EP2462233A1

EP2462233A1 - Method for producing biogas or sewage gas

Info

Publication number: EP2462233A1
Application number: EP10749596A
Authority: EP
Inventors: Lothar Günther
Original assignee: DGE Dr Ing Guenther Engineering GmbH
Current assignee: DGE Dr Ing Guenther Engineering GmbH
Priority date: 2009-08-03
Filing date: 2010-08-02
Publication date: 2012-06-13
Also published as: DE102009035875A1; WO2011015328A1; CN102482686A; US20120135491A1

Abstract

The invention relates to a method for producing biogas or sewage gas by a multi-stage anaerobic reaction of biomass and/or sludge. Considering the disadvantages of the known prior art, a method is to be provided that leads to a higher yield of raw gas or biogas and a higher content of methane in the raw gas and enables an economically improved operating method. To this end, the reaction is carried out in the first fermentation stage (F1) while maintaining a TS content of 3 to 8% and a volume load of 1 to 3 kg OTS/m³ d. In the second fermentation stage (F2), a further reaction of the solid matter phase is carried out while maintaining a TS content of 8 to 40% and a volume load of over 2 kg OTS/ m³ d. In the second fermentation stage, the fermentation substrate is set to a TS content that is higher than the TS content of the first stage. In both fermentation stages, the reaction is carried out in the range from slightly acidic to neutral (pH value 6.5 to 8). The biogas obtained in the fermentation stages (F1, F2) is combined or removed separately and is subjected to further purification.

Description

Process for the production of biogas or sewage gas

The invention relates to a process for the production of biogas or sewage gas by a multi-stage anaerobic conversion of biomass and / or sewage sludge.

The production of biogas in a conventional manner in one or more reactors or fermenters, the mesophilic (temperatures below 45 ⁰ C) or thermophilic (temperatures 45 to 80 ⁰ C) can be operated.

As biomass organic materials are used, for example, as manure (manure, manure), renewable resources and biological waste materials incurred.

Sewage sludge is only suitable for anaerobic conversion if it is obtained from organically polluted wastewater or process water with a COD content of more than 5,000 mg / l, and thus is anaerobically convertible biomass. COD is the abbreviation for "Chemical Oxygen Demand, which uses a COD measurement to determine how much oxygen the chemical digestion / purification processes in wastewater consume. For the production or production of biogas, various biodegradation processes take place during the reaction, such as hydrolysis, acidification, acetic acid formation and methane formation. The decomposition processes caused by bacteria can take place under aerobic or anaerobic conditions. The most commonly used method is wet fermentation where the dry matter content TS is <15% and the water content is> 85%.

Depending on the raw materials used and the process conditions, biogas with a methane content of up to 65% can be achieved in practice.

Biogas is used inter alia for heating purposes, e.g. used in combined heat and power plants, or as an energy source for feeding into natural gas networks.

In addition to the removal of other impurities, in particular hydrogen sulfide, nitrogen and ammonia, the CO ₂ contained in the biogas must still be separated in order to obtain a high quality methane suitable for further processing.

The purification or processing of biogas is a technologically complicated process, which is associated with a high expenditure on apparatus.

As the proportion of methane in the biogas produced increases, so does the cost of subsequent purification or workup to methane gas. Therefore, solutions are already known to change the process of biogas production so that a biogas is produced with the highest possible proportion of methane.

In DE 103 16 680 A1 it is proposed to feed a pre-fermentation reactor with nutrient solution and to feed into it an untreated biomass until a pH value of 4.3 to 4.8 is reached. Subsequently, the pre-fermented biomass is fed to the main reactor in such an amount that sets a constant pH of 6.7 to 7.7 and remains constant. The prereactor is fed with rotted material from the main reactor as the nutrient medium. This can be fed constantly new biomass. Part of the product of the pre-fermentation reactor is fed into the main reactor and vice versa, which should be approximately equal amounts. Both reactions are recycled, with the key control variable being the pH. The disadvantage of this procedure is that the bacteria are mixed for the hydrolysis, acidification, acetic acid formation and methanation. The biogas produced in the primary reactor has a very low proportion of methane of 5 to 20%, so that it can only be used by mixing it with biogas from the main reactor.

