DE2805054A1 - METHOD FOR DEGRADING SLUDGE - Google Patents

Description

L-11234-1-G

UNION CARBIDE CORPORATION 27O Park Avenue, New York, N.Y. 10017, V.St.A.

Process for breaking down sludge

The invention relates generally to a method for hot degradation of sludge under aerobic and anaerobic conditions.

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 Include activated sludge treatment, the water pollutants into a concentrated form called sludge. Especially with the activation process, which is the most popular one of the conventionally used wastewater treatment systems, it usually comes to one significant resulting production of volatile

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Suspended solids (MLVSS), d. i.e., the cell synthesis rate exceeds the rate of cell breakdown. As a result, an increasing supply of sludge builds up; the revitalized excess sludge must be removed from the process continuously or periodically .

With the increase in the total accumulation of sewage, the one Treatment requires, especially under the influence of ever stricter legal containment measures 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 in this way process so that it can be eliminated easily and economically without causing further pollution of the ecosphere. Although great efforts have been made Achieve improvements in sludge treatment technology and existing sludge treatment processes To refine, there is still a great need for better and more efficient 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 deliver that for a final elimination without further ado

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physical or chemical treatment is fully suitable. Conventionally, the sludge removal is usually carried out by introducing the sludge into the sea Incineration or through agricultural sludge utilization (Spreading mud). In many cases, sludge is disposed of on land; this is in view of the minimal long-term environmental influences particularly attractive. Agricultural sludge utilization can be highly beneficial for soil renewal to promote. An agricultural sludge recovery by spreading sludge on land as the final However, sludge removal procedures require a good pasteurized end product so that the concentration of pathogenic organisms in the sludge is sufficiently low, in order to exclude potential damage to health when removing 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 Basins allow the biological oxidation of organic

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niche substances through natural or artificially accelerated oxygen transfer from the surrounding air into the Water. During the biological oxidation process, the solids in the wastewater are reduced to a certain extent Scope biodegraded; they eventually settle at the bottom of the pond, where they become anaerobic and continue can be stabilized. The pond can be drained periodically to dredge out the settled sludge and in this way to restore the pond's capacity for further wastewater treatment. The extracted sludge is then used, for example, for landfilling. Oxidation ponds form on this Way a functionally simple system for wastewater and sludge treatment. The use of oxidation ponds However, there are limits in practice because the operation of such ponds requires considerable land. In addition, this treatment and disposal process does not significantly reduce the amount of Pathogens achieved in the mud.

Anaerobic degradation is the most widely used degradation process for stabilizing concentrated organic Solids, such as those drawn off from settling basins, biological filters and activated sludge systems will. Conventionally, the excess sludge is collected in large, vaulted excavation rooms where the Sludge is fermented anaerobically for 2O to 30 days. the

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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 questionable, becomes the anaerobic Degradation widely applied in practice because he converts the solid residues into a reasonably stable form that can be used for landfilling purposes without that it comes to greater nuisance. The anaerobic degradation is characteristically carried out in large tanks or rooms 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 stated above, the anaerobic degradation was in general carried out with long residence times of the order of 20 to 30 days without heat being added to the system became. It was already recognized earlier that elevated temperatures in the mesophilic range from 30 ° C. to 40 ° C. Reduction of the necessary length of stay to around 12

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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 about 35 ° C up to 38 ° C with minimum residence times of the order of 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 goes, while temperatures below 35 ° C make longer periods of stay necessary.

Methane gas is generated during anaerobic degradation; it is commonly used in combustion heaters, to compensate for heat losses from the anaerobic degradation system operating at elevated temperatures. Seasonal However, temperature fluctuations and fluctuations in the suspended matter concentration of the inflowing sludge have has a significant impact on both methane gas production and the amount of heat that is required is to keep the degradation zone at the desired, elevated working temperature. If, therefore, elevated temperature conditions should be maintained in the anaerobic degradation zone throughout the year

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an auxiliary heat source usually a substantial part the sludge removal facility.

Because the anaerobic degradation rate and the resulting methane gas formation on the suspended matter concentration of the treated Sludge and the temperature prevailing in the mining zone are strongly influenced, it is generally desirable to supply the mining zone with a sludge that is as concentrated as possible, thereby minimizing heat losses in the outgoing stabilized sludge stream coming from the anaerobic Mining zone is discharged while methane production in the mining zone is maximized. Even with such However, it is difficult to take precautions to economically maintain elevated temperatures in the anaerobic degradation zone in particular to maintain during the winter months. aside from that Even comparatively small temperature fluctuations in the anaerobic degradation zone can be too disproportionate cause severe disruption of the process and acidification of the content of the degradation zone.

In the anaerobic digestion process, the treated sludge solids are sequentially separated into essentially three separate parts Exposed treatment phases, first a period of solubilization, then a period more intense Acid production (acidification) and finally egg ·. a period of intensive degradation and stabilization (gasification). Each of these process stages is determined by the production

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tion of various intermediate and end products in the mining zone. Under normal working conditions, all three phases occur simultaneously. The main gases produced 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 in opposition to process changes extremely sensitive to their environment. For these reasons, no oxygen should be present in the anaerobic degradation zone be. Unintentional introduction of air into the mining zone impairs and leads to methane fermentation

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because of the combination of the combustible methane gas with oxygen possible fire or explosion hazard. In addition, methane-forming bacteria are sensitive to it Process conditions such as fluctuations in the pH value and the presence of heavy metals, detergents, Ammonia and sulphides. For these reasons, a temperature stabilization of the anaerobic degradation zone is of particular importance Importance. The methane generators required within the degradation process are resistant to temperature fluctuations particularly sensitive. Such fluctuations reduce their activity and viability; they lead to a relative excessive growth of acidifiers. This in turn leads to insufficiently stabilized sludge as well as a sludge product that, without further treatment, cannot be used for landfilling or similar purposes suitable is. In addition, these methane generators have a relatively low growth rate, which is the long Requires residence time that is 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 ' In this way, long residence times are required to ensure the presence of sufficient methane generators, and because the sludge flow rate to the mining zone in

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is usually quite low, this is for the mining zone necessary capacity very large. Operation at elevated 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 generated by the anaerobic degradation process is used as fuel gas for the degradation zone, in order to help itself maintain a constant elevated temperature in the event of extreme outside temperature fluctuations. Such a commitment 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 broken down aerobically. For this purpose, air was used as an oxidizing agent in practice generally. It is known that aerobic degradation occurs more rapidly at elevated temperatures. As the temperature rises from 35 ° C, the population of mesophilic microorganisms decreases, while q [ie thermophilic forms increase. The temperature range of 45 ° C to 75 ° C is often referred to as the thermophilic region, where thermophiles predominate and where most of the mesophiles are annihilated. Above this range, the thermophiles decrease. At 90 C the system becomes essentially sterile. Because of the more rapid oxidation of the sludge,

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A more complete elimination of biodegradable volatile suspended matter (VSS) than at ambient temperature can be achieved with a longer degradation time. A more stable residue is obtained which can be disposed of without inconvenience. It has also been shown that thermophilic degradation effectively reduces or eliminates pathogenic bacteria in the sludge, thereby avoiding potential health hazards which might otherwise be associated with the sludge disposal.

If diffusion air systems are used to supply the oxygen for the decomposition, the heat losses are usually very large. As a result, aerobic degradation using air is typically limited to degradation with mesophilic microorganisms. Air systems cannot work effectively in the thermophilic temperature range. Air contains only 21 % oxygen, and only about 5 to 10 % of the oxygen component 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, at outside or ambient temperature (20 ° C or less) in the case of aerobic decomposition with air, the sludge retention time is typically 12 to 20 days, and huge containers are required to contain the sludge, even if measures are taken

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taken to reduce the rate of heat loss through conduction To reduce convection and radiation, the large one that is available for heat transfer leads to Area to strong heat loss.

As a result of the heat losses described above during decomposition with air, autothermal heat effects are 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 significantly reduced 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 for the autothermal heat alone to keep the temperatures at values which are appreciably higher than the outside temperature so that the degradation zone in the thermophilic temperature range can work effectively with a minimal 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 becomes with the thermophilic

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Operation greatly reduced. This in turn allows smaller pools to be used, which reduces heat losses to the Environment are further depressed. Because of the more rapid oxidation of the sludge can aerobic with the thermophilic Degradation a usefully large reduction in the biodegradable volatile suspended matter, for example a Reduction of 8O to 9O%, with comparatively short ones Sludge retention times in the order of 3 to 10 days can be achieved.

