DE2805054B2 - Process for breaking down sludge - Google Patents

Description

The invention relates to a method for breaking down sludge, in which at least part of the sludge guided through at least two covered dismantling / ons and thereby aerobic and anaerobic in succession with the formation of stabilized sludge and methane gas Conditions is exposed.

Three methods are currently being used on a large scale in l'r.ixis to break down sludge: and / was degradation in oxidation ponds, anaerobic degradation and aerobic degradation.

Oxidation ponds require considerable land areas and do not allow any significant reduction in the Amount of athogens in the mud.

The most widespread is the anaerobic breakdown of sludge, such as is extracted from settling tanks, biological filters and wastewater aeration systems. The sludge is collected in large abattoirs, where it is fermented anaerobically for 20 to 3 days without heat .andauffüllung can be used. by mechanical agitators or iimgewäl / us compressed gas reduction of the volume will mixture ?, to increase Schlummstabilisieriingsrcakiion u /. Fs is known that elevated temperatures in the range of inesophilen 30 ^'1 C to 40'C to shorten the Allow a residence time of 12 to 20 days, because the activity of the organisms responsible for the breakdown is strongly influenced by the temperature and / between JO "C and 40" C ^- highly active mcsophilic microorganisms represent the dominant microbial stamina in the iliziibalizing sludge. The most favorable temperatures for mesophilic degradation, between J>"C and 38 ° C with minimum residence times of 12 to 15 days. During anaerobic degradation, methane gas is generated, which is commonly used in vibienmiiigshe'z equipment to reduce heat loss from the anacroobic degradation system. Seasonal temperature fluctuations and fluctuations in the suspended matter con / enlr.itioneii of the inflowing sludge have a considerable influence on methane gas production and the amount of heat required. If, therefore, elevated temperature conditions are to be maintained in the anaerobic degradation zone throughout the year, then in -. usually an auxiliary heat source is provided. A sludge that is as concentrated as possible is expediently fed to the extraction zone in order to minimize heat losses in the outgoing stabilized sludge flow and to increase methane production in the extraction zone

ι »maximize. Even with such precautions, it is difficult to obtain elevated temperatures in the anaerobic degradation zone in an economical manner in particular maintain during the winter months.

During the anaerobic degradation process, the

π treated sludge solids essentially sequentially exposed to three separate treatment phases, initially a period of loosening, then a period of intense acid production and finally a Perioc! ' intensive degradation

_ ■ »and stabilization (gasification), each of these process stages is due to the production of different Intermediate and end products marked. Under normal working conditions, all three phases occur at the same time. The one during the gasification phase

. '"> The gases produced are mainly methane and carbon dioxide. They usually make more than 95 "/ o des evolved gas, with 65 to 70% methane being present. The Methaner / .eujjung is on the Decomposition of numerous connections by many of-

iii attributing interdependent biochemical reactions. In particular, the complex organic sludge components act as acidifiers designated bacteria are converted into volatile acids and alcohols without the formation of methane, which then

i> by other bacteria known as methane generators converted into methane gas. The acid-forming bacteria are robust and resistant to process changes highly resilient. Moderate temperature fluctuations change their metabolic activity

in iii ht noteworthy. Methane producing bacteria require on the other hand strictly aerobic conditions; they are opposed to changes in the rate of change, such as fluctuations in the pH value and the presence of heavy metals. Detergents. Ammonia and sulfides, extreme

Γι sensitive. Even very small amounts of toxic Metals such as copper prevent the activity of methane generators. The acidifiers begin to dominate. The pH drops, which increases the activity of the animal Methane generator is additionally impaired. Also may

mi no oxygen present in the anacrobene Abhau / one scm. Unintentional introduction of I.lift into this Zone impairs methane fermentation and leads because of the combination of the flammable methane gas with oxygen -ίι fire or explosion hazard.

· ") The milk formers are also particularly sensitive against temperature fluctuations. Already fluctuations of only a few degrees diminish their activity and capacity; they have a relative excessive growth of acid producers / ur consequence.

mi f! s comes to an accumulation of acid degradation / whisk products. In this case, too, the pH value in the degradation zone drops. The activity of the methane generator will be further reduced. This leads to serious litigation problems. The result is an insufficiently stabilized sludge

in received that not without further treatment / ur I.andaiif filling or for similar purposes.

To the described disturbances in the an.ieioben Ablwu / o'ie / u are often used in ilicsi · / mn-

Large amounts of lime introduced, which strengthen the buffer effect and increase the pH value should. However, this corrective action is usually only suitable for short-term fluctuations or l'process disturbances. It usually does not offer any advantages in the case of long-term fluctuations or disturbance conditions appear. In addition, the methane generators have a relatively low growth rate, what makes a long residence time necessary even at mesophilic temperatures. Because of the low There is a danger that the methiine-forming Organisms from the degradation zone are washed out when the sludge solids depletion the mentioned minimum value is lowered. The long dwell times require a large capacity the dismantling / one.

The aerobic degradation of biodegradable sludge can also be achieved through increased temperatures accelerate. When the temperature rises from 35C, the population of the mesophile increases Microorganisms decrease, while clic thermophilic forms increase. In the thermophilic area of 45 "C up to 75'C, thyrophilic predominates; most of the mesophiles are destroyed. Above this range the thromophiles decrease. At 90 C the system becomes essentially sterile. Because of the faster oxidation the sludge will have a more complete elimination of biodegradable within the same degradation time volatile suspended solids (VSS) than reached at ambient temperature. F. it becomes a more stable one A residue that can be eliminated without nuisance. Become through a thermophilic degradation pathogenc bacteria in the sludge effectively diminished or eliminated, thereby creating potential health Hazards are avoided.

When using diffusion air systems, the heat losses are usually very large. As a result, in the aerobic degradation with air is typically limited to the exploitation of mesophilic microorganisms. Because air contains only 21% oxygen and only about 5 to 10% of the oxygen is dissolved a very large air flow rate is necessary to meet the oxygen demand. The palpable warmth of the stale air and the latent heat that is required. around the stale air with water vapor to satiate are substantial. The sludge retention time is at ambient temperature (20 "C or less) in the case of aerobic degradation with air, typically 12 to 20 days: to absorb the Very large containers are required for the sludge. As a result of the heat losses, there are autothermal heat effects small amount. An uneconomical large amount of external heat is required to raise the temperatures to keep usable values.

If, as is known, instead of air, an oxygen-enriched gas or pure oxygen is used, is the amount of gas that is fed into the aerobic decomposition zone and leaves it, significantly less than air. Heat losses due to the noticeable warming up of the gas and the Water evaporation in the gas are reduced to such an extent that the autothermal heat alone increases the temperature noticeably higher than the outside temperature. The degradation zone can therefore be in the thermophilic temperature range work effectively with minimal supply of external heat. Because the thermophilic stabilization Much faster than a mesophilic stabilization takes place, the necessary residence time in the aerobic degradation zone greatly reduced. This allows the use of smaller pools, which reduces the heat loss continue to be depressed. A reduction in biodegradable volatile suspended matter from 80 to 90%, for example, can be of the order of magnitude with comparatively short sludge processing times 3 to 10 days can be achieved.

Despite its considerable attractiveness, the thermophilic aerobic degradation is compared to an anaerobic one Degradation is associated with disadvantages. Because the thermophilic aerobic degradation process is oxidizing, it becomes a bio-oxidizing reaction gas formed, which contains carbon dioxide and water vapor, which can no longer be used. in the In contrast, anaerobic degradation produces methane gas as a reaction by-product. Also requires The aerobic degradation zone requires a significantly greater amount of energy to be used for mixing and for the incinceration of (jas and sludge than this in the anaerobic digestion system for mixing the contents of the digestion zone necessary is.

