WO2015092003A1

WO2015092003A1 - Method for removing impurities from aqueous media

Info

Publication number: WO2015092003A1
Application number: PCT/EP2014/078839
Authority: WO
Inventors: Oliver Lüdtke; Michael SCHLIMBACH; Jan KÜHLING; Enrico Fichter
Original assignee: Verbio Vereinigte Bioenergie Ag
Priority date: 2013-12-20
Filing date: 2014-12-19
Publication date: 2015-06-25
Also published as: DE102013226991A1

Abstract

The invention relates to a method for removing at least one organic impurity from an aqueous medium, comprising the following steps: • a) feeding the aqueous medium (101) to be treated into a reactor, with active microbial biomass (8), • b) directly and/or indirectly introducing molecular oxygen (103) into said reactor (8), • c) implementing a microbial selective oxidation in the suboxic conditions of at least one of the supplied organic impurities, without the majority of the supplied COD being reduced, • d) discharging the treated aqueous medium (102) from the reactor (8), and • e) discharging a waste gas flow (104) containing carbon dioxide from the reactor (8).

Description

Description BACKGROUND OF THE INVENTION Technical Field

The invention relates to a process for the removal of organic acids and / or aromatic compounds in aqueous media for the purpose of treatment, recovery and / or recycling as process water.

The production of industrial goods places different demands on the water quality of process water. In general, the use of fresh water for the running processes is beneficial. A high fresh water use, however, is an ecologically unacceptable high water consumption of the corresponding production processes as well as in particular high costs for the fresh water itself, the wastewater treatment and / or disposal. Especially for industries with production-related high water consumption such as textile and leather processing, pulp and paper production plants, biorefineries and breweries or biogas production plants, the recycling of process water is ecologically and economically sensible, but in many cases limited by the production process negatively affecting substances.

The present invention enables a very efficient treatment of partially heavily contaminated process water for a controlled in-process recirculation. Optionally, the invention may, under certain circumstances, together with further purification steps, also be used for the efficient treatment of contaminated process water for subsequent disposal.

Description of the Prior Art

Many production processes inherent in an accumulation of water-soluble substances of different origin in the process water. This may for example be by-products and reactants or so-called From ^¬ gang groups in chemical and / or biochemical reactions. To the For example, in fermentation processes unwanted metabolic end products such as acetic acid, lactic acid or glycerol can be delivered to the medium and enriched there.

The recirculation of a materially polluted process water often causes an impairment of the production process, for example, by a decreasing pH in the accumulation of organic acids. Especially in industrial fermentation processes with microorganisms, increasing acid concentrations such as acetic and lactic acid or, for example, aromatic compounds such as cresols and phenols often lead to the inhibition of metabolic activity. The traceable volume flow of such polluted process waters is thus limited by the content of foreign and / or impurities in the process water. If critical concentrations are exceeded, the potential of process water recycling can not be fully exploited. In practice, at least a proportionate replacement of the theoretically available process water by fresh water takes place in order to avoid critical concentrations of foreign substances and contaminants.

For the circulation and / or possibly also for a possible subsequent disposal, it is advantageous to extract the foreign and / or contaminants from the process water. There are physical and / or chemical methods for this. These are for example adsorption and membrane processes or ion exchangers. By precipitation reactions, for example, ionically charged molecules as well as fats and proteins can be withdrawn from the process water. A disadvantage of these methods is the only conditional suitability for solids-laden process waters.

Solids often cause nonspecific adsorption and / or a clogging example of membranes and cause in this way a disturbance of the process water conditioning, which must be counteracted with increased technical and economic effort. As a rule, there is an upstream mechanical separation of the solids, for example by centrifugation. Subsequently, for example, the regeneration of membranes and / or disposal of the process water-extracted substances, for example in the form of sludges after precipitation reactions.

An alternative conditioning of process water is the classical wastewater treatment in so-called sewage treatment plants. These aerobic and anaerobic wastewater treatment by microorganisms have been widely described.

The main component of wastewater treatment is the aerobic stage, in which substances contained in the water are microbially oxidized. The biodegradable substances contained in the waste water are proportionally converted into carbon dioxide and water as well as into separable sludge biomass. The oxygen required for this process is supplied to the medium under high, technical and energy expense, usually by introducing air. A disadvantage of classical aerobic wastewater treatment is the non-specific and almost complete oxidation of the substances contained. In particular, nitrogen compounds are also microbially oxidized to nitrate. Depending on the composition of a process water to be treated such oxidation is associated with very high oxygen demand. This must be supplied by introducing air with high energy requirements. In addition, the formation of nitrate and / or nitrite in the process water treatment and subsequent recycling of this water even lead to negative effects. For example, fermentation processes can be inhibited. In these cases, a denitrification is necessary, in which the nitrate formed is biologically reduced to molecular nitrogen. Such biological denitrification is associated with further apparatus engineering and energy expenditure.