Despite its considerable attractiveness, the is thermophilic There are several disadvantages associated with aerobic degradation compared to anaerobic degradation. Because the thermophilic aerobic If the degradation process is oxidizing in nature, the process creates a bio-oxidation reaction product gas, which is carbon dioxide and contains water vapor that can no longer be used, but is expediently released into the atmosphere will. In contrast, anaerobic degradation creates methane gas as a reaction by-product that is beneficial to others Applications can be given and that can also be used as fuel gas to cover the heating energy demand, which is associated with degradation at elevated temperatures. In addition, the aerobic degradation zone requires an essential greater energy expenditure for mixing and contacting of gas and sludge than the anaerobic digestion system for mixing the contents of the digestion zone necessary is.

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The present invention is therefore based on the object of creating an improved method for breaking down sludge. A sludge degradation process is to be obtained in which aerobic degradation and anaerobic degradation at elevated temperature are provided in such a way that the respective advantages are exploited, but the deficiencies in question are minimized.

In the sludge degradation process according to the invention, the sludge and at least 50% by volume of oxygen become Aeration gas introduced as fluids into a first covered mining zone and while maintaining the content the mixed liquid dissolved oxygen of at least 2 mg / 1 as well as the total suspended solids concentration (MLSS) of the sludge of at least 20,000 mg / l. The sludge is in the first degradation zone during this process stage at a temperature in the thermophilic range held at 45 to 75 C.

Mixing in the decomposition zone at thermophilic temperature is continued for a sludge residence 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. Partially stabilized sludge and oxygen-depleted decomposition gas with an oxygen content of at least 21 % are discharged separately from the first decomposition zone. This out-

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Carried, partially stabilized sludge is then fed into a second covered mining zone. The sludge is kept in the second degradation zone under anaerobic conditions at a temperature of 30 C to 60 C for a sludge retention time sufficient to keep the biodegradable volatile suspended matter content of the sludge below about 40 % of the content of the in the First degradation zone introduced sludge of biodegradable volatile suspended matter to lower further and to form methane gas. Thereafter, further stabilized sludge and the methane gas are discharged from the second mining zone.

The terms "sludge" and "activated sludge" are understood here to mean a solid-liquid mixture, having a sludge solids phase and an associated liquid phase, the sludge solids are at least partially biodegradable, i.e. decomposed under the influence of living microorganisms can be. Biodegradable sludge is, im generally labeled according to its content of biodegradable volatile suspended matter (VSS), In the present case, the "content of biodegradable volatile suspended matter" is essentially the understood maximum solids reduction achievable by adding Op-containing gas to the sludge Outside temperature is ventilated, for example at 20 ° C

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and a dissolved oxygen content of at least 2 mg / l. It is assumed that a maximum reduction of the solids collected is achieved after a period of gassing of 30 days. Instructions for such Determinations 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 in the fresh sludge and again after 30 days of fumigation, the biodegradable proportion of the total volatile suspended matter can be calculated as follows will:

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

The term "stabilized sludge" means sludge • with a reduced content of biodegradable volatile substances Understood sulfur substances following a degradation treatment and on the basis of such a treatment. The term "sludge residence time" denotes the mean period of time during which the sludge in a given Mining zone is present; it is calculated according to the following formula:

where "C = sludge retention time (days or hours);

V
d = volume of that treated in the degradation zone

Sludge (m); and

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

The invention is based on the surprising finding that an aerobic degradation zone working in the thermophilic temperature range with an anaerobic one located downstream Degradation zone can be integrated to allow for partial degradation of the sludge in each of the successive zones and that such integration leads to process improvements beyond those which one based on considerations regarding the befrref-. expected degradation stages alone.

So far, for numerous reasons, no attempts have been made to aerobic and anaerobic degradation at elevated temperatures of sludge in the manner proposed here. 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 as heating gas to produce an economical operation of the voluminous dismantling tanks. The combination, tion of an anaerobic degradation zone with an aerobic degradation stage therefore appears on the basis of considerations regarding the total tank capacity requirement for the combined process as undesirable; one would expect the tank space required to be larger than for each of the degradation processes alone.

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Such a combination seems to be the most aerobic as well Functions normally assigned to anaerobic degradation processes only have to be doubled without that an increase in the efficiency of the treatment is to be expected.

The combination of an anaerobic degradation zone with an aerobic degradation stage also appears undesirable because it can be assumed is that the anaerobic degradation stage is not able to work within the combined system even for. a To provide partial degradation of the sludge with sludge retention times that are below the long retention times that are for conventional anaerobic, stand-alone degradation zones are characteristic. As discussed above, are when anaerobic 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 to within to ensure only a partial degradation of 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.

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Besides the above reasons, the combined aerobic / anaerobic degradation system appears in view of the Operational stability is disadvantageous because both the aerobic and the anaerobic degradation stage alone require tight control of the operating temperature require when working with elevated temperature values, so that a coupling of the two processes concerned would apparently make an even closer temperature control necessary and with possible intensified adverse influences due to temperature instabilities and fluctuations are to be expected.

After all, you'd be doing a combined aerobic / anaerobic Expect degradation 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, in the anaerobic degradation zone there are Methane-producing bacteria are strictly anaerobic and extremely sensitive to changes in their environment. It is known, that any significant introduction of oxygen into the anaerobic degradation zone stabilizes the sludge through methane formation adversely affected and that there is a risk of oxygen from the liquid in the methane-containing Gas phase passes and a combustible gas mixture is formed in the decomposition zone.

Contrary to the above-described, to be expected

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hold it was surprisingly found that the use of a thermophilic aerobic degradation zone upstream ■ of an anaerobic degradation zone working at an elevated temperature and the operation of these zones in accordance with Process of the present invention not only to a functional and economical sludge treatment system leads, but results in a breakdown system that is based on synergistic Effects between the aerobic and the anaerobic The dismantling part of the present process has decisive advantages compared to known processes. For example the method according to the invention is able to achieve a thermal within the entire sludge degradation system To ensure work stability, which cannot be achieved in each of the individual dismantling stages alone. Furthermore, the integrated degradation process of the invention provides a highly stabilized sludge, the is also completely pasteurized, although the residence time within the overall process is reduced compared to that duration is what one would expect given the length of stay requirements each of the separate partial dismantling stages is taken into account alone. What is particularly surprising is the finding that the anaerobic degradation zone of this process is able to operate at sludge retention times that are significantly below those required for a full stabilization treatment of the sludge in conventional, alone working anaerobic digestion zones are necessary and that such operation is achieved without

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that as a result, as would be expected, the efficiency of the treatment decreases. As an example of residence times suitable for the present process, it should be mentioned that a test facility 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 advantages mentioned above 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 facility is retained, as shown in detail below. For example, the plant according to the invention can operate with only about 6 % of the capacity that must be provided in a known anaerobic degradation zone, but have approximately 75 % of the methane production capacity of the known zone. Such an improvement leads to the generation 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 significantly different from that

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Sludge from the first mining zone into the gas phase of the second Mining zone is transferred.

The reasons for the unexpected benefits of the present Procedures are not fully clarified. It may be that there is no significant transition of oxygen from the first to the second mining zone is that the elevated temperature conditions in the second degradation zone for sufficiently intense anaerobic bacteriological Conditions provide for the content of the sludge passed from the first to the second mining zone Thoroughly break down dissolved oxygen before dissolved Oxygen can pass into the gas phase to a significant extent within the second degradation zone. The surprising short residence times of the present process, especially in the anaerobic degradation stage, can be combined with the thermal stability of the process and the surprisingly high methane production capacity of the anaerobic stage the consequence of a chemical or biological acclimatization of the sludge and the microorganisms in the aerobic Be the degradation zone for improving the efficiency of the subsequent anaerobic treatment stage cares. Regardless of this, no commitment is made to a specific theoretical explanation of this operating behavior take place. Only the method steps and features disclosed in the present case are essential.

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The invention is explained in more detail below on the basis of preferred exemplary embodiments. In the enclosed Drawings show:

Fig. 1 is a flow diagram of a degradation process according to an embodiment of the invention, wherein Heat from the effluent streams of both the first and second covered The mining zone is reclaimed,

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

Fig. 3 is a flow diagram of a further embodiment of the method according to the invention, wherein the sludge from the primary and secondary waste water treatment stage, the slurry is fed to decomposition zones,

4 shows a graphic representation of the temperature of the sludge entering the first degradation zone, which is necessary to maintain a working temperature of ^: 50 C in the first degradation zone.