Fs is also known (DF-OS 15 84 958). to be dismantled Sewage sludge in an animal manner sequentially expose aerobic and anaerobic conditions that the sludge is introduced into a first 1 aulturm above, which is in its ·, upper part is aerobic and in which the Degradation conditions become increasingly anaerobic downwards, as well as that the sludge at the transition point withdrawn between the aerobic and anaerobic zones and on top for anaerobic degradation a second digester is abandoned. The anaerobically degraded sewage sludge is then in the middle taken from the second Faiilturm and in the same way by a third and possibly further ones Fauliürmc passed, with each of the digestion towers substantially completely degraded sludge is withdrawn below. This should also apply to the usual The humic matter remaining in the sludge digestion can be completely decomposed. The arrears should no longer be flammable and predominantly composed of mineral components. To the aerobic conditions to maintain in the upper part of the first digestion tower, a well-aerated sewage sludge is used. The dismantling then takes place in this digestion tower down through facultative aerobic, facultative anaerobic in purely anaerobic degradation. The removal of the aerobic putrefaction substance from the middle part of the The first digestion tower takes place while avoiding turbulence and mixing with the dead Substance. It follows that in the first Far'turm itself no ventilation gas is blown and also It is not allowed to cingebias, because otherwise in the digestion tower together with the one from the lower one anaerobic part of the digestion tower rising methane forms an explosive gas mixture. The good aerated sewage sludge quickly loses its aerobic character in the first digestion tower. A primary sewage sludge, as in the known method an upstream of the first digestion tower This is because the primary clarifier has an oxygen uptake rate of around 200 to 300 mg / l / h. If the sludge going to the first digestion tower has a dissolved oxygen content of 9 mg / 1, which corresponds to the saturation value with conventional aeration with air, the oxygen content becomes of the sludge is consumed within a sludge retention time of only a little more than 2 minutes. This is extremely short compared to the total length of stay of months for the known

Process is necessary to completely decompose the humic substances. The known process is consequently subject to essentially the same problems as those discussed above in connection with the purely anaerobic degradation process. In fact ί in the period that followed, experts did not take up cumulative aerobic and anaerobic sludge stabilization; on the contrary, only aerobic or anaerobic treatment alone was always considered in practice. m

The F.rfindiing is based on the task of a To create sludge degradation processes with successive aerobic and anaerobic sludge treatment, in which a considerable shortening of the treatment time with complete stabilization under possible r> low energy consumption is achieved.

This object is achieved according to the invention in that 15

a) in a first covered degradation zone the sludge and at least 50 vol .-% oxygen contained- '" of the ventilation gas introduced and maintained a content of dissolved oxygen in the mixed liquid of at least 2 mg / 1 and a total woven fabric concentration of at least 20,000 mg / l mixed in the sludge "' will,

b) the sludge in the first degradation zone during the mixing process at a temperature in the thermo- -.hilen range is kept from 45 C to 75 "C,

c) the mixing is continued in the thermophilic temperature range for a sludge residence time of 4 to 48 hours with partial reduction of the biodegradable volatile suspended matter content of the sludge introduced into the first decomposition zone. ^{! l}

el) partially stabilized and oxygen-depleted sludge Degradation gas with an oxygen content of at least 21% from the first degradation zone are carried out separately and

e) the stabilized sludge from the process ^{4 {|} Step d) to a second covered Abl ~ auzone at a temperature of 30'C to 60 ⁰ C under anaerobic conditions for a solids residence time of about 4 to 12 days is kept and sufficient volatile degradable biologically to the content of the sludge to ^4> To further reduce suspended solids to below approximately 40% of the biodegradable volatile suspended solids content of the sludge introduced into the first degradation zone in process step a). '"

Due to the procedure according to the invention, compared to the known combined aerobic and anaerobic sludge degradation processes a very unusual stability of the overall process achieved. Surprisingly, this allows the treatment time to be shortened considerably with complete treatment Stabilization or pasteurization of the sludge. In particular, the thermophilic aerobic Degradation stage due to the heat content of the partially stabilized one passed from the aerobic to the anaerobic stage The sludge stream contributes more than enough heat to the anaerobic stage regardless of climatic conditions Stabilize conditions thermally. Temperature disturbances in the anaerobic zone can therefore practically eliminate by parameters such as the sludge retention time in the aerobic zone, the Solids content of that fed to the aerobic zone Sludge and the degree of heat exchange ^ due to which the feed sludge before entering the aerobic zone is heated, can be changed. In this way, the anaerobic degradation zone can typically operated at one temperature regardless of seasonal outside temperature fluctuations which deviates from the optimal temperature state by no more than 1 degree. Furthermore is the Increased tolerance to toxic metals in the supplied sludge. This is likely to point out It can be traced back to the fact that the metals are toxic only in a soluble ionic form, the metal ions but in the aerobic decomposition stage with the intended sludge retention time and the thermophilic temperature Form harmless complex compounds for the anaerobic stage. The thermophilic aerobic degradation stage is also able to absorb sporadic disturbances, for example shock loads, without affecting the efficiency the process suffers. If a conventional anaerobic degradation zone occurs suddenly high solids load, solubilization and acidification run at a faster rate when the methane-producing bacteria can use the acidic intermediates. As a result, collect acidic constituents accumulate in the degradation zone. The pH falls. A souring of the contents of the The mining zone threatens to enter. In the present process, the upstream thermophile promotes aerobic stage not only a rapid solubilization of biodegradable material in the sludge; much more this level also tends to decrease the population of mesophilic acid-producing bacteria. The aerobic degradation stage then allows these organisms to grow again. Your population however, it is smaller and more in balance with the population of methane-producing organisms. Therefore, when the aerobic zone is subjected to shock loading, the solubilization in is rapid the aerobic degradation zone as well as a stabilization of the most volatile parts of the sludge, reducing the impact load smoothed and their influence on the downstream anaerobic zone is greatly reduced. In the Further treatment, the anaerobic zone takes on a partially stabilized sludge, in which the acid-forming and the methane-producing bacteria can grow in mutual equilibrium.

The substances that interfere with anaerobic digestion are preferentially oxidized in the aerobic stage. Because the high temperature in the aerobic stage, at which nitrifying bacteria are not viable, appears the released nitrogen as ammonia, which together with the released CO2 Ammonium bicarbonate forms an excellent buffer medium for those facing changes in pH represents extremely sensitive anaerobic level compared to a conventional, purely anaerobic Mining rich mining zones with much lower, z. B. amounting to only 60% of the value of known systems Capacity, which, however, is approximately 75% of the methane production capacity of the known Have attachments. Much more methane is therefore generated than for heating purposes within the process is required so that relatively large amounts of gas with a high methane content are available for other purposes stand. Eventually it was found that oxygen was not in any appreciable amount from the sludge of the first Breakdown zone is transferred into the gas phase of the second breakdown zone. This is likely to be attributed to it

be that the elevated temperatures in the anaerobic second degradation zone for sufficiently intense anaerobic bacteriological conditions ensure the content of the extracted from the first to the second degradation zone Thoroughly break down sludge in dissolved oxygen, bev ^ - dissolved oxygen in noteworthy Scope in.Yürhalb the second degradation zone can pass into the gas phase. The surprisingly short ones 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 result of chemical or biological acclimatization of the sludge and the Microorganisms in the aerobic degradation zone are responsible for improving the efficiency of the subsequent anaerobic treatment stage.

Preferably, the sludge introduced into the first breakdown zone has a total concentration of suspended matter between 20,000 and 60,000 mg / l. This ensures a high speed of the biological Sludge degradation with good oxygen solubility.

With a view to minimizing the total duration of treatment and the tank capacity requirement, a sludge retention time in the first mining zone was found between 12 and 24 hours is particularly beneficial.

] e according to the process parameters given in the individual case, it can be useful for a maximization the thermal efficiency of the process to the sludge before it is introduced into the first degradation zone heat to maintain the thermophilic temperature in the aerobic degradation zone.

For operation with a particularly high degree of efficiency, the temperature in the anaerobic degradation zone is preferably kept in the range from 35 ° C. to 40 ° C. for mesophilic degradation. Due to the excellent operating stability, a further shortening of the duration of treatment is possible in accordance with a modified embodiment in that the temperature is maintained in the anaerobic degradation zone for a thermophilic degradation in the range of 45 ° C to 50 ⁰ C.

Preferably, the sludge residence time in the anaerobic degradation zone is selected to be sufficient to Biodegradable volatile suspended matter content of the sludge to less than approximately 20% the biodegradable content of the sludge introduced into the aerobic first degradation zone to further press down volatile suspended matter.

The stabilization speed in the anaerobic second degradation zone can be further increased by that the sludge in the second degradation zone is mixed by adding methane gas against the one located there Sludge is circulated.

In order to control the temperature in the aerobic degradation zone, the aeration gas supplied to this zone can be used be heated. The heating energy requirement can also be minimized in that the sludge before introduction into the first mining zone by indirect heat exchange with that from the second Dismantling zone discharged, further stabilized sludge is heated. It is useful if the temperature in the anaerobic degradation zone is maintained in the range of 35 ° C to 40 ° C and the heated mud before pouring into the "" o.robe first Degradation zone through indirect heat exchange with the partially stabilized one discharged from the first degradation zone Mud is further heated.

