DE10249081A1 - Simplified sewage sludge treatment comprises an enzyme treatment step, and optionally a peroxide treatment step at an acidic pH - Google Patents

Abstract

Treatment of sewage sludge, especially of thickened sludge after a putrefaction process, is effected in the presence of an enzyme.

Description

The invention relates to a method for the treatment of, especially thickened, sewage sludge, preferably after a rotting process.

When anaerobically or aerobically stabilized sewage sludge is disposed of, this suspension, which typically contains 15 to 30 grams of dry residue per liter, is first thickened to a higher concentration of dry residues. The thickened sewage sludge is then conditioned by adding divalent or trivalent metal ions or alkaline earth metal ions such as Fe ²⁺ , Fe ³⁺ or Al ³⁺ and / or organic, polymeric, primarily cationically modified flocculation aids. The sewage sludge conditioned in this way is then dewatered via centrifuges or filter presses and then disposed of in agricultural, thermal or landfill. Because this type of disposal entails relatively high costs, the conditioned sewage sludge should be drained as well as possible so that the highest possible dry matter content can be obtained. For various reasons, the dry matter content cannot be increased arbitrarily. The presence of various surface-active substances in sewage sludge poses a major problem, such as surfactants or microbially produced slimy exocellular polymeric substances (EPS), which act as protective colloids. These protective colloids are not adequately eliminated by the methods described above, which means that the waste disposal companies require larger containers and apparatus as well as a greater use of apparatus and energy. This in turn poses higher drainage costs.

There is an approach to remove the hydration shell by means of a depolymerization of the mucus acting as a protective colloite. For this purpose, sewage sludge is mixed with 15 to 30 mmol H ₂ O ₂ per liter sludge at a temperature of 50 ° Celsius to 90 ° Celsius and a pH value of 3.0 in the presence of FeSO ₄ and the sludge thus prepared is about 1 treated up to 2 hours. In another approach, the sewage sludge is catalytically partially oxidized with substoichiometric amounts of H ₂ O ₂ . For this purpose, H ₂ O ₂ with an addition of 0.75 g FeCl ₂ per kg H ₂ O ₂ (100% strength ₎ is added at a pH of 3.0 to 4.0 and a temperature of 20 ° Celsius to 30 ° Celsius ) metered in, the amount of metered H ₂ O _{2 being} regulated in such a way that the redox potential is measured and stabilized at 200 to 500 millivolts. The pH is then raised to a value of 9.0 to 11.0 by adding Ca (OH) ₂ .

With the approaches mentioned, an improvement in drainage can be achieved. However, lowering the pH value to values around 3.0 to 4.0 leads to high stress on the container material used. In particular, undesirable corrosion can occur. The neutralization that is subsequently required leads to an undesirable salting-up of the conditioned sludge. These salts in turn have to be disposed of in a complex manner. The temperature range of 50 ° Celsius to 90 ° Celsius required in the first approach also means an undesirably high energy consumption. Furthermore, the required amounts of H ₂ O ₂ of 15 to 30 mmol per liter of sewage sludge are also quite high, as a result of which the consumption costs of H ₂ O _{2 are} also undesirably high.

The problem underlying the ending is to provide a process for treating sewage sludge that high in a simple way and without annoying by-products dewatering of the conditioned sewage sludge results.

The problem is solved in that one Process of the type mentioned sewage sludge in the presence at least of an enzyme is treated.

Using an enzyme even at relatively low Temperatures reach a high metabolic rate, which prevents undesirably high Energy costs are incurred. Under unsuitable conditions, i.e. after the actual treatment, enzymes disintegrate relatively quickly in harmless Components, so here also no complex unwanted to dispose of By-products are incurred. In particular, surprisingly, that sewage sludge this way even at low temperatures and near neutral pH range using only lower Amounts of chemicals can be treated so that only small amounts of residual sludge with improved drainability be preserved.

