CA1073731A - Biochemical process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A biochemical process is provided for the manufacture of a proteinaceous product, useful as a soil additive or as a feed supplement from animal waste and sewage sludge from municipal waste. The process comprises the aerobic microbial treatment of an aqueous suspension of animal waste and includes the introduction of oxygen into the process at a sufficient rate to obtain a maximum digestion rate and a maximum temperature of the aqueous suspension under treatment. Suitable rates are provided by introducing air at a rate of from 0.01 to 0.3 volume air per minute per volume of aqueous suspension under treatment. The suspension is also agitated thoroughly to ensure intimate mixing of the oxygen with the liquid, contributing to optimum thermophilic microbial activity. Preferably the reaction is maintained under adiabatic or near-adiabatic conditions thereby ensuring that the microorganisms that are congene ic in the waste adapt to and remain active at the high treatment temperatures which are employed. If necessary, any increase in pH during the fermentation can be neutralized by the addition of acid. The high temperature also effects pasteurization of the treatment liquid, thereby sterilizing pathogens present therein so that the microorganism cultures can be readily harvested to produce proteinaceous soil additives or feed supplement.

Description

BACKGROUND OF THE IN~ENTIOM
.

Field of the Invention:
This invention relates to a method for the treatment o animal waste and, in particular, to a method for obtaining a highly proteinaceous product which is useful as a soil lS an~andment or feed supplement.

Description of the Prior Art Animal wastes, which have traditionally been employed as crop fertilizers, are of dwindling value for this applica-tion because of the high cost of handling and applying these wastes. The increasing concern ~or protection of the environ-ment further complicates treatment and disposal of these wastes because of their odoriferous emissions and because water runoff from their storage areas contaminates the watershed, contri~
bu~ing to a high nitrate content in surface and underground waters, which can render these waters objectionable as a source of potahle water.
Heretoforel little effort has been expended in .

,-: . . , : - , , ~ ~
: ... . . . . . . . .

, :,~ , . . , . , ' `: - ' ' ~ , . . : ' , . : , , :
- : : . .,. . :

~ 17~'7~1 converting anlmal wa.stes/to useful products, despite th~
knowledge that these wastes can be utilized as a food and energy~source for microbial activit~. Recently some attempts have been made to treat the animal waste with thermophilic microorganisms under aerobic conditions to produce a protein-rich product as illustrated in U.S. Patent 3,462,275. While the aerobic microbial processiny of animal wastes appears an auspicious solution to disposal of ~uch wastes, particularly since it provides a source of proteinaceous material which could be used as a feed supplement and thereby reduce the con-sumption of cereal products by animals, its ~ull promise has yet to be demonstrated on a commercial scale. It is believed that the failure of prior attempts to find commercial applica-tion chiefly results from failure by prior investigators to is maximize process variables such as temperature and aeration rates.

SUMMAR~ OF THE INVENTION

, It has been discovered that aqueous suspension of animal wastes can be treated in an aerobic microbial process operating at relatively high temperatures with a thermophilic microorganism. The thermophilic microor~anism is, prefer~bly, congeneric in th~ wastes and is adapted or cwlditioned to the I relatively high temperature processing by an induction period I in the presence of a high oxygen concentration. In the process, an aqueous suspension of animal waste comprising from 40 to about 75, preferably from 50 to a~b~out 70, weight percent solids of decomposable organic matter is treated at a tempera-ture of at least about 50 C and, preerably, a~ lea~t !
.

, 10'~;~'7~
,, about 65 C. The processing is performed under adiabatic or near-adiabatic conditions and the temperature of the culture suspension is, preferably, the autogenetic temperature achieved in the processing. The a~ueous suspension of animal waste is aerated at an aeration rate of fxom 0.01 to about 0.3 volume air per minute per volume of liquid suspension. Preferably, the rate of aeration is adiusted to achieve a maximum pro-cessing temperature. The elevated temperature promotes rapid growth of single cell thermophilic bacteria which are desir-able protein sources. The high temperature also reduces thenecessary reaction time for the processing and pasteurizes the material under treatment, destroying any pathogens that may be present. The treatment also minimizes, or eliminates .
totally, odoriferous emissions from the processing, thereby rendering the process compatible for practice in populated areas. The process also permits centralized treatment of wastes, thereby permitting feedlot or dairy operations in confined areas and/or areas having limited access and not ~;
normally considered as useful for agricultural purposes.

