DE102017109733B4 - Method for operating a bioreactor system - Google Patents

Abstract

A method for operating a bioreactor system comprising the steps of supplying substrate to an anaerobically operated first bioreactor, removing digestate from the first bioreactor, separating undecomposed solids from the digestates to obtain an aqueous first phase, supplying the aqueous first Phase to an aerobically operated second bioreactor, - second phase taken from the second bioreactor, resulting from the aerobic treatment containing biomass to a settling device, - indirectly or directly supplied from the settler supernatant removed water to the second bioreactor and- indirect or direct feeding sediment taken from the settler to the first bioreactor, wherein - introduction of oxygen into the second bioreactor in response to the redox value in the second bioreactor is such that at a redox value Rim bioreactor off the oxygen supply and at a redox value RS oxygen is supplied and the difference between the redox value and the redox value R is R - R≥ | 100 mV | and / or ratio of sediment fed to the first bioreactor to the first bioreactor, sediment removed from the settler, and / or filtered sediment is from 10: 1 to 4: 1.

Description

The invention relates to a method for operating a bioreactor system.

In sewage treatment processes, sewage sludge, i. Solid-liquid mixtures, which are rinsed with wastewater in a sewage treatment plant, and dissolved compounds that are bound by microorganisms in the biomass formed, treated in digestion towers and converted into digester gas.

In biogas plants, biowaste such as leftovers, overlying foodstuffs, slaughterhouse waste and renewable raw materials are converted into biogas.

A bioreactor is a container in which certain microorganisms, cells or small plants are cultivated under optimal conditions. Operation of a bioreactor is an application of biotechnology that utilizes biological processes in engineering facilities.

An important factor for the operation of a bioreactor is in particular the composition of the nutrient medium, also called nutrient solution, nutrient medium or substrate.

Very large bioreactors can be found in sewage treatment plants with biological process stages. In the activated sludge process, an aerobic step is first carried out, in which dissolved compounds of microorganisms are bound in the form of the biomass formed. The biomass can be fermented in the digester to methane-rich sewage gas, also called fermentation gas.

Bioreactors of biogas plants are often referred to as fermenters. The used biomass is degraded in an anaerobic process in several steps to biogas and digestate.

A biogas plant is used to produce biogas by fermenting biomass. In agricultural biogas plants mostly animal excrements and energy crops are used as substrate, ie nutrient medium. In non-agricultural facilities, material from the bio-waste bin is used. As by-product, a fertilizer called fermentation residue is produced. In most biogas plants, the resulting gas is either used locally in a combined heat and power plant to generate electricity and heat or fed into the gas network after gas treatment.

In well-degradable substrates, a large part of the dry matter is converted into biogas. There remains an aqueous mixture of poorly degradable organic material, such as lignin and cellulose, as well as organics, e.g. Sand or other mineral substances, the so-called digestate back. This is mostly used as an agricultural fertilizer, as it contains all standard substrates containing trace elements, nitrogen, phosphorus and sulfur. The remaining aqueous fraction may optionally be reduced in mass by an aerobic post-treatment.

Due to tightened legislative measures fertilization with the aqueous fermentation residues, which can also be referred to as biogas manure, only in a few months a year possible, so that increased storage capacity for a biogas plant are required. Also, the emission of ammonia and possibly nitrous oxide leads to the necessity to take countermeasures.

In order to reduce the amount of fermentation residue, it is preferable to carry out mechanical interventions in order to reduce the biogas slurry produced. Using separators such as centrifuges, screw presses or appropriate equipment, the dry matter content TS can be increased from 4% to 6% up to 30%. In the solid phase, a greatly reduced proportion of ammonium (NH ₄ ⁺ ) remains behind. However, more than half of the ammonium is in the separated process water, ie filtrate. By separating into two fractions, although a part of the problems is solved, ie the storage capacity and the ammonium content are reduced. However, the problem has shifted to the aqueous phase.

The state-of-the-art technical processes use a simple flow-through system with homogeneously mixed reactors for producing gas, and chemical-physical processes for solid-liquid separation for sludge and digestate treatment.

The achievable conversion rates of the organic substances introduced into the bioreactors are subject to a technical digging limit. Due to many variations in compositions, concentrations or the like, gas yields of 60% to 80% based on the organic substances introduced are found.

The quantities of sludge and digestate are in many cases applied to agricultural land without further treatment.

The treatment with solids-liquid separation aggregates causes a volume reduction without changing the amounts of contaminants.

The present invention has for its object to operate a bioreactor system for generating gas such that the accumulation of substances to be disposed of is minimized, at the same time an energetically favorable operation of the bioreactor system while high gas yield is possible. Storage capacities should be reduced. Also, the proportion of ammonium (NH ₄ ⁺ ) is to be reduced.