In a further development of the invention a combination of several enzymes is used. By a suitable one The achievable metabolic rate can be selected by selecting the enzymes of this combination increase significantly. As enzymes can for example cellulase, hemicellulase, protease and / or lysozyme be used. Especially the combination of lysozyme with protease has proven to be particularly effective. When using A particularly effective mechanism results from lysozyme. The Lysozyme dissolves Mucus and thus destroys cells. That way the enzymes present in the cells are also released. This are relatively short-lived under the prevailing conditions. However, this will triggered a kind of chain reaction, what the effectiveness is extraordinary increases. As a protease use pepsin and / or pankratin in an advantageous manner.

In one development, an enzyme from an extremophile organism and / or an enzyme from a genetically modified extremophile organism is used. An extremophile organism is one that lives under extreme conditions, especially in the Arctic Ocean at low temperatures and high salt levels hold occurs. The enzymes of such extremophilic organisms have been shown to be extremely resistant. In contrast to normal enzymes, which are only stable in a very narrow environmental range with regard to temperature, pH, salinity and other conditions over a longer period of time, the enzymes of such an extremophilic organism are also surprisingly stable outside their natural environmental conditions. In particular, it has been shown that the enzymes of a genetically modified and in particular a recombinant organism are extremely resistant.

Another enzyme found in sewage sludge treatment can be used advantageously one that is the product of the fungus Trichoderma reesei or of the fungus Trichoderma viride, especially obtained by fermentation becomes. This fungus occurs when wood and cellulose are broken down. On this way can be the cellulose content in sewage sludge break down effectively.

In a further development of the invention 200 to 1,200 mg, preferably 300 mg to 1,000 mg, in particular 400 mg to 900 mg of the enzyme or the combination per kg, in particular organic, dry matter of the sewage sludge added to this. This relatively small Amounts of the enzyme or combination of the enzymes have been shown to be Completely proven sufficiently.

The treatment is preferably carried out by means of the enzyme anaerobic. The fermentation processes that occur here or putrefaction processes devalue a high proportion of methane gas, which is beneficial lets use.

In a further development of the invention the treatment is carried out at a pH of 6.6 to 7.5, preferably from 6.8 to 7.3 and especially from 6.9 to 7.2. In this relatively neutral Only small additions of chemicals are required in the pH range.

It has proven to be beneficial the sewage sludge to heat for treatment, preferably to 30 ° Celsius to 37 ° Celsius, especially to 35 ° Celsius. With these relatively small Temperatures require only minimal energy for heating. At the same time, however, a high metabolic rate is achieved using the enzymes.

An advantageous combination shows 10% to 30% cellulase, 50% to 70% hemicellulase and 5% to 30% Protease on. This combination enables particularly good ones Get results.

According to another aspect of the invention is used in a process for treating sewage sludge in an acidic pH treated by adding a peroxide, the treatment at a pH of 4.5 to 6.8. It has turned out surprisingly shown that already in this only weakly acidic pH range by adding of a peroxide has good drainability of the sewage sludge treated in this way results. Treatment can be in a pH range from 4.7 to 6.5, preferably from 4.9 to 6.3 and in particular from 5.0 to 5.8 only small amounts of chemicals are required here. in the Test, the best results were achieved with a pH of 5.0. About the use of chemicals and the risk of corrosion from the equipment but it may be useful to reduce the pH anyway to 5.3 to 6.0, for example. Come as peroxide expediently suitable, storage-stable peroxides or those in their storage-stable Form for use.

In a further development of the invention the pH is adjusted by adding an acid, preferably a mineral acid, especially hydrochloric acid (HCl). Especially when using hydrochloric acid will be extraordinary good results with the least possible Expensive burden chemicals to be disposed of.

A is preferably used for treatment Peroxide, an organically or inorganically bound peroxide, hydrogen peroxide, Potassium peroxydisulfate, performic acid, or peracetic acid added. These peroxides have proven to be particularly effective. Just in the case of hydrogen peroxide, it was discovered that this is among the specified Conditions not on conventional Decays to form an OH radical. This is OH radical extraordinarily reactive.