DE 10 2007 037 202 A1 describes a process for the conversion of biomass into biogas, which takes place under anaerobic conditions in fermenters. In the first fermenter renewable raw materials are introduced together with liquid and other necessary for the methagines starting materials and subjected to a fermentation process. Subsequently, the digestate is subjected to a separation into a solid-liquid phase and subjected to the solid phase of a thermal pressure hydrolysis at temperatures of at least 170 ⁰ C and pressures of at least 1 MPa. The solid phase treated in this way can either be returned to the first fermenter or fed into a second fermenter for a further fermentation process. The process step of subjecting the separated solid phase to a thermal pressure hydrolysis is complicated and cost-intensive.

In DE 10 2007 000 834 A1, it is proposed to wash and comminute ensiled renewable raw materials, to remove part of the washing water and to subject it to hydrolysis. The hydrolysis products are then further treated for biogas production in a conventional manner in fermenters.

The use of ensiled renewable raw materials is disadvantageous for ecological reasons. The required levels washing and crushing are energy and costly.

A general disadvantage of the known processes are too low yields of methane in the conversion of biomass and / or sewage sludge to biogas or sewage gas. The invention has for its object to provide a process for the production of biogas or sewage gas, which is characterized by a higher yield of raw or biogas and a higher content of methane in the raw gas and enables an economically improved operation.

According to the invention the object is achieved by the features specified in claim 1. Advantageous developments of the procedure are the subject matter of claims 2 to 13.

The biomass is reacted in both fermentation stages in the slightly acidic to neutral range (pH 6.5 to 8). In the first fermentation stage, the reaction is carried out while maintaining a TS content of 3 to 8% and a space loading of 1 to 3 kg OTS / m ³ d. The solid phase of the fermentation substrate from the first fermentation stage is further reacted in the second fermentation stage while maintaining a DM content of 8 to 40% and a space load of more than 2 kg OTS / m ³ d. It is crucial that the TS content of the fermentation substrate in the second fermentation stage is set to a value which is greater, preferably 1.5 to 20 times, than the TS content of the first stage.

In the first fermentation stage, the processes hydrolysis, acidification and acetic acid formation proceed in parallel. The hydrolysis occurs at a pH in the weakly acidic to neutral range. This represents a departure from the usual practice (pH 4.5 to 6). In conjunction with the low Faulraumbelastungen it comes to a lower acidification, whereby the methane formation is accelerated. The first fermentation stage produces a biogas with a high CO ₂ content. Since this is continuously discharged and purified, biogas with a higher methane content is produced in the fermenter. Surprisingly, it was found that a higher yield of biogas with a higher content of methane can be achieved by adhering to the above-mentioned values of the process parameters pH value, DM content and room load as well as a higher DM content in the second fermentation stage.

The first fermentation stage is carried out as wet fermentation. The second fermentation stage can also be operated as a dry fermentation. The optimum procedure in each case depends primarily on the composition of the biomass.

A further improvement of the abovementioned results is achieved if the biomass is pretreated without pressure in a hydrolysis stage upstream of the first fermentation stage, at temperatures of 25 to 60 ^° C. The hydrolysis takes place here at a pH of 5 to 8. The residence time of the biomass in the Hydrolysis stage should be 3 to 8 days, preferably 4 to 6 days. The residence time in the hydrolysis step can also be made on the measured in the withdrawn biogas H ₂ S concentration. For this purpose, the H ₂ S concentration is measured and evaluated continuously or at certain time intervals.

The measured values recorded as a curve diagram (H ₂ S concentration in ppm and time course in hours) clearly show a peak in the course of the curve (increased H ₂ S concentration). After that, the values slowly drop off again. Depending on the raw materials used and the specific hydrolysis conditions, a lower limit for the H ₂ S concentration is set. If this is reached after the peak, the hydrolysis is stopped.