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hold, plotted as a function of the total suspended matter concentration (MLSSj of the sludge flowing into the first extraction zone, and

Fig. 5 is a flow chart of a further embodiment

Rung form of the invention, in which a smaller part of the sludge flowing into the process system is diverted to the second Aboauzone.

Fig. 1 shows a flow diagram of a process which is suitable for a sludge treatment is suitable, with a first thermopni-Ie aerobic degradation stage is provided, followed by a mesophilic anaerobic degradation. Mud, for example from a primary settling basin, the septic tank a wastewater treatment plant working according to the activated sludge process, a trickle filter or an anaer one sludge-producing system occurs via egg ~ ne line 8 and is successively in heat exchangers 22 and 15 Pe for example to a temperature of 30 ° C to 35 C heated before it is introduced into the first covered mining zone 1O to bring the temperature in the zone to a Maintain thermophilic value in the range of 45 ° C to 75 ° C. The outside temperature having sludge in the line 8 is first heated in the heat exchanger 22 by the sludge in indirect heat exchange with the opposite

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stream is brought through further stabilized sludge, which is a second covered mining zone 2O via a line 24 leaves. This way it becomes warm recovered from the further stabilized sludge. The cooled, stabilized sludge obtained leaves the heat exchanger 22 and is from the system via a Line 25 discharged for final disposal or other use. The in the heat exchanger 22_über further stabilized sludge entering the line 24 can expediently have a temperature of 35 C to 40 C, so that the incoming sludge, which leaves the heat exchanger via a line 9, is brought to a temperature of 28 ° C is heated to 3O C. The flowing in via line 9, partially heated sludge is further heated in the heat exchanger 15 to a temperature of 30 C to 35 C by it is brought into indirect heat exchange in countercurrent with the partially stabilized sludge that comes from the first Degradation zone 10 is discharged via a line 14 and from the heat exchanger via a line 16 into the second Mining zone 20 reached.

As an alternative to the previously discussed heat exchange with stabilized sludge product streams from the The inflowing sludge can precede the degradation zones in question the introduction into the first degradation zone by indirect heat exchange with an appropriate, externally supplied Heating medium, e.g. steam or hot water,

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be heated, although a heat recovery from the warm Degradation zone product streams are preferred as this effectively utilizes the heat within the process and the heating energy requirement of the process is minimized. Although the warming of the incoming mud before the introduction into the first mining zone does not form an essential part of the present process, it may in practice it may be desirable to increase the thermal efficiency of the process taking place at elevated temperature to maximize. 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.

The further heated sludge that passes through the heat exchanger 15 a line 11 leaves, is in the first mining zone 1O introduced together with aeration gas from a line 17, the sludge and the aeration gas being the process fluids for the first stage of mining. The vent gas in line 17 contains at least 50 and preferably at least 80 vol.% oxygen in order for one to use it appropriately 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. The line 17 is connected to a (not shown) source for an oxygen-containing ventilation gas.

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closed. This source can be, for example, a low-temperature oxygen storage facility, a storage container or an adsorption air separation system operating with an adiabotic pressure cycle process , as is often provided in the relevant technology in order to provide oxygen-containing gas. As illustrated, the oxygenated © vent gas in line 17 may also heated by a heater 19 '.' / Ground to assist in that di © Temperstur in aer ~ AEB building zone 10 on the. desired l'isrt is kept.

In the aerobic degradation zone 10, the sludge and the aeration gas are mixed - at the same time, one hot fluid is circulated with respect to the other fluid in sufficient quantity and at sufficient speed. to keep the content of the sludge cm of dissolved oxygen at at least 2 nig / l and the total suspended matter consontration (MLSS; ds-s sludge) to at least 2O 000 mg / 1 a submerged turbine and a gas compressor, which is connected to the gas head space in the decomposition zone and to the gas injection device, in order to circulate the oxygen-containing aeration gas against the sludge the sludge circulates against the aeration gas in the gas headspace of the Abbauzon® 10. The circulation of one of the sludge and aeration

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supply gas existing. Fluids as opposed to the other fluid in the aerobic building zone are preferably used in practice in order to obtain a high content of dissolved oxygen in the sludge and to make extensive use of the oxygen in the aeration gas. Nonetheless provides such circulation no Zwangsmerkmai of the present process. In some cases it may be possible to provide sufficient dissolved oxygen in the mud and high utilization of oxygen in Beiüftungsgas by 3elüftungsgas only once by the aerob.e degradation zone hindurchgeieitsT. will. The content of the sludge in the first Abbcuzon-3 ar. dissolved oxygen must be at least 2 mg / l; um oen thermophiier; To steep microorganisms in the sludge for sufficient oxygen eir.e '-asche decomposition of the biodegradable ^f ähigen Schiammbestcndteile available, which goes back to these microorganisms. The total suspended matter concentration of the sludge is at least -20 OOD mg / 1 in order, based on kinetic considerations, to achieve a high rate of biological sludge degradation in the aerobic defrosting zone, in order to simultaneously keep the heat of reaction from the exothermic ascrben degradation at a sufficient level to keep the temperature of the sludge in the first degradation zone within the thermophilic range, and to achieve a satisfactory level of partial sludge stabilization in the degradation zone with short residence times.

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Under the process conditions mentioned above, Sludge kept in the first degradation zone for degradation at a temperature in the thermophilic range of 45 C to 75 C, which ensures rapid oxidation of the volatile suspended matter content of the sludge. The thermophilic degradation stage is used for a sludge retention period in the first Degradation zone continued from 4 to 48 hours to reflect the content of the sludge introduced into the first degradation zone to partially reduce biodegradable volatile suspended matter. The sludge retention time in the aerobic The mining stage should last at least 4 hours in order to achieve sufficient partial stabilization in the first mining zone bring about. If the stay is less than 4 hours, this will be Measure of the subsequent anaerobic treatment stage required sludge stabilization disproportionately large compared to the degree of stabilization in the first aerobic Step; the total system residence time and the tank capacity requirement begin to approach the values of conventional ones to approach anaerobic degradation systems; the unexpected improvement in these process parameters necessary for operation at Dwell times of four hours or more are characteristic are increasingly lost. For similar reasons, the sludge retention time in the aerobic degradation zone should be Do not exceed 48 hours. Above this value, the degree of sludge stabilization in the aerobic degradation zone excessively large compared to the rest Stabilization in the downstream anaerobic stage.

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The length of stay necessary in the last-mentioned stage to maintain an appropriately large population of methane generators in the mining zone tend to be much longer than this with regard to one effective operation is desired. Again, the unexpected improvement is in terms of overall system residence time and tank capacity requirements are increasingly lost with a dwell time range of 4 to 48 hours is achievable. On the basis of the above considerations, a dwell time in the range of worked up to 24 hours.

Following the aerobic degradation treatment explained above, partially stabilized sludge is discharged from the aerobic zone via line 14, while oxygen-depleted degradation gas with at least 21 % oxygen content and preferably at least 4% oxygen content is separately removed from the aerobic zone via line 18. The oxygen concentration of the exhaust gas from the decomposition zone in the line 18 can easily be kept at the appropriate value by regulating the relative flow rates of the gas supplied via the line 17 and the gas exiting via the line 18. For this purpose, for example, gas flow control valves can be provided in the gas inlet and / or gas outlet line, which are influenced in a known manner by an oxygen concentration analyzer which is in the

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Outlet line 18 is seated.

Because the sludge is under in the aerobic degradation zone thermophilic process conditions is maintained, can -like has been found to achieve essentially complete pasteurization of the sludge. From the aerobic Zone 1O via line 14 outgoing, partially stabilized Mud has a temperature in the thermophilic range between 45 ° C and 75 ° C. Because in this embodiment a mesophilic anaerobic degradation covered in the second Degradation zone 20 is provided, heat is preferably withdrawn from the partially stabilized sludge in line 14, efficient operation of the anaerobic sludge treatment stage to ensure. Accordingly, the sludge in the line 14 is passed through the heat exchanger 15 and brought into indirect heat exchange with the partially heated, inflowing sludge, 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 second covered degradation zone 20. Alternatively, the partially stabilized sludge in line 14 can also be supplied externally by means of an external device cool the cooling medium, for example with the clarified Drain of a sewage treatment plant. When operating in winter it may not be necessary to to provide a heat exchange stage for cooling the partially stabilized sludge flow, because heat losses to the

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Surroundings of the second mining zone and that of the first sludge stream flowing to the second degradation zone can satisfactorily compensate for such a cooling stage.