• Verfahren zum Betreiben einer ersten Bioreaktoranlage, umfassend die Verfahrensschritte:
  • - Zuführen von Substrat zu einem anaerob betriebenen ersten Bioreaktor,
  • - Abziehen von Gärrest aus dem ersten Bioreaktor,
  • - Separieren von nicht abgebauten Feststoffen aus den Gärresten zur Gewinnung einer wässrigen ersten Phase,
  • - Zuführen der wässrigen ersten Phase zur einem aerob betriebenen zweiten Bioreaktor,
  • - Zuführen von dem zweiten Bioreaktor entnommener durch die aerobe Behandlung entstandene Biomasse enthaltender wässriger zweiter Phase zu einer Absetzeinreichtung,
  • - mittelbares oder unmittelbares Zuführen von der Absetzeinrichtung entnommenem überstehenden Wasser zu dem zweiten Bioreaktor,
  • - mittelbares oder unmittelbares Zuführen von der Absetzeinrichtung entnommenem Sediment zu dem ersten Bioreaktor,
• wobei Einleiten von Sauerstoff in den zweiten Bioreaktor in Abhängigkeit vom Redoxwert in den zweiten Bioreaktor derart erfolgt, dass bei einem Redoxwert R₁ im Bioreaktor die Sauerstoffzufuhr abgeschaltet und bei einem Redoxwert R₂ Sauerstoff zugeführt wird und die Differenz zwischen dem Redoxwert R₁ und dem Redoxwert R₂ beträgt R₁ - R₂ ≥ | 100 mV | und/oder das Verhältnis von dem ersten Bioreaktor zugeführten Substrat zu dem ersten Bioreaktor zugeführten der Absetzeinrichtung entnommenem Sediment und/oder gefiltertem Sediment sich verhält wie 10:1 bis 4:1.

To solve one or more of the aforementioned aspects, the invention essentially provides a

• Method for operating a first bioreactor system, comprising the method steps:
  • Supplying substrate to an anaerobically operated first bioreactor,
  • Withdrawing digestate from the first bioreactor,
  • Separating undecomposed solids from the digestate to obtain an aqueous first phase,
  • Supplying the aqueous first phase to an aerobically operated second bioreactor,
  • Feeding a biomass-containing aqueous phase containing biomass from the second bioreactor to a settling unit,
  • direct or indirect supply of supernatant taken from the settler to the second bioreactor,
  • indirectly or directly feeding sediment taken from the settler to the first bioreactor,
• wherein introduction of oxygen into the second bioreactor in dependence on the redox value in the second bioreactor is such that at a redox value R ₁ in the bioreactor, the oxygen supply is turned off and oxygen is supplied at a redox value R ₂ and the difference between the redox value R ₁ and the redox value R ₂ is R ₁ - R ₂ ≥ | 100 mV | and / or the ratio of sediment taken from the first bioreactor to the first bioreactor to the sediment removed from the settler and / or filtered sediment is from 10: 1 to 4: 1.

In this case, provision is made in particular for sediment from the settling tank to be fed to a filter and for filtered sludge taken from the filter to be supplied to the first bioreactor. In particular, both the sediment immediately removed from the sedimentation basin and the filtered sludge are added to the first bioreactor.

According to the invention, the bioreactor has two cycles, wherein in a first cycle sediment and / or filtered sludge the first bioreactor and in a second cycle supernatant water of the settling tank and / or filtrate of the filter are fed to the second bioreactor.

The ratio of substrate fed to the first reactor to the concentrated sludge after sedimentation and filtration should be 10: 1 to 4: 1, that is to say that in a sewage treatment plant the first bioreactor 10 to 4 Parts sewage sludge and 1 Part of the coming from the first bioreactor and concentrated on the sedimentation and filtration suspended solids are supplied.

In the second cycle, the ratio of the aqueous first phase fed to the second bioreactor to the supernatant removed from the settling tank and the filtrate recovered in the filter should be from 1: 1 to 1: 7.

According to the invention, concentrated suspended solids taken from the first reactor are fed back into the first bioreactor quasi as co-substrate, so that the sewage sludge to be degraded in a sewage treatment plant or the biowaste or renewable raw materials to be degraded in a biogas plant can be reduced , Regardless, the amount of gas generated is not reduced. If, in contrast to the prior art, the same amount of substrate is supplied to the first bioreactor, then the yield of the gas increases.

By the method according to the invention less fermentation residues, e.g. Applied on open spaces, so that the nitrogen load is reduced and thus results in a better humus balance. Furthermore, there is the advantage that less space for the fermentation storage is required. A reduction of the odor nuisance by digestate is accompanied. This shows the advantage that due to the teaching of the invention, both the sediment and the filtered sludge - possibly after an intermediate storage - completely fed back to the first bioreactor. Consequently, the substance to be disposed of is exclusively that which is separated in the separator connected downstream of the first bioreactor.

