GB1563335A - Process for the treatment of biologically degradeable waste - Google Patents

Description

(54) PROCESS FOR THE TREATMENT OF BIOLOGICALLY DEGRADEABLE WASTE (71) We, EUROC ADMINISTRA TION AB, a Swedish Body Corporate, of Stormgatan 14, S--211 20, Malmo, Sweden, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be partlcularly described in and by the following statement:- This invention relates to a method of treating heterogeneous biologically degradable waste, whereby a rapid and far reaching microbial degradation of the material can be obtained.

The invention provides a method of rapid and far-reaching microbial batchwise degradation of biologically degradable material which method comprises forming a slurry containing 0.001 to 15% by weight (dry solids) of the material in a finely divided state and added enzymes in an amount of up to 5% by weight based on the weight of dry solids in the slurry and containing thermophilic micro-organisms, and maintaining the slurry at from 50 to 70"C whilst agitating the slurry and supplying oxygen containing gas thereto.

The invention is a modification of a process described and claimed in our British Patent No 1459551, namely a method of treating heterogeneous, at least partly biologically degradable waste, such as domestic waste, comprising a substantial proportion of biologically degradable solid and liquid constituents, such as fat, grease and oil comprising the following steps: comminuting said solids to particles having a particle size of up to 2mm and producing a slurry of said comminuted solids and liquid constituents by adding water and mixing the constituents, homogenizing said slurry by finely dividing said solids to form a well homogenized slurry having a dry solids content of about 1 to 15% by weight, preferably 5 to 10% by weight, stirring said slurry and mixing its constituents in a sufficient degree to prevent stratification or sedimentation of its solid constituent said stirring and mixing being performed under conditions ensuring a sufficient contact surface between said slurry and an oxygencontaining gas such as air or oxygen enriched air so as to satisfy the oxygen requirement of the a'erobic microorganisms originally present in the slurry and such microorganisms that are produced in the course of the treatment, and causing the temperature of the slurry to rise to a thermophilic temperature range of 50 to 70"C to activate said microorganisms, and maintaining the temperature of the slurry within said temperature range while said conditions for satisfying the oxygen requirement of said microorganisms are maintained until substantially all biologically degradable material in the slurry has been spent, whereupon the slurry may be separated substantially into a sanitarily unobjectionable aqueous fraction and sanitarily unobjectionable nondegradable residual products.

The present invention opens up new uses for the degradation of heterogeneous mixtures of biological material. In conformity with the present invention, it has proved possible, in a very broad sense, to make the method independent of the original consistency of the biological material by finely comminuting said material and suspending it in water to an easy-flow liquid. The dry solids content can lie betweeen 0.001-15, but should preferably be from 0.1 to 5 percent by weight depending upon the composition of the biological material. When the material is rich in oxygen-consuming organic compounds the dry solids content may be very low, say 0.001--0.1 percent by weight.

The particles of the biological material should be as small as possible, but not so small as to make the comminution uneconomical, that is an optimum lower comminution limit.

The enzymes are added to the slurry of biologically degradable material to increase and accelerate the microbiological degradation. The sedimentation and filtering properties of the slurry can thus be improved quite considerably. The specific filtering resistance of a material otherwise predegraded to a satisfactory degree can be reduced for instance a thousandfold and a clear filtrate is obtained.

In an embodiment of the invention, the enzymes are added to the suspension prior to the microbiological degradation for initiating an enzymatic degradation, specific to the microorganism species, of biologically degradable material prior to the microbiological degradation. When the microorganisms are then added the slurry will form a nutrient substance which the enzymes are better apt to process. Without a preliminary enzyomatic degradiation specific to the microorganism species, the microorganisms themselves must in fact carry out a coarse splitting of the biological material and they can do this only by their own production of specific enzymes. With regard to certain substances, this can be quite impossible for the microorganisms.

The residual amount of biologically oxygenconsuming dry solids can be reduced by up to 95 percent. A total reduction of biologically oxygen-consuming substance by up to 99.7 percent can thus be obtained.

In another embodiment of the invention, the enzymes are added to the slurry during or after microbiological degradation. They then partake in or enable the conclusion of the microbiological degradation by way of an enzymatic degradation.

Marcromolecular or polymeric, particularly non-biologically oxygen-consuming substances of specific resistance to biological degradation, can be degraded in this way. The residual amount of nonbiologically oxygen-consuming substance obtained without these enzymes can be degraded to over 90 per cent. As a consequence, almost no residual sludge at all remains. The final degradation, however, can take a relatively long time in this case, say 5-10 days.