The partially stabilized sludge introduced into the second degradation zone via line 16 is kept there under anaerobic conditions at temperatures of 30 ° C to 45 ° C for a sufficiently long sludge retention time to reduce the biodegradable volatile suspended matter content of the sludge to less than approximately 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 mud covered in the second The degradation zone is maintained in the range of 30 ° C to 60 ° C. this includes both operation in the mesophilic range of 30 ° C up 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 bio-

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Logically degradable volatile substances by the relevant microbial strains.

When operating the anaerobic degradation zone 20, the content the degradation zone is constantly mixed by means of a stirring device 21, creating a large zone for active degradation formed and the speed of the stabilization reactions is increased significantly. The dwell time of the Sludge in the second degradation zone can suitably be in the range of 4 to 12 days and preferably in the range of 5 to 9 days. Sludge retention times in the second degradation zone of less than 4 days can be inappropriate be; the residence time is less and less sufficient to maintain a large viable population of methane generators in the maintain anaerobic stage; the overall sludge stabilization behavior the degradation system is adversely affected. On the other hand, staying in the anaerobic Degradation stage of more than 12 days, the time spent in the second degradation zone is unnecessarily long; it is increasing more difficult, the synergistic advantages of the integrated process in terms of dwell time and tank space requirements to realize that are achieved within the residence time range of 4 to 12 days.

After the anaerobic treatment of the sludge in the second Mining zone 20 is completed, the further stabilized sludge obtained in this way from the two-

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th mining zone discharged 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 the plant via line 25 finally leaves. That formed in the second degradation 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 As discussed, changes in temperature affect the relative growth rates of acid-forming and acid-forming methane-producing bacteria. The acid-producing bacteria are typically very robust; moderate temperature fluctuations do not change their metabolic activity to any significant extent. In contrast, methane-producing bacteria are extreme sensitive to environmental conditions. If the maintenance of a constant temperature in the other

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aerobic degradation zone due to temperature fluctuations of only a few Disturbed degrees, instabilities arise in terms of the activity and growth of the methane generators. As a result, the activity of the acid generators dominates; 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.

Another problem associated with conventional anaerobic digestion systems is that the methane-forming Bacteria are sensitive to the presence of toxic metals such as copper. Even very small amounts of these metals in the sludge prevent the methane generators from working. As in the previous one Falls begin after continued delivery of toxic metal concentrations to the anaerobic degradation zone to dominate the acid generators, producing an excess of acidic decomposition intermediates will. The pH value in the degradation zone drops and causes a additional impairment of the activity of methane generators. This cumulative effect inevitably leads to serious process disturbances.

To avoid the above-mentioned disturbances in the conventional To counteract anaerobic mining zone, large amounts of lime are usually introduced into the mining zone in order to achieve the

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To strengthen the buffer effect and thereby the pH value in the Increase mining zone. This corrective action can be successful when the mining zone has a shock load on it Substances have been added that can be flushed out of the system or assimilated there. By lifting the pH-value and lowering the inflow amount it is sometimes possible to correct such a disturbed degradation zone again To bring work. However, the corrective measures mentioned above are usually only suitable for short-term, early fluctuations or process disturbances; they usually offer no benefits if there are long-term fluctuations or interference 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 aerobic degradation stage is integrated with a subsequent anaerobic sludge treatment stage. In the case of the present During the process, the thermophilic aerobic degradation stage can normally contribute more than enough heat to to thermally stabilize the anaerobic stage due to the heat content of the partially stabilized sludge flow, which is passed from the aerobic degradation zone to the anaerobic stage. As a result, temperature disturbances can occur present in the anaerobic zone can be practically eliminated by changing process parameters, too

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which the sludge retention time in the aerobic zone, the Solids content of the sludge fed to the aerobic zone and the degree of heat exchange, due to of which the feed sludge before its introduction into the aerobic Zone is heated. The anaerobic degradation zone can typically be independent of seasonal outside temperature fluctuations operated at a temperature that is no longer from the optimal temperature state deviates more than 1 degree.

The present method can also often have an increased tolerance to toxic metal components in the sludge fed to the mining system. Though a conventional anaerobic digestion system toxic metals cannot tolerate has the presence of such * pollution in the sludge fed to the present process has a comparatively reduced influence on the stability and methane production capacity of the anaerobic degradation stage. Signs suggest that these metals are only toxic when they are in a soluble ionic form. It is believed that the present processes during the aerobic degradation stage these metal ions with solids in the treated sludge Complex compounds enter into, so that these metals remain in complex compounds during the anaerobic process stage run through. As a result, the anaerobic part of the present integrated process can be more stable with respect to

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of the inhibiting influences that normally act on the sludge treatment process due to the presence of heavy metals in the inflowing sludge.

A further essential advantage of the integrated method according to the invention, besides the advantages which can be attributed to working temperature stability and resistance to toxic metal inhibiting effects, is the ability to absorb sporadic disturbances, such as shock loads, without the efficiency of the process being impaired. In a conventional anaerobic degradation zone, the initial phase of solubilization within the degradation process not only occurs rapidly, but the microbial exploitation of this material by mesophilic and, optionally, by acid-forming bacteria occurs at high speed. If a sudden high solids load occurs in the conventional anaerobic degradation system, the solubilization and acidification take place at a faster rate than the methane-forming bacteria can use the acidic intermediates. As a result, there is an accumulation of acidic constituents in the degradation zone. The pH value in the decomposition zone falls *, the content of the decomposition zone threatens to become acidic. In the present process, the upstream thermophilic aerobic stage not only promotes rapid solubilization of biodegradable material in the sludge; rather, this stage is inclined

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also to the population of mesophilic acid-forming Reduce bacteria. Then the anaerobic degradation stage allows these organisms to grow again; however, their population is typically smaller and more in balance with the population of the methane-producing organisms. Therefore, when the aerobic zone is subjected to shock loading, the solubilization is rapid in the aerobic degradation zone as well as to a stabilization of the most volatile sludge components, whereby the Shock loading is smoothed and its influence on the downstream anaerobic zone is greatly reduced. In The anaerobic zone takes on the next stage of treatment partially stabilized sludge, in which the acid-forming bacteria and the methane-forming bacteria in mutual Balance can grow.

So much for the first stage of the present sludge treatment process If an aerobic thermophilic degradation zone is used, the process known from US Pat. No. 3,926,794 can be used use advantageously in connection with the method according to the invention to treat wastewater, the biological Contains degradable suspended matter, and around BOD in the activated sludge process with the resulting sludge treated by the present process will.

For example, wastewater treatment with revitalized

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tem sludge is known to be carried out as follows. BOD-containing Wastewater, for example municipal wastewater, can initially pass through a sand trap and a primary settling basin be directed to separate a primary sludge from the wastewater, which contains biodegradable suspended matter, and in this way to obtain a solids-depleted primary effluent which is then fed to the aftertreatment system is initiated. In the aftertreatment, the primary effluent and return sludge are mixed and fed into ventilated to a sufficient extent and for a sufficient period of time to obtain a mixed liquid with reduced BOD content to build. After that, the mixed liquid is purified into Liquid and activated sludge separated. At least a larger part of the activated sludge is returned, to be mixed with the primary effluent as said return sludge. This sewage treatment system can be used appropriately in connection with the process according to the invention, the primary sludge and activated sludge not returned to the first degradation zone of the present process are fed 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 ventilation gas in a cooler covered zone for

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a wastewater treatment with activated sludge is used. The patent shows that for the degradation stage an oxygen gas of relatively high purity as a vent gas should be used to achieve the high mass transfer driving force required for an effective Dissolving oxygen in the aerobic degradation zone working at elevated temperature is necessary. At elevated temperatures becomes significant due to the stronger biochemical degradation effect on the sludge in the aerobic degradation zone Amount of carbon dioxide generated as a gaseous reaction product. 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, which lowers the effective concentration of oxygen in the aeration gas in this zone will. 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.

Due to the effects mentioned above, the driving force for an oxygen mass transfer from the gas phase to the Sludge in the thermophilic mining zone is significantly reduced. The driving force for oxygen mass transfer in the liquid sludge phase is also due to the

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lower oxygen solubility with increased thermophilicity Temperature values reduced. For these reasons, U.S. Patent 3,926,794 recommends that this be incorporated into the thermophile Oxygen-containing gas introduced into the decomposition zone has an oxygen concentration of at least 80% by volume. Under The venting gas leaving the thermophilic degradation zone can with advantage in such working conditions can be used as oxidizing agent gas in an aftertreatment with the aid of the activation process.