According to the invention, a substantial conversion of the organic substances of the substrate into methane-rich gas takes place. It is known that the methane content in the gas is dependent on the degree of oxidation of the substrate contents. Thus, from carbohydrates (sugar, starch) a gas with 50 vol .-% to 52 vol .-% methane, from fatty substrates a gas with 65 vol.% to 68 vol.% methane. The fermentation residues taken from the first bioreactor contain microorganisms, non-gasified solids and dissolved substances. The unconverted solids are separated. According to the invention, the aqueous first phase removed from the separator is then fed to the second bioreactor. This will u. a reduces the ammonium ammonia content, which is detrimental to a high turnover rate.

The solutes contained in the aqueous first phase are biologically treated in the second bioreactor to recover biomass. To oxygenate the microorganisms, air or pure oxygen can be introduced into the second bioreactor. It is advantageous that a rapid removal of the already existing organic solids from the second bioreactor through the second cycle, so supplying the supernatant water of the settling tank and the filtrate of the filter is made possible, so that consequently reduces the oxygen consumption and the degree of oxidation of the solids low can be held. At the same time a rapid and better conversion of the dissolved substances, in particular ammonium / ammonia is achieved.

In order to make this possible, it is provided in particular that the conversion of the dissolved organic ingredients and of ammonium / ammonia takes place in lower than previous Redoxbereichen.

In order that the gas generation in the first bioreactor is not inhibited by a large amount of ammonium, according to the invention the first cycle is provided, that is, the suspended solids coming from the first bioreactor with the supernatant water or filtrate from the settling tank fed to the second bioreactor of the downstream filter and after the concentration of the suspended solids by the sedimentation or filtration are fed again to the first bioreactor. As a result, the proportion of ammonium in the first bioreactor can be reduced and thus the gas production can be positively influenced.

Thus, the dry matter concentration in the second bioreactor influenced, ie can be controlled and thereby simultaneously the concentration of oxygen supply and thus the oxidation of the organic matter and thus the self-heating can be controlled, the second bioreactor to the extent necessary supernatant water of the settling tank or filtrate of the filter fed. Is z. B. the organic dry matter (TS) of the separator removed aqueous first phase 20 kg / m ³ organic TS and is the value of 10 kg / m ³ org. TS, the ratio of the aqueous first phase to the supplied supernatant water / filtrate is 1: 1.

By adjusting the TS concentration, a temperature control that is a condition for the maintenance of optimal growth rates of the desired organisms, in particular the maintenance of the activity of Methanbaktieren.

Equally important is the cultivation and conservation of organisms that convert dissolved organic matter and the contaminant ammonium. Important for this are temperature and TS content in the second bioreactor. Such parameters may be controlled by the second circuit as well as the amount of oxygen supplied.

In particular, it is provided that the supplied amount of oxygen takes place as a function of the redox value in the second bioreactor. The redox value should be between 0 mV and -600 mV, in particular in the range between -50 mV and -450 mV.

According to the invention, a method for operating a bioreactor system is provided, wherein in a bioreactor, such as aeration tank, the oxygen supply is controlled or regulated as a function of the redox value of the medium or suspension present in the bioreactor. In particular, it is provided that in the case of a redox value R _1, the oxygen supply is switched off and oxygen is supplied at a redox value R ₂ , where R ₁ > R ₂ , in particular R ₁ ≥ -50mV and / or R ₂ ≤ -400mV. In a further development, it is provided that R ₁ - R ₂ ≥ | 200 mV |, more preferably R ₁ - R ₂ ≥ | 300 mV |, is.

Furthermore, the invention is characterized in that the oxygen supply is regulated or controlled in addition to or superimposed on the actual oxygen concentration in the second bioreactor.

In particular, it is provided that in an oxygen supply, the amount per unit time is constant, such as at a content of 1,000 m ³ in the bioreactor eg 50 - 90 m ³ / h.

In order to work cost-effectively, a further development of the invention provides that the difference between the temperature-dependent saturation value of oxygen in the aeration tank and the actual value is not less than 5 mg / L, preferably not less than 10 mg / L, particularly preferably not less than 15 mg / L is. If the difference is undershot, the oxygen supply is switched off.

A control or regulation of the oxygen supply depending on the redox value can be repealed according to a further proposal of the invention, if it is determined that a desired increase in temperature of the im Bioreactor medium is not carried out, so the necessary to increase the temperature energy release by oxidation of organic components is not carried out to a sufficient extent. In this case, regardless of the redox value, the oxygen supply is maintained, possibly also increased. If the desired temperature is reached or this is detected, the control of the oxygen supply is basically a function of the redox value, as previously explained.