In a further embodiment of the invention, the second degradation zone is provided with an acidification subzone and a methane fermentation subzone, and partially stabilized sludge from the first degradation zone is introduced into the acidification subzone and held there for a sludge retention time of 24 to 60 hours to acidify the sludge, while acidified sludge is removed the Ansäuerungsteilzone discharged and introduced into the methane fermentation part zone and there at a temperature between 35 ⁰ C and 40 ⁰ C for a slurry residence time of 4-8 T; strength is maintained. This allows a particularly good adaptation to the most favorable process conditions for the acidification of the sludge and the subsequent methane fermentation. The sludge in the methane fermentation sub-zone is preferably kept at a temperature between 37 ° C and 38 ° C, while the sludge in the acidification sub-zone is advantageously kept at a temperature between 45 ° C and 75 ° C and the acidified sludge discharged from the acidification sub-zone Sludge is cooled to a temperature of 35'C to 40 "C before it is introduced into the methane fermentation subzone.

The sludge introduced into the first degradation zone can expediently consist of primary sludge and excess sludge consist of a wastewater activation system.

According to a further development of the invention it is provided that the introduced into the first mining zone Aeration gas contains at least 80% by volume of oxygen, the decomposition gas withdrawn from the first decomposition zone has an oxygen content of at least 40% and at least 35% of the oxygen content of the in the first Abpuzone introduces ventilation gas, and this decomposition gas in a covered fumigation zone a wastewater activation system than at least the larger part of that fed to a fumigation zone Aeration gas is introduced, while the excess sludge of the sewage system into the first mining zone is fed. By conducting the process in this way, the degradation gas from Jer can be aerobic first degradation zone for the excess lamb of the activated sludge plant analogous to a known wastewater treatment process (LIS-PS 39 26 794 and corresponding DE-PS 25 28 800) as an oxidant gas for Sewage ventilation can be used.

Depends on the respective climatic conditions an external supply of heat is required to keep the mining zones at the intended working temperatures to keep, is preferably a part of the methane gas discharged from the second degradation zone with Oxygen-containing gas mixed and burned to form heat, by means of which the sludge in at least one of the two degradation zones is kept at an elevated temperature. In particular, it can be expedient by burning methane gas with oxygen-containing gas, the sludge in the first extraction zone is raised the temperature of 45 ° C to 75 ° C are maintained.

In the present case, sludge is a mixture of a liquid phase and an at least partially Understood biodegradable solid phase. The sludge can be classified by its content of biological Mark degradable volatile suspended matter (VSS). Underneath is the reduction in solids understood, the maximum achievable by the Sludge is aerated with Orhaltigem gas at outside temperature, for example at 20 ° C and a content of dissolved oxygen of at least 2 mg / 1. It is assumed that a maximum reduction

the solids content is reached after a period of fumigation of 30 days ("Water Pollution Control", W. W. Eckenfelder and D. L. Ford, The Pemberton Press, 1970, Page 152). By determining the VSS values of the fresh sludge and after 30 days of fumigation, the biodegradable proportion of the total volatile suspended matter present can be calculated as follows:

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

Stabilized sludge is understood to mean a sludge with a reduced content of biodegradable volatile suspended matter following a degradation treatment. The sludge dwelling period denotes the mean time τ (in days or hours) during which the sludge is present in a mining zone; it will be according to the formula

calculated, where

V _tl = volume of the sludge treated in the degradation zone (m ^! ) And

Q, = volumetric flow rate of the sludge fed to the degradation zone (mVday or m Vh).

The invention is explained in more detail below with reference to preferred exemplary embodiments. In show the drawings

Fig.! a flow sheet of a degradation process according to an embodiment, in which heat the outflowing streams of both mining zones is recovered.

F i g. 2 is a flow diagram of a modified embodiment, in the oxygen-depleted decomposition gas discharged from the first mining zone for the Oxygen enrichment post-treatment of water containing BOD is used,

Fig. 3 is a flow sheet of another embodiment in which sludge from the primary and the secondary wastewater treatment stage is fed to the sludge removal 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. there, plotted as a function of the total suspended matter concentration (MLSS) of the sludge flowing into the first degradation zone and

F i g. 5 is a flow diagram of a further embodiment in which a smaller part of the in the plant incoming sludge is discharged to the second degradation zone.

F i g. Fig. 1 shows a flow sheet of a sludge degradation process that utilizes a first thermophile aerobic degradation stage is followed by a mesophilic anaerobic degradation. Mud, for example from a primary settling basin, the clarifier of a wastewater treatment plant working according to the activated sludge process, a trickle filter or another schiammerzeuger. the system can come over a line 8 and is successively in heat exchangers 22 and 15, for example on a Heated temperature from 30 ° C to 35 ° C before going into the first covered mining zone 10 is initiated to

to keep the temperature there at a value in the thermophilic range of 45 ^° C. to 75 ^{° C.} The sludge at the outside temperature in the line 8 is first heated in the heat exchanger 22 by being brought into indirect heat exchange with the further stabilized sludge which is passed through in countercurrent and which leaves a second covered degradation zone 20 via a line 24. In this way, heat is recovered from the further stabilized sludge. The cooled, stabilized sludge obtained leaves the heat exchanger 22 and is discharged via a line 25 for final disposal or other use. The slurry via line 24 entering the heat exchanger 22 can advantageously be a temperature of 35 ° C to 40 ⁰ C have, so that the incoming sludge, which leaves the heat exchanger via a line 9 to a temperature of 28 ° C to 30 ° C is heated. This sludge is further heated in the heat exchanger 15 to a temperature of 30 "C. to 35 ° C. by being brought into countercurrent indirect heat exchange with the partially stabilized sludge , which is discharged from the first degradation zone 10 via a line 14 and from the heat exchanger via a line 16 enters the second mining zone 20 .

As an alternative to the explained heat exchange with sludge product streams from the relevant degradation zones, the inflowing sludge can be heated prior to entering the first degradation zone by indirect heat exchange with an externally supplied heating medium, for example steam or hot water, although heat recovery from the warm degradation zone product streams is preferred, because in this way the heat within the process is used effectively and the heating energy requirement of the process is minimized . The heating dos inflowing sludge prior to introduction into the first reduction zone may be desired in practice, depending on the solids content of the incoming sludge, the sludge retention time in the aerobic degradation zone and other process parameters to the thermal efficiency of under elevated Temperati; maximize · ibkufenden process .

The further heated sludge, which leaves the heat exchanger 15 via a line 11 , is introduced into the first degradation zone 10 together with aeration gas from a line 17 . The aeration gas in line 17 contains at least 50 and preferably at least 80 vol .-% oxygen in order for a high mass transfer driving force and oxygen dissolution rate. indibility in the sludge at the high sludge temperatures envisaged in the first degradation zone. Line 17 is connected to a source of ventilation gas (not shown). This source can be, for example, a low-temperature oxygen system, a storage container or an adsorption air separation system operating with an adiabatic pressure cycle process. The ventilation gas can also be heated in the line 17 by means of a heating device 19 in order to keep the temperature in the decomposition zone 10 at the desired value.

In the aerobic degradation zone 10, the sludge and the Beiüftur.gsgas are mixed; at the same time, one of these fluids is circulated in relation to the other fluid in sufficient quantity and with sufficient speed to keep the dissolved oxygen content of the sludge at least 2 mg / 1 and the

Total suspended solids concentration (wILSS) des Keep the sludge at at least 20,000 mg / l. A contact device 12 is provided for mixing and circulating provided, which in practice may have a submerged turbine and a gas jet compressor attached to the Gas head space in the decomposition zone and connected to the gas injection device to the oxygen-containing To circulate aeration gas against the sludge. A surface ventilation device can also be used instead be present, which the sludge against the aeration gas in the gas head space of the degradation zone 10 overturned. The mutual circulation of the fluids in the The aerobic degradation zone is preferably used to maintain a high level of dissolved oxygen in the sludge and to use the oxygen in the ventilation gas to a large extent. In some cases it can be possible for sufficient dissolved oxygen in the sludge and for high utilization of the oxygen in the Provide ventilation gas by passing ventilation gas through the aerobic degradation zone only once will. The dissolved oxygen content of the sludge in the first decomposition zone should be at least 2 mg / 1 to give the thermophilic microorganisms in the sludge sufficient oxygen for rapid To provide decomposition of the biodegradable sludge components. The total suspended solids concentration of the sludge is at least 20 00 mg / 1 µm, based on kinetic considerations, to achieve a high rate of biological sludge degradation in the aerobic degradation zone in order to at the same time, the heat of reaction from the exothermic aerobic decomposition to a sufficient level Worth keeping in order to keep the temperature of the sludge in the first degradation zone within the thermophilic Area remains, and to a satisfactory level of j5 To achieve partial sludge stabilization in the degradation zone with short residence times.