Fig. 2 shows a flow diagram of a further embodiment of the invention, which shows how that from the No. 3,926,794 known procedure with the inventive method Process can be combined advantageously.

According to FIG. 2, water containing BOD arrives, for example municipal wastewater, via a line 101 into a gassing zone 102. The gassing zone 102 are also a first gas containing at least 40% by volume of oxygen via a line 118 (dashed) and more animated Return sludge is supplied via a line 1O8 in which a pump 109 is seated. Supernatant from one Sludge thickener 151 also goes via line 150 into the covered gassing zone 102. In FIG. 2, lines carrying liquid and sludge are shown in solid lines, while gas-carrying lines are shown in dashed lines. For simplicity, valves are not

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shown; the appropriate use of such Valves, however, are understood by those skilled in the art. The currents mentioned are in the gassing zone 102 by means of a mechanical stirrer 1O3 thoroughly mixed. The stirring device can be motor-driven, sitting near the surface of the liquid or in the Have liquid immersing impellers; the oxygen gas can be via line 118 above or below the Liquid level are supplied. Devices of this type are known; they should be chosen so that a large contact area between the fluids is obtained with minimal expenditure of energy. Will the oxygen gas blown into the liquid or to diffuse in brought, the bubbles should be so small that their total surface large and their buoyancy is low. The dissolution of oxygen is also aided by the fact that the The arrangement provided for introducing the gas is immersed so deeply into the liquid that the hydrostatic Effect plays a role.

Means are provided for in the gassing zone 1O2 to constantly overturn one medium in relation to the other media. For example, an appropriate line arrangement can be used to connect to the gas space in the gassing zone Compressor (not shown) connected to circulate ventilation gas to the lower part of the zone and in the form of small bubbles via a conventional ventilation device

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Kind of release. Alternatively, said mixing device can also be used to circulate the fluids, such as this is the case with surface gassing impellers. Fumigation devices are generally measured according to the so-called "normal air transition efficiency", which is the capability of the device indicates to dissolve oxygen from air in tap water that does not contain dissolved oxygen contains, is under one atmosphere pressure and has a temperature of 20 ° C. Suitable devices have one Air normal transition efficiency of at least 0.92 kg Op / kWh and preferably an efficiency vpn at least 1.85 kg Op / kWh. For these purposes it is the one used for dimensioning the device Energy around the total energy required both for stirring the liquid and for bringing the gas into contact and liquid is consumed.

The above-mentioned oxygen is introduced; At the same time, one of the media is constantly circulated in relation to the other media in sufficient quantity and speed to keep the dissolved oxygen content of the mixed liquid at at least 0.5 mg / l. The liquid temperature is also preferably maintained at at least 15 ° C., so that means may be required to avoid a lower temperature in the gassing zone 102 in cold weather. For example, the incoming sewage can be in the line for this purpose

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101 are heated. Structure and mode of operation of the wastewater fumigation zone 1O2 can be found in US Pat. No. 3,547,811, 3 547 812 or 3547 815 may be selected in a known manner.

The mixed liquid enriched with oxygen is diverted from the covered gassing zone 1O2 and reaches a clarifier 105 via a line 104, 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 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 clarification basin 105 via a line 106, while activated sludge is discharged via a line 107. The activated sludge contains microorganisms in concentrated form corresponding to a total suspended matter content (MLSS) of approximately 10,000 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 108 and pump 109, preferably in such a flow rate based on the BOD-containing wastewater that the volume ratio of return sludge to BOD-containing

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Wastewater is between 0.1 and 0.5. The flow rates the media introduced into the covered aeration zone 1O2 are preferably dimensioned in such a way that the total suspended matter concentration there is between 40,000 and 12,000 mg / l and the content of volatile suspended solids (MLVSS) 3,000 to 10,000 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 gets in the clarifier for two reasons separated sludge is returned to the aeration zone 102. On the one hand, the activation process produces an overall excess of microorganisms because the mass which is synthesized from the impurities in the wastewater new cells is greater than the mass of the cells that experienced self-oxidation during treatment. To the others, the wastewater usually contains non-biodegradable solids that settle and collect accumulate with the biomass. As a result, a small portion of the activated sludge has to be excreted, to ensure a balance between the microorganism population and the supply of organic substances (BOD)

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and to suppress the accumulation of inert solids within 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 extracted from the clarifier 1O5 via the sludge circulation loop withdrawn in a line 111. It has a total suspended matter concentration of 10,000 to 40,000 mg / l and initially approximately the same temperature as the wastewater in the gassing zone 102; d. H. 15 ° C to 25 ° C. The sludge is fed to the thickening tank 151. Of the Thickening tank 151 concentrates the sludge on a total

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Suspended matter concentration between 20,000 and 60,000 mg / l. The thickened sludge withdrawn from below is fed to the sludge digestion system via a line 152.

In some cases, such as wastewater treatment at high outside temperatures, thickening of the Sludge from the clarifier may not be necessary; the sludge in line 111 can then pass through a line are expediently led past the thickening tank 151 and then get into line 152 to connect to the Sludge removal system to go. The overflow of the sludge thickener As described above, (supernatant liquid) is fed via line 150 to gassing zone 102 .

The thickened sludge in line 152 can, if necessary, be heated by means of a methane boiler 130 before being introduced into an aerobic degradation zone. Instead of of this, the sludge can also be in heat exchange with the stabilized sludge drainage from an anaerobic degradation zone 120b are brought, similarly as explained above in connection with the embodiment of FIG is. Blow-down is placed in the first covered mining zone 110 from line 152 either continuously or initiated intermittently. The aerobic degradation zone 11O is at a temperature in the thermophilic range of Held at 45 ° C to 75 ° C. If an autothermal operation is in

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the aerobic degradation zone is achieved, the slurry temperature are expediently kept at temperatures in the range from 55 ° C to 65 ° C in the degradation zone. It's tough, Maintain degradation temperatures above 65 ° C autothermally. The increased temperature covered in the first Degradation zone 110 can also be reached by adding external worms, for example by circulates an appropriate heated fluid in a heat exchanger, not shown, which is in the degradation zone sits. Because of the tendency of the solids to form coatings and causing clogging, heat exchanger surfaces located within the degradation zone should not complicated or closely spaced; advantageous they can be embedded in or connected to the wall of the tank.

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

Preferably, the elevated temperature is covered in the first Degradation zone 11O achieved autothermally without the need for heat exchangers such as device 130.

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The concentrated sludge, as it is in the oxygen fumigation process according to the US-PS 3,547,813 usually occurs, 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, with high solids concentrations, the The size of the digestion tank is smaller, which also reduces heat conduction losses through the walls of the digestion tank will. 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 of the aerobic degradation zone are essentially determined by two factors. In general, the maximum concentration depends on the ability of conventional settling and thickening devices starting to reduce the water content. Flotation devices, centrifugal separators and gravity thickeners often provide total suspended solids concentrations from 6O,000 mg / 1. The solids content can also be thereby be increased that fresh sludge or concentrated waste from a source other than the wastewater is admixed will. The second factor limiting solids concentrations is the increasing difficulty in the breakdown zone Dissolve oxygen and mix the solids. A preferred upper limit is 60,000 mg / l, whereby ensures that the dissolved oxygen in the

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Sludge is sufficiently uniformly distributed. aside from that can be when using the method according to the invention in most cases temperatures that almost the correspond to maximum aerobic, thermophilic degradation rates, achieve autothermal if the solids content is not higher than 60 000 mg / l. A further increase in the solids concentration would result in more CO-.in enter the gas space of the mining zone; the partial pressure of oxygen of the ventilation gas would be unnecessarily reduced.

The construction of the digestion tank also affects the autothermal temperature values. Concrete walls are due the lower heat conduction losses of concrete over metal walls. The heat loss can continue Press down by having the tank embedded underground and soil against any exposed plumb tank walls is raised. If necessary, thermal insulation, for example a low density concrete or a foam, can be applied over a metallic cover.

Preferably for the method according to the invention furthermore, aerobic and anaerobic digestion tanks are used, the one

Surface / volume ratio of less than 2.62 m / m to have. The term "surface" includes the entire wall surface of the covered mining tank including Base, lid and side walls. Surfaces / volume

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ratios of more than 2.62 m / m lead to large heat conduction losses through the walls, based on the amount of heat required in the digestion tank. One of those Heat loss usually requires thermal insulation on the walls exposed to the outside atmosphere. In addition, larger surface / volume ratios require generally degradation tanks with smaller dimensions, in which a fumigation and / or a uniform Mixing is difficult.