The invention provides that the temperature control in the second bioreactor is carried out as a function of supplied pure oxygen, the amount of pure oxygen should be 20 NL / m ³ * h to 150 NL / m ³ * h (NL = standard liters, h = hour, m ³ = cubic meters of activated sludge tank content). Preferably, the value is 50 NL / m ³ * h to 70 NL / m ³ * h.

Furthermore, the invention is characterized in that the sediment or the filtered sludge, which is fed back to the first bioreactor in the first cycle, is stored prior to feeding into the first bioreactor, preferably until a redox value <-2 mV, preferably in the Range between -450 mV and -600 mV results.

In a further development it is provided that the recirculated filtered sludge or the sediment or a mixture of these, in each case or collectively called Rezi sludge, a post-drainage by storage on water-permeable ground or a drainage container over a period between 1 day and 30 Days, especially of 7 Days, is subjected.

Due to the teachings of the present invention, it is possible that, depending on the need for gas, the post-dewatered recycle slurry is supplied. Also, a dependence depending on the TOC content (TOC = total organic carbon) take place.

However, the invention is characterized by further measures.

In particular, it is provided that filtered sludge having a TS content of more than 5%, in particular between 10% and 15%, is fed to the first bioreactor.

The invention is also distinguished by the fact that sediment accumulated in the settling tank is fed to the first bioreactor at a dry content of between 3% ≦ TS ≦ 10%, in particular 4% ≦ TS ≦ 8%.

The inventive method of the NH ₄ ⁺ content is converted by specially conditioned microorganisms in several steps to elemental nitrogen in a biological stage, so that an environmentally friendly solution to the nitrogen removal is ensured. In addition, the nitrogen content of microorganisms ensures that COD, TOC and other parameters are reduced to such an extent that the purified water is optically clear.

Measurements have shown that the TOC content is reduced to 100 to 200 mg / l. Before the biological treatment after leaving the first bioreactor, the proportion is about 3000 mg / l. With regard to the COD content, a reduction of 10,000 mg / l to 250 to 500 mg / l could be achieved.

For further development, it is provided that for the sedimentation of very fine particles of a size between 1 .mu.m and 50 .mu.m in the sedimentation device with at least one adjuvant influencing the sedimentation is added in this existing sediment and above this protruding fluid in the supernatant fluid, wherein at least one substance from the group metal salt, in particular aluminum and / or iron salt such as chlorides or sulfates, and / or polymers such as cationic and / or anionic polyacrylamide derivatives and / or as auxiliaries a mixture consisting of or containing aluminum hydroxide and / or highly basic aluminum hydroxide chloride and / or cationic aluminum hydroxide and / or anionic starch derivatives.

It should also be emphasized that a mixture consisting of or containing aluminum hydroxide chloride and / or polyaluminum chloride and / or cationic and / or anionic starch derivatives is used as auxiliaries.

In particular, the invention provides that aluminum hydroxide chloride having a basicity between 35% and 45% and a weight fraction in the mixture of more than 40% by weight, in particular between 40% by weight and 95% by weight, and / or highly basic Aluminum hydroxide chloride having a basicity greater than 80% and a weight proportion in the mixture of between 0 wt .-% and 40 wt .-%, in particular 5 wt .-% and 10 wt .-% and / or cationic and / or anionic starch derivatives having a weight fraction in the mixture between 0 wt .-% and 30 wt .-%, in particular 5 wt .-% to 10 wt .-%, is used.

In particular, it is provided that a mixture containing aluminum hydroxide chloride is used as auxiliary. In addition, anionic and / or cationic, optionally anionic and cationic starch derivatives can be used. With regard to the aluminum hydroxide chloride, it should be noted that this has a basicity between 35 should be% and 45%. The proportion by weight in the mixture should be more than 40% by weight, with values between 40% by weight and 95% by weight being preferred. The highly basic aluminum hydroxide chloride should have a basicity greater than 80%, wherein the proportion by weight in the mixture between 0 wt .-% and 40 wt .-%, in particular between 5 wt .-% and 10 wt .-%, should be. If cationic and / or anionic starch derivatives are present in the mixture, the proportion by weight should be between 0% by weight and 30% by weight, preferably between 5% by weight and 10% by weight.

Further details, advantages and features of the invention will become apparent not only from the claims, the features to be taken these features - alone and / or in combination - but also from the following description of a drawing to be taken preferred embodiment.

The invention will be explained in more detail below with reference to a biogas plant without this being intended to limit it. Rather, the teaching of the invention applies equally to sewage treatment plants.