The activated sludge produced in the aerobic stage can be used under anaerobic conditions for biogas production and energy production. In this case, the decomposition of organic substance in the absence of oxygen (anaerobic) essentially to carbon dioxide and methane.

For the treatment of wastewater or process water, direct anaerobic treatment is also possible. A disadvantage of the anaerobic treatment is that in particular aromatic compounds are not or only partially degraded in the absence of oxygen. In technically relevant periods these substances would remain almost unchanged in the process water and be enriched during a continuous recirculation without the discharge of partial streams.

The anaerobic treatment of stillage to increase the recirculation of process fluid into the ethanol process with the simultaneous production of biogas is described in DE102010005818A1. Thus, it is possible to recycle significant quantities of anaerobically treated vinasse directly into the ethanol process and thereby reduce the water requirement of the overall process. It is further described that outlets for non-degradable substances must be present in the overall system.

The recirculation of process water within a process for the combined production of bioethanol and biogas is, for example, in

WO2004113549A1 described. In this process, however, the disadvantages of the presence of proteins and solids for the ethanolic fermentation or the subsequent production of biogas are expressly pointed out. For this reason, the method is designed such that after several separation steps only a medium with preferably less than 0.5% dry matter content is fed into the methane reactor. The aqueous phase emerging from the methane reactor is accordingly a very low-loaded water, which has a very low dry matter content. In addition, it is not burdened by the previous protein separation with complex compounds from the anaerobic protein degradation. The described aerobic treatment of this process water corresponds to an aerobic treatment known in the art in the sense of a wastewater treatment. The resulting processed process water can either be returned to the mashing process of ethanol production or introduced (disposed of).

The aerobic treatment of waste water from a methane plant for vinification is disclosed in EP1790732A1. In this case, only the aqueous phase of the slurry is fed to the methane plant after a solids separation. The methane fermentation and a separation of solids and nitrogen subsequent aerobic treatment corresponds to a well-known from the prior art wastewater treatment of industrial wastewater treatment plants, where expressly also a denitrification is described. The obtained aerobically treated wastewater has a chemical oxygen demand (COD) of 40-190 mg / l. In addition, an optional distillation of the aerobically treated wastewater is listed. It also mentions the options of discharging the treated water or returning it to the process.

WO2001060752A1 describes a process for the continuous processing of lignocellulose-containing material into biofuels. It is described that the recirculation of process water has a cost-reducing effect, but is limited by substrate treatment inhibiting substances such as acetic acid, furfurals and phenolic acids. The concentrations of corresponding substances can be reduced to such an extent by aerobic and anaerobic treatment that process inhibition is no longer present. It is not described in this publication how such an aerobic treatment can be designed. It is therefore to be assumed that this is a state-of-the-art aerobic wastewater treatment.

Previously known methods for process water purification involve complex separation operations and / or comprehensive aerobic treatment. In this case, the vast majority of the COD contained is removed with high equipment and energy expenditure. Methods for energy-saving selective oxidation of relevant impurities would be much more energy-efficient and thus resource-saving, but are not known in the current state of the art.

TASK AND SOLUTION

It is therefore an object of the invention to remove energy contained in aqueous media energetically efficient and inexpensive, so that an in-process feedback and / or disposal of this water are possible. The problem is solved by a method comprising the following steps:

a) Supply of the aqueous medium to be treated in a reactor with active microbial biomass

b) Direct and / or indirect introduction of molecular oxygen into this reactor

c) carrying out a microbial selective oxidation under suboxic conditions of at least one of the supplied organic impurities without major degradation of the supplied COD

d) removal of the treated aqueous medium from the reactor

e) removal of a carbon dioxide-containing exhaust gas stream from the reactor.

To solve this problem, the invention provides a method according to claim 1 ready. Advantageous developments are mentioned in the dependent claims. The wording of all claims is incorporated by reference into the content of the specification.

In a preferred embodiment, the inventive method is designed so that the molecular oxygen is introduced in the form of air in the reactor.

In a preferred embodiment, the method according to the invention is designed so that a part of the exhaust gas stream is returned to the reactor.

In a preferred embodiment, the inventive method is designed so that the introduction of molecular oxygen optionally takes place continuously in the form of air.

In a preferred embodiment, the process according to the invention is designed so that the reactor contents are optionally mixed using suitable stirring technology, such as at least one propeller agitator and / or at least one jet pump or other directed gas introduction systems.

In a preferred embodiment, the process according to the invention is designed such that the reactor is occasionally and / or continuously, if necessary together with the medium to be treated, active microbial biomass is supplied.

In a preferred embodiment, the method according to the invention is designed such that the active microbial biomass is at least partially immobilized in the reactor, for example by suitable carrier materials.

In a preferred embodiment, the process according to the invention is designed so that the average residence time in the reactor is at least as long as the doubling time of the active microbial biomass.