Depending on the raw materials used and the composition of the biomass, different H ₂ S concentrations and curves occur.

The resulting during the hydrolysis CO ₂ -containing gas mixture (biogas) with a high H ₂ S concentration is withdrawn and purified. Thus, a biogas is obtained with a 3 to 10 times higher methane content. The cleaning can be operated as a pressureless water wash. The hydrolysis or biogas can be purified to a methane content of 50 vol .-% or higher. The thereby separated carbon dioxide is recycled elsewhere. The advantage of an advanced hydrolysis step is also a reduction of the H ₂ S content in the subsequent fermentation stages. In the subsequent fermentation stages then no or only a very weak hydrolysis can take place. Under these conditions arise biocultures, which have an advantageous effect on the methagonesis.

Biogas withdrawn from the hydrolysis stage and the two fermentation stages is purified and then combined for further utilization to form a gas stream. Alternatively, the gas streams can also be cleaned individually or after a merger. This depends primarily on the composition of the biogas obtained in the individual stages. It should also be taken into account the resulting cleaning effort, which should be kept as low as possible.

It may also be possible to integrate another hydrolysis step in the second fermentation stage. If necessary, even small amounts of raw material or biomass can be supplied in the second fermentation stage.

Depending on the starting material used, up to 80% of the methane yield can be achieved in the first fermentation stage and up to about 20% in the second fermentation stage. However, this depends on the type and composition of the raw materials used and the desired methane concentration for subsequent recovery. A further additional advantage is achieved if at least a portion of the liquid phase separated from the fermentation residue of the first fermentation stage is fed to a stripping stage in which ammonia contained in the liquid phase is removed. The thus purified fermentation water with an ammonia content of less than 2 g / l, preferably up to 0.5 mg / l, for example, stored temporarily. Purified fermentation water can then be used for further approaches to biomass or fermentation substrate. As a result, the biology in the starting material improves compared to addition of fresh water, whereby a higher methane content in biogas can be achieved.

The separated from the digestate of the first fermentation stage solid phase can be mixed before being fed into the second fermenter with purified liquid phase (dehydrated) or thermally treated in an intermediate reactor, at temperatures up to 180 ⁰ C and a pressure of up to 10 bar, if necessary with the addition of acidic or alkaline additives. The contaminated stripping gas can be treated in a subsequent washing step by means of an acidic wash solution. As a result, ammonia contained in the gas stream is converted to ammonium or phosphorus sulfate or other salts. The discarded sulfate can be used as a fertilizer in agriculture.

The invention will be explained below with some examples.

In the accompanying drawing, an apparatus for carrying out the procedures is shown. The system will be explained in more detail in connection with the examples.

example 1

For the production of biogas the following raw materials are used as biomass:

Cattle slurry with a TS content of 6%, manure with a TS content of 25%, maize with a TS content of 32% and grass silage with a TS content of 30%.

The raw materials (1512 kg of cattle slurry, 302 kg of manure, 116 kg of maize and 349 kg of grass silage) are conveyed via line 1 into a mixing tank A1 (1.96 m ³ / h). The mixture has a TS content of 12.2% and is adjusted in this with already existing unpurified fermentation water (1, 6 m ³ / h) so that a TS content in the batch tank of 6% is present. The supply of fermentation or process water via line 2. The fermentation substrate, no further additives are added and after a residence time of about 1 hour in the batch tank, the fermentation substrate in an amount of 3.57 m ³ / h continuously via line 11th promoted to the first fermenter F1. This is operated mesophilic (temperature 38 ⁰ C) and with a space load OTS of 1 kg / m ³ d. The load on the room is continuously monitored by means of suitable measuring methods and, in the case of under- or overshoots, via the supply of fermentation substrate to the aforementioned value set. In addition, the pH is continuously monitored, which is set to a value of 7.5 to 7.8. The procedure in the first fermenter F1 takes place in the neutral range. The fermentation substrate is kept at the aforementioned temperature via the fermenter heating and / or cooling. The fermenter is equipped in a conventional manner with an insulation and a stirrer for mixing the fermentation substrate.

