biodegradable volatile suspended matter by 8O%). The methane fermentation subzone generates around 2O7O m methane gas per day, which is a total calorific value of 12,600 kWh / day. Because 710 m of methane gas per day are necessary to to operate the methane boiler 130, there are 1360 m of methane gas per day, corresponding to a total calorific value of 8500 kWh / day, for discharge from the sludge removal system Disposal.

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If the combined sludge in the above-mentioned amount of 3.4 10 l / day is instead fed to a conventional anaerobic high-performance digestion tank, an approximately 13-day sludge retention time is necessary in order to achieve the same reduction in volatile suspended matter. Although the conventional high-performance degradation tank generates 3625 m of methane gas per day, corresponding to approximately 22,600 kWh / day, with a 50 % conversion of the calorific value into heat, approximately 17,600 kWh / day of heating energy are required to achieve the optimal working temperature conditions in the high-performance tank maintain. The conventional system therefore requires, in comparison to the embodiment of the invention explained above, based on the necessary dwell time, 86 % more tank space; In addition, under normal working conditions, about 40 % less methane is available for delivery.

Example II

This example describes a mode of operation corresponding to the embodiment according to FIG. 5. The incoming feed sludge consists of 50% primary and 50% secondary sludge from a wastewater treatment plant in an amount of 2.27 10 l / day. The incoming sludge stream in line 311 has a temperature of 20 ° C. and a total suspended matter concentration of 4 % (VSS / TSS = 0.75); he

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284U98

is divided into a partial flow of 1.74 10 l / day, which goes directly to the thermophilic aerobic degradation zone via line 331, and a partial flow of 5.3 χ 10 l / day, which forms the bypass flow in line 329. Because the temperature and the suspended matter concentration of the sludge in the line 311 are sufficient to ensure autothermal operation in the thermophilic, aerobic decomposition zone 31Ο, it is not necessary in this case to heat the sludge before it is introduced into the aerobic zone. The residence time in the first mining zone 310 is approximately 24 hours; thermophilic temperatures are reached autothermally. A pasteurized sludge is discharged from the aerobic digestion zone in line 316 at a temperature of 50 C and mixed with the cool bypass flow from line 329. This combined sludge stream then flows to the anaerobic digestion zone 320 where the sludge is held in the absence of oxygen for approximately 8 days, resulting in an overall volatile particulate matter reduction of approximately 40% (80% biodegradable volatile particulate matter reduction). The anaerobic degradation zone produces methane gas in an amount of approximately 2040 m / day, which corresponds to approximately 11,700 kWh / day. This methane can be completely released from the process system.

If the combined inflowing feed sludge of 2.27 χ 1O l / day is instead

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Roben high-performance degradation tank is fed, a residence time of approximately 15 days is necessary in order to achieve the same reduction in the content of volatile suspended matter. Although the conventional anaerobic digestion tank generates 2550 m of methane gas per day, corresponding to around 14 700 kWh / day, with a 50% conversion of the calorific value into heat, around 13 200 kWh / day are necessary to maintain the optimal anaerobic working temperature in the high-performance tank . In this case, a conventional anaerobic degradation system therefore requires an approximately 65 % longer sludge retention time, while only resulting gas energy corresponding to 1500 kWh / day compared to 11,700 kWh / day in the combined system is generated. After using the internally generated methane gas as a heat source, there is consequently in the conventional system significantly less methane gas available for delivery than in the method according to the invention.

Example III

This example compares the performance of the method according to the embodiment of FIG. 1 with a conventional anaerobic high-performance system.