The mud temperature from 45 ° C to 75 ° C in the The first degradation zone is a rapid oxidation of the volatile suspended matter content of the sludge secure. The thermophilic degradation is for a sludge retention time in the first degradation zone from 4 to 48 Hours continued to biodegrade the sludge discharged into this zone to partially reduce volatile suspended matter. The 4-, sludge retention time in the aerobic degradation stage should be at least 4 hours in order to bring about sufficient partial stabilization there. With shorter ones Residence times become the degree of sludge stabilization required in the subsequent anaerobic treatment stage disproportionately large compared to the degree of stabilization in the aerobic stage; the total system dwell time and the tank capacity needs begin to rise to levels from conventional anaerobic To approach mining systems; the unexpected improvement -, 5 tion of these process parameters, which are characteristic of an operation with dwell times of four hours or more are increasingly lost. For similar reasons, the sludge retention time in the Do not exceed the aerobic degradation zone for 48 hours. t, o The extent of sludge stabilization in the aerobic degradation zone is above this value excessively large compared to the remaining stabilization in the downstream anaerobic stage. The one in the the last-mentioned stage necessary residence times to «maintain a suitably large Population of methane generators in the mining zone tend to be significantly longer than in the Desirable for Efficient Operation Again, the unexpected improvement is for the total system dwell time and the tank capacity requirement are increasingly lost Dwell time range of 4 to 48 hours can be achieved. Preferably with a dwell time in the area worked from 12 to 24 hours

Partially stabilized sludge is discharged from de ^r aerobic zone via line 14, while separately to Sauerstofi degradation depleted gas with at least 21% oxygen and preferably at least 40% oxygen content from the aerobic zone via a line 18 is discharged. The oxygen concentration in the line 18 can easily be maintained 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 located in the outlet line 18.

Because the sludge is held in the aerobic degradation zone under thermophilic process conditions, an essentially complete pasteurization of the sludge can be achieved. The partially stabilized sludge leaving the line 14 has a temperature in the thermophilic range between 45 ° C. and 75 "C. Because this embodiment provides for a mesophilic anaerobic degradation in the second covered degradation zone 20, the partially stabilized sludge in the line 14 heat is preferably withdrawn in order to ensure effective operation of the anaerobic sludge treatment stage. The sludge passes through the heat exchanger 15 for this purpose Wastewater treatment * plant. When operating in winter, it may not be necessary to provide a heat exchange stage to cool the partially stabilized sludge flow, because heat losses to the surroundings of the second decomposition zone and the sludge flow flowing from the first to the second decomposition zone will satisfy such a cooling step able to compensate.

The partially stabilized sludge introduced into the mining zone 2 (via line 16) is there underneath Anaerobic conditions at temperatures from 30 "C to 45 ° C for a sufficiently long sludge retention period kept the content of biodegradable volatile suspended matter in the sludge to less than: about 40%, and preferably less than 20% de: content of that introduced into the first mining zone Pushing sludge down on biodegradable volatile suspended matter; in addition, Me thangas formed.

The temperature of the mud in the second! covered degradation zone is kept in the range of 30 ⁰ C to 60 ° C. This includes both an operation in the mesophilic range of 3O ⁰ C to 45 ° C and express working in the thermophilic range of from 45 ° C to 6O ⁰ C for operation with particularly high Wirkungsgrai, the anaerobic zone in the mesophilic work be a sludge treatment temperature is between 35 ° (and 40 ° C and preferably between 37 ° C and 38 "(held. A preferred working temperature range for the anaerobic thermophilic degradation is between

45 ° C and 50 ⁰ C. The operation in the above-mentioned preferred temperature ranges, provides a particularly rapid degradation of the bioabsorbable volatiles by the relevant microbial strains.

During operation of the anaerobic degradation zone 20, the content of the degradation zone is controlled by means of a stirring device 21 constantly mixed, creating a large zone for active degradation and the speed of the formed Stabilization reactions is significantly increased. The to dwell time of the sludge in the second degradation zone ranges from 4 to 12 days and preferably between 5 and 9 days. Sludge retention times in the second mining zone of less than 4 days is inexpedient; the length of stay is less and less to maintain a large viable population of methane generators in the anaerobic stage; the Overall sludge stabilization behavior of the mining system is adversely affected On the other hand, if there is a stay in the anaerobic degradation stage of more than? n than 12 days the residence time 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 sludge treatment in the degradation zone 20 is completed, the will continue stabilized sludge discharged through the line 24 and with: incoming feed sludge in the heat exchanger 22 brought to heat exchange before the sludge finally leaves the system via line 23. This in the degradation zone 20 leaves methane gas formed due to the biochemical reactions carried out there the anaerobic treatment stage via a line 23 in which a flow control valve 26 is located.

F i g. Fig. 2 shows a flow diagram of a further embodiment which shows how that of the US-PS 39 26 794 known procedure can advantageously be combined with the present method.

According to Figure 2 passes BOD containing water, such as municipal wastewater, via a line 101 in a covered Begasungszone 102. The Begasungszone 102 are (in phantom) further comprises a first gas containing at least 40 vol .-% oxygen through a line 118 and activated return sludge is supplied via a line 108 in which a pump 109 is located. Supernatant liquid from a sludge thickener 151 also passes via a line 150 into the covered aeration zone 102. In FIG. 2 are shown liquid-extended w keit- and schlammführendc lines while gas-carrying lines are gezeichnrt dashed lines. Valves are not shown for the sake of simplicity. The streams mentioned are thoroughly mixed in the aeration zone 102 by means of a mechanical stirring device 103. The stirring device can have motor-driven impellers located near the surface of the liquid or immersed in the liquid wedge; the oxygen gas can be supplied via line 118 above or below the liquid level w>. Devices of this type are known; they should be chosen so that a large contact area between the fluids is obtained with a minimum expenditure of energy. If the oxygen gas is blown into the liquid or caused to diffuse in, the bubbles should be so small that their total surface area is large and their buoyancy is low. The dissolving of oxygen is also aided by this.

that the arrangement provided for introducing the gas is immersed so deeply in the liquid that the hydrostatic effect plays a role

In the aeration zone 102 , a medium is constantly circulated compared to the other media.For example, a compressor (not shown) can be connected to the gas space of the aeration zone in order to circulate aeration gas to the lower part of the zone and release it in the form of small bubbles via a conventional type of aeration device. Alternatively, the mentioned mixing device can also be used to circulate the fluids, as is the case with surface gas impellers. under Atmospnärendruck and a temperature of 20 ⁰ C has Suitable devices have an air-normal transfer efficiency of at least 032 kg Oj / kWh, and preferably an efficiency of at least 1.85 kg O ₂ / kWh. The energy used for dimensioning the device is the total energy that is used both for stirring the liquid and for bringing the gas and liquid into contact.

The media are circulated 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 wastewater can be heated in line 101. The structure and mode of operation of the waste water gasification zone 102 can be selected in the manner known from US Pat. No. 3,547,811, 3547,812 or 3,547,815.

The mixed liquid enriched with oxygen passes from the aeration zone 102 via a line 104 into a clarifier 105, where it is separated into purified, supernatant liquid and into activated sludge. Unused oxygen-containing gas leaves the gassing zone 102 via a line 119 and can, for example, be vented into the atmosphere. This gas is discharged from the gassing zone in a flow rate which is regulated so that its oxygen content does not make up more than 40% of the total oxygen that is introduced into the (.n the following explained) covered aerobic degradation zone. Supernatant, purified liquid is drawn off from the clarifier 105 via a line 106 , while activated sludge is discharged via a line 107. The activated sludge contains microorganisms in 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 Wastewater is between 0.1 and 0.5. The flow rates of the media introduced into the gassing zone 102 are preferably dimensioned such that the total suspended matter concentration there is between 4000 and 12,000 mg / l and the content of volatile suspended matter (MLVSS) 3000 to

The liquid-solid contact time is 10,000 mg / l in the gassing zone 102 for the absorption and assimilation of organic substances is between 30 Minutes and 24 hours. It fluctuates depending on the BOD content of the wastewater, the type of Contaminants, the solids content in the aeration zone and the temperature.