BRIEF DESCRIPTION OF THE DRAWING

The preferred embodiment of the process is illus-trated with regard to the schematic ~low diagram of Fig l; and Fig 2 illustrates the thermophilic digestion 9tagç~0 "' ' ' ' '.

The process is provided with a supply o~ liquid manure in the form o~ a liquid suspe~sion o~ animal wastes .. ... ~ ......

.
- - ~

~'7~'~3~

~rom the various animal areas. Generaliy, the animal wastes will contain all of the nutrients for the growth and pr~paga-, tion of the aerobic thermophilic microorganisms as illustrated by the following table which summarizes the major nutrient contents:

TABLE I

Reported Nutrient Contents (weightpercent~ of Animal and Poultry Wastes NUTRIENT CA~ LE HOG SHEEP HORSE HEN
__ 10 Nitrogen 0.3-1.3 0.2~0.9 0.9 0.66 1.8-5,9 Phosphorus (P205) O.lS-0.5 0.14-0 83 0.34 0.23 1.0-6.6 Potassium (K~0) 0.13-0.92 0.18-0.52 1.0 0.68 0.8-3.3 .
In some instances, some nutrients such as sulfur~
magnesium, potassium, calcium, sodium, iron, zinc, copper, man-ganese, phosphorous or nitrogen can be added, in regulatedamounts, to ensure the optimum grow~h and propagation of the microorganisms. These nutrients can be added as water soluble salts. The pH value of the suspension will usually ~e slightly acidic~ e.g., a pH value of 5~5 to 7 and will not need adjust-ment. Vigorous growth of thermophilic bacteria occurs at pH
; values of 7 to 8 and it may be desired to add regulated amounts of acids such as phosphoric or hydrochloric acid or bases suoh as ammonia to adjust to optimum pH values. During the digestion, thè pH value of the liquid usually increases slightl~, to a final value of about 8 to 9, the result ofammonia and amino acid production.
The suspension is passed to a solids separation or concentration stage where the amount of suspended solids in l th2 liquid is adjusted o provide a suspen~ion for further ,i . " i . ,: .

. ~; . . . .

. .

processing that has a concen~ratlon of at least about 40 and pre~erably at leas~ about 50 weight percent. It has be~n found that the maximum digestion temperature and ~naximum propagation rates of the thermophilic microorganisms can be S achieved when the concentration of the solids is maintained from 50 to about 75 weight percent. The excess liquid which is recovered from the solids separation step can be passed to further processing by conventional secondary sewage treat--ment, e.g., to oxidation in an oxidation pond or treatmen~
in an acti~ated sludge process to reduce its quantity of finely sub-divided solid and dissolved organic matter.
The concentrated suspension o solids is passed into ~he thermophilic digestion stage where it is con~acted with an oxygen-containing gas, t~pically air, which is intro-duced at a high relative flow rate, typically from 0.01 toabout 0.3 volume air per minute per volume:of liquid. The preferred rate of air introduction is from 0. 02 to about 0.1 volumes per minute. It has been found that the rate of air introduction has a significant influence on the progress of the digestion. The air must be introduced a~ relatively high rates to achieve the growth of the desired thermophilic - microorganisms and to achieve the necessary temperatures for their growth. Conversely, an excessive rate of introduction of air will cool the liquid and prevent attainment of ~he desired elevated temperatures for propagation of ~he thermophilic m~croorganisms. The process can be regulated ., - to a maximum temperature rise by control of the rate of air introduction.

The liquid ~uspension i~ subjected to rapid agita-tion during the digestion stage to purge waste gases, typically 1 ' ' .
~ -6-. , .
-. . . . .

3~3~

carbon dloxidë, and to insurç intimate con~act of the oxygen introduced into the process with the microorganisms~ .
Under the aforedescribed conditions, the start-up of the process will require an induction phase for the development of the necessary concentration of the thermo-philic microorganisms to ensure, a rapid treatment of the waste. The, types of bacteria which are present in the animal wastes and the optimum temperature range for ~heir propaga~ion is set forth in the following~table:

.
~BLE I I

BACTERIA TYPE OPTIMUM GROWTH TEMPERATURE
Psychrophilic ~ '15-20 C
Mesophilic30-37 C
Thermophillc55-6.5 C

15. The digestion is preferably practiced under adiabatic or near-adiabatic conditions with the energy released duri~g the aerobic digestion being retained in the process and contributing to the lncrease in temperature of ' ' the liquid suspension. The temperatures which can be ob-;. 20 tained in the process and which are preferred for the de-` sired proc~ssing are at le~st about 50 C, and, preferably, at least about 60 C. Desira~l~, t~e process is operated s . to maximize the temperature increase and the rate o~ air introduction an~/or agitation of the liquid suspen~ion under-going digestion is controlled to achieve this maximum temper-` ` ature inGrease, The maximum temperature which can be achieved '' i ` in this processing is usually about 75; however, operable '. ' temperatures ~s high as 88 degree~ C have been achieved in ., .