The length of time the sludge remains in the aerobic decomposition zone also influences the autothermal temperature values, that can be sustained. The relationship between residence time and temperature is determined by numerous factors determined, among other things, by the degradability and the strength (the solids content) of the sludge. In general should with a sludge retention time in the first degradation zone of 4 to 48 hours and preferably of 12 can be worked for up to 24 hours.

The first mining zone 11O is equipped with a mechanical agitator 112 which is of the same type as that Agitator 103 can be in the aeration zone 102. In addition, means are provided for the second gas in the mining zone or to constantly circulate the activated sludge in relation to the other fluids.

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The second gas containing at least 80 % oxygen is fed to the covered aerobic degradation zone 110 in sufficient quantity and speed to keep the dissolved oxygen content of the sludge at at least 2 mg / l.

An oxygen-depleted decomposition gas with an oxygen concentration of at least 40% is withdrawn from the covered decomposition zone 110 via 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 line 117. The gas in the line 118 reaches the covered gassing zone 102, with at least a larger part of the mentioned first gas providing the oxygen which 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 reached in zone 110, is partially stabilized Sludge, which, however, is essentially completely pasteurized, from the first covered digestion zone 110 over a line 114 discharged and fed to the anaerobic treatment part of the integrated system. At this

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In the embodiment, the second anaerobic degradation zone comprises an acid formation subzone 120a and the methane fermentation subzone 120b. The partially stabilized sludge coming from the first degradation zone 110 in line 114 is introduced into the acid formation subzone 12Oa and held there for a sludge retention time of 24 to 60 hours in order to ensure the necessary acidification of the sludge. The contents of the sub-zone 120a are continuously mixed by an agitator 121a in order to break down carbohydrates, fats and proteins at a uniform rate into 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. Since the temperature of the sludge leaving zone 120a is still in or near the thermophilic temperature range of 45 ° C to 75 ° C and thus above the optimal methane formation values, the temperature of the acidified sludge is generally lowered in order to ensure satisfactory operation of the methane-forming partial zone 12 Whether to ensure. 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 to the methane fermentation subzone 120b. The heat exchange medium used for cooling in the line 160 can appropriately be a flow of cooling water, for example a

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Part of the drain that runs the secondary clarifier over the pipe 1O6 leaves, or, as in the case of those previously discussed Embodiment, the incoming feed sludge stream flowing into the mining system.

The anaerobic decomposition zone 12Ob represents the methane-forming Stage of the process. For optimal operation becomes the sludge in the methane fermentation sub-zone at a temperature between 35 ° C. and 40 ° C. and preferably held between 37 ° C and 38 ° C. The content of zone 12Ob is constantly mixed by means of an agitator 121b, which ensures a large active decomposition zone and the speed of the stabilization reactions taking place there is increased significantly. The sludge retention time in the methane fermentation subzone is on Because of the considerations discussed above regarding the sludge retention time in the anaerobic second degradation zone preferably between 4 days and 8 days. Methane gas produced by the biochemical which runs off in the subzone 12Ob Reactions is generated, leaves this zone via a Line 128 in which a flow control valve 129 is located. A Part of this discharged methane gas can be fed to the boiler 130 via a line 132, during the remaining part withdrawn from the process in a line 131 to undergo further treatment and / or to be fed to other end-use levels. Of the further stabilized sludge that does not exceed 40% and

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preferably does not contain more than 20% of the original biodegradable volatile solids content of the inflowing sludge, is discharged from the process via a line 133.

Fig. 3 shows a flow diagram of a further embodiment in which sludge from wastewater pre- and post-treatment stages be fed to the sludge removal system. This embodiment represents a process sequence in which integrates a thermophilic aerobic first degradation stage with a thermophilic anaerobic second degradation stage. So far, thermophilic anaerobic degradation was little more as a laboratory curiosity. The problems associated with mesophilic anaerobic operation discussed above known systems with regard to thermal instability and extreme sensitivity to changes in process conditions are even more pronounced with thermophilic anaerobic degradation. Because of the uncontrollable This sludge treatment process has hitherto been commercially stable in terms of thermophilic anaerobic degradation Sludge removal applications received little attention. The problems of operational instability and excessive sensitivity against process fluctuations are in the thermophilic aerobic / anaerobic embodiment of the invention overcome in the same way as described in connection with the embodiments of the invention, which provide an anaerobic mesophilic second degradation stage.

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In the arrangement according to FIG. 3, raw sewage flows, for example consists of municipal sewage, industrial sewage and rainwater, via a line 24O into one primary settling zone 241. The settling zone 241 can appropriately consist of a conventional gravity clarifier Kind exist. In the settling zone, that which flows Wastewater in a primary drain with reduced BOD content, which arrives via a line 201 in a gassing zone 202, and a settled sludge downstream 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 via a line 208 activated return sludge fed. A fluid mixing and circulating device 203 is located in the aeration zone 202 in order to to mix fluids fed to the gas supply zone, to form a mixed liquid and, at the same time, to form the mixed liquid or the oxygen-containing ventilation gas 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 gassing time, for example 2 to 6 hours, become a mixed liquid depleted in BOD

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and an oxygen-depleted vent gas with at least 21 vol.% Oxygen from the aeration zone 202 Discharged via lines 2O4 or 219.

The BOD-depleted, oxygen-enriched mixed liquid in 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 202 via line 208, in which a circulating pump 209 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 sludge thickener 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 line 245 and combined with primary sludge in line 242 from the primary settling zone 241, so that a combined sludge flow is created in one line. The supernatant liquid from the sludge

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thickener 251 is applied in the manner previously described the line 250 is fed to the gassing zone 2O2.

The combined sludge flow in line 211 can, if desired, by indirect heat exchange with the warm stabilized sludge from a second mining zone 220 are partially warmed up; it then arrives via a line 248 to the first mining zone 210. Before being introduced into the first mining zone 210, the sludge can be in the line 248 are further heated by means of a heating device 231 in which methane gas is burned, which is via 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 first covered mining 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 incoming sludge mixture and the oxygen-containing gas and constantly circulates one of these media in relation to the other. The inflow amount of ventilation gas and that of the mechanical agitator

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212 supplied energy are chosen so that in the sludge a concentration of dissolved in the first degradation zone 210 Oxygen of at least 2 mg / L is maintained.

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

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

The second covered degradation zone 220 is a thermophilic anaerobic degradation zone. With regard to optimum working conditions of the mud is kept in this degradation zone at a temperature in the anaerobic thermophilic temperature range between 4O ° C and 6O ⁰ C and preferably between 45 ° C and 5O ° C. Because thermophilic operation takes place in both the first and the second degradation zone in this embodiment, the partially stabilized sludge can be fed directly from the first degradation zone to the second degradation zone, as illustrated

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will. 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, it can in some cases be desirable in the second mining zone with sufficiently higher or lower temperatures compared to the first aerobic degradation zone to work, so that a heating or cooling of the partially stabilized sludge from the anaerobic Mining stage between the zones is advantageous. The heating can be done with the help of a methane-fired heating device similar to the heater 231 can be performed. A heat exchange of the partially stabilized Sludge from the first extraction zone with the inflowing sludge supplied to the extraction system, as described above in connection with the embodiments Figs. 1 and 2 is explained. Since it is also more critical with a thermophilic anaerobic degradation than with a mesophilic Anaerobic degradation is to ensure that no temperature fluctuations can occur in the degradation zone it may be useful to use a well-insulated tank as the sludge treatment volume for the thermophilic anaerobic degradation stage to provide, which offers security against strong climatic fluctuations.