Up to 5% of enzymes by weight of the total solids of the slurry, preferably 0.1--1 per cent by weight, may be added. In certain cases, the time of degradation can be reduced by 40 percent with the use of an enzyme amount of 0.1 per cent by weight.

In most cases it is necessary to use mixtures of enzymes specific to the process if benefit is to be obtained from them. This applies in general to mixtures of lipases and amylases as well as proteinases, that is enzymatically fat-splitting, disaccharideand polysaccharide-splitting and proteinsplitting enzymes. The quantitive proportion of the enzyme mixtures preferably used substantially corresponds to that of the fatty substances and the sacchariferous and proteinaceus substances in the biological material. Suitable thermostable enzymes are commercially available, but they have hitherto been intended for quite other uses.

In a specifically preferred embodiment of the invention, the agitation necessary for bringing about the enzymatic or microbiological degradation is caused to cease periodically for reducing energy consumption. This can be realised using substantially the same time of degradation or by an insignificant extension thereof.

Thus, the degree of energy economy that may be realised compared to continuous operation is substantially proportional to the idle period of a complete operating cycle.

In an installation for microbiological and/or process specific enzymatic degradation of domestic waste including as main constituents food rests, feces and paper and having a capacity for 50 households the yearly pump energy cost can be reduced, at intermittent operation, by at least U.S. dollars 500,- calculated in the energy prices of 1974. The test results will appear from the following table: Influence of different operating cycles on the time of degradation

One complete Change of time Working period Idle period operating cycle of degradation minutes minutes minutes in per cent 1/2 1/2 1 +0 2 1/2 7 1/2 10 * 0 3 6 9 +0 5 5 10 +0 5 15 20 +10 15 15 30 +0 30 60 90 +30 60 120 180 +50 Methods of treating biologically degradable material according to the invention are exemplified in the following Examples: Example 1.

Mixtures of finely divided, water suspended domestic refuse and/or feces with a dry solids content of 0.001, 0.01, 0.1, 1.0 and 0.5 per cent by weight, after being grafted with microorganisms, are degraded aerobically for 5 days at a temperature of 55600 C. The biologically degradable material will be degraded to over 90 per cent, in all of the cases. Water tests show that the content of coliform bacteria is zero (0) per 100 ml in all of the cases.

Example 2.

Mixtures of finely divided, water suspended household refuse and/or feces having a dry solids content of 1 per cent by weight are treated with lipases, amylases and proteinases, individually or in combination, in an amount of 0.001, 0.01, 0.1, 1.0 and 5.0 per cent by weight of the dry solids content of the slurry when the material is degraded for three days at a temperature of 55600 C. The biologically degradable material will be degraded to 97 per cent also with an enzyme amount of 0.001 per cent by weight. Water tests show that the content of coliform bacteria is zero (0) per 100 ml. The experiment is repeated but without any enzyme treatment. The amount of solid waste residues is considerably larger. In particular, the paper material of the waste has been degraded only to a small extent.

Example 3.

Example 1 is repeated. The content of coliform bacteria is zero (0) after degradation, but the filterability and the dewatering capacity of the treated waste is surprisingly low. The material is treated under agitation with an enzyme mixture according to Example 2. The filterability increases twentyfold to thousandfold. The filtrate is clear and pale yellow.

Example 4.

Cheese whey having a dry solids content of about 0.5 per cent by weight is degraded with aerobic and thermophilic microorganisms at 55600C for 5 days. The biologically degradable material is reduced by 80 per cent. Cheese whey is treated aerobically and thermophilically with an addition of enzymes as in Example 2. The biologically degradable material is now reduced by 95 per cent. Here, the time of degradation is 3 days.

WHAT WE CLAIM IS: 1. A method of rapid and far-reaching microbial batchwise degradation of biologically degradable material which method comprises forming a slurry containing 0.001 to 15% by weight (dry solids) of the material in a finely divided state and added enzymes in an amount up to 5% by weight based on the weight of dry solids in the slurry and containing thermophilic microorganisms, and maintaining the slurry at from 50 to 700C whilst agitating the slurry and supplying oxygen containing gas thereto.