In a preferred embodiment, the method according to the invention is designed such that the supply of molecular oxygen, if appropriate also in the form of air, is limited to such an extent that no significant oxidation of nitrogen compounds contained in the reactor takes place.

In a preferred embodiment, the process according to the invention is designed such that the supply of molecular oxygen, if appropriate also in the form of air, is regulated by measuring the redox value in the reactor, the redox value in the reactor being in a range between 0 and -400 mV, preferably between 100 and -300mV, more preferably between -200 and -280mV.

In a preferred embodiment, the method according to the invention is designed so that the supply of molecular oxygen, if appropriate also in the form of air, is regulated by the measurement of the dissolved oxygen in the reactor, the content of dissolved oxygen in the reactor being in a range between 0 and 2 mg / 1, preferably less than 1 mg / l, more preferably less than 0.3 mg / l, most preferably less than 0.15 mg / l.

In a preferred embodiment, the process according to the invention is designed such that nutrients and / or trace elements are optionally fed to the reactor together with the medium to be treated.

In a preferred embodiment, the process according to the invention is designed such that the medium to be treated in the reactor is at least quantitatively sicontinually supplied and treated medium is discharged from the reactor at least quasi-continuous.

In a preferred embodiment, the method according to the invention is designed so that the medium treated in the reactor is recycled to a process which is directly or indirectly connected to the process from which the medium to be treated has previously been removed.

In a preferred embodiment, the inventive method is designed so that the treated medium in the reactor is returned to a process to replace, for example, drinking water, well water, condensate and / or other process water.

In a preferred embodiment, the inventive method is designed so that the COD of the supplied aqueous medium is reduced by not more than 50%, preferably not more than 30%, more preferably not more than 20%, most preferably not more than 15% ,

In a preferred embodiment, the process according to the invention is designed such that the pH in the reactor, if appropriate by adding an acidic or basic material stream in a range from 6.5 to 10.5, preferably from 7.5 to 9.5, is particularly preferred is set in a range of 8.0 and 9.0.

In a preferred embodiment, the inventive method is designed so that the temperature in the reactor, for example, directly via the inlet or, for example, is set indirectly by heat exchange.

In particular, the method according to the invention also relates to all combinations of the preferred embodiments described above.

Description of the solution

Process water streams, in particular from biological production processes, generally contain dissolved and suspended organic as well as inorganic components. The TS content of such waters rarely exceeds 10%, usually much lower. The content of the dissolved organic substance can be up to several percent.

For a recirculation of such process waters, in particular in biological processes, for example within a biorefinery, the contents of organic acids and / or aromatic compounds are particularly relevant since these substances can interfere with subsequent processes or inhibit biochemical reactions. If such substances are organic acids (aliphatic and / or aromatic), they can be combined with the sum parameter FOS (Volatile Organic Acids) known from biogas technology.

Examples of such impurities are short-chain organic acids (for example acetic acid, propionic acid, lactic acid, formic acid, succinic acid, oxalic acid, citric acid, butyric acid, valeric acid, caproic acid), long-chain organic acids (for example fatty acids such as oleic acid, palmitic acid, lauric acid) and or aromatic acids (for example phenolic acids such as, for example, benzoic acid, hydroxybenzoic acid, dihydroxybenzoic acid, phenylacetic acid, hydroxyphenylacetic acid, phenylpropionic acid, hydroxyphenylpropionic acid, ferulic acid, gallic acid, cinnamic acid, hydroxycinnamic acid, caffeic acid).

In addition, other aromatic compounds without an acid group such as benzene, phenol, cresol, furfural, hydroxymethylfurfural (HMF) and / or more complex compounds such as tannin, cutin and / or indolic compounds such as indole, skatole may also be present in process waters which can be present in relevant quantities depending on the process conditions.

The dissolved contaminants can not be separated by solid-liquid separation process.

Thermal separation processes for the separation of these substances present in low concentrations have the disadvantage of a high expenditure on equipment, a high energy requirement and / or possibly an insufficient separation or too high a residual concentration of the contaminants. The anaerobic degradation of FOS and / or other organic ingredients is possible for some contaminants. Part of the chemically bound in the resulting process water energy can be converted into biogas / methane and used materially and / or energetically. However, anaerobic fermentation is a relatively slow process. This requires long substrate residence times, which at low concentrations of the impurities to be degraded means uneconomically large reaction volumes. In particular, the degradation of more complex compounds is not possible at technically relevant residence times. For example, the anaerobic degradation of some phenolic compounds is hardly possible.