The only Fig. Is a schematic representation of a biogas plant to refer, in which a fermentation residues preparation according to the invention takes place. The plant includes one as a fermenter 10 designated first bioreactor, the biogas production via a pipe 12 Raw materials (input material) are supplied, which are also referred to as substrates or culture media. Furthermore, via a line 14 Additives are added to influence the microbial degradation (fermentation) of the substrate used. The fermenter 10 can be a post-fermenter 11 be subordinated. In that regard, however, reference is made to well-known facilities of biogas plants.

In the fermenter 10 the biogas is produced from biological raw material with the exclusion of oxygen. In this case, the fermenter 10 be operated with a continuous fermentation, ie, that the processes supplied at regular intervals substrate and biogas and digestate is removed.

The digestate is then a separator 16 supplied, in which it is z. B. may be a centrifuge or a screw press. By means of the separator 16 the substances that are not fermentable are separated from the digestate. These are solid substances, such as straw or wood, which mainly contain cellulose and lignocellulose.

The an aqueous first phase forming liquid fraction (Fugat) is via a conduit 18 a first container 20 as activated sludge tank as a second bioreactor, in which a single or multi-stage aerobic process is carried out in order to achieve a further degradation. About a line 19 Can that be in the aeration tank 20 homogenized liquid of a device 21 for separating solid liquid such as sedimentation tank, oblique clarifier and / or inclined filter 35 be fed to a dewatered sludge, which may have a solids content in the range between 8% and 25%, via a conduit 22 the fermenter 10 supply.

The invention is characterized in particular by the fact that the aeration tank 20 - So the second bioreactor - in which the aerobic treatment takes place, a settling device such as settling tanks such as diagonal clarifier 21 is downstream. The in the aeration tank 20 resulting suspension as an aqueous second phase is the sedimentation tank 21 fed so that precipitate solids and water. This supernatant water can the aeration tank 20 over a line 32 be fed, the ratio of the aeration tank 20 supplied aqueous fraction to the supplied supernatant water from the settling tank 21 behaves as 1: 1 to 1: 7, in particular should behave in about 1: 5, without the corresponding numerical values are limiting. By feeding the water into the aeration tank 20 the substances not dissolved in the aqueous fraction, ie dry substances, are only slightly oxidized.

At the same time, the organic dry matter content in the second bioreactor, ie in the aeration tank 20 to be discontinued. This in turn means that a temperature control is enabled. As a result, optimal propagation rates of the desired organisms can be achieved. Also, the cultivation and maintenance of the organisms to convert the dissolved organic matter and the impurity ammonium can be influenced. Furthermore, an introduction of oxygen depending on the redox value in the aeration tank 20 respectively. The redox value should be set such that it is <0 to -600 mV, in particular in the range between -50 mV and -450 mV.

The temperature control can also be carried out by the supplied amount of pure oxygen, with values of 20 NL / m ³ * h (20 standard liters per cubic meter and hour) to 250 NL / m ³ * h, in particular in the range between 50 NL / m ³ * h and 70 NL / m ³ * h.

The oxygen itself should be introduced intermittently. In particular, oxygen is introduced when the redox value of the suspension present in the bioreactor within a previously defined area. When a first limit value is reached, the oxygen supply is switched on. When a second limit value of the redox value is reached, the oxygen supply is switched off. If the first limit value is reached again, oxygen is supplied again, etc.

There is also the possibility that supernatant water from the settling tanks 21 over the line 32 . 34 be drained directly, for example, for infiltration in a subsoil, for rainfall, for discharge into a sewage treatment plant or into a body of water.

To be in the settling tank 21 The finest particles deposit, preferably particles of a size between 1 .mu.m and 50 .mu.m, the settling tank 21 a sedimentation-influencing adjuvant is added, optionally at different heights of the settling tank 21 , the Z. B. may have a cylindrical geometry. The remedy will be in the settling tank 21 the protruding fluid 23 fed. Through the arrows 26 it should be suggested that the aid is at different heights of the supernatant water 23 in the settling tank 21 can be initiated. Thus, a good mixing is possible.

The sediment 28 can over a line 30 the fermenter 10 be fed again. Mentioned may be over the line 32 the supernatant water 23 the aeration tank 20 is supplied. Alternatively, there is the possibility of the supernatant water 23 immediately deduce (arrow 34 ).

Furthermore, the sediment may be the inclined filter in the exemplary embodiment 35 trained filter device are fed, in which a solid-liquid separation takes place. The resulting sludge is or can over the line 22 the fermenter 10 be supplied. However, there is also the possibility that the sediment is directly over the pipe 30 the fermenter 10 is supplied.

About the supply line 26 or supply lines 26 is mentioned the auxiliary to the supernatant fluid 23 fed. This is in particular a metal salt, in particular aluminum and / or iron chloride or sulfate. Polymers such as cationic or anionic polyacrylamide derivatives can also be used. A mixture of these substances is also possible.