2. A method as claimed in claim 1

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. Influence of different operating cycles on the time of degradation One complete Change of time Working period Idle period operating cycle of degradation minutes minutes minutes in per cent 1/2 1/2 1 +0 2 1/2 7 1/2 10 * 0 3 6 9 +0 5 5 10 +0 5 15 20 +10 15 15 30 +0 30 60 90 +30 60 120 180 +50 Methods of treating biologically degradable material according to the invention are exemplified in the following Examples: Example 1. Mixtures of finely divided, water suspended domestic refuse and/or feces with a dry solids content of 0.001, 0.01, 0.1, 1.0 and 0.5 per cent by weight, after being grafted with microorganisms, are degraded aerobically for 5 days at a temperature of 55600 C. The biologically degradable material will be degraded to over 90 per cent, in all of the cases. Water tests show that the content of coliform bacteria is zero (0) per 100 ml in all of the cases. Example 2. Mixtures of finely divided, water suspended household refuse and/or feces having a dry solids content of 1 per cent by weight are treated with lipases, amylases and proteinases, individually or in combination, in an amount of 0.001, 0.01, 0.1, 1.0 and 5.0 per cent by weight of the dry solids content of the slurry when the material is degraded for three days at a temperature of 55600 C. The biologically degradable material will be degraded to 97 per cent also with an enzyme amount of 0.001 per cent by weight. Water tests show that the content of coliform bacteria is zero (0) per 100 ml. The experiment is repeated but without any enzyme treatment. The amount of solid waste residues is considerably larger. In particular, the paper material of the waste has been degraded only to a small extent. Example 3. Example 1 is repeated. The content of coliform bacteria is zero (0) after degradation, but the filterability and the dewatering capacity of the treated waste is surprisingly low. The material is treated under agitation with an enzyme mixture according to Example 2. The filterability increases twentyfold to thousandfold. The filtrate is clear and pale yellow. Example 4. Cheese whey having a dry solids content of about 0.5 per cent by weight is degraded with aerobic and thermophilic microorganisms at 55600C for 5 days. The biologically degradable material is reduced by 80 per cent. Cheese whey is treated aerobically and thermophilically with an addition of enzymes as in Example 2. The biologically degradable material is now reduced by 95 per cent. Here, the time of degradation is 3 days. WHAT WE CLAIM IS:

1. A method of rapid and far-reaching microbial batchwise degradation of biologically degradable material which method comprises forming a slurry containing 0.001 to 15% by weight (dry solids) of the material in a finely divided state and added enzymes in an amount up to 5% by weight based on the weight of dry solids in the slurry and containing thermophilic microorganisms, and maintaining the slurry at from 50 to 700C whilst agitating the slurry and supplying oxygen containing gas thereto.

2. A method as claimed in claim 1

wherein the temperature at which the slurry is maintained is from 55 to 600 C.

3. A method as claimed in claim 1 or claim 2 wherein 0.1 to 1% by weight of enzymes based on the total dry solids of the slurry is added.

4. A method as claimed in claim 3 comprising adding the enzymes to the slurry before the microbiological degradation to initiate an enzymatic degradation of enzymatically degradable material prior to the microbiological degradation.

5. A method as claimed in claim 3 comprising adding the enzymes to the slurry during the microbiological degradation to initiate an enzymatic degradation of enzymatically degradable material during the microbiological degradation.

6. A method as claimed in claim 3 wherein the slurry defined in claim 1 is produced by carrying out a thermophilic microbial degradation of a finely divided degradable material in the presence of oxygen containing gas to produce a slurry containing material resistant to microbial degradation, adding enzymes in an amount up to 5% by weight based on the weight of dry solids in the slurry and carrying on an enzymic degradation to produce materials susceptible of microbial degradation by the thermophilic bacteria present.

7. A method as claimed in any one of claims 3 to 6, wherein the enzymes added are lipases, amylases and cellulases and proteinases, substantially in such a proportion as corresponds to the proportion between fats, sacchariferous and proteinaceous substances in the biologically degradable material.

8. A method as claimed in any one of claims 1 to 7, in which the agitation is interrupted periodically in an operating cycle comprising alternating idling and agitating periods.

9. A method as claimed in claim 8, wherein the ratio of each agitating period to each idling period is from 1:1 to 1:3 and each agitating period is 1/2 to 60 minutes long and each idling period is 1/2 to 120 minutes long.

10. A method as claimed in any preceding claim wherein the solids content of the slurry is from 0.1 to 5% by weight.

11. A method of batchwise treating biologically degradable material with microorganisms as claimed in claim 1 and substantially as hereinbefore described.

12. A method of batchwise treating biologically degradable material with microorganisms substantially as hereinbefore described in any one of the Examples.

13. A material obtained by treating a degradable material by the application thereto of a method as claimed in any one of claims 1 to 12.