In comparison to anaerobic degradation much shorter residence times are required for the aerobic degradation of organic substances. The degradation of, for example, indole derivatives such as skatole, furan derivatives such as furfural and benzene derivatives such as phenol or benzoic acid but also of lactic and acetic acid is faster under aerobic conditions than under anaerobic. In the presence of oxygen, organic matter is completely oxidized by microorganisms to carbon dioxide and water. In addition, via the respiratory chain it is possible for the microorganisms to generate and store more energy compared to anaerobic digestion. This also makes it possible to break up the chemically extremely stable ring systems of aromatic compounds by mono- and / or dioxygenases.

The aerobic decomposition of organic matter is carried out in sewage treatment plants in the form of an aerobic stage. In this case, the dissolved organic substance is almost completely degraded while supplying oxygen. At oxygen contents of 2 mg / l to more than 5 mg / l, in addition to the oxidation of organic matter, nitrification also takes place, in which ammonium nitrogen is bacterially converted via nitrite into nitrate. In classic wastewater treatment, nitrification is subsequently coupled with denitrification, with the conversion of nitrate into molecular nitrogen taking place, with the exclusion of oxygen and the consumption of dissolved organic matter. Such or similar aerobic methods for the purification of wastewater are in principle well suited if the water meets the strict requirements of a single in rivers. In particular, the very high energy expenditure of the oxygen supply is to be mentioned as a disadvantage.

Especially in the presence of ammonia or ammonium in the process water, the oxygen demand of an aerobic treatment with nitrification by the high COD of ammonia increases significantly. In addition, a nitrification of contained ammonium as it takes place in an aerobic wastewater treatment may even be disadvantageous if the nitrate formed disturbs the subsequent processes and / or the ammonium would be used in a later process as a valuable and / or nutrient.

For the treatment of process water for recirculation and / or disposal, the complete oxidation of all dissolved ingredients is not economically viable. Here, the conversion of the relevant contaminants is generally sufficient, while the majority of the ingredients can remain in the recirculated process water. A corresponding selective oxidation of the contaminants leads to a significantly lower oxygen demand and thus also to a significant economic and finally also ecological improvement.

Accordingly, the targeted removal of certain organic impurities is desirable with significantly lower technical equipment and energy costs.

Surprisingly, in experiments with process waters containing facultative anaerobes, the oxidation of FOS to carbon dioxide and water in the presence of gaseous oxygen could be found, with the supply of atmospheric oxygen significantly accelerating the complete oxidation of aromatic compounds. In addition, it was found that controlled air supply could almost completely inhibit the nitrification of contained ammonium while retaining the accelerated decomposition of organic matter. The conversion of ammonium nitrogen to nitrate and / or nitrite nitrogen can be kept well under 2% of the supplied ammonium nitrogen with sufficiently low oxygen supply. It has also been found that particulate matter and fibrous materials do not significantly reduce the decomposition of dissolved organic impurities. influence. A previous solid-liquid separation is therefore not mandatory. In addition, the suspended and / or fibrous materials can serve as a colonization area for bacteria. The COD load, which is often significant in process waters, in the form of nitrogen compounds (eg ammonium) or suspended TS (eg fibrous materials) is not oxidised or is not oxidized in non-relevant quantities.

Consequently, the selective removal of organic contaminants from an aqueous medium by targeted introduction of molecular oxygen in the presence of active microbial biomass is possible. Compared to a classic aerobic stage, significantly less oxygen is needed.

It was found in comparative batch experiments with process water from an anaerobic fermentation process that FOS as well as phenolic and indolic compounds from an anaerobic medium were degraded below the detection limit after oxygen could diffuse into the medium over a period of time. In contrast, no significant degradation of these compounds took place in comparative experiments without oxygen contact.

In further stirred tank experiments, it was found that no significant dissolved oxygen concentration is required for degradation of the contaminants. Upon introduction and distribution of atmospheric oxygen into the medium, degradation also occurs when the concentration of dissolved oxygen is in the suboxic range. The degradation process is usually limited by the diffusion of oxygen into the aqueous phase, while the biochemical conversion of dissolved oxygen proceeds comparatively quickly.

In an energy-efficient and cost-effective technical process, the medium to be treated (process water) is fed into a reactor with active microbial biomass. In addition, molecular oxygen is introduced directly and / or indirectly into this reactor and brought into contact with the medium to be treated, so that a selective oxidation of the organic contaminants is carried out by the microorganisms, but without reducing the majority of the supplied with the medium to be treated COD. The introduction of oxygen can be done directly by, for example, injecting air and / or indirectly, for example, by supplying an oxygen-saturated liquid. From the reactor, the treated medium (treated process water) and a carbon dioxide-containing exhaust gas are withdrawn.

Such a process is possible with respect to the liquid and / or gas streams both as a batch, semi-continuous or continuous process. The process may be such that the active biomass is reformed in the reactor and / or occasionally and / or continuously supplied to the system with, for example, the medium to be treated. If the active biomass is to be newly formed in the reactor, the average residence time of the medium to be treated in the reactor should be at least as large as the doubling time of the active biomass. In addition, it is possible to immobilize the active biomass in the reactor, for example by means of suitable support materials.