-7-~ .
~ .
. - ;.............................. . .
~" '''' ' ' .

, .

~ 3'7~
.. .. ..., ~ , ..
in some instances.
The residence time of the liquid suspension in the digestion phase is minimiæed b~ the high di~estion temperature and the thermophi~ic aerobic processing. When batch processing is employed, with the necessary induction period ~or develop-ment of a sufficient population of thermophilic bacteria, the processing can be completed in about 15 days or less. The continuous processing of the waste, which would include in-noculation of the incoming wastes with an active culture of the thermophilic bacteria at a rapid growth stage, can reduce this processing time somewhat, thereby minimizing the capacities and sizes of processing vessels.
The thermophilic bacteria which are active under the aforedescribed conditions include gram-positive, rod-shaped cells and gram-negative, rod-shaped cells. The development of these bacteria and the course of a typical thermophilic diges-tion is set forth by the data in the following table of the concentration of colony-forming units per milliliter of ~acteria in samples withdrawn from a thermophilic digestion at the : .
indicated time and temperature~

TAB LE I I I
`~ Sampled after- PSYCHROPHILES MESOPHILES THERMOPHILES
. . ~ _ , 4 days at 44 C* 2.1 x lO~1.2 x lO9 ~.2 x 106 14 days at 54 C 7.7 x 1045.1 x 106 3 x 108 ~Temp-rature at ~he time of sampling - ~ ;

` The preceding data evidence the decreasing concentra-"~ tion of the psychrophilic and mesophilic bacteria and the concurrent, rapid increase in thermophilic bacteria which results from~~processing at the aforedescribed conditions . ' ' ' . . ' ' .
. .. . .

; . ~ . . .
: .~. .. . ~

1iO~7~
of high solids concent~tion, near-adiabatic condit;ons, high aeration ~ates and rapid agitation o~ the solid suspensipn during processing.
During the processing, fresh li~uid suspension of animal waste can be continuously added, displacing a con~
_ . .
tinuous over-flow of treated liquid from the processing. The li~uid can be screened, filtered or centrifuged to recover the bacteria and the clarified liquid can be processed in the same manner as described for the excess liquia processing removed in the solids separation step, uslng conventional secondary and tertiary sewage treatment to obtain an efluent .. .... _ .
acceptable for return to the environment.
The solids recovered from the processing as a liquid s'uspension can be treated to obtain the high protein '~ 15 feed supplement. The solids are concentra~ed by dewatering using various processing equipment such as'a centrifuge, - vibrating screen t~pically of about 100-225 mesh~ or the ' like to reduce their moisture content to an optim~m level' for processing in the sludge drying step. The supernatant liquid separated during the dewatering step can be further pxocessed by solids separation treatments such as filte~ing, - centrifuging and the like to obtain a more complete recovery ~ of solids. This can be particularly val'ua~lewhen seeking ;~ production of a protein-rich feed supplement since the fine colloidal 501ids, which pass through a scresning step, have the hîghest protein concen~ration. Such urther ~olids separ-ation~also reduces the loading on the secondary treatment facilitles~u~ed to process the separated liquid. Generally it is desirable to reduce the water conten* of the solids $o / ' 30 a maximum of about 75% moi~ture. Although higher moigt~re . .

-9-~ .
; ,. . : , , ~ ' ' .
- ~ .