The activated sludge process produces an overall excess of microorganisms because the mass of the the impurities in the sewage synthesized ι ο new cells larger than the mass of the cells that is self-oxidize during treatment. In addition, the wastewater usually contains biological non-degradable solids that settle and collect with the biomass. Consequently a small proportion of the activated sludge has to be excreted in order to achieve equilibrium to ensure between the microorganism population and the supply of organic substances (BOD) as well as to suppress the accumulation of inert solids within the system. The sludge makes usually less than 3% of the total separated sludge and rarely more than 15% the end.

It is true that the sludge represents a small proportion of the total solids separated in the clarifier; nevertheless, viewed in absolute terms, it often forms a large one Amount of substance. Regardless of the amount, the elimination of this sludge is a significant part the cost of wastewater treatment; in addition, the lamb forms a considerable ecological part Problem. The sludge is putrid and highly biologically active; often contains t, pathogenic bacteria. The mud is potentially used as a fertilizer and / or to fill the terrain However, when it is used, it must be well stabilized in order to avoid nuisances and health risks avoid. Its high water content (e.g. 96 to 98%) must be reduced.

The sludge is from the clarifier 105 via the sludge circulation loop in a line Ul deducted. It has a total suspended solids concentration of 10,000 to 40,000 mg / l and initially approximately the same temperature as the wastewater in the fumigation zone 102, i.e. 15 ° C to 25 ° C. Of the Sludge is fed to the sludge thickener 15Ί. This concentrates the sludge to a total concentration of suspended matter between 20,000 and 60,000 mg / l. The thickened one peeled off below Sludge is fed to the sludge digestion system via a> <> line 152.

In some cases, such as wastewater treatment at high outside temperatures, it may not be necessary to thicken the sludge from the clarifier; the sludge in line 111 can y, df.nn via line 153 at the sludge thickener

151 are bypassed and then enter the line 152 to enter the sludge removal system to get. The overflow of the sludge thickener is fed to the aeration zone 102 via line 150. f, o

The thickened sludge in the line 152 can be heated by means of a methane boiler 130 before it is introduced into an aerobic decomposition zone UO. Instead, the sludge can also be brought into μ heat exchange with the stabilized sludge discharge from an anaerobic degradation zone 1206. Sludge is drained into the first covered mining zone 110 from the line

152 either continuously or intermittently

The aerobic decomposition zone UO is initiated on a Maintained temperature in the thermophilic range of 45 ° C to 75 ° C. If an autothermal operation in the aerobic degradation zone is achieved, the sludge temperature in the degradation zone can expediently in the range of 55 ° C to 65 "C. It is difficult to Maintain degradation temperatures above 65 ° C autothermally. The elevated temperature in the mining zone 110 can also be achieved by using external heat is supplied, for example by circulating a heated fluid in a heat exchanger, not shown which sits in the breakdown zone Because of the tendency of the solids to form overcoats and blockages cause, should not be complicated or arranged heat exchanger surfaces within the mining zone be arranged at close intervals; advantageously they can be embedded in the wall of the tank or with this be connected.

An ^x second oxygen gas, which is at least 80 VoI .-% oxygen has the heated degradation zone 510 supplied via a line 117. The amount of this gas is sufficient to provide the first oxygen gas for a part which in the Begasungszone 102 via line 118 is initiated.

Preferably, the elevated temperature in the degradation zone 110 is achieved autothermally without Heat exchangers such as the methane boiler 130 become necessary.

The concentrated sludge as used in the oxygen gassing process according to US Pat 35 47 813 usually accrues, is particularly suitable for an autothermal operation because it has a has a lower water content compared to the content of biodegradable »fuel«. aside from that the size of the digestion tank becomes smaller with high solids concentrations, which also leads to heat conduction losses can be reduced through the walls of the digestion tank. Because of such considerations, also in the embodiment according to FIG. 2 the total suspended matter content of the sludge in the aerobic Degradation zone 110 maintained to at least 20,000 mg / l.

The upper limit values for the solids concentration in the aerobic degradation zone are essentially determined by two factors. In general, the maximum concentration depends on the salinity of conventional Settling and thickening facilities to reduce the water content. Flotation equipment, Centrifugal separators and gravity thickeners often provide total suspended solids concentrations of 60,000 mg / l. The solids content can also be increased by using fresh sludge or more concentrated Waste from a source other than wastewater is mixed in. The second factor that the Limited solids concentrations, the increasing difficulty is to dissolve and oxygen in the decomposition zone to mix the solids. A preferred upper limit is 60,000 mg / l, which ensures that the dissolved oxygen is sufficiently uniformly distributed in the sludge. In addition, the most cases temperatures close to the maximum aerobic, thermophilic degradation rates correspond to, achieve autothermal, if the solids content is not higher than 60,000 mg / l. At a further increase in solids concentration would more CO? get into the gas space of the mining zone; the Oxygen partial pressure of the ventilation gas would be reduced unnecessarily.

The construction of the digestion tank also affects the autothermal temperature values. Concrete walls are preferable to metal walls because of the lower heat conduction losses of beeches. Heat loss can be further reduced by burying the tank underground and throwing soil against any exposed vertical tank walls. If necessary, thermal insulation, such as a low density bit or foam, can be applied over a metallic cover.

Aerobic and anaerobic digestion tanks which have a surface / volume ratio of less than 2.62 m ² / m ³ are preferably used for the present process. The term "surface" includes the entire wall surface of the covered mining tank including the bottom, cover and side walls. Surface / volume ratios of more than 2.62 m ² / m ³ lead to large heat conduction losses through the walls, based on the amount of heat required in the digestion tank. Such heat loss usually requires thermal insulation on the walls exposed to the outside atmosphere. In addition, larger surface / volume ratios generally require digestion tanks with smaller dimensions, in which gassing and / or uniform mixing is difficult.

The retention time of the sludge in the aerobic degradation zone also influences the autothermal one Temperature values that can be sustained. The relationship between length of stay and temperature is determined by numerous factors, including the degradability and the strength (the solids content) of the mud.

The mining zone 110 is equipped with a mechanical agitator 112 of the same type as the agitator 103 can be in the aeration zone 102. Funds are also provided for in the mining zone to constantly circulate the second gas or the activated sludge in relation to the other fluids.

The second gas containing at least 80% oxygen is the covered aerobic degradation zone 110 in Sufficient quantity and speed supplied to the dissolved oxygen content of the sludge to be kept at at least 2 mg / 1.

An oxygen-depleted decomposition gas with an oxygen concentration of at least 40% is turned off withdrawn from the degradation zone 110 via the line 118 in such a flow rate that its oxygen content makes up at least 35% of the oxygen content of the oxygen feed gas that is passed through the line 117 eip. Flows. The gas in line 118 arrives the covered gassing zone 102, wherein at least a larger part of the mentioned first gas den Provides oxygen, which is necessary for the biochemical oxygen enrichment of the wastewater. If If necessary, additional oxygen-containing gas can be supplied from an external source to the to enlarge oxygen-containing gas stream in line 118.

Partially stabilized sludge, which is essentially completely pasteurized, is removed from the digestion zone 110 via a line 114 to the anaerobic treatment part fed. The second anaerobic degradation zone includes an acidification subzone 120a and the degradation zone 1206, which is to be referred to as the Metha fermentation sub-zone. The incoming line 114 partially stabilized sludge is introduced into the acid formation sub-zone 120a and there for a sludge retention period held for 24 to 60 hours to ensure the necessary acidification of the sludge. Of the The content of the subzone 120a is controlled by an agitator 121a constantly mixed to lower carbohydrates, fats and proteins at a uniform rate Break down fatty acids. The acidified sludge is then extracted from sub-zone 120a via line 126

ίο carried out. Since the temperature of the zone 120a leaving sludge is still in or near the thermophilic temperature range of 45 ° C to 75 ° C and thus above the optimal methane formation values, the sludge temperature is generally lowered in order to ensure satisfactory operation of the methane-forming degradation zone 1206. The sludge is therefore passed through the heat exchanger 115 in countercurrent to a coolant flow, which flows through the heat exchanger via a line 160 The one leaving the heat exchanger 115 Sludge then flows to the via line 127 Methane fermentation subzone. The heat exchange medium in line 160 may be used as appropriate Be the cooling water flow, for example part of the drain that the secondary clarifier via line 106 leaves, or the feed sludge flow flowing into the mining system.