It is also advantageous to treat that 0.05 gmol to 1.18 gmol, preferably 0.07 gmol to 1.5 gmol, in particular 0.1 gmol to 1.0 gmol, namely 0.6 gmol to 0.8 gmol peroxide per kg dry matter of the sewage sludge be added. GMol is the weight in grams, which corresponds to 1 mole of the peroxide. These extremely small amounts are fully sufficient under the specified conditions. This will little cost peroxide consumption raised.

The treatment is advantageously carried out by adding the peroxide for 20 minutes to 120 minutes, preferably 30 minutes to 60 minutes. With this relatively short Treatment time can be achieve high throughput with good results.

A third aspect of the invention relates to a process for treating sewage sludge, comprising the steps:

• - To adjust a predetermined first pH value of the sewage sludge to be treated and adding a predetermined amount of the enzyme, subsequent anaerobic Treatment of the prepared sewage sludge for one predetermined first time,
• - Lowering the pH of the sewage sludge to a lower second pH, adding one before determined amount of the peroxide and then treating the sewage sludge thus prepared for a predetermined second time. By means of these two steps, good drainability can be achieved with little pollution.

In the case of further training, a protease was added to the second time, the sewage sludge thus prepared then for a predetermined third time is treated. This allows not completely dismantled Continue to break down proteins. So that can the drainability further increase so that smaller quantities must be disposed of with residual sludge.

Another training course the step of lowering the pH to the second pH before and / or after the step of adjusting the first pH. By the possibly additional Carry out lowering the pH even before setting the first pH let yourself further reduce the amount of residual sludge and drainability of the residual sludge continue to improve.

The following is an embodiment the invention closer explained. Show it:

1 1 shows a schematic representation of a device for carrying out the method with the features of the invention,

2 a flowchart of a process sequence with the features of the invention,

3 the individual steps of a digestion step by 2 .

4 the steps of a peroxide treatment step of 2 and

5 a flow chart of another process flow with the features of the invention.

1 shows a schematic representation of an apparatus for performing the method with the features of the invention. One line 10 is, as indicated by an arrow A, sewage sludge to be treated. In particular, the sewage sludge supplied at A has already been pretreated and thickened in a sewage treatment plant. The administration 10 is with a sensor 11 and an addition device 12 connected. The feeder 12 is used to add hydrochloric acid (HCl). The feeler 11 and the addition unit 12 stand by means of a line 13 with funding 14 in connection. The exit of the funding 14 is with a line 15 connected. The administration 15 stands with an addition unit 16 by means of a line 17 in connection. The addition unit 16 is used to add an enzyme or combination of enzymes.

The administration 15 stands by their funding 14 opposite end with a reactor 18 in connection. The reactor 18 is by means of lines 31 . 32 with a heat exchanger 33 connected. The heat exchanger 33 stands with lines 34 . 35 for supplying and discharging steam or hot water in combination.

An outlet of the reactor 18 is with a line 19 with funding 22 connected. The funding 22 are similar to the funding 14 a feed pump. It is also in the area of management 19 a sensor 20 for measuring the pH and an addition unit for adding an acid, in particular hydrochloric acid (HCl). The exit of the funding 22 is by means of a line 23 with a decanter 25 connected. The administration 23 also stands with an addition unit 24 in connection. The addition unit 24 serves to add a peroxide.

The decanter 25 stands with an outlet with a pipe 36 in connection. By means of the line 36 liquid is withdrawn from the decanter, as indicated by an arrow D. Another outlet from the decanter 25 stands by means of a line 26 with release agents 27 in connection. The release agent 27 in the 1 has a sieve 28 on. As a release agent 27 can also use a cyclone. The release agent 27 is with an output with a line 29 connected. By means of the line 29 is that of the release agents 27 retained solids content removed, as indicated by an arrow B. Another exit of the release agent 27 is with a line 30 connected. The administration 30 serves to drain the liquid from the release agents 27 , as indicated by an arrow C.