If the nutrient requirement of the active microbial biomass is not sufficiently covered by the supplied material flows, appropriate nutrients or trace elements must be supplied to the reactor. Advantageously, this can be done directly with the medium to be treated or by a separate feed.

Depending on the contaminant to be removed and the active bacterial biomass, different temperatures may be advantageous. As a rule, temperatures in the mesophilic and thermophilic range are particularly advantageous. Compliance with a preferred temperature can be particularly advantageous by the temperature of the supplied medium to be treated (feed). Additionally or alternatively, known heat transfer methods can be used, such as the indirect heat exchange from a separate circulation stream of the reactor.

The microbial degradation of the contaminants takes place efficiently in a favorable pH range for the active biomass. This can be regulated by feeding acidic and / or basic streams into the reactor in a range from 6.5 to 10.5, preferably from 7.5 to 9.5, more preferably in a range of 8.0 and 9.0 become. It is advantageous to use known process engineering measures for the improved introduction of oxygen into the aqueous phase. The mass transfer from the gas phase into the liquid phase is promoted in particular by a high oxygen partial pressure, a large phase boundary and the longest possible contact times between gaseous and liquid phase. This can be technically realized, for example, by the use of ejectors / jet pumps and / or use of pure oxygen instead of atmospheric oxygen, by high, slim reactors with a correspondingly high hydrostatic pressure and / or by the use of stirrers or other mixing units.

Control of the degradation process is advantageously possible by measuring and controlling the content of dissolved oxygen in the liquid reaction space. The content of dissolved oxygen in the reactor should be kept in a range between 0 and 2 mg / l, preferably below 1 mg / l, more preferably below 0.3 mg / l, most preferably below 0.15 mg / l.

It is particularly advantageous to control the redox value in the reactor in order to control the decomposition process. The supply of molecular oxygen is optionally regulated in the form of air by measuring the redox value in the reactor, the redox value in the reactor in a range between 0 and -400mV, preferably between -100 and -300mV, more preferably between -200 and -280mV is kept.

The control can be carried out in such a way that the volume flow of the added molecular oxygen is adjusted and / or the mass transfer conditions are influenced by a changed mixing. The volumetric flow of the added molecular oxygen can also be influenced, for example, by varying the oxygen content in the gas stream. Thus, in addition to air, for example, pure oxygen can also be used and / or part of the supplied gas stream can be replaced by recirculating exhaust gas.

Such a method is particularly advantageous if the oxygen input is limited to such an extent that, although the impurities have been broken down, the nitrogen compounds contained in the reactor are not or only to a small extent be oxidized to nitrate and / or nitrite. In addition, it is advantageous to limit the oxygen input to such an extent that the COD supplied with the medium to be treated is not degraded by a majority. Preferably, the process is designed so that the COD is not more than 50%, preferably not more than 30%, more preferably not more than 20%, most preferably not more than 15% is reduced, while the impurities to the desired concentration be reduced.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 shows a possible first embodiment according to the invention;

Fig. 2 shows a flow chart of a possible second embodiment according to the invention;

Fig. 2a shows a possible second embodiment according to the invention;

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the invention are illustrated in the drawings and will be described in more detail below.

101 inlet (contaminated medium)

102 process

103 Oxygen-containing gas stream

104 exhaust

105 auxiliaries

120 cereals

121 fresh water

121a mashing water

122 vinasse

123 bioethanol

132 digestate (biorefinery outflow)

132a digestate (drainage of the biogas plant) 133 biogas

1 feed entry

2 drainage

2a process return

2b fluid entry

3 gas supply

4 exhaust gas removal

4a exhaust gas removal

4b gas recirculation

5 excipient entry

6 mixers

7 revolution

8 reactor

9 measuring device

10 plant for selective oxidation

11 feed pump

12 circulation pump

13 compressors

14 ejector

15 auxiliary pump

20 bioethanol plant

30 biogas plant

EMBODIMENT 1

The possibility of a technical implementation of the process is illustrated below by the removal of acetic acid from a process water. Essential features of this embodiment are also shown in FIG. 1.

A process water from an evaporation plant charged with acetic acid is to be prepared for a downstream fermentation process so that the acetic acid concentration does not inhibit the fermentation process. This is achieved by microbially oxidizing the acetic acid. The process water In addition to acetic acid, it also contains significant amounts of organic suspended solids and other organic components.

This process water is the feed (101) into the reactor (8). The reactor is predominantly filled with the treated process water and contains active biomass, which ensures the acetic acid degradation. The feed is conveyed with the feed pump (11) via the feed entry (1) in the reactor. Advantageously, the feed is conveyed into a region of intensive mixing in order to promote the mass transfer. The intensive mixing is achieved by a circulation (7) of the reactor contents by means of a mixer (6) and the ascending gas flow, which is introduced and distributed via the gas supply (3) in the lower part of the reactor.