For optimal operation, the sludge in the methane fermentation sub-zone is at one temperature

jo between 35 ° C and 40 ° C and preferably between Maintained 37 ° C and 38 ° C. The content of zone 1206 is constantly mixed by means of an agitator 1216, which ensures a large active decomposition zone and the speed of the stabilizing

j-i ization reactions is increased significantly. Of the Sludge residence time in the methane fermentation subzone is preferably between 4 days and 8 days. Methane gas generated by the biochemical reactions taking place in Abbcuzon ^ 1206,

4 (i leaves this zone via a line 128 in which a St /; m control valve 129 is located. A portion of this discharged methane gas can be transferred to the methane boiler 130 a line 132 are fed, while the remainder of the process in a line 131

4) is withdrawn for further treatment experienced and / or fed to other end consumption levels. The further stabilized sludge will Discharged via a line 133.

Fig. 3 shows a flow diagram of a further embodiment

Vi approximately form, in the sludge from sewage feed and -after-treatment steps fed to the sludge removal system will. There is a thermophilic aerobic first degradation stage with a thermophilic anaerobic second Integrated mining stage. Previously was a thermophile

Anaerobic degradation is little more than a LaLoratorium curiosity. The problems associated with mesophilic anaerobic operation discussed above are more well known Facilities related to thermal instability and extreme sensitivity to changes in Pro-Mi Measuring conditions are anaerobic for a thermophile Degradation even more pronounced. Hence hey! this sludge treatment process so far at commercial Sludge removal applications received little attention. The problems of operational instability and excessive

high sensitivity to process fluctuations are overcome in the same way in the thermophilic aerobic / anaerobic embodiment, like this in connection with the embodiments

is described, which provide an anaerobic mesophilic second degradation stage. In the arrangement according to FIG. 3, raw sewage, which consists, for example, of municipal sewage, industrial sewage or rainwater, flows via a line 240 into a primary settling zone 241 , which can consist of a conventional gravity septic tank. There the wastewater is separated into a primary drain with a reduced BOD content, which reaches a gassing zone 202 via a line 201 , and a settled sludge flow, which is discharged from the zone 241 via a line 242. The gassing zone 202 is also fed via a line 218 an oxygen-containing aeration gas, via a line 250 excess sludge thickening liquid and via a line 208 activated return sludge. A mixing and circulating device 203 is located in the gassing 7nnp 202. ^v ? rschi? d? n? n, d? r Β6 ^σ ?.? ϋπ ^σ 5? οπ? to mix supplied fluids and to circulate the mixed liquid formed or the oxygen-containing aeration gas with respect to the other fluids. After a gassing time of, for example, 2 to 6 hours, a mixed liquid depleted in BOD and an oxygen depleted ventilation gas with at least 21% by volume of oxygen are discharged from the gassing zone 202 via lines 204 and 219, respectively.

The oxygen-enriched mixed liquid in line 204 passes to the secondary settling zone 205, where activated sludge is separated from the purified liquid; the latter leaves the process via a line 206. The settled sludge is discharged via a line 207. A larger part of this sludge is returned as return sludge to the aeration zone 202 via line 208, in which a circulating pump 209 is located. The remaining 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 concentrates the sludge to a solids content between 2% and 6%, so that the total suspended matter concentration is between 20,000 and 60,000 mg / l. The thickened sludge underflow is discharged via a line 245 and combined with primary sludge in the line 242 from the primary settling zone 241, so that a combined sludge flow in a line 211 is produced. The supernatant liquid from the sludge thickener 251 is fed to the aeration zone 202 via a line 250.

The sludge flow in line 211 can be partially heated by indirect heat exchange with the sludge from a second degradation zone 220; it then reaches a first degradation zone 210 via a line 248. Before this, the sludge can be further heated in the line 248 by means of a heating device 231 in which methane gas is burned, which flows in via a line 227.

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

In the first covered decomposition zone 210, the thermophilic aerobic decomposition of the inflowing sludge is carried out in the manner explained. in which a mechanical agitator 212 sits.

Degradation gas leaves the degradation zone via the line 218. Partially stabilized sludge is introduced from the aerobic degradation zone 210 via a line 216 into the second covered degradation zone 220 . In de degradation zone 220 is a thermophili anaerobic degradation zone in which the sludge to a temperature between 40 ⁰ C and 60 ⁰ C as well as preferential is maintained between 45 ° C and 50 ⁰ C. Because it

ίο there is a thermophilic operation in both mining zones the partially stabilized sludge can move from the first mining zone directly to the second mining zone be directed. Instead, in some cases it may be desirable to use higher egg in the second mining zone

can work ii or lower temperatures compared to the erstet aerobic degradation zone and for this purpose the partially stabilized sludge between the zones zi heat nrfer v \\ cool the F.rhil ^ s with pinp heating device similar to the device 231 Runaway leads are. For cooling, the partially stabilized sludge can be heat exchanged with the inflowing sludge, as described in connection with FIG. I and 2 is explained. Since it is even more critical with a thermophilic anaeiobic degradation than with a mesophilic

2 ^r > anaerobic degradation is to avoid temperature fluctuations in the degradation zone, an appropriately insulated "tank can be provided, which offers security against strong climatic fluctuations.

In the mining zone 220, the sludge is processed by means of a:

Thus mechanical agitator 221 is constantly mixed. Methane gas is discharged via a line 223. Part of the methane gas is fed in via line 227 to the heating device 231 and burned in order to keep the sludge in the first degradation zone at the temperature of 45 ° C to 75 ° C. The remainder of the wire is discharged via a line 228. The further stabilized sludge is discharged from the second degradation zone via a line 225 and is passed via the heat exchanger 244. He leaves the facility over

jo a line 243.

Due to the differences with regard to the swelling of the sludge, the biological activity in the aerobic degradation zone according to FIG. 3 differs greatly from the biological activity in the aerobic zone of the embodiment according to FIG. 2 from. In the embodiment according to FIG. 2 , the sludge supplied to the digestion system as feed sludge is only activated sludge from the secondary wastewater treatment system, while in the case of the embodiment according to FIG The organic material of the secondary sludge consists primarily of viable microorganisms, the aerobic decomposition of this sludge comprises the various biochemical reaction stages of cell lysis, the assimilation of lysis products for the synthesis of new viable material, and respiration, raw sludge, on the other hand, consists primarily of non-viable material organic material that the microorganisms present in the sludge can use as nutrients. Accordingly, during the aerobic decomposition of raw sludge, the microbial population of the sludge experiences a considerable cell synthesis phase in addition to cell lysis, assimilation of lysis products and respiration. Therefore, the aerobic degradation of the raw sludge takes place with a greater degree of both cell synthesis and cell respiration

than with the aerobic degradation of secondary sludge. In addition, the aerobic degradation of raw sludge leads to a smaller overall reduction in biodegradable volatile particulate matter than is the case with a comparable sludge retention time is the case with aerobic decomposition of secondary sludge. the resulting reduction in biodegradable suspended volatile matter in the mud during degradation represents a difference in terms of rival Represents the breakdown 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 solids that are removed during degradation than is the case with secondary sludge. Accordingly is for primary sludge in the Vprgleirh 711 .SpWiinrJärschlamm a lower resulting reduction in volatile matter required to be in the aerobic degradation stage to reach and maintain a certain temperature level. So can the Embodiment of Figure 3 at a given temperature with a lower degree of degradation operated by volatile suspended matter in the aerobic degradation zone than the aerobic zone after F i g. 2. A lower reduction in degradable volatile particulate matter in the aerobic zone of the The degradation system in turn requires that the sludge dwellings in the anaerobic degradation zone be adjusted accordingly is extended in order to achieve a given total removal of volatile particulate matter. Because a increased proportion of the total elimination of volatile particulate matter in such a case in the anaerobic If the decomposition zone takes place, the primary sludge processing system can do more in the anaerobic decomposition zone Generate methane as the mining system in which only secondary sludge is processed. The embodiment according to FIG. 3 is therefore inherently able to to deliver greater amounts of methane than the system of Figure 2; but this is at the expense of increased Sludge retention time in the aerobic degradation zone. ·.