A controller for recording the measured values of the sensors 11 . 20 and for controlling the addition units 12 . 16 . 21 . 24 is in the 1 not shown.

The mode of operation of the in 1 shown device based on the 2 to 4 explained. 2 shows a flow chart for the method steps with the features of the invention.

The method is started in step S10. Here comes in 1 as indicated by arrow A, sludge to be treated through the line 10 into the device. The sludge added at A is the resulting sludge from a sewage treatment plant in the exemplary embodiment shown. This sludge has already been largely pre-treated and thickened.

Step S12 follows next. In step S12, an anaerobic treatment of the sewage sludge, namely digestion, is carried out, as will be explained below with reference to FIG 3 is explained in more detail.

It continues with step S14. In step S14, a peroxide treatment of the sewage sludge already subjected to the digestion in step S12 is carried out. The individual process steps of the peroxide treatment are described below with the aid of 4 discussed in more detail.

In step S16 there is also a protease addition, which is shown in 1 is not provided. The addition this protease in step S16 is not absolutely necessary for the method with the inventive features. The appropriateness of this protease addition depends on the economic boundary conditions. With the help of this protease addition, the sewage sludge treated in this way can be better dewatered. In this way, smaller amounts of dry matter are obtained, which would then be difficult to dispose of. In step S16, a predetermined amount of a protease, such as pepsin or pancratin, is added to the sewage sludge from the peroxide treatment. The sewage sludge thus treated with the protease remains for one to two hours for treatment with this protease. Since the proteases are usually sold as powders and are not stable in the long term in the dissolved, liquid form, a minimum treatment time of one hour is required for the powdery protease to be dissolved and to begin its activity. After a treatment period of about two hours, the metabolism caused by the protease is largely complete. A significantly longer treatment period appears to be of little use.

Next follows in step S18 the end of the process. Here, the treated sewage sludge is removed known way drained. This can be done, for example, using presses, a screen or one Cyclones take place. A centrifuge is preferred for dewatering used. The separated solids content is suitably such as agricultural, thermal or by landfill disposed of. The separated liquid Phase can be a so-called activation stage of a sewage treatment plant are fed. The solved Degradation products of depolymerization are due to their content of saccharides, Peptides and amino acids an excellent stimulator of mud activity. on the other hand is the content of toxic or otherwise problematic substances so small that the Processes in the aeration stage are not unduly affected.

3 shows the individual steps of the digestion S12. First of all, the pH is regulated in step S20. To do this, use the sensor 11 in 1 the pH value of the sewage sludge is determined and dependent on this pH value by means of the addition unit 12 a mineral acid, especially hydrochloric acid (HCL) added. In this way, the pH is adjusted to an almost neutral pH of 6.6 to 7.5.

The enzyme is then added in step S22. In doing so, the addition unit 16 an enzyme or combination of enzymes is added. Hydrolytic enzymes, cellulase, hemicellulase, protease, lysozyme, in particular also the combination of lysozyme with a protease, can be used as enzymes. It has also proven to be effective to use enzymes that can be produced from the fungus Trichoderma viridee or Trichoderma reesei. The enzymes can be obtained from the fungus, for example, by fermentation. This fungus plays a role in the degradation of wood, especially in the degradation of cellulose fibers. The advantage of lysozyme is that it does not attack the archa bacteria, which means that a high yield of methane gas can be achieved. At the same time, lysozyme dissolves the mucilage and has a cell-destroying effect. In this way, the enzymes inside the cells are released. These are short-lived under the prevailing conditions. However, a real chain reaction is triggered in this way. Enzymes that are very effective are those that can be obtained from extremophilic organisms. Such extremophilic organisms live under extreme conditions, such as in the Arctic Ocean at low temperatures and high salt levels. The enzymes obtained from these extremophilic organisms are surprisingly characterized by extreme stability even under very different and otherwise inhospitable conditions. It has also been shown as a further surprising result that the enzymes from genetically modified extremophilic organisms and in particular from recombinant organisms are particularly resistant and effective.