The necessary for the oxidation of acetic acid oxygen (103) is conveyed through the compressor (13) in the system. In addition to pure oxygen, alternatively, another oxygen-containing gas stream such as air can be used. With a correspondingly lower proportion of oxygen in the stream 103, however, the volume flow to be compressed increases, and accordingly also the exhaust gas flow (104). The exhaust gas flow is discharged via the exhaust gas outlet (4) from the reactor or from the entire system (4a). Via the gas recirculation (4b) a circulation of the gas within the system is possible. A portion of the exhaust gas can thereby be led to the compressor (13) and fed together with the gas stream 103 into the system. Such a circulation can on the one hand increase the conversion of the oxygen supplied with the stream 103. In addition, the oxygen content in the reactor can be influenced by the circulation of the gas. In addition, the circulation of the gas increases the gas volume flow through the reactor and thereby improves the mixing in the reactor, which has a positive effect on the mass transfer, in particular on the oxygen input into the liquid phase.

The control of acetic acid degradation is based on the oxygen content in the reactor. This is possibly detected together with other process parameters such as pH value, redox value and / or temperature by the measuring device (9). For efficient acetic acid degradation, the oxygen content in the reactor is advantageously kept below 0.5 mg / l, preferably in the suboxic range. In the event of deviations from the setpoint, the volume flow 103, the exhaust gas recirculation and / or the inlet are varied. An alternative control can be realized on the basis of the redox value.

The microorganisms responsible for acetic acid degradation are initially metered into the system as a starting culture or recurring, for example, as an adjuvant stream (105) via a separate pump (15) and the excipient feed (5). This arrangement also doses pH-effective auxiliaries, such as, for example, caustic soda, as well as nutrients such as, for example, ammonium bicarbonate and trace elements. The temperature in the reactor results from the temperatures of the incoming streams and the heat of reaction released during the oxidation reaction and the heat losses of the system. In the case of deviations between the temperature which is established and the temperature which is favorable for the microbial conversion, it is possible, in an advantageous embodiment of the method, to install suitable process-engineering heat transfer technology. This can be done for example via a temperature of the incoming streams and / or by tempering the reactor contents.

In an advantageous embodiment, the microorganisms are enriched in the reactor, for example, by carrier materials suspended in the water. The microorganisms colonize these support materials, which are mixed in the reactor, but are not removed by the appropriate constructions on the effluent (2) from the reactor. In another advantageous embodiment, carrier materials are installed in the reactor as fixed growth surfaces in order to increase the microorganism concentration in the reactor.

According to the time required for a sufficient depletion of acetic acid in the reactor, the reactor contents are discharged via the effluent from the reactor. The process (102) still contains relevant amounts of the ingredients fed with the feed and the supplied auxiliaries, but only traces of acetic acid. The process can thus be supplied for further use, if appropriate after further conditioning steps. The quality of the process is controlled by determining the acetic acid content by conventional analytical methods such as liquid or gas chromatography. EMBODIMENT 2

A further possibility of a technical execution of the method is illustrated below with reference to the removal of aromatic compounds from a process water of a biorefinery, whereby a process-comprehensive recirculation of the process water within the biorefinery is made possible in a very efficient and cost-effective manner. Essential features of the embodiment are shown in FIGS. 2 and 2 a. The raw materials and products mentioned in Fol ^¬ constricting are just some examples. The process of removal of contaminants can be easily applied or transferred to a person skilled in the art for other raw materials and / or coupled production processes. Further raw materials may be, for example, straw, carbohydrate-rich, fatty and / or protein-rich substances. Examples of coupled production processes are the production of second generation ethanol, fermentative butanol production, the production of pulp, cellulose and / or paper, protein separation, fermentative production of phenolic compounds, biodiesel and / or glycerine production and feed production.

In a biorefinery, for example, cereals (120) produce bioethanol (123) and biogas (133). In the process, bioethanol is first fermentatively produced from grain in a bioethanol plant (20) and recovered as valuable material. For the mashing of the grain water (121) is used. While most streams are recirculated within the bioethanol plant, the by-product is the stillage (122). The vinasse contains essentially not only water but also the organic and inorganic constituents of the cereal which have not been converted to ethanol and has a DM content of about 10-20%, the organic content of the dry substance generally being more than 90%. It is used as a raw material for the production of biogas in the biogas plant (30). Includes the biogas plant, bio ^¬ gas preparation it may also be the biomethane fuel stream 133 of a specific embodiment of the method. In the anaerobic fermentation of the vinasse, most of the organic ingredients are degraded to methane and carbon dioxide. The organic and inorganic components are more or less completely hydrolyzed, reduced and / or degraded. Accordingly, there are still significant amounts of suspended and dissolved dry matter in the digestate. The dry matter content is typically in the range of 2-8% and consists of inorganic and organic components. Standard values of 20-120 g / l for the digestate are given for the customary measure of COD in sewage technology.