A secondary sludge from any of the oxygen enrichment serving waste water treatment system, which is initially a

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Temperature of 15 ° C, is first in the heat exchanger 22 heated by the anaerobic degradation zone effluent, followed by further heating by the thermophilic effluent aerobic degradation zone in the heat exchanger 15 takes place. The first heat exchange stage in the heat exchanger 22 increases the temperature of the incoming sludge from 15 C to about 25 C, while the temperature of the stabilized Sludge exiting the anaerobic digestion zone 20 is lowered from approximately 35 ° C to 25 ° C. The second stage of heat exchange in the heat exchanger 15 increases the temperature of the inflowing sludge to about 3O C, during the temperature of the sludge leaving the aerobic degradation zone 10 is lowered from approximately 50 ° C to 45 ° C. The incoming sludge has a total concentration of suspended matter of 34,400 mg / 1 and a ratio of volatile suspended solids to total suspended solids of 78%. He is in 'the first mining zone 10 in an amount of 2.27 χ 1O l / Day initiated. In the aerobic first zone there is a working temperature of 5O C for a sludge residence time of 24 hours.

A reduction of about 16% of the volatile suspended solids (reduction of 32 % of the biodegradable volatile suspended solids) is achieved in the aerobic stage, so that a partially stabilized sludge with a content of volatile suspended solids of 22,500 mg / l via the line 16 into the anaerobic degradation zone is fed in,

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after a heat exchange with inflowing in the heat exchanger 15 Mud has taken place.

The anaerobic degradation zone works with a residence time of 8 days, which leads to an overall reduction in volatile suspended matter of 42% (reduction in biodegradable volatile suspended matter of 84 %) for the integrated system. The anaerobic degradation zone 20 generates approximately 1470 m of methane gas per day, corresponding to a total calorific value of approximately 8200 kWh / day. All of the methane gas is available for delivery from the mining system.

If, on the other hand, the sludge flowing in at 2.27 10 l / day is fed into a conventional anaerobic high-performance digestion tank, a sludge retention time of at least 14 days is necessary in order to achieve the same reduction in the content of volatile suspended matter. Although a conventional high-performance system of this type generates 2,400 m of methane gas per day, corresponding to approximately 13,800 kWh / day, with a 50% conversion of the calorific value into heat, approximately 13,200 kWh per day are required in order to maintain optimal working temperature conditions in the high-performance tank. The conventional anaerobic system therefore requires approximately 55 % more tank space; it can emit methane gas energy of about 7600 kWh / day less than the corresponding one above

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- 111 explained .System according to the invention.

While preferred embodiments are explained in detail it goes without saying that modifications are possible. For example, the aerobic breakdown phase of the present Process can be carried out in a series of treatment tanks or in a partitioned basin, wherein the individual tanks of the sequence or the separate volumes of the separated basin as sub-zones of the aerobic Act mining zone. The aerobic decomposition zone can take the form of a sludge decomposition space with several chambers, through which sludge and aeration gas are gradually passed in cocurrent. Such training the aerobic degradation zone are known per se (US Pat. No. 3,926,794).

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Empty soap

Claims (48)