Each of the exemplary embodiments described offers the possibility of heating the inflowing sludge before it is introduced into the aerobic degradation zone. Whether or not such heating is necessary depends on various factors, for example the sludge solids content, the outside temperature, the sludge residence time in the aerobic digestion zone and the type of sludge to be treated. 4 shows the temperature of the air flowing into the first reduction zone slurry which is required to maintain therein a working temperature of 50 ⁰ C at a sludge residence time of 24 hours, as a function of the supplied Gesamtschwebstoffkonzentration Henden the first reduction zone slurry. Curve A illustrates a combined primary and secondary sludge stream in which the ratio of the content of volatile suspended solids to Gesamtschwebstoffen (WS / TSS) is 0.75, and the biological Wärmein- _Μ halt at 47 χ 10 ⁶ J / kg eliminated volatile suspended solids The curve B applies to a non-combined secondary sludge with a VSS / TTS ratio of 0.79 and a heat content of 33 χ 10 * J / kg of removed volatile suspended matter.

As can be seen from the curves, for a given total suspended matter concentration, the combined sludge of curve A requires a higher inlet temperature for the aerobic degradation zone than the secondary sludge according to curve B. As a result, heating the sludge before it is introduced into the first degradation zone can be particularly beneficial if the Sludge contains a significant proportion of primary sludge from a wastewater treatment plant.

Figure 4 also shows that thermophilic operation can be achieved without the need to heat the sludge prior to introduction into the aerobic degradation zone when the sludge is sufficiently thickened. For example, if a combined sludge (curve A) with a total solids concentration of 4% is to be degraded, the temperature of the sludge introduced into the thermophilic aerobic zone need only be about 15 ° C.

The described embodiments provide a fully pasteurized product slurry as in all Cases of ir! dss Abb2'js * 'stsrri inflowing Schlsnirri is passed through the thermophilic aerobic zone, the high temperature of which a complete Sludge pasteurization guaranteed. However, there may be use cases where no complete pasteurized sludge is required or the sludge itself does not require pasteurization, because there are no significant concentrations of pathogens. F i g. 5 shows a flow diagram of a Another embodiment, in which a smaller part of the inflowing sludge to the second degradation zone is diverted and which is suitable for such applications. A larger part of the over a Line 311 entering sludge of a first covered mining zone 310 via a line 331 fed. The sludge in line 331 can, if is desired to be heated by means of a methane-heated kettle 330.

Aeration gas containing oxygen is added to the aerobic decomposition zone provided with a stirring device 312 310 supplied via a line 317. Oxygen-depleted decomposition gas is transferred from the decomposition zone 310 a line 318 discharged. Fully pasteurized and impoverished in biodegradable suspended solids Sludge arrives via a line 316 to a second covered degradation zone 320, which is in the mesophiien Temperature range works. Because the temperature of the sludge leaving the first breakdown zone is between 45.degree. C. and 75.degree. C., its temperature must be lowered before it is introduced into the degradation zone 320. A A smaller part of the inflowing sludge bypasses a methane-heated boiler 330 and the degradation zone 310 on line 329; it is immediately mixed with the warning sludge in line 316. the The flow rate of the diverted sludge is adjusted so that the temperature of the combined Sludge flow that goes to the anaerobic degradation zone 320 is sufficient to a working temperature between Maintain 35 ° C and 40 ° C in zone 320.

Methane gas leaves the decomposition zone 320 via a line 323. A side stream of this gas is in a Line loop 340 derived in which a compressor 326 sits Compressed methane gas is added to the sludge in the degradation zone 320, for example via a blowing device (not shown), in order for the Mix and stir the sludge. Part of the methane gas can be transferred from line 323 a pipe 327 to the methane-heated kettle! 330 go; the remaining part is via a line 328 discharged The further stabilized sludge is discharged via a line 325. The advantages of the

explained procedure can be made clear with the help of the following examples:

Example [

In this example, the operating behavior of the embodiment according to FIG. 2 compared to a conventional anaerobic high-performance system. The further explanation is based on the treatment of the sludge in a wastewater treatment plant with a capacity of 3.8 ⁷ l / day based on the flow diagram according to FIG. 2 off.

A mixture of 50% primary sludge and 50% secondary sludge, which initially has a temperature of ι> 18 ° C., is introduced into the degradation system according to FIG. 2 via line 111. The sludge which has a Gesamtschwebstoffkonzentration of 39 400 mg / 1 and a Verhäiiiiis of MÜcniigeu suspended iu Gesamtschwebstoffen of 72% is introduced in a> o flow rate of 3.4 χ 10 ⁵ l / day. To keep the sludge in the aerobic digestion zone 110 at a 24-hour residence time at a working temperature of 50 ⁰ C, the inflowing sludge by means of the methane boiler 130 to about 23 ° C >> is heated. Assuming an efficiency of 50% for converting the calorific value of methane gas into heat, approximately 710 mVday of the methane gas generated in the anaerobic degradation zone are required to feed the heating boiler 130. j ₍₎

In the aerobic degradation zone, the volatile suspended matter content is reduced by approximately 8% (16% biodegradable volatile suspended matter; the biodegradable volatile suspended matter makes up about 50% of the total volatile suspended matter content), so that, via line 114 a partially degraded sludge with a volatile suspended matter content of 26,100 mg / l is fed to the acid formation subzone 120a. 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 goes via line 126 to the αϊ degradation zone \ 20b, which is a methane fermentation sub-zone. Sufficient heat is extracted from the discharged sludge in the heat exchanger 115 to ensure a working temperature of 38 ° C. in the degradation zone 1206. to

The methane fermentation part zone is operated with a 5-day sludge retention time, which leads for the integrated system to an overall reduction in volatile suspended solids of 40% (reduction of the biologically degradable volatile suspended solids to 80%) of the methane fermentation part zone produces approximately 2070 m ³ methane gas per day, giving a total calorific value of 12 600 kWh / day. After deduction of the methane gas for the operation of the methane boiler 130 , 1360 m ^{3 of} methane gas per day, corresponding to a total calorific value of 8500 kWh / day, are available for delivery from the sludge removal system.

If the combined sludge in the amount of 3.4 χ to ⁵ l / day instead a conventional f ;. anaerobic high-capacity digestion tank is fed, approximately 13 days of sludge retention time is necessary to. achieve the same reduction in volatile suspended matter r. <. Although the conventional high-performance degradation tank ^{generates 3625 m 3 of} methane gas per day, corresponding to around 22 600 kWh / day, with a 50% conversion of the calorific value into heat, around 17 600 kWh / day of heating energy are required to achieve the optimal working temperature conditions in the high performance tank. The conventional system therefore requires, as compared with the embodiment of FIG. 2, based on the required dwell time, 86% more tank space; In addition, under normal working conditions, about 40% less methane is available for delivery.

Example II

This example relates to the embodiment according to FIG. 5. The inflowing insert sludge consists of 50% primary and 50% secondary sludge from a wastewater treatment plant in an amount of 2.27 10 ⁵ l / day. The sludge stream in line 311 has a temperature of 20 ° C. and a total suspended solids concentration of 4% (VSS / TSS = 0.75); it is divided into a substream of 1.74 10 'l / day, which enters the thermophilic aerobic degradation zone 310 via line 331, and a substream of 5.J χ ΙΟ ⁴ l / day, which is the bypass flow in line 329 forms. As shown in FIG. 4, it is not necessary in this case to heat the sludge before it is introduced into the degradation zone 310. The residence time in the mining zone 310 is approximately 24 hours; thermophilic temperatures are reached autothermally. A pasteurized sludge is discharged from the degradation zone 310 in the line 316 at a temperature of 50 ^° C. and mixed with the cool bypass flow from the line 329. This combined sludge stream then flows to the anaerobic digestion zone 320 where the sludge is held in the absence of oxygen for approximately 8 days, resulting in an overall volatile particulate matter reduction of approximately -0% (80% biodegradable volatile particulate matter reduction) . The mining zone 320 generates methane gas in an amount of approximately? 040 mVday, which corresponds to approximately 11,700 kWh / day. This methane can be completely released from the process system.