In particular, in the degradation of proteins, aromatic compounds are formed, which are only very slowly degraded very slowly or under anaerobic conditions. These aromatic compounds which are generally dissolved are then found again in the course of the biogas plant, the liquid digestate (132a). Fibrous components of the grain, which are also in the vinasse, are only partially degraded in the biogas plant and are also suspended in the digestate. The nitrogen fed with the vinasse is converted to at least 50% ammonia nitrogen during anaerobic fermentation. Depending on the process control within the biogas plant and / or the biorefinery, levels of ammonium nitrogen of 2,000-10,000 mg / l can result in the digestate. Corresponding to the stoichiometric conversion to nitrate, a COD of approximately 9-50 g / l results solely from the stated contents for ammonium nitrogen.

Substantial resource savings could be realized by recycling digestate as a substitute for water in the bioethanol plant. While most of the ingredients are not critical for recirculation of the fermentation residue into the bioethanol plant, the contained aromatic compounds can inhibit fermentation and limit or even make repatriation impossible. This problem is inventively solved by the relevant aromatic compounds are microbially removed from the digestate in the plant for selective oxidation (20) and the flow of this plant (102) can be returned to the ethanol plant. The mashing water (121a) for ethanol In this case, there would be significantly less fresh water, which would reduce the digestate stream 132 and significantly improve the economic and ecological efficiency of the overall process.

The plant for selective oxidation consists essentially of a treated with treated digestate reactor (8), in which the microbial conversion takes place, as well as some internals and ancillaries. The process occurring in this plant is operated continuously as well as the upstream and downstream processes, although a quasi-continuous and / or discontinuous operation is possible.

The fermentation residue loaded with the aromatic compounds constitutes the feed (101). It is conveyed together with the feed pump (11) together with recirculated discharge into the liquid feed (2b). This leads the liquid to one or more ejectors (14). In the ejector, air is mixed with the liquid according to the propulsion jet principle and introduced finely distributed into the reactor. The air, so the oxygen-containing gas (103) is passed from the environment via at least one compressor (13) and the gas supply with the necessary form to the ejector. By this known principle, a good mass transfer of the oxygen is achieved in the liquid. In addition, the mass transfer is favored by a mixing of the reactor contents, for example by one or more mixers (6). These may be, for example, laterally arranged propeller stirrers. Thus, a circulation (7) of the reactor contents and thus a good metabolic rate are achieved.

The microorganisms required for the degradation of the aromatic compounds are continuously fed to the process with the fermentation residue. These are various facultative anaerobes. These absorb the oxygen introduced into the liquid and oxidize the aromatic impurities. Within certain limits, the system has a self-regulating effect, since it is exactly the bacteria that reproduce which are able to live particularly well with the supplied impurities as a substrate in the existing process conditions. The pH determined by the feed is usually in a favorable range for the bacteria degrading the impurities. However, it is of course possible, for example, to influence the pH value in the reactor (8) by a preceding conditioning of the fermentation residue.

The temperature in the reactor results from the temperatures of the incoming streams and the heat of reaction released during the oxidation reaction and the heat losses of the system. Due to the released reaction enthalpy of the oxidation reaction, depending on the content of impurities to be converted in the feed, a significant temperature rise of more than 10-15 Kelvin can occur in the system. It is possible to operate the degradation process at mesophilic as well as thermophilic conditions. In the case of deviations between the temperature which arises and the temperature which is favorable for the microbial conversion, it is possible, in an advantageous embodiment of the method, to install suitable process-engineering heat transfer technology. This can be done for example via a temperature of the incoming streams and / or by tempering the reactor contents.

The process is operated in the suboxic range at very low levels of dissolved oxygen to selectively remove predominantly the impurities and not oxidize other organic and / or inorganic constituents or only to a very limited extent. Advantageously controllable is the method of controlling the redox value in the reactor. With the measuring device (9), the redox value is measured in the reactor. By maintaining a redox value of less than 0 mV, preferably less than -100 mV, it is possible to suppress most of the oxidation reactions, such as the oxidation of ammonium to nitrate, while the oxidation of the aromatic impurities is realized. As a result, the required air volumes are significantly lower compared to classic aerobic wastewater treatment processes. The regulation of the redox value takes place by adjusting the supplied air quantities and / or the inflow quantities.

The oxidation of ammonium to nitrate is not significant at these process conditions. Only through the gas flow through the reactor portions of the ammonium are discharged in the form of ammonia. This ammonia can be recovered from the exhaust (104) by a downstream condenser and / or scrubber. The content of ammonium nitrogen of the effluent (102) is temperature- and pH-dependent at over 90% of the content in the feed.

The exhaust gas discharged from the reactor via the exhaust gas outlet (4) contains significant amounts of carbon dioxide in accordance with the effluent reactions.