Under the conditions mentioned above, a superimposed hydrolysis and acidification phase and methane formation take place in the first fermenter F1. By adding air or oxygen or iron salts, the content of hydrogen sulphide in the biogas can be reduced.

During the biological conversion of the fermentation substrate in the first fermenter, a biogas of the following composition results:

CH ₄ 55 vol.%

CO ₂ 41 vol.%

H ₂ O 3.5% by volume

H ₂ S 60 ppm

NH ₃ 35 ppm.

On average, the first fermenter F1 produces a gas volume of 96 Nm ³ / h. The biogas formed is removed via the line 21 and mixed with biogas from the fermenter F2. The mixture (biogas) is then cleaned and recycled.

After a residence time of the fermentation substrate of 20 days, the reaction of the fermentation substrate in the first fermenter F1 is stopped.

The fermentation substrate is withdrawn via line 5 from the first fermenter F1 and fed to a separation apparatus D1 (separator), for separation into a liquid phase and a solid phase. The solid phase (water content of 30 to 70 wt .-%) can be supplied via lines 17, 18 either a reactor R1 or directly to the second fermenter F2. The reactor R1 is heated, the supply of heating medium via the line 19. The separated liquid phase (fermentation water) passes via line 6 into a container B1 and is stored for further use. A subset may be returned to the batch tank or to the first fermenter.

The solid phase of the fermentation substrate is adjusted in the second fermenter F2 to a TS content of 9%. The procedure in the second fermenter F2 takes place under mesophilic conditions (temperature 38 to 42 ⁰ C) and with a space load OTS of 2.2 kg / m ³ d. The biological conversion of the fermentation substrate is carried out in the absence of air or oxygen and at pH values of 7.5 to 7.8. The residence time in the second fermenter F2 is about 40-60 days. To reduce the formation of hydrogen sulfide small amounts of iron salts can be added. During the reaction in the second fermenter F2 arise 18 NnfVh biogas of the following composition:

CH ₄ 54% by volume

CO ₂ 43 vol.%

H ₂ O 3 vol.%

H ₂ S 40 ppm

NH ₃ 42 ppm.

The biogas is discharged via the line 22, merged with the biogas from the first fermenter and cleaned for further use.

In total, about 114 Nm ³ / h of biogas with a methane content of 54.8% by volume are produced in both fermenters F1 and F2. The amount of methane produced is 62.5 m ³ / h, which is 35% above the known conventional method.

The different conditions in terms of the TS content and the space load for the implementation of the fermentation substrate in the first and second fermenter, each in the neutral range, lead to a higher biogas yield and an increase in the methane content.

Example 2

The approach of biomass in approach tank A1 is carried out under the same conditions as in Example 1. The fermentation substrate, no further additives are added and after a residence time of about 1 hour in the mixing tank A1, the fermentation substrate (amount 3.57 m ³ / h) on the Line 3 promoted in a hydrolysis H1 and pretreated in a preceding the fermentation process hydrolysis, pressureless, at temperatures of 35 ⁰ C and a pH of 6.5 to 7.5. The residence time for the hydrolysis and acidification reaction in the hydrolysis vessel H1 is 4 days. The hydrolysis reactor is operated batchwise. As shown in the drawing, two hydrolysis containers are provided.

In comparison to other known hydrolysis stages, the hydrolysis does not take place in the acidic but in the neutral range.

Under these conditions, a CO ₂ -containing gas is produced in the hydrolysis with small traces of hydrogen and methane and high concentration of hydrogen sulphide. The escaping via line 20 biogas (32 Nm ³ / h) has the following composition:

CO ₂ 60 to 85 vol.%

H ₂ to 5 vol.%

CH ₄ to 10% by volume

H ₂ S 800 ppm (mean)

Rest air.

During the hydrolysis, the H ₂ S concentration rises after about 52 hours to a value of 2850 ppm (peak) and then drops slowly again. The H ₂ S concentration is measured at intervals of 60 minutes. After about another 43 hours, the H ₂ S concentration drops to a value of 420 ppm and the hydrolysis is stopped.