~, :... ' ''' " ,, .:

3~

, content solids can be dried, higher moisture contents are generally not economically processed because o the high fuel requirements for drying.
The dewatered solids obtained from the centri~uging and/or screening treatment are passed to a dryer which can be a rotating drum dryer that receives hot combustion gases from burning of natural gas or other fuel. The solids are tumbled into contact with the hot gases during their transit through the dryer and the product from the dryer can be discharged into a suitable so3ids-gas separation facility such as a cyclone separator and the like. Part of the gas effl~ent from the c~clone separator can be recycled to the inlet of the dryer while the remainder can be exhausted after suitable treatment to remove any r~sidual, entrained solids. Typically the gas can be passed through a wet scrubber using fresh water or a clarified effluent from the secondary sewage treat-.
ment facilities. The dried solids can be conveyed to asuitable bulk storage area and packaged for shipment as a degraded animal waste useful for animal feed rations.
.. . . .
! 20 It has been ound that the degraded animal wastes ! ., , . . , . ~
processed in accordance with this invention are acceptable feed supplements which can be used to replace from 5 to about 1 ' ., ,~ 20 percent o cereal products in an animal or poultry diet, , Pre~erably the degraded animal wastes are employed at con-~5 centrations o rom 5 to ab~u~t lQ percent based on the dry weight o~ the cereal products in diet.
- Referring now to Fig 2, there is illustratPd a typlcal digestion processing sequence. The liquid ~uspensio~
~¦ of animal waste is supplied to vessel 10 through line 14.
Pump 12, whi~ ca~ be a positive displacement pump, pre~erably `I . ' , ' ' ~:
,, , , , ~10-- . ' ' -: , . .

' ' .

:~ , _ . . .. . . ...... .... .... .... .. .
. ~

~ 0'7~73~
a Moyno-type helical displacement pump,~removes the liquid suspension from vessel 10 and passes it through li~e 16 to a screening apparatus 18 that can be used to control the con~
centration of the suspension introduced into the digestion vessel 20, The screening apparatus 18 is operated to in-crease the solids concentration in the suspension to a level from 50 ~o about 75 weight percent, thereby ensuring optimum concentration for processing.
The concentrated suspension is introduced into the first of a series of digestion vessels 20, 24, 26 and 28.
The separated liquid removed from the screens 18 can be .. . . ...
- passed through line 22 ~o a secondary and tertiary treatment to obtain a liquid ef~luent for retuxn to the environment.
The plurality of digestion vessels can be operated in batch l 15 or continuous series flow. Whan operated in series flow, the `l sizes of the digestion vessels can be varied to obtain reten tion times that provide the typical distribution of successive ~ temperatures of 15, 55, 65 and 65 degrees C in these vessels, I as indicated in F~gure 2. The vessels are preferably insu~ated `1 20 to minimize heat loss and for this purpose, ~uitable insulation is installed around the sides and bottom of the vessels.
Duxing the processing, a blanket of foam forms on the suxface of the liquid undergoing trea~ment and this foam adequately insulates the liquid and minimizes heat losses therefrom. In some instances it may be desirable to minimize the amount of foam by the addition of defoamin~ agents such as various conventional silicon de~oaming additives or, preferably, ~iodegradable materials such as vegetable o~ls ` and the like.
3~ Tho liquid suspension is su~jected ~o rapid agita~ion ' i: .

'7373~

in the diges-ti~n vessels, ~nd, for this purpose, each of the vessels i5 furnished with a mixing apparatus such as a pro-peller or turbine mixer generally indicated at 38, 40, 42 and 44. Air is introduced through line 46 and branch lines 48, 50, 52 and 54 at metered quantities into each of the digestion vessels to maximize the temperature within each of these vessels.
During the continuous processing, the overflow from vessel 20 is passed to the succeeding vessel 24, displacing suspension therefrom to the succeeding vessel. The final digester 28 is maintained at an adequatè temperature to en-- sure pasteuri~ation of the product and eliminate any pathogens, viruses or parasites that may be present in the animal waste received by the process. The final product of the digestor 28 i5 is passed to a holding tank 30 from which it is withdrawn and l pa~sed to the dewatering, sludge drying and packaging staps i pxeviously described.
1 Typical protein contents of the processed animal I and poultry wastes obtained from the process of the in~ention are set for~h in the following table:
.

~ABLE IV

PROTEIN CONTENT, WEIGHT
SOURCE P~R OEN5 DRY K~IGHT ~GI6 Poultry 11" 7 - Swine 6.3 Beef 6.2 Dairy 5-3 , - .

.

, . . . .

~0'73~
The followin~-~table au~narizes. the amino acid analyses o~ the wastes processed by the invention;

TABLE V
AMINO ACID CONTENT OF THERMOPHILIC DIGESTED ANIMAL MATE:RIAL.
.