L-11234-2-G Expectations [1.) Process for the degradation of sludge according to patent 28 05 054.6, characterized in that (α) the sludge and an aeration feed gas containing at least 20% by volume of oxygen are introduced into a first decomposition zone and mixed there in an amount and sufficient degree for aerobic decomposition of the sludge, while the total suspended matter concentration of the sludge is at least 20,000 mg / l and maintaining a sludge temperature in the range of 35 C to 75 C in the first breakdown zone; (b) the aerobic degradation of process step (a) for a Sludge retention time from 4 to 48 hours with partial reduction of the content of the first Degradation zone introduced sludge of biodegradable volatile suspended matter continued and partially stabilized sludge is discharged from the first mining zone; 909816/0951 ORIGINAL INSPECTED (c) the partially stabilized sludge discharged from the first decomposition zone is decomposed anaerobically in a covered second decomposition zone while maintaining a ~ "sludge temperature of 25 ° C to 60 ° C for a sufficient solid residence time to increase the biodegradable volatile suspended matter content of the sludge below approximately 40 % of the biodegradable volatile suspended matter content of the sludge introduced into the first degradation zone in process step (a) and to form methane gas, and (d) further stabilized sludge and the methane gas are discharged from the second mining zone. 2. A method for breaking down sludge according to patent 28 05 054.6, characterized in that (a) the sludge and an aeration feed gas containing at least 20% by volume of oxygen are introduced into a first breakdown zone and mixed there in sufficient quantity and measure to meet the respiratory needs of the sludge for aerobic breakdown and the total suspended matter concentration of the sludge in the first breakdown zone to maintain at least 20,000 mg / l; 909816 / 09S1 (b) the sludge in the first mining zone during the Process step (a) is maintained at a temperature in the range from 35 ° C to 75 ° C; (c) process step (b) for a sludge residence time from 4 to 48 hours with partial reduction of the biodegradable volatile suspended matter content the sludge introduced into the first mining zone is continued; (d) partially stabilized sludge from the first mining zone is carried out; (e) the partially stabilized sludge from process stage (d) is introduced into a covered second degradation zone will; and (f) the sludge in the second degradation zone is kept under anaerobic conditions at a temperature of 25 ° C to 60 ° C for a sufficient solids retention time to reduce the biodegradable volatile suspended matter content of the sludge to below approximately 40 % of the content of the process stage (a) to further lower the sludge of biodegradable volatile suspended matter introduced into the first decomposition zone and to form methane gas, as well as further stabilized sludge and that 909816/0951 Methane gas from the second reduction zone held · will. 3. Process for breaking down sludge according to patent 28 05 054.6, characterized in that (a) the sludge and at least 20% by volume oxygen aeration feed gas containing introduced into a first degradation zone and in sufficient quantity and Sufficiently mixed to a utilization of at least 0.03 kg of oxygen per kg of volatile To achieve suspended solids in the sludge introduced into the first mining zone, while the total suspended solids the concentration of the sludge in the first degradation zone is maintained at at least 20,000 mg / l; (b) the sludge in the first mining zone during the process stage (a) is maintained at a temperature in the range of 35 C to 75 C; (c) process step (b) for a sludge retention period, from 4 to 48 hours with partial reduction of the biodegradable volatile suspended matter content the sludge introduced into the first mining zone is continued; 909816/0951 (d) partially stabilized sludge from the first mining zone is carried out; (e) the partially stabilized sludge from process stage (d) is introduced into a covered second degradation zone will; and (f) the sludge in the second degradation zone is kept under anaerobic conditions at a temperature of 25 C to 60 ° C for a sufficient solids retention time to keep the biodegradable volatile suspended matter content of the sludge below approximately 40 % of the content of the process stage (a) to further lower the sludge of biodegradable volatile suspended matter introduced into the first extraction zone and to form methane gas, and further stabilized sludge and the methane gas are discharged from the second extraction zone. 4. The method according to any one of claims 1 to 3, characterized in that that the oxygen-containing aeration feed gas and sludge in the first degradation zone are sufficient Amount and sufficient proportions are mixed to achieve a utilization of 0.10 to 0.35 kg of oxygen per kg to obtain volatile suspended matter in the sludge introduced into the first mining zone. 909816/0951 5. The method according to any one of claims 1 to 4, characterized in that the content of volatile suspended matter in the sludge introduced into the first degradation zone is reduced by 5 to 20% in the first degradation zone. 6. The method according to any one of the preceding claims, characterized characterized in that the first degradation zone for the purpose of forming an overlying sludge in this zone Gas space is equipped with a cover and that the ventilation feed gas is at least 50 vol.