The one or more different flocculants is / are from a container 27 or more containers over the line 29 or several lines to the supply line 26 or supply lines. In this case, the one or more aids via a line 31 Clear water from the embodiment in the form of an oblique filter 35 trained device are supplied, in which a solid-liquid separation takes place. The ratio of clear water and auxiliaries is preferably chosen according to the following information.

As auxiliaries, a mixture of aluminum hydroxide chloride and polyaluminum chloride is preferably used, it being possible for cationic and / or anionic starch derivatives to be added if appropriate. The aluminum hydroxide chloride should have a basicity between 35% and 45% and the polyaluminium chloride should have a basicity of more than 80%. The proportion by weight in the mixture of aluminum hydroxide chloride should be more than 40% by weight, in particular in the range between 40% by weight and 95% by weight, and that of the polyaluminum chloride between 0% by weight and 40% by weight, in particular in the range between 5 wt .-% and 10 wt .-%, are. The proportion by weight of the cationic and / or anionic starch derivatives should be from 0% by weight to 30% by weight, in particular from 5% by weight to 10% by weight.

As a result of the aids, the finest particles in the settling tank are mentioned 21 deposited.

The teaching according to the invention makes it possible for the NH ₄ ⁺ fraction contained in the fugate to be replaced by specially conditioned microorganisms in the second bioreactor 20 be converted to elemental nitrogen. The microorganisms also ensure by their nitrogen turnover that COD, TOC and other parameters are reduced so much that purified water is delivered via one pipe 24 can be dissipated.

The water can be seeped into the ground or rain, be discharged into a sewage treatment plant or in the best case even directly into a surface water.

The fermenter 10 taken biogas is over a line 33 a combined heat and power plant 36 fed, by means of which electricity and heat are generated.

Due to the teaching of the invention, it is necessary if compared to known systems, an equal amount of electricity and heat to be generated, less substrate, via the line 12 the fermenter 10 is supplied. If the same amount is added as in known systems, then a higher amount of CH _{4 can be} achieved, ie a higher gain in electricity and heat.

Regardless of this, the return of the sludge increases the CH ₄ content in the biogas.

As the process sequence illustrated in FIG., It is possible that before the biological stage in the container 20 a warehouse 25 is provided, in which first the aqueous fraction 18 is collected, then the biodegradation in the container 20 to be subjected to. It can via a connection 28 Additives are added to accelerate biodegradation.

It also follows from the drawing that of a tank 17 Oxygen in the aeration tank 20 can be entered.

The invention will be explained in more detail below with reference to a preferred embodiment.

According to the teaching of the invention, the fermenter 10 over a line 12 Substrate fed. For example, 100 m ^{3 of} substrate and 20 m ^{3 of} recirculated (reci-) sludge composed of the sediment and the filtered sludge are passed over the line 22 the fermenter 10 fed. At a residence time of about 70 days in the fermenter 10 - Whilst it is to speak of a continuous process, that is continuously supplied substrate and digestate is subtracted - the ammonium content of the substrate is 6 kg / m ³ . After the separator 16 the total amount amounts to approx. 100 m ³ . The difference results from that through the separator 16 retained solid and entrained liquid. The amount of the ammonium-Rezi sludge is 0.5 kg / m ^3. This results in about a total amount of ammonium of about 490 kg / 100 m ³ . This concentration is basically the one after the separator 16 is measurable. However, the same concentration is also found in the fermenter 10 because of the high residence time of the substrate in the fermenter 10 (about 70 days).

By reducing the ammonium content results in a higher gas yield compared to an operation in which only substrate is fed to the fermenter.

In the separator 16 The non-degradable solids such as lignin, cellulose, sand or other minerals are separated. Also, a certain amount of liquid is separated with. These parts alone are to be disposed of, since the sludge or sediment arising in the subsequent process steps, that is to say the so-called Rezi sludge, is completely discharged to the fermenter 10 is fed again.

The after the separator 16 resulting aqueous first phase is then fed to the second bioreactor, which serves as aeration tank 20 can be trained. In the aeration tank 20 flows according to the invention the second cycle, a water cycle, that of the oblique clearer 21 and the oblique filter 35 accumulating water the occupation basin 20 returns, in a desired ratio to that over the line 18 the aeration tank 20 aqueous first phase to be supplied to a desired organic dry matter content in the aeration tank 20 adjust. As a result, the temperature in the aeration tank 20 with regulated, whereby the multiplication rate of the desired organisms is influenced. In addition, a temperature control by supplying air or oxygen (oxygen tank 17 ), the amount depending on the redox value in the aeration tank 20 is set. The oxygen should be introduced intermittently, the redox value should be between -50 mV and -450 mV in particular.

The recycled in a second cycle and the settling tank 21 and the oblique filter 35 originating water is to be called recirculated or Rezi water.