In the second degradation zone 220, the sludge is by means of a mechanical agitator 23 constantly mixed to a high Maintain stabilization rate. Methane gas, that

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is generated due to the biochemical reactions occurring during the anaerobic degradation, is discharged from the second degradation zone via a line 223. This gas can be mixed with oxygen-containing gas, for example air, or the oxygen-depleted decomposition gas from the aerobic decomposition zone and burned as fuel to generate heat with the aid of which sludge is kept at an elevated temperature in one or both decomposition zones. In the arrangement shown, part of the methane gas from line 223 is fed via line 227 to the heating device 231 and burned in order to obtain the thermal energy with the aid of which the sludge in the first degradation zone is kept at a temperature of 45 ° C to 75 ° C . 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 in sludge sources gives way to the type of biological activity in the aerospace

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ben degradation zone of the embodiment according to FIG. 3 greatly from the biological activity in the aerobic zone of the embodiment according to FIG. 2. In the embodiment according to Fig. 2 is the sludge fed to the digestion system as feed sludge, only activated sludge from the secondary wastewater treatment system, while in the case of the embodiment according to FIG. 3, the inflowing sludge is both secondary sludge from the activated sludge treatment stage as well as raw sludge from the raw sewage settling stage. because the organic material of the secondary sludge consists primarily of viable microorganisms, includes the aerobic degradation of this sludge the different biochemical reaction stages of the cell lysis, the assimilation of lysis products for the synthesis of new viable ones Material, and the respiration. Raw sludge, on the other hand, consists primarily of non-viable organic material Material that the microorganisms present in the sludge can use as a nutrient. Accordingly, learns during aerobic degradation of a raw sludge, the microbial population of the sludge requires a considerable cell synthesis phase in addition to cell lysis, for the assimilation of lysis products and for respiration. Therefore, the aerobic degradation of the raw sludge takes place to a greater extent both Cell synthesis as well as cell respiration than in the aerobic decomposition of secondary sludge takes place. In addition, the aerobic degradation of raw sludge to a smaller overall reduction of the biodegradable volatile suspended matter

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substances than is the case with a comparable sludge retention time in the aerobic decomposition of secondary sludge. The resulting reduction in biodegradable Suspended volatile matter in the sludge during degradation represents a difference in terms of rival 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 heat generation capacity per unit weight of biodegradable volatile suspended matter that can be eliminated during degradation than is the case with secondary sludge. Accordingly, in the case of primary sludge Compared to secondary sludge, a lower resulting reduction in volatile suspended matter is required, in order to reach and maintain a certain temperature level in the aerobic degradation stage Embodiment according to FIG. 3, in which the mining system supplied sludge includes both primary and secondary sludge, at a given temperature with a lower degree of "volatile" particulate matter reduction be operated in the aerobic degradation zone than the aerobic zone according to FIG. 2, which only processes secondary sludge. A smaller reduction in degradable volatile suspended matter in the aerobic zone of the degradation system requires in turn that the sludge residence time in the anaerobic degradation zone is extended accordingly, by one

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_ ₇₅ _ 28D50S4

envisaged total elimination of volatile suspended matter to achieve. Because an increased proportion of the total removal of volatile particulate matter in such a case takes place in the anaerobic degradation zone, the primary sludge processing system can therefore be in the anaerobic degradation zone generate more methane than the mining system, which only uses secondary sludge is processed. The embodiment according to FIG. 3 is therefore inherently capable of larger amounts of methane than to provide the system of Figure 2; but this is at the expense of an increased sludge retention time in the aerobic 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. Such heating may or may not be necessary in a given application; 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 sludge to be treated. 4 shows a graph of the temperature of the sludge flowing into the first degradation zone, the is required to maintain a working temperature of 50 ° C in the first extraction zone with a sludge retention time of 24 Hours as a function of total suspended solids concentration of the sludge going to the first mining zone. Curve A represents a combined

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Primary and secondary sludge streams at which the ratio of content of volatile suspended solids to total suspended solids (VSS / TSS) is 0.75 and the biological heat content is 47 χ 10 J / kg of removed volatile suspended matter (VSS) lies. Curve B applies to a non-combined secondary sludge with a VSS / TSS ratio of 0.79 and a heat content of 33 χ 10 J / kg removed volatile suspended matter.

As can be seen from the respective curves of this graph, the one represented by curve A requires combined sludge has a higher inlet temperature for the aerobic digestion zone than the secondary sludge according to Curve B for a given total suspended solids concentration. Consequently The sludge flowing into the digestion system can be heated before it is introduced into the first digestion zone be particularly favorable if the input medium for the mining system has a substantial proportion of primary sludge from a wastewater treatment plant.

The graph according to Pig. Figure 4 also shows that thermophilic operation can be achieved without the need to heat the sludge going to the digestion system prior to introduction into the aerobic digestion zone if the inflowing sludge is sufficiently thickened. For example, if a combined sludge (curve A) with a total solids concentration of 4 % is degraded

8Ü9832 / 0919

Must be the temperature of the aerobic thermophilic needs Zone of introduced sludge to be only about 15 ° C.

All of the embodiments of the invention described above deliver a completely pasteurized product sludge, since in all cases the sludge flowing into the digestion system Sludge is passed through the thermophilic aerobic zone in which the high temperatures used ensure complete pasteurization of the sludge. However, there may be use cases where the final sludge disposal does not require a fully pasteurized product or the sludge itself Pasteurization makes it necessary because there are no significant concentrations of pathogens. Fig. 5 shows a Flow diagram of a further 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 such applications. at the embodiment according to FIG. 5 becomes a larger part of the sludge entering the process system via a line 311 of a first covered degradation zone 310 via a Line 331 supplied. Before entering the first degradation zone 310, the sludge can be in line 331, if is desired to be heated by means of a methane-heated kettle 330.

Aeration gas containing oxygen that is at least 50% by volume

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and preferably contains at least 80% by volume of oxygen, is fed to the aerobic building zone 310 via a line 317. The sludge flowing into this zone is appropriately mixed by means of a stirring device 312 and against the oxygen-containing ventilation gas constantly rolled to maintain a dissolved oxygen content of at least 2 mg / l in the sludge. Of the Sludge is in the aerobic degradation zone at a temperature between 45 C and 75 C for a residence time between Held for 4 and 48 hours. Degradation gas depleted in oxygen is discharged from the first degradation zone via a line 318. Sludge that is impoverished in biodegradable suspended matter and fully pasteurized leaves the degradation zone separately via a line 316. The partially stabilized Sludge in line 316 is then covered with a second one Degradation zone 32O supplied, which is in the mesophilic temperature range is working. Because the temperature of the sludge leaving the first mining zone is between 45 ° C and 75 ° C is, its temperature must be lowered prior to introduction into the second mining zone, so that an efficient operation 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

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is adjusted so that the temperature of the combined Sludge flow that goes to the anaerobic degradation zone 32O, sufficient to maintain a working temperature between 35 ° C and 40 ° C in zone 320.

In the second mining zone, the sludge is mixed by circulating methane gas against the sludge located there in order to actively maintain the stabilization speed in the second zone at high values. Methane gas, which is generated as a result of the biochemical reactions taking place in the second degradation zone 320, leaves this zone via a line 323. A secondary flow of this gas is diverted into a line loop 340 in which a compressor is located. The compressed methane gas obtained is added to the sludge in the second degradation zone, for example via an injection device (not shown), in order to ensure the above-mentioned mixing and circulation of the sludge. A part of the methane gas can go from the line 323 via a line 327 to the methane-heated boiler 330; the remaining part is discharged from the process system via line 328. The further stabilized sludge, which contains less than 40 % of the original biodegradable volatile suspended matter content of the sludge introduced into the system via line 331, is discharged from the second degradation zone via line 325 for further treatment, e.g. B. drained, and / or finally disposed of.

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28Q5Q54

The advantages of the method explained can be seen in Make clear the following examples:

Example I.

In this example, the performance is the embodiment 2 compared to a conventional anaerobic high-performance system. The further explanation starts with the treatment of the sludge in a wastewater treatment plant with a capacity of 3.8 10 l / day based on the flow diagram of FIG. 2 from '.

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 matter to total suspended solids ratio of 72 % , is introduced into the system at a flow rate of 3.4 10 l / day. In order to keep the sludge in the aerobic decomposition zone 110 at a working temperature of 50 ° C. for a 24-hour residence time, the inflowing sludge is heated to approximately 23 ° C. by means of the methane boiler 130. Assuming an efficiency of 50 % for converting the calorific value of methane gas into heat, approximately 701 m / day of the amount generated in the anaerobic degradation zone is required to feed the boiler 130

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Methane gas required.

In the aerobic decomposition zone, a reduction in the content of volatile suspended solids of approximately 8 % is achieved (16% biodegradable volatile suspended solids; the biodegradable volatile suspended solids make up about 50 % of the total volatile suspended solids content), so that the acid formation subzone via line 114 12Oa a partially degraded sludge with a volatile suspended matter content of 26,100 mg / l is fed. This sub-zone is operated with a 24-hour residence time at a 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 goes via line 126 to methane fermentation subzone 120b. Sufficient heat is drawn off from the discharged sludge in heat exchanger 115 to ensure a working temperature of 38 G in methane fermentation subzone 120b.