% Oxygen contains. 7. The method according to claim 6, characterized in that in the first decomposition zone the ventilation gas or the Sludge is circulated against the other fluid and that from the first degradation zone is depleted of oxygen Degradation gas with at least 21 vol.% Oxygen from the partially stabilized gas discharged from the first degradation zone Sludge is discharged separately. 8. The method according to any one of the preceding claims, characterized in that the in the first mining zone discharged sludge has a total suspended matter concentration between 20,000 and 80,000 mg / l. 9. The method according to any one of the preceding claims, 909816/0951 characterized in that the sludge residence time in the first degradation zone is between 12 and 30 hours. 10. The method according to any one of the preceding claims, characterized characterized in that the sludge is heated to the temperature prior to introduction into the first degradation zone in the first degradation zone between 35 ° C and 75 ° C to keep. 11. The method according to any one of the preceding claims, characterized characterized in that the temperature in the second degradation zone for a mesophilic degradation in the second The degradation zone is kept in the range of 35 ° C to 40 ° C. 12. The method according to any one of claims 1 to 10, characterized in that that the temperature in the second breakdown zone for a thermophilic breakdown in the second breakdown ο zone is kept in the range of 45 ° C to 50 ° C. 13. The method according to any one of the preceding claims, characterized in that the sludge residence time in the second degradation zone is selected to be sufficient to reduce the content of the sludge of biodegradable volatile suspended matter to less than about 20 % of the content of the in process step (a) in the "first degradation zone of introduced sludge on biodegradable 909816/0951 able to further reduce volatile suspended matter. 14. The method according to any one of the preceding claims, characterized in that the sludge residence time in the second degradation zone is 4 to 12 days. 15. The method according to any one of the preceding claims, characterized in that each of the first and second mining zones has a surface / volume ratio of we- 2 3
has less than 2.6 m / m. 16. The method according to any one of the preceding claims, characterized characterized in that the sludge is mixed in the second breakdown zone by adding methane gas against the sludge located there is circulated. 17. The method according to any one of the preceding claims, characterized in that the aeration feed gas is ^{heated from 35 ° C to 75 0} C in order to maintain the temperature prevailing there before being introduced into the first degradation zone. 18. The method according to any one of the preceding claims, characterized characterized in that the sludge prior to introduction into the first degradation zone by indirect heat exchange with the one discharged from the second mining zone, 909816/0951 further stabilized sludge is heated. 19. The method according to claim 18, characterized in that the sludge temperature in the second degradation zone is kept in the range of 35 ° C to 4Ü ° C and that the heated sludge before being introduced into the first Degradation zone through indirect heat exchange with the partially stabilized one discharged from the first degradation zone Mud is further heated. 20. The method according to any one of the preceding claims, characterized in that the second degradation zone is provided with an acidification subzone and a methane fermentation subzone, that partially stabilized sludge from the first degradation zone is introduced into the acidification subzone and acidification of the sludge there for a sludge retention time of 24 to 60 hours is held, and that acidified sludge is discharged from the acidification sub-zone and introduced into the methane fermentation sub-zone and held there at a temperature between 35 ° C and 40 ° C for a sludge retention time of 4 to 8 days. 21. The method according to claim 20, characterized in that the sludge is kept at a temperature between 37 ⁰ C and 38 ° C in the methane fermentation subzone. 909816/0951 - 1O - 22. The method according to claim 20 or 21, characterized in that that the sludge in the acidification sub-zone is kept at a temperature between 45 ° C and 75 ° C and the acidified one discharged from the acidification subzone Sludge prior to introduction into the methane fermentation sub-zone is cooled to a temperature of 35 ° C to 40 ° C. 23. The method according to any one of the preceding claims, which treats wastewater containing biodegradable volatile suspended matter for the purpose of BOD removal is characterized in that a primary sludge comprising the biodegradable suspended matter is separated from the wastewater with the formation of a primary runoff depleted in solids, the primary effluent and return sludge mixed and in sufficient throughput as well as for sufficient Be ventilated for a period of time in order to ·. with reduced BOD content to form the Mixed liquid