The biogas withdrawn from the hydrolysis stage H1 is treated in a purification stage not shown. This is operated, for example, as a pressureless water wash. The hydrolysis or biogas is purified to 4 NrrvVh with a methane content of 50 vol .-%. The separated carbon dioxide is recycled elsewhere.

The fermentation substrate from the hydrolysis stage H1 is continuously fed via the line 4 to the fermenter F1 and treated in this under the same conditions as in Example 1.

Due to the upstream hydrolysis, the metered addition of air or oxygen or iron salts to reduce hydrogen sulfide in the biogas can be reduced by about 80%, since the major part of hydrogen sulfide was already separated in the hydrolysis step.

During the biological conversion of the fermentation substrate in the first fermenter F1, biogas is produced with the following composition:

CH ₄ 72.26 Vol .-%

CO ₂ 24.24 Vol .-%

H ₂ O 3.50 vol.%

H ₂ S 20 ppm

NH ₃ 31 ppm.

On average, a gas volume of 73 Nm ³ / h. This biogas discharged via the line 21 can be mixed with biogas from the second fermenter F 2 or, if necessary, also be utilized separately. After a residence time of 20 days, the reaction of the fermentation substrate in the first fermenter F1 is stopped.

The fermentation substrate withdrawn from the first fermenter F1 via line 5 is subjected, as in Example 1, to a separation into a liquid phase and a solid phase (water content of 30 to 70% by weight).

The solid phase of the fermentation substrate is treated in the second fermenter F2 under the same conditions as in Example 1.

During the reaction in the second fermenter F2 arise 18 NrrvYh biogas of the following composition:

CH ₄ 54% by volume

CO ₂ 43 vol.%

H ₂ O 3.5% by volume

H ₂ S 40 ppm

NH ₃ 39 ppm.

The biogas is removed via line 22 for further utilization.

Overall, in the hydrolysis stage H1 and the two fermenters F1 and F2 approx.

95 NnfVh of biogas with a methane content of 67.9% by volume. The methane produced ge is 64.5 m ³ / h, which is 39.3% above the known conventional method.

In the fermenter F1, a biogas stream with a methane content of 72.26 vol .-% is generated. The methane content can be increased by an extension of the residence time by about 2 to 3 days in the hydrolysis step to over 80 vol .-%.

Example 3

This differs from Example 2 merely by a stripping step K1 interposed after the first stage of the invention F1, in which under elevated pressure, preferably from 10 to 100 mbar, of heated fermentation water by means of stripping gas ammonia up to a concentration of 0.5 mg / l is separated.

The separated liquid phase (fermentation water) is fed via line 6 to the container B1. For this, a partial flow (about 50%) is branched off via the line 7 and heated in a downstream heat exchanger W1 to about 50 to 70 ⁰ C and optionally adjusted the pH so that it is greater than 8. Subsequently, the heated partial stream is fed to a stripping column K1 in which stripping gas is increased to a pressure of about 10 to 20 mbar via the compressor V1 integrated into stripping gas lines 23, 24, and ammonia contained in the dehydrating water is stripped off. The contaminated circulation or stripping gas is treated in a wash column K2 with an acidic wash solution. The guided in line 25 washing solution is driven by the pump P1 in the circuit. The ammonia contained in the stripping gas is reacted on contact with the acidic wash solution to ammonium sulfate or phosphorus sulfate. The concentration of sulfate is adjusted to about 10 to 30 wt .-%, wherein via the line 26, the dosage of acid. At the bottom of the scrubbing column K2, the sulfate formed as fertilizer via the line 27 is removed.

The stripping process reduces the ammonium concentration in the fermentation water from 2 to 0.5 mg / l.

The nearly ammonia-free fermentation water can then be used again in the biological process for adjusting the DM content of the biomass used during the batch. This has an advantageous effect on the biology of the implementation of the fermentation substrate.