The first and the second cycle together constitute a self-inventive suggestion.

In the second bioreactor 20 may be the residence time of the separator 16 over the line 18 be fed significantly reduced in the aqueous first phase by recirculation of Rezi-water.

For example, the second bioreactor, so in the embodiment of the aeration tank 20 , fed exclusively aqueous first phase in an amount of 100 m ³ per day and is the capacity of the volume of the aeration tank 20 1,000 m ³ , the residence time is 10 Days (1,000 m ³ / 100m ³ / d = 10d). However, according to the teaching of the invention via the second circuit ReZi water the aeration tank 20 supplied, for example in the ratio of 4: 1 (400 m ³ REZI-water per day / 100 m ³ aqueous first phase per day), then the residence time of the solids is reduced to 2 days (1,000 m ^3/500 m ³ / d = 2d).

A mixing in the bioreactor 20 can be done by a "banana stirrer".

The oxygen should be introduced via mats in the form of pure oxygen fine bubbles.

The suspension from the aeration tank 20 as aqueous second phase is then formed in the embodiment as a diagonal clarifier settling 21 fed in which precipitate solids as sediment. As previously discussed, adjuvants may be introduced into the second aqueous phase. The sediment can then directly to the fermenter 10 or over the slanted filter 35 in the form of filtered sludge the fermenter 10 be supplied.

Prior to supplying the Rezi slurry, which may be mentioned to be a mixture of sediment and filtered sediment, it is preferred that the filtered slurry be stored to increase the solids content. For this purpose, the sludge is stored on water-permeable ground or in drainage containers, for example over a period of 1 to 30 days. It can also be done after draining another storage to that of the first bioreactor 10 to determine the amount of sludge to be supplied depending on its TOC content.

The teaching of the invention results in a significant number of advantages. By doing that, the fermenter 10 not only substrate, but also Rezi sludge is fed, the ammonium content is reduced and thus results in an increase in methane gas yield compared to plants in which a Rezi sludge is not used.

By introducing the Rezi-water, so clear water, which is obtained in the sedimentation and filtering, the dry matter content in the second bioreactor and thus the temperature and in turn dependent on the residence time can be adjusted.

By introducing oxygen, the redox value can also be controlled, with the result that the conversion of the dissolved constituents in the aqueous first phase into biomass and the conversion of the ammonium is optimized.

The redox value of the Rezi sludge can be adjusted depending on the storage, which in turn can be influenced by the formation of methane.

The only solid which is obtained in the substrate treatment and is to be disposed of is that which is in the separator 16 is deposited.

It was found that the dry substance can be up to 80% if the Rezi sludge is stored for 30 days. Depending on the TOC content of the Rezi sludge, the redox value of the fermenter 10 be set to be supplied Rezi mud.

Dissolved substances of the aqueous first phase are converted into biomass in the second bioreactor and can be used for methane production.

The fact that, apart from the separated solids sludge or sediment resulting is recycled, there is the advantage that the use of trace metals, if they are needed, is minimized.

Claims (26)