is separated into purified liquid and activated sludge and at least one larger Part of the activated sludge is returned as the return sludge for mixing with the primary effluent being the primary sludge and not recirculated activated sludge in process stage (a) be introduced into the first mining zone as the feed sludge for that zone. 909816/0951 24. Process for removing BOD from wastewater in one covered fumigation zone as well as for the decomposition of activated sludge with oxygen gas, in which (a) a first gas with an oxygen content of at least 40% by volume is introduced and mixed as a ventilation gas with the waste water and return sludge in the covered fumigation zone to form a mixed liquid and the aeration gas is brought into contact with the mixed liquid in sufficient quantity and extent In order to keep the dissolved oxygen content of the mixed liquid at at least 0.5 mg / l, the mixed liquid is separated into purified liquid and activated sludge and non-consumed oxygen-containing gas is discharged from the gassing zone in such a flow rate that its oxygen content does not exceed Makes up 40 % of the total oxygen introduced into the degradation zone; (b) at least about 85% by weight of the activated sludge returned as the return sludge to the fumigation zone; (C) a second gas is provided which has at least 80 Vol .% oxygen and a part of the 909816/0951 - Includes 12 first gas? (d) the second gas and the non-recirculated animate one Sludge from process step (b) is introduced into a covered mining zone and darted in be mixed in sufficient quantities and proportions for aerobic decomposition of the sludge., while a total suspended solids concentration des Maintain sludge of at least 20 COO mg / l will; (e) the sludge during process step (d) in the degradation zone at a temperature in the range of Maintained at 35 ° C to 75 ° C; (f) partially stabilized sludge and oxygen- depleted decomposition gas with an oxygen content of at least 40 % are discharged separately from the decomposition zone in such a flow rate that the oxygen content of the oxygen-depleted decomposition gas is at least 35 % of the oxygen content of the second gas entering the decomposition zone and (g) the degradation gas partially depleted in oxygen from process stage (f) as at least the larger part of the in process step (a) in 909816/0951 the covered fumigation zone of the introduced first gas is used, according to patent 28 05 054.6, characterized in that (h) process stage (e) with partial reduction the biodegradable content of the sludge introduced into the first degradation zone volatile suspended matter for a sludge retention time continued from 4 to 48 hours; (i) the partially stabilized sludge from process stage (f) is introduced into a second covered mining zone will; (j) the sludge in the second degradation zone is kept under anaerobic conditions at a temperature of 25 C to 60 C for a sufficient sludge retention time to reduce the biodegradable volatile suspended matter content of the sludge to less than approximately 40 % of the content of the process stage (d) to further lower the activated sludge of biodegradable volatile suspended matter introduced into the extraction zone and to form methane gas, and further stabilized sludge and the methane gas are discharged from the second extraction zone. 909816/0951 25. The method according to any one of the preceding claims, characterized characterized in that the methane gas discharged from the second mining zone is mixed with oxygen-containing gas and as fuel is burned with the formation of heat to the sludge in at least one of the to keep both degradation zones at an elevated temperature. 26. The method according to claim 25, characterized in that the methane gas and oxygen-containing gas are mixed and burned as fuel with the formation of heat, by means of the sludge thereof in the first mining zone is kept at a temperature of 35 ° C to 75 ° C. 27. The method according to any one of the preceding claims, characterized in that the temperature of the sludge in the first degradation zone in the thermophilic range of 45 ° C to 75 C as well as the temperature of the sludge in the second degradation zone is kept in the range of 30 ° C to 60 ° C. 28. A method for breaking down sludge according to Patent 28 05 054.6, characterized in that (α) the sludge and at least 50 vol.% oxygen Aeration gas containing introduced into a first covered mining zone and there in for a 909816/0951 aerobic degradation of sufficient quantity and sufficient proportions are mixed while the total suspended matter concentration the sludge is maintained at at least 20,000 mg / l; (b) the sludge in the first mining zone during the Process step (a) at a temperature in the thermophilic Range of 45 ° C to 75 ° C is maintained; (c) process step (b) for a sludge residence time from 4 to 48 hours with a partial reduction in the content of that introduced into the first mining zone Sludge of biodegradable volatile suspended matter is carried away; (d) partially stabilized sludge and oxygen-depleted decomposition gas with an oxygen content of at least 21 % are discharged separately from the first decomposition zone; (e) the partially stabilized sludge from process stage (d) is introduced into a second covered mining zone will; (f) the sludge in the