If the combined inflowing feed sludge of 2.27 10 ⁵ l / day is instead fed to a conventional anaerobic high-performance 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 ^{3 of} methane gas per day, corresponding to around 14 700 kWh / day, with a 50% conversion of the calorific value into heat, around 13 200 kWh / day are necessary to maintain the optimal anaerobic working temperature in the high-performance tank. In this case, a conventional anaerobic 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 using the internally generated methane gas as a heat source, the conventional system has significantly less methane gas available for delivery.

example

This example compares the performance of the embodiment of Figure 1 with a conventional high performance anaerobic system.

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 ', 12 by the outflow of the anaerobic degradation zone 20, followed by further heating by the outflow of the thermophilic aerobic degradation zone 10 in the heat exchanger 15 follows. In the heat exchanger 22 , the temperature of the inflowing sludge is increased from 15 ° C avf to approximately 25 ° C, while the temperature of the stabilized sludge from the degradation zone 20 is decreased from approximately 35 ° C to 25 ° C. In the heat exchanger 15, the temperature of the incoming slurry to about 30 "C is increased, while the: temperature of the degradation zone 10 leaving the slurry is reduced from about 50 ⁰ C to 45 ° C, the inflowing sludge has a Gesamtschwebstoffkonzentration of 34 400 mg /. 1 and a ratio of volatile suspended solids to total suspended solids of 78%. It is introduced into the mining zone 10 in an amount of 2.27 χ 10 ⁵ l / day. In the mining zone 10 , a working temperature of 50 ° C is achieved during a sludge residence time of 24 hours maintain.

A reduction of about 16% of the volatile sulfur matter (reduction of 32% of the biodegradable volatile suspended matter) is achieved in the aerobic stage, so that a partially stabilized sludge with a volatile matter content of 22,500 mg / l via the line 16 into the Mining zone 20 is fed.

The anaerobic degradation zone 20 works with a residence time of 8 days, which leads to an overall reduction in volatile suspended matter of 42% (Vermin change of biodegradable volatile suspended matter

Hi substances of 84%) for the integrated system leads. The mining zone 20 generates approximately 1470 m ^{1 of} methane gas per day, corresponding to a total calorific value of approximately 8200 kWh / day. All the methane gas is available for delivery.

ι = · If, on the other hand, the ^{sludge flowing in at 2.27 χ 10 5} l / day is fed into a conventional anaerobic high-performance degradation tank, a dwell time of at least 14 days is necessary in order to achieve the same reduction in the volatile content

2 (i to achieve suspended solids. Although with such a conventional high-performance system 2400 m ^J methane gas per day, corresponding to about 13 800 kWh / day, are generated with a 50% conversion of the calorific value into heat, about 13 200 kWh per day

-'j day required to be optimal in the high-performance tank Maintain working temperature conditions. The conventional anaerobic system therefore needs about 55% more tank space; it can produce a methane gas energy of about 7600 kWh / day less

in as the system according to Fi g. 1.

For this purpose 3 sheets of drawings

Claims (18)

Patent claims: 1. Procedure for. Degradation of sludge, in which at least part of the sludge by at least two covered mining zones passed and thereby; with the formation of stabilized sludge and Methane gas is successively exposed to aerobic and anaerobic conditions, characterized in that that a) in a first covered degradation zone the '"sludge and a sludge containing at least 50% by volume of oxygen Venting gas introduced and while maintaining a content of Mixed liquid of dissolved oxygen of at least 2 mg / 1 and a total suspended '' A concentration of at least 20,000 mg / 1 in the sludge is mixed, b) the sludge in the first degradation zone is kept during the mixing process at a temperature in the thermophilic range of 45 ⁼ C to 75 ⁼ C ~, c) mixing in the thermophilic temperature range for a sludge retention time of 4 to 48 hours with partial reduction in the content of the "'' introduced into the first mining zone th sludge of biodegradable volatile suspended matter is continued, d) partially stabilized sludge and oxygen-depleted degradation gas with an oxygen content. m at least 21% off the first ^! "The mining zone will be removed separately and e) the leilstabilisieric sludge from process step d) is kept in a ^ wide covered degradation zone at a temperature of 30 ° C to 60 ⁰ C under anaerobic conditions for a '' solids residence time of about 4 to 12 days and which is sufficient to maintain the content of the sludge of biodegradable volatile suspended matter to less than about 40% of the content of the sludge introduced in tier process step a) "'into the first ablation: further lowering in biodegradable volatile suspended matter. 2. The method according to claim I, daduich kenn- r. draws that the initiated in the first dismantling / onc Sludge has a total solids concentration between 20,000 and 60 (K) O mg / l. 3. The method according to claim I or 2, characterized in that the Schlamniverwcildauer in > <i the first oj / uu / one between 12 and 24 hours amounts to. 4. The method according to any one of the preceding claims, characterized in that the Sludge before filling in the first dismantling / onc ■ · is heated to the temperature in the process stage b) maintain. ■ ">. Method according to one of the preceding Claims, characterized in that the temperature in process run e) for a ·> » Mesophilic degradation in the second degradation / onc is kept in the range of) 5 "C to 40" C. 6. A method according to any one of claims I to 4, characterized in that dal) the temperature in the Verfahrensslufe e) for a reduction in Ihermophilen "> · the / wide degradation zone in the range of 4 ¹ J" C to ■ Ί0Τ is maintained. 7. Method according to one of the preceding Claims, characterized in that the sludge retention time in process stage e) is chosen sufficiently to the content of the sludge of biodegradable volatile Suspended solids to less than about 20% of the content of the process step a) in the first Degradation zone introduced sludge to further press down biodegradable volatile suspended matter. 8. The method according to any one of the preceding claims, characterized in that the Sludge in the second mining zone is mixed by adding methane gas against the one located there Sludge is circulated. 9. The method according to any one of the preceding claims, characterized in that the ventilation gas before being introduced into the first mining zone in order to maintain the temperature in the Process stage b) is heated. 10. Procedure n: i any of the preceding Claims, characterized in that the sludge before being introduced into the first mining zone further stabilized by indirect heat exchange with the alis carried from the second mining zone Mud is heated. 11. The method according to claim 10, characterized characterized in that the temperature in the process stage e) is kept in the range from 35 ° C to 40'C and that the heated sludge before it is fed into the first mining zone by indirect Heat exchange with that from the first Abbaiizone applied, partially stabilized sludge is heated. 12. The method according to any one of the preceding claims, characterized in that the second degradation zone is provided with an Säiierungteil / one and a Mcthunfcrmcntationstcil / ouc, partially stabilized sludge from the first Abbaiizonc introduced into the Aiisaucrungstcil / one and for acidification of the sludge there for an ivchiammverweilduuer is held by 24 to 60 hours, discharged and introduced into the Mclhanfcrmciitaiionsteilzone and there at a temperature between 33 ¹ C and K) 'C for a Schlammverweii> wi "r of I l) is 8 days held acidified sludge from the Ansäiieningsteil / one will. I 3. The method according to claim 12, characterized in that the sludge in the Melhanfermcntationstcil / one is kept at a temperature between 37 '(' and IK'C. 14. The method according to claim 12 oiler I 3. characterized in that the sludge in the Ansäiicrungstcil / one held at a temperature between ti'C and 7 ^r ) 'C and the acidified, .ins the Ansäiieningstcilzone aiisgciragcnc sludge before diverting into the MclIianfcrmcnlalionMcilzoiic ; it is cooled to a temperature of 3 ^° C to 10 ° C. 15. Method according to one of the preceding Claims, characterized in that) in the first dismantling / om * initiated dissolution from l'rimiirschlamni and (iberschiißsclilainm a wastewater activated sludge plant considered. 16. Procedure nacii one of the preceding Claims, characterized in that the ventilation gas introduced into the first ventilation gas at least Contains 80% by volume of oxygen, the extraction gas withdrawn from the first Abbaii / mic one Has an oxygen content of at least 40% and at least 35% of the oxygen content of the aeration gas introduced into the first degradation zone makes up, and this degradation gas in a covered fumigation zone of a wastewater activation system as at least the greater part of the aeration gas supplied to a gassing zone is introduced, during the excess sludge of the wastewater activation system is fed into the first mining zone. 17 The method according to any one of the preceding claims, characterized in that a part of the methane gas discharged from the second extraction zone is mixed with oxygen-containing gas and is burned with the formation of heat, by means of which the sludge in at least one of the both degradation zones is kept at an elevated temperature. 18. The method according to claim 17, characterized in that the sludge in the first degradation zone is kept at the temperature of 45 "C to 75 ° C by burning methane gas with oxygen-containing gas.