When using purified fermentation water in the batch phase, a biogas of the following composition is formed during the biological conversion of the fermentation substrate in the first fermenter F1:

CH ₄ 72.61 Vol .-%

CO ₂ 23.89 Vol .-%

H ₂ O 3.50 vol.% H ₂ S 20 ppm

NH ₃ 8 ppm.

The average amount of gas produced is 75 Nm ³ / h.

During the reaction in the second fermenter F2 arise 18 NπrVh biogas following

Composition:

CH ₄ 54% by volume

CO ₂ 43 vol.%

H ₂ O 3 vol.%

H ₂ S 40 ppm

NH ₃ 6 ppm.

In total, approximately 97 Nm ³ / h of biogas with a methane content of 68.2% by volume are formed in the hydrolysis stage and the two fermenters F1 and F2. The amount of methane produced is 66.2 m ³ / h. The increase in the methane yield compared to Example 2 is due to the lower proportion of ammonia in the added fermentation water.

Fermentation residue treated in reactor R1 can be fed directly to second fermenter F2. This can also be preceded by a second approach tank A2, which can be supplied via the line 8 purified fermentation water. Purified fermentation water can be supplied both to the first batch tank A1 and to the second fermenter F2 via the pipes 9, 10, 12 connected thereto.

After completion of the reaction in the second fermenter F2, the fermentation residue is fed via the line 13 to a second separator D2. The solid phase is removed via the line 16 and the liquid phase passes via the line 14 into a second feed tank B2 and can be discharged from the latter via the line 15.

Example 4

This example differs from Example 3 in that the hydrolysis step was run until the H ₂ S concentration in the discharged hydrolysis or biogas after the peak had dropped to a lower limit of 240 ppm. This value was reached after about 142 hours. As a result, a higher yield of biogas is achieved. In addition, the proportion of methane in the biogas also increases.

In the hydrolysis 43 Nm ³ / h CO ₂ -containing biogas in identical composition as in Example 3.

The biogas from the hydrolysis stage is treated by means of a pressureless water wash while the hydrolysis or biogas to 8 Nm ³ / h cleaned with a methane content of 50 vol .-%.

During the biological conversion of the fermentation substrate in the first fermenter F1, a biogas of the following composition is formed:

CH ₄ 81, 97 Vol .-% CO ₂ 14.53 VoI. -%

H ₂ O 3.50 vol.%

H ₂ S 17 ppm

NH ₃ 8 ppm.

The average amount of gas produced is 64 Nm ³ / h.

During the later conversion in the second fermenter F2, 18 Nm ³ / h of biogas with the following composition are formed:

CH ₄ 54% by volume

CO ₂ 43 vol.%

H ₂ O 3 vol.%

H ₂ S 40 ppm

NH ₃ 6 ppm.

In total, in the hydrolysis stage and the two fermenter stages F1 and F2 90 NrrvVh biogas with a methane content of 73.6 vol .-%. The amount of methane produced is 66.2 m ³ / h, which is 43.0% above the known conventional method.

In fermenter 1, a biogas stream with a methane content of 81, 971 vol .-% is generated. The high methane content even makes it possible to feed the biogas after fine desulphurisation and drying in a gas network.

In practice, the adjustment of the respective pH values can take place via the raw material, fermentation water or fresh water supply as well as the TS content.

Vergleichserqebnisse:

From the literature, "Biogas Basic Data Germany, as of August 2007", Agency for Renewable Resources e.V. (FNR), 18276 Gülzow, the following yields of biogas and methane are known for the production of biogas from the following starting materials:

13,000 1 cattle manure (TS content 6%) 325,000 m ³ biogas 195,000 m ³ methane

2,600 1 bovine manure (TS content 25%) 117,000 m ³ biogas 70,200 m ³ methane

1,000 1 maize silage (TS content 30%) 202,000 m ³ biogas 105,040 m ³ methane

300 1 grass silage (TS content 30%) 51,600 m ³ Bioqas 27,864 m ³ methane

Total 695,600 m ^{3 of} biogas 398,104 m ^{3 of} methane

Consequently, with a continuous operation of a conventional biogas plant of 8600 hours 80.9 Nm ³ / h of biogas with a methane content of 57.23 vol .-%. The amount of methane produced is 46.3 Nm ³ / h.