The methane fermentation sub-zone is operated with a 5-day sludge retention time, which leads to an overall reduction in volatile suspended solids of 40% (reduction in biodegradable volatile suspended solids by 80 %) for the integrated system.

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28ÜS054

which represents a total calorific value of 12,600 kWh / day. Because 710 m of methane gas per day are necessary to run the methane boiler 130 to operate, there are 1,360 m of methane gas per day, corresponding to a total calorific value of 8500 kWh / day, available for delivery from the sludge removal system.

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 around 22 6OO kWh / day, with a 50% conversion of the calorific value into heat, around 17 6OO kWh / day of heating energy are required to achieve the optimal working temperature conditions in the high-performance tank maintain. Compared to the embodiment of the invention explained above, the conventional system therefore requires 86 % more tank space, based on the required dwell time, in addition, approximately 40 % less methane is available for delivery under normal working conditions.

Example II

This example describes a mode of operation corresponding to the embodiment according to FIG.

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280S054

sludge consists of 50 % primary and 5U % secondary sludge from a wastewater treatment plant in an amount of 2.27 χ 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); it 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. As can be seen from Fig. 4, it is not necessary in this case, the sludge before it is introduced into the thermophilic aerobic. To heat the degradation zone. The residence time in the first mining zone 31Ο 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 32Ο 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 2Ο4Ο m / day, which corresponds to approximately 11,700 kWh / day. This methane can be completely released from the process system.

8U9832 / 0919

If the combined inflowing feed sludge of 2.27-1O l / day is instead fed to a conventional high-performance anaerobic digestion tank, 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 7OO kWh / day, with a 50% conversion of the calorific value into heat, around 13 2OO kWh / day are necessary in order to maintain the optimal anaerobic working temperature in the high-performance tank. In this case, a conventional anaerobic digestion 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 utilizing 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.

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A secondary sludge from a wastewater treatment system used for oxygen enrichment, which initially has a temperature of 15 ° C, is first heated in the heat exchanger by the outflow of the anaerobic degradation zone, whereupon further heating takes place through the outflow of the thermophilic aerobic degradation zone in the heat exchanger 15. The first heat exchange stage in heat exchanger 22 increases the temperature of the incoming sludge from 15 ° C to approximately 25 ° C, while the temperature of the stabilized sludge leaving the anaerobic digestion zone 20 is decreased from approximately 35 ° C to 25 ° C. The second heat exchange stage in the heat exchanger 15 increases the temperature of the inflowing sludge to approximately 30 ° C., while the temperature of the sludge leaving the aerobic digestion zone 10 is reduced from approximately 50 ° C. to 45 ° C. The incoming sludge has a total suspended solids concentration of 34,400 mg / l and a ratio of volatile suspended solids to total suspended solids of 78 %. It is introduced into the first degradation zone 10 in an amount of 2.27 10 l / day. In the aerobic first zone, a working temperature of 50 ° C is maintained during a sludge retention period of 24 hours.

A reduction of approximately 16% of the volatile suspended matter (reduction of 32 % of the biodegradable volatile suspended matter) is achieved in the aerobic stage, so that a partially stabilized sludge with a content of volatile suspended matter of 22,500 mg / l via the line

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16 is fed into the anaerobic degradation zone after im Heat exchanger 15, a heat exchange with the incoming sludge 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 around 1470 m of methane gas per day, corresponding to a total calorific value of around 8,200 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 χ 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 have a methane gas energy of about

ÖUÜÖ32 / 0919

Deliver 76OO kWh / day less than the corresponding above explained system according to the invention.

öüyö32 / 0919

eerse ite

Claims (20)

PATENT Attorney DlPL-ING. GERHARD SCHWAN ELFENSTRASSE32 D-8000 MUNICH 83 2805QS4 L-11234-1-G Expectations f 1 Λ method for breaking down sludge, characterized in that (α) the sludge and at least 50% by volume of oxygen containing aeration gas introduced as fluids into a first covered mining zone and maintained the dissolved oxygen content of the mixed liquid of at least 2 mg / l and the Total suspended matter concentration of the sludge of at least 20 0OO mg / l are mixed; (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; 809832/0919 ^ l inspected TELEPHONE: 089/6012039. CABLE: ELECTR1CPATENT MUNICH (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 the process stage (d) is introduced into a second covered mining zone; (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 sufficient the biodegradable volatile suspended matter content of the sludge to less than approximately 4O% of the content of the in process step (a) in the first degradation zone introduced sludge to further lower biodegradable volatile suspended matter and to form methane gas, as well as further stabilized sludge and the methane gas from the second mining zone be carried out. 2. The method according to claim 1, characterized in that the sludge introduced into the first degradation zone is a total of suspended matter concentration between 20,000 and 60,000 mg / l. 809832/0919 3. The method according to claim 1 or 2, characterized in that that the sludge residence time in the first degradation zone is between 12 and 24 hours. 4. 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 process step (b). 5. The method according to any one of the preceding claims, characterized characterized in that the temperature in process step (f) for a mesophilic degradation in the two th degradation zone is kept in the range of 35 ° C to 40 ° C. 6. The method according to any one of claims 1 to 4, characterized in that that the temperature in the process stage (f) for thermophilic degradation in the second degradation zone is maintained in the range of 45 ° C to 50 ° C. 7. The method according to any one of the preceding claims, characterized in that the sludge retention time in process step (f) is selected to be sufficient to reduce the biodegradable volatile suspended matter content of the sludge to less than approximately 20 % of the content of the in process step (a) in the 809832/0919 ~ ⁴ ~ 280 ^ 054 The first degradation zone of the biologically absorbable volatile suspended matter of the introduced sludge is to be further pressed down . 8. The method according to any one of the preceding claims, characterized characterized in that the sludge retention time in process step (f) is 4 to 12 days. 9. Verfanren according to any one of the preceding claims, characterized 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. 10. 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. 11. The method according to any one of the preceding claims, characterized 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. 12. The method according to any one of the preceding claims, characterized in that the sludge prior to introduction into the first degradation zone by indirect heat 809832/0919 exchange with the one carried out from the second mining zone, further stabilized sludge is heated. 13. The method according to claim 12, characterized in that the temperature in process step (f) is 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. 14. The method according to any one of the preceding claims, characterized characterized in that the second degradation zone comprises an 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 held there for a sludge residence time of 24 to 60 hours to acidify the sludge acidified sludge from the acidification sub-zone discharged and introduced into the methane fermentation zone and there at a temperature between 35 C and 40 C for a sludge retention time of 4 to Is held for 8 days. 15. The method according to claim 14, characterized in that the sludge in the methane fermentation subzone a temperature between 37 ° C and 38 ° C is maintained. 809832/0919 280 ^ 054 16. The method according to claim 14 or 15, 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. 17. 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 containing 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 and ventilated for a sufficient period of time to create 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 is returned to the primary effluent for mixing, 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. 809832/0919 18. 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 the 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 is more sufficient than the other fluid The amount and speed is constantly circulated 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 make up more than 40 % of the total oxygen introduced into the degradation zone; (b) at least about 85% by weight of the activated sludge than the return sludge to the aeration zone be returned; 809832/0919 2805Q54 (C) a second gas is provided which has at least 80% by volume of oxygen and part of the first gas includes; (d) the second gas and the non-recirculated animate one Sludge from process step (b) introduced into a covered mining zone and maintained the yellow oxygen content of the sludge of at least 2 mg / 1 and the Total suspended solids concentration of the sludge of at least 20 COO mg / 1 are mixed; (e) the sludge during process step (d) in the The degradation zone is maintained at a temperature in the thermophilic range of 45 ° 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; (g) the degradation gas partially depleted in oxygen from process stage (f) as at least the largest 809832/0919 re part of the covered in process step (a) Gassing zone introduced first gas _used, characterized in that (h) the process stage (e) with partial reduction of the content of the introduced into the first mining zone Sludge of biodegradable volatile suspended matter for a sludge retention time of Continues for 4 to 48 hours; (i) the partially stabilized. Sludge from the process stage (f) is introduced into a second covered mining zone; (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) 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. 809832/0919 -1O- 280 & 054 19. The method according to any one of the preceding claims, characterized characterized in that the methane gas discharged from the second degradation zone with oxygen-containing gas mixed and burned as fuel with the formation of heat, the sludge in at least «one of the to keep both degradation zones at an elevated temperature. 20. The method according to claim 19, 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 is kept at a temperature of 45 C to ^: 75 C in the first degradation zone. 809832/0918