The average residence time of the feed in the reactor, depending on the content of impurities, is up to 30 days, preferably about 15 days, more preferably less than 10 days. The conversion of impurities is usually limited by the mass transfer of oxygen from the gaseous to the liquid phase and not by the degradation reaction itself. The discharge of the process (102) via a drain (2). From this, a recirculation (2a) goes to the circulation pump (12), which promotes a part of the process (together with the inlet) via the ejector as propulsion jet back into the reactor. The freed from the impurities, drained from the system process contains in addition to the predominant proportion of nitrogen also almost the same amount of fiber and a total of only slightly reduced compared to the feed TS. The COD degradation during the selective oxidation is, depending on the composition of the feed and the content of impurities not more than 50%, preferably not more than 30%, more preferably not more than 20%, most preferably not more than 15%. The process is run directly or after conditioning as recirculated into the bioethanol plant.

Claims

A process for removing at least one organic contaminant from an aqueous medium, comprising the steps of:

b) Direct and / or indirect introduction of molecular oxygen into this reactor

c) carrying out a microbial selective oxidation under suboxic conditions of at least one of the supplied organic impurities without majority degradation of the supplied COD

d) removal of the treated aqueous medium from the reactor e) removal of a carbon dioxide-containing waste gas stream from the reactor.

2. The method according to claim 1,

d a d u r c h e c e n c i n e s that

the molecular oxygen is introduced in the form of air into the reactor.

3. The method of claim 1, wherein:

a portion of the exhaust stream is recycled to the reactor.

4. The method according to at least one of the preceding claims, characterized in that a

the introduction of molecular oxygen optionally takes place continuously in the form of air.

5. The method according to claim 1, wherein:

the reactor contents are optionally mixed using suitable stirring technology such as at least one propeller agitator and / or at least one jet pump or other directed gas introduction systems.

6. Method according to at least one of the preceding claims, characterized in that a

occasionally and / or continuously, optionally together with the medium to be treated, active microbial biomass is supplied to the reactor.

7. The method according to at least one of the preceding claims,

d a d u r c h e c e n c i n e s that

For example, the active microbial biomass is at least partially immobilized in the reactor by suitable carrier materials.

8. The method according to at least one of the preceding claims,

d a d u r c h e c e n c i n e s that

the mean residence time in the reactor is at least as long as the doubling time of the active microbial biomass.

9. The method according to at least one of the preceding claims,

d a d u r c h e c e n c i n e s that

the supply of molecular oxygen, if appropriate also in the form of air, is limited to such an extent that no significant oxidation of nitrogen compounds contained in the reactor takes place.

10. The method according to at least one of the preceding claims,

d a d u r c h e c e n c i n e s that

the supply of molecular oxygen, if appropriate also in the form of air, is regulated by measuring the redox value in the reactor, the redox value in the reactor being in a range between 0 and -400 mV, preferably between -100 and -300 mV, particularly preferably between -200 and 280mV is maintained.

11. The method according to at least one of the preceding claims,

d a d u r c h e c e n c i n e s that

optionally controlling the supply of molecular oxygen in the form of air by measuring the dissolved oxygen in the reactor is maintained, wherein the content of dissolved oxygen in the reactor in a range between 0 and 2mg / l, preferably below lmg / l, more preferably below 0.3mg / l, most preferably below 0.15mg / l is maintained.

12. The method according to at least one of the preceding claims,

d a d u r c h e c e n c i n e s that

optionally, nutrients and / or trace elements are fed to the reactor together with the medium to be treated.

13. The method according to at least one of the preceding claims,

d a d u r c h e c e n c i n e s that

The medium to be treated to the reactor to be treated at least quasi-continuously fed and treated medium is removed from the reactor at least quasi-continuous.

14. The method according to at least one of the preceding claims,

d a d u r c h e c e n c i n e s that

the treated in the reactor medium is recycled to a process that is directly or indirectly connected to the process from which the medium to be treated was previously removed.

15. The method according to at least one of the preceding claims,

d a d u r c h e c e n c i n e s that

the treated in the reactor medium is returned to a process to replace, for example, drinking water, well water, condensate and / or other process water.

16. The method according to at least one of the preceding claims,

d a d u r c h e c e n c i n e s that

the COD of the supplied aqueous medium is reduced by not more than 50%, preferably not more than 30%, more preferably not more than 20%, most preferably not more than 15%.

17. Method according to claim 1, wherein:

the pH in the reactor is optionally adjusted by supplying an acidic or basic material stream in a range from 6.5 to 10.5, preferably from 7.5 to 9.5, particularly preferably in a range from 8.0 to 9.0 becomes.

18. The method according to at least one of the preceding claims,

d a d u r c h e c e n c i n e s that

the temperature in the reactor is set, for example, directly via the inlet or, for example, indirectly by heat exchange.