Claims

claims

1. A process for the production of biogas or sewage gas by a multi-stage anaerobic conversion of biomass and / or sewage sludge by wet fermentation in at least two separate fermentation stages, wherein after the first fermentation stage (F1) a separation of the digestate is carried out in a solid phase and a liquid phase, the solid phase further treated and then subjected to a further fermentation process in the second fermentation stage (F2), characterized in that the reaction in the first fermentation stage (F1) while maintaining a TS content of 3 to 8% and a space load of 1 to 3 kg OTS / m ³ d is performed and in the second fermentation stage (F2), a further implementation of the solid phase while maintaining a TS content of 8 to 40% and a space load of about 2 kg OTS / m ³ d is made, wherein the fermentation substrate is set in the second fermentation stage to a TS content which is greater than the T S content of the first stage, and the reaction in both fermentation stages in the weakly acidic to neutral range (pH 6.5 to 8) takes place, and merging the biogas formed in the fermentation stages (F1, F2) or separated separately and another Cleaning is subjected.

2. The method according to claim 1, characterized in that the biomass in a first fermentation stage (F1) upstream hydrolysis (H1) is pretreated without pressure, carried out at temperatures 25 to 60 ⁰ C and the hydrolysis at a pH of 5 to 8 becomes.

3. The method according to any one of claims 1 or 2, characterized in that the residence time of the biomass in the hydrolysis step (H 1) is 3 to 8 days, wherein a CO ₂ -containing gas mixture is formed with a high H ₂ S concentration, the removed and cleaned.

4. The method according to any one of claims 1 to 3, characterized in that the residence time of the biomass in the hydrolysis step (H 1) is controlled by the measured in the withdrawn biogas H ₂ S concentration, wherein, depending on the raw material composition and the hydrolysis set a lower limit and after reaching a peak and then lowering the H ₂ S concentration to this limit, the hydrolysis is terminated.

5. The method according to any one of claims 1 to 4, characterized in that from the hydrolysis stage (H1) withdrawn biogas is purified, wherein the methane content in the biogas is increased by 3 to 5 times.

6. The method according to any one of claims 1 to 5, characterized in that from the hydrolysis stage (H1) and the two fermentation stages (F1, F2) withdrawn biogas are purified and then combined for further utilization to a gas stream.

7. The method according to any one of claims 1 to 6, characterized in that at least a portion of the from the digestate of the first fermentation stage (F1) separated liquid phase of a stripping (K1) is supplied, removed in the ammonia contained in the liquid phase and the cleaned liquid phase is stored.

8. The method according to any one of claims 1 to 7, characterized in that the separated from the digestate of the first fermentation stage (F1) solid phase mixed with purified liquid phase and the second fermentation stage (F2) is supplied.

9. The method according to any one of claims 1 to 8, characterized in that the crude product biomass in a Ansetzstufe (A1) is pretreated, with the addition of ammonia-reduced fermentation water from the process cycle.

10. The method according to any one of claims 1 to 9, characterized in that the solid phase obtained from the first fermentation stage (F1) is pretreated in a second Ansetzstufe (A2), with the addition of ammonia-reduced fermentation water from the process cycle.

11. The method according to any one of claims 1 to 10, characterized in that the separated after the first fermentation stage solid phase of a thermal treatment (R1) at temperatures of up to 180 ⁰ C and a pressure of up to 10 bar is subjected, with the addition of acid or alkaline additives.

12. The method according to any one of claims 1 to 11, characterized in that in the stripping step (K1) under elevated pressure from heated fermentation water by means of stripping gas ammonia is separated to a concentration of 0.5 mg / l.

13. The method according to any one of claims 1 to 12, characterized in that the contaminated stripping gas is treated in a washing step (K2) by means of an acidic wash solution, wherein ammonia contained in the gas stream is converted to ammonium or phosphorus sulfate or other salts and removed.