Method for operating a bioreactor system, comprising the method steps - supplying substrate to an anaerobically operated first bioreactor, - removing digestate from the first bioreactor, - separating undecomposed solids from the fermentation residues to obtain an aqueous first phase, - supplying the aqueous first Phase to an aerobically operated second bioreactor, - second phase taken from the second bioreactor, resulting from the aerobic treatment containing biomass to a settling device, - indirectly or immediately supplied from the settler supernatant removed water to the second bioreactor and - direct or indirect feeding sediment taken from the settler to the first bioreactor, wherein - introduction of oxygen into the second bioreactor in response to the redox value in the second bioreactor is such that at a redox value R ₁ in the bioreactor, the oxygen supply is switched off and oxygen is supplied at a redox value R ₂ and the difference between the redox value R ₁ and the redox value R ₂ is R ₁ - R ₂ ≥ | 100 mV | and / or ratio of sediment fed to the first bioreactor to the first bioreactor, sediment removed from the settler, and / or filtered sediment is from 10: 1 to 4: 1. Method according to Claim 1 , characterized in that sediment of the settling tank is fed to a filter and that filtered sludge taken from the filter is supplied to the first bioreactor. Method according to Claim 1 or 2 , characterized in that both the sediment and the filtered sludge are optionally fed back to the first bioreactor completely, optionally after an intermediate storage. Process according to at least one of the preceding claims, characterized in that supernatant water taken from the sedimentation tank and / or filtrate taken from the filter is used as clear water for seepage underground, for rainfall, for introduction into a sewage treatment plant or for discharge into a body of water. Method according to at least one of the preceding claims, characterized in that the ratio of the aqueous first phase to be supplied to the second bioreactor to the supplied supernatant water from the settling tank and / or the filtrate is adjusted to 1: 1-1: 7. Process according to at least one of the preceding claims, characterized in that filtered sludge having a solids content of more than 5%, preferably 10 to 15%, is fed to the first bioreactor. A method according to at least one of the preceding claims, characterized in that the first bioreactor in sedimentation tank accumulated sediment with a dry content of between 3% TS to 10% TS, in particular 4% TS to 8% TS, is supplied. Method according to at least one of the preceding claims, characterized in that the aqueous first phase is stored prior to feeding to the second bioreactor. Method according to at least one of the preceding claims, characterized in that at least one additive is added to the aqueous first phase before being fed to the second bioreactor. Method according to at least one of the preceding claims, characterized in that the temperature in the second bioreactor is controlled by self-heating depending on the dry matter content in the second bioreactor. Method according to at least one of the preceding claims, characterized in that the dry matter content in the second bioreactor is adjusted by proportion of the second bioreactor supplied supernatant water and / or filtrate. Method according to at least one of the preceding claims, characterized in that the second bioreactor is adjusted in its temperature by amount of oxygen supplied taking into account the redox value in the second bioreactor, wherein the redox value <0 mV, in particular between 0 mV and -600 mV, in particular between -50 mV and -450 mV. Method according to at least one of the preceding claims, characterized in that the temperature in the second bioreactor is controlled by the amount of pure oxygen fed in, the amount preferably being between 20 NL / m ³ * h to 105 NL / m ³ * h, preferably between 50 NL / m ³ * h and 70 NL / m ³ * h. Method according to at least one of the preceding claims, characterized in that the pure oxygen is intermittently fed to the second bioreactor such that the redox value in the second bioreactor is between 0 mV and -600 mV, preferably between <0 mV and -450 mV. Method according to at least one of the preceding claims, characterized in that the sludge consisting of sediment and filtered sludge attributable to the first bioreactor is adjusted to a redox value <-200 mV, in particular to a value between -450 mV to 600 mV. Method according to at least one of the preceding claims, characterized in that the recirculating sludge is subjected to post-drainage, preferably over a period of between 1 and 30 days, preferably over a period of 7 days. Method according to at least one of the preceding claims, characterized in that the post-drainage is carried out on water-permeable ground or in at least one dewatering container. Method according to at least one of the preceding claims, characterized in that the post-dewatered recirculating sludge is stored and supplied to the gas to be generated in the first bioreactor depending on this. Method according to at least one of the preceding claims, characterized in that the amount of recirculating sludge to be supplied to the bioreactor is effected as a function of the TOC content of the sludge. Method according to at least one of the preceding claims, characterized in that an additive or flocculation aid is added to the supernatant water in the settling device. Method according to at least Claim 1 for the sedimentation of very fine particles of a size between 1 .mu.m and 50 .mu.m in the sedimentation device with sediment present in this sediment and fluid overlying it, characterized in that at least one auxiliary agent influencing the sedimentation is added to the supernatant fluid, at least one substance being used as auxiliary agent the group metal salt, in particular aluminum and / or iron salt such as chlorides or sulfates, and / or polymers such as cationic and / or anionic polyacrylamide derivatives and / or as auxiliaries a mixture consisting of or containing medium-basic aluminum hydroxide chloride and / or highly basic aluminum hydroxide chloride and / or cationic and / or anionic starch derivatives is used. Method according to at least Claim 21 , characterized in that at different heights of the settling device, in particular cylindrical geometry, the aid is supplied to the supernatant fluid. Method according to at least Claim 22 , characterized in that aluminum hydroxide chloride having a basicity between 35% and 45% and a weight proportion in the mixture of more than 40 wt .-%, in particular between 40 wt .-% and 95 wt .-%, and / or aluminum hydroxide of a basicity greater than 80% and a weight proportion in the mixture of between 0% by weight and 40% by weight, in particular 5% by weight and 10% by weight, and / or cationic and / or anionic starch derivatives having a proportion by weight in the mixture between 0 wt .-% and 30 wt .-%, in particular 5 wt .-% to 10 wt .-%, is used. Method according to Claim 1 , characterized in that the redox value R ₁ ≥ -50mV and / or the redox value R ₂ ≤ -400mV. Method according to Claim 1 , characterized in that the difference between the redox value R ₁ and the redox value R ₂ is R ₁ - R ₂ ≥ | 200 mV |, preferably R ₁ - R ₂ ≥ | 300 mV |. Method according to at least one of the preceding claims, characterized in that the oxygen supply is additionally controlled by the actual oxygen concentration in the bioreactor, wherein in particular the oxygen supply is interrupted when the difference between the saturation value of the oxygen concentration and the actual value of the oxygen concentration is 5 mg / L, preferably 10 mg / L, in particular 15 mg / L.

Images