The actual treatment follows in step S24. This treatment is carried out anaerobically, that is to say in the absence of air in the reactor 18 , Numerous digestion and fermentation processes occur here. The resulting methane gas, as well as the carbon dioxide is not in the 1 shown lines from the reactor 18 taken. The next step is the peroxide treatment in step S14.

4 shows the individual steps of the peroxide treatment S14. First, in step S26, the pH is reduced to a value from 4.5 to 6.8. To do this, use a sensor 20 the pH value is measured and depending on this measured value by the addition unit 21 a mineral acid, especially hydrochloric acid (HCl) is added.

Next in step S28 is a peroxide addition using the addition unit 24 , About 0.05 gmol to 1.5 gmol of a peroxide, an inorganic or organically bound peroxide, hydrogen peroxide, potassium peroxydisulfate, performic acid, peracetic acid, or a combination of the aforementioned are added. In particular, it has been shown that adding 0.65 to 1.0 gmol per kg of dry matter of the sewage sludge brings very effective results.

This is followed in step S30 actual treatment for a time of 20 to 120 minutes. In individual cases 30 up to 60 minutes are sufficient.

5 shows a further flow chart of a method with the features of the invention. The same steps are identified with the same reference numbers. In contrast to the in 2 After the start in step S10, the method explained is followed by a first peroxide treatment in step S32. The peroxide treatment in step S32 is the same as the peroxide treatment in step S14. After the peroxide treatment in step S32 follows next the digestion in step S12.

The additional peroxide treatment before the digestion in step S12 it, even poorly degradable high molecular compounds, such as Partially pre-degrading more of the microbial cell wall. This improves the methar gas yield and drains of the treated sewage sludge elevated.

It has been shown that through lowering the pH metal ions are released, causing a additional The addition of divalent metallic activators is not necessary is. In this way there is an additional load on the sewage sludge avoided. Surprised is the fact that the In contrast, depolymerization of the sludge pretreated with peroxide to the usual Methods without the addition of divalent metallic activators of the peroxidic catalysts is almost quantitative. at On the one hand, the process with the features of the invention becomes more biogas formed, on the other hand falls less residual sludge, which is also easier to drain is. As an indicator of the drainability let yourself the capillary flow time Use (CST in seconds). In the case of the method according to the invention treated sewage sludge can achieve a capillary flow time reduction of 80 to 90%.

The following examples are for explanation of the method with the features of the invention. Examples 1 and 2 describe the influence of Type of catalyst, its amount used and the set pH value on the drainability. Example 3 concerns the complete process. The results presented illustrate the advantages of the method according to the invention. In particular small doses of the catalysts fall, comparatively mild reaction conditions, improved biodegradation, higher biogas formation and low CST values in reductive treatment as well as better ones Drainability of the treated sludges on.

example 1

4 × 1000 ml of a digested sludge sample containing 34.20 g / L dry residue, with 57.6% loss on ignition (GV), with pH 7.67 and a CST value of 620 seconds while stirring in 37% hydrochloric acid the desired pH values set with the amounts given in the table and type of catalyst blended, 30 to 60 minutes at room temperature stirred, after which the individual CST values were determined.

Example 2

4 × 1000 ml digested sludge, with 43.2 g / L dry residue, 45.4% loss on ignition, pH 8.0 and CST 785 sec. is according to example 1 treated.

Example 3

*820 mg pro kg org. Trockensubstanz eingesetztes Enzympräparat mit den Aktivitäten Cellulase, Hemicellulase und Protease.2 × 2000 ml holding, thermostatted at 35 ° C, magnetically stirred and provided with gas burette, discontinuous laboratory anaerobic plants are each with 600 ml digested sludge and 600 ml raw filled sludge, as indicated in the table, doped with additives and subjected to a 7-day reductive treatment.

* 820 mg per kg org. Enzyme preparation used in dry matter with the activities cellulase, hemicellulase and protease.