Amino Percent Amino Aclds Acids SwinePoultry Bovine Lysine .243 .225 .197 Histidine - - ~
Arginine .193 .206 .134 Aspartic Acid.461.505 .417 . Threonine .207 .218 .212 `/ Serine .230 .251 .215 Glutamic Acid.566.641 .444 Proline .261 .155 ~.146 ~lycine .340 .356 .234 l Alanine .394 .406 .293 ¦ Valine .339 .295 ~ .269 . Methionine -. .3~2 Isoleucine .236 .246 . .188 Leucine .392 .~30 . .315 . Tyro~ine .143 ~125 - .114 Phenylalanine.181.197 .164 , . The processed wastes also contain a significant amount o~ Vitamip B12 and are~ for this reason a1so, a valuable animal feed supplement.

~ .
``,; ~ ~ . ' ' ' ~, ' ' ' .
' ' ' -13~.

'~ ' . ` ' ' .

1~)''~3'73~

The invention has been described with reference to the illustrated and presently preferred embodiment thereof.
It is not intended tha~ the invention be unduly restricted . ~ .
i by this disclosure of presently preferred embodiments. In-li stead, it is inteindéd that the invention be defined by the steps and reagents~ and thelr obvious equivalents, set forth in the ollowing claims: i 5; ' : ?. ~; ', : ;

.~ ~ ' . 1 ... .

.
'` . ' ' '' 'i ' ' '` ' ' ~, ' '', ~ ' ' , ~

i . , !

- 1()73731 SUPPLEM~NTARY DISCLOSUR~

The invention heret~fore disclosed is specifically applicable to the treatment of human wastes and municipal sewage sludge.
The treatment and disposal of sewage sludge, which is a produc~ der-ived from the organic and inorganic material removed from the wastewater pro-cessed at sewage treatment plants, is currently one of the sewage plants' great-est problems. The nature of the sludge depends on wastewater sources and the method of treatment. With an increasing demand for more complete treatment of wastewater, the problem will be accentuated in the future.
Apart from the treatment difficulties, there is the everincreasing pro-blem of sludge disposal. Many municipal treatment plants utilize the sludge for methane gas production, only to be confronted with a disposal problem of the residual product. Incineration is considered by some authorities, while others seek a solution through land spreading, and some unfortunately still practice a water disposal method.
Dewatering, drying and fortifying municipal sludge with suitable chemicals provides a good method of disposal as a soil ferti].iæer amendment. While this ;~
system of recycling converts a waste material into a useful and beneficial pro duct, the conversion of a sludge waste into a beneficial source of nutrient for ~ ;
animal feed material is more attractive economically than utiliæing it for a soil fertilizer. In a short food supply situation, the possibility of convert~
ing sewage to a nutritious single cell protein feed for animals is most desir-able.
Current methods of sewage sludge treatment are not entirely suitable.
~ewage sludge within municipal treatment works is commonly digested under an-aerobic condition, to produce methane, carbon dioxide and a stabilizer sludge.
The gas produced has a high calorific heat value (700-750 BTU/ft3) which may be used for heating the digester and the surplus for auxiliary power production.

Normally, under suitable conditions, the gas production is averaged at 1 ft per capita day. The overall yield of gas as an energy source is not economic-ally attractive, particularly in cold climates, where additional energy is con-sumed to heat the anaerobic digesters~ The problem of sludge disposal, although ~' ~ ' ~i.

~ , :

~Lo737~

diminished in volume, still remains unsolved.
The method of the present invention has been found to be applicable to municipal sewage sludge. Thus the invention also provides a method for the treatment of sewage sludge comprising; aerating said sludge, in the presence of thermophilic bacteria normally occurring therein, under thorough continuous agitation, with sufficient air to satisfy the high BOD5 and COD demands of the sludge, while allowing the sludge -to achieve and maintain a temperature of from 50C. to about 80C. over a processing period of from 10 to 25 days; separating solid material suitable for use as a proteinaceous animal feed supplement.
EXAMPLE
Several fermentation batch tests were carried out with primary seteled municipal sludge. A 50 ft3 insulated fibre glass tank, equipped with a mechanical aerator and stirrer, served as the digester. The raw sludge was pumped into the digester and diluted with fresh water to reduce the viscosity to a point where adequate stirring and aeration could be maintained. The thickened raw sludge required dilution only for adequate aeration and mixing, excessive dilution will reduce the value of the substrate nutrient and increases the heating demand unnecessarily.
The sludge did not require an