second degradation zone under anaerobic conditions Conditions are maintained at a temperature of 30 ° C to 60 C for a solids residence time, 909816/0951 which is sufficient to further lower the biodegradable volatile suspended matter content of the sludge to below approximately 40 % of the biodegradable volatile suspended matter content of the sludge introduced into the first degradation zone in process step (a) and to form methane gas, as well as further stabilized sludge and the methane gas can be discharged from the second extraction zone. 29. A method for breaking down sludge according to Patent 28 05 054.6, characterized in that (a) the sludge and at least 50% by volume oxygen containing aeration gas introduced as fluids into a first covered mining zone and maintained a content of dissolved oxygen in the mixed liquid of at least 2 mg / l and mixed to a total suspended matter concentration of at least 20,000 mg / l in the sludge; (b) the sludge in the first mining zone during the Process step (a) at a temperature in the thermophilic Range of 45 ° C to 75 ° C is maintained; (c) process step (b) for a sludge residence time from 4 to 48 hours with partial reservation 909816/0951 change in the content of the in the first mining zone ■ discharged sludge of biodegradable volatile suspended matter is continued; (d) partially stabilized sludge and oxygen-depleted decomposition gas with an oxygen content of at least 21 % are discharged separately from the first decomposition zone; (e) the partially stabilized sludge from process stage (d) is introduced into a second covered mining zone will; (f) the sludge in the second degradation zone is held under anaerobic conditions at a temperature of 30 ° C to 60 ° C for a solids retention time sufficient to keep the biodegradable volatile suspended matter content of the sludge below approximately 40 % of the content of in of process step (a) to further lower the biodegradable volatile suspended matter introduced into the first degradation zone and to form methane gas, and further stabilized sludge and the methane gas are discharged from the second degradation zone. 909816/0951 30. The method according to claim 29, characterized in that the introduced into the first degradation zone sludge a total suspended matter concentration between 2O 0OO and has 60,000 mg / l. 31. The method according to claim 29 or 30, characterized in that that the sludge residence time in the first degradation zone is between 12 and 24 hours. 32. The method according to any one of claims 29 to 31, characterized characterized in that the sludge is heated to the temperature prior to introduction into the first degradation zone in process step (b). 33. The method according to any one of claims 29 to 32, characterized characterized in that the temperature in process step (f) for a mesophilic degradation in the second The degradation zone is kept in the range of 35 ° C to 40 ° C. 34. The method according to any one of claims 29 to 32, characterized characterized in that the temperature in process step (f) for a thermophilic degradation in the second The degradation zone is maintained in the range of 45 ° C to 50 ° C. 35. The method according to any one of claims 29 to 34, characterized characterized in that the sludge residence time in the process step (f) is selected to be sufficient to the 909818/0951 Content of the sludge of biodegradable
volatile particulate matter to less than approximately
2O % of the content of the in process step (a) in
the first degradation zone introduced sludge of biodegradable volatile suspended matter
to push down. 36. The method according to any one of claims 29 to 35, characterized in that the sludge residence time in the
Process stage (f) is 4 to 12 days. 37. The method according to any one of claims 29 to 36, characterized characterized in that each of the first and second mining zones has a surface / volume ratio of a few 2 3
is less than 2.6 m / m. 38. The method according to any one of claims 29 to 37, characterized characterized in that the sludge is mixed in the second breakdown zone by adding methane gas contrary to that there located sludge is circulated. 39. The method according to any one of claims 29 to 38, characterized in that the aeration gas prior to introduction into the first degradation zone for the purpose of maintenance
the temperature in process step (b) is heated
will. 909816/0951 - 2Q - 40. The method according to any one of claims 29 to 39, characterized characterized in that the sludge prior to introduction into the first degradation zone by indirect; Heat exchange is heated with the further stabilized sludge discharged from the second mining zone. 41. The method according to claim 4O, characterized in that that the temperature in process step (f) is kept in the range from 35 ° C. to 40 ° C. and that the heated Sludge before being introduced into the first mining zone by indirect heat exchange with that from the The partially stabilized sludge discharged from the first mining zone is further heated. 