The reductively treated samples were adjusted to pH 6.0 and aftertreated according to the following table:

10

management

11

sensor

12

adding unit

13

management

14

funding

15

management

16

adding unit

17

management

18

reactor

19

management

20

sensor

21

adding unit

22

funding

23

management

24

adding unit

25

decanter

26

management

27

release agent

28

scree

29

management

30

management

31

management

32

management

33

heat exchangers

34

management

35

management

36

management

Claims (20)

Process for the treatment of, in particular thickened, sewage sludge, preferably after a digestion process, characterized in that the sewage sludge is treated in the presence of at least one enzyme. A method according to claim 1, characterized in that a Combination of several enzymes is used. A method according to claim 1 or 2, characterized in that that as Enzyme cellulase, hemicellulase, protease and / or lysozyme used especially the combination of lysozyme and protease. A method according to claim 3, characterized in that as Protease pepsin and / or pankratin is used. Method according to one of the preceding claims, characterized through the use of an enzyme of an extremophile, in particular halophilic, organism and / or an enzyme of a genetic engineering changed extremophile, especially halophilic, organism. Method according to one of claims 1 to 4, characterized in that that as Enzyme a product of the fungus Trichoderma reesei or the fungus Trichoderma viride is used. Method according to one of the preceding claims, characterized characterized in that for Treat 200 mg to 1,200 mg, preferably 300 mg to 1,000 mg, in particular 400 mg to 900 mg of the enzyme or combination per kg, in particular organic, dry matter of the sewage sludge this is added. Method according to one of the preceding claims, characterized characterized that the Treatment is anaerobic. Method according to one of the preceding claims, characterized characterized that the Treatment at a pH of 6.6 to 7.5, preferably 6.8 to 7.3 and in particular from 6.9 to 7.2. Method according to one of the preceding claims, characterized characterized in that the sewage sludge is heated for treatment, preferably to 30 ° Celsius to 37 ° Celsius, especially to 35 ° Celsius. Method according to one of claims 2 to 10, characterized in that that the Combination 10% to 30% cellulase, 50% to 70% hemicellulase and Has 5% to 30% protease. Method, in particular according to one of the preceding Expectations, for the treatment of, especially thickened, sewage sludge after a digestion process in which the sewage sludge at an acidic pH, namely from 4.5 to 6.8, is treated by adding a peroxide. A method according to claim 12, characterized in that the Treatment at a pH of 4.7 to 6.5, preferably 4.9 to 6.3 and in particular from 5.0 to 5.8. Method according to one of claims 9 to 13, characterized in that that this The pH is adjusted by adding an acid, preferably a mineral acid, especially hydrochloric acid (HCl). Method according to one of claims 12 to 14, characterized in that that as Peroxide, an organically or inorganically bound peroxide, hydrogen peroxide, Potassium peroxydisulfate or performic acid is added. Method according to one of claims 12 to 15, characterized in that that for Treat 0.05 gmol to 1.8 gmol, preferably 0.07 gmol to 1.5 g mol, in particular 0.1 g mol to 1.0 g mol, namely 0.6 g mol to 0.8 g mol Peroxide per kg of dry matter of the sewage sludge can be added. Method according to one of claims 12 to 16, characterized in that that this Treatment by adding the peroxide for 20 minutes to 120 minutes, preferably 30 minutes to 60 minutes. Method, in particular according to one of the preceding claims, for treating, in particular thickened, sewage sludge, characterized in that the following steps are carried out. - Setting a predetermined first pH of the sewage sludge to be treated and adding one predetermined amount of the enzyme, subsequent anaerobic treatment of the sewage sludge thus prepared for a predetermined first time, - lowering the pH value of the sewage sludge to a lower second pH value and adding a predetermined amount of the peroxide, subsequent treatment of the sewage sludge thus prepared for a predetermined time second time. A method according to claim 18, characterized in that after a protease is added to the second time and that the so groomed sewage sludge for one predetermined third time is treated. Method according to claim 18 or 19, characterized in that that the Step of lowering the pH to the second pH and / or after the step of adjusting the first pH.