42. The method according to any one of claims 29 to 41, characterized in that the second degradation zone with a Acidification sub-zone and a methane fermentation sub-zone is provided, partially stabilized sludge from the first degradation zone is introduced into the acidification sub-zone and to acidify the sludge is held there for a sludge retention time of 24 to 60 hours, acidified sludge discharged from the acidification sub-zone and into the methane fermentation sub-zone introduced and there at a temperature between 35 C and 40 C for a sludge retention time of 4 to Is held for 8 days. 909816/0951 43. The method according to claim 42, characterized in that the sludge in the methane fermentation subzone is maintained at a temperature between 37 ° C and 38 ° C. 44, method according to claim 42 or 43, characterized in that that the sludge in the acidification subzone is kept at a temperature between 45 ° C and 75 ° C and the acidified one discharged from the acidification subzone Sludge prior to introduction into the methane fermentation sub-zone is cooled to a temperature of 35 ° C to 40 ° C. 45. The method according to any one of claims 29 to 44, in which wastewater containing biodegradable volatile suspended matter is treated for the purpose of BOD removal, characterized in that a primary sludge comprising the biodegradable suspended matter from The primary drain is separated from the wastewater with the formation of a primary drain that is depleted of solids and return sludge mixed and in sufficient throughput and for a sufficient Duration of ventilated by a mixed liquid With reduced BOD content to form the mixed liquid into purified liquid and revitalized Sludge is separated and at least a larger part of the activated sludge than the return sludge 9G9818 / 095T is returned for mixing with the primary effluent, wherein the primary sludge and non-recycled activated sludge in process step (a) in the first Mining zone can be introduced as the mud for that zone. 46. Process for removing BOD from wastewater in one covered fumigation zone as well as for the decomposition of activated sludge with oxygen gas, in which (a) a first gas with an oxygen content of at least 40% by volume is introduced and, as the aeration gas, is mixed with the waste water and return sludge in the covered gassing zone to form a mixed liquid and, at the same time, in the gassing zone one of these fluids versus the other fluid in sufficient quantity and the speed is continuously circulated in order to keep the content of the mixed liquid in dissolved oxygen at at least 0.5 mg / 1, the mixed liquid is separated into purified liquid and activated sludge and non- consumed oxygen-containing gas is discharged from the gassing zone in such a flow rate that its oxygen content does not exceed 40 % of the total oxygen introduced into the degradation zone; 909816/0951 (b) at least about 85% by weight of the activated sludge than the return sludge to the aeration zone be returned; (c) a second gas is provided which has at least 80% by volume of oxygen and a portion of the first gas includes; (d) the second gas and the non-recirculated animate one Sludge from process step (b) into a Covered mining zone initiated and while maintaining the dissolved content of the sludge Oxygen of at least 2 mg / l and the total suspended matter concentration of the sludge from - at least 20 000 mg / l are mixed; (e) the sludge during process step (d) in the degradation zone at a temperature in the thermophilic Range of 45 ° C to 75 ° C is maintained; (f) partially stabilized sludge and oxygen-depleted decomposition gas with an oxygen content of at least 40 % are discharged separately from the decomposition zone in such a flow rate that the oxygen content of the oxygen-depleted decomposition gas is at least 35 % of the oxygen content of the second gas entering the decomposition zone 909816/0951 matters; (g) the degradation gas partially depleted in oxygen from process stage (f) as at least the larger one Part of the process step (a) in the ab-r covered gassing zone introduced first gas is used, according to patent 28 05 054.6, thereby marked that (h) process stage (e) with partial reduction the biodegradable content of the sludge introduced into the first degradation zone volatile suspended matter for a sludge retention time continued from 4 to 48 hours; (i) the partially stabilized sludge from process stage (f) is introduced into a second covered mining zone will; (j) the sludge in the second degradation zone is kept under anaerobic conditions at a temperature of 30 C to 60 C for a sufficient sludge retention time to reduce the biodegradable volatile suspended matter content of the sludge to less than approximately 40 % of the content of the process stage (d) activated sludge introduced into the decomposition zone of biodegradable volatile suspended matter 909816/0951 lower and form methane gas, as well as further stabilized sludge and the methane gas from the second mining zone. 47. The method according to any one of claims 29 to 46, characterized characterized in that the methane gas discharged from the second mining zone is mixed with oxygen-containing gas and as fuel is burned with the formation of heat to the sludge in at least one of the to keep both degradation zones at an elevated temperature. 48. The method according to claim 47, characterized in that that the methane gas and oxygen-containing gas mixed and burned as fuel with the formation of heat by means of whose sludge is kept at a temperature of 45 ° C to 75 ° C in the first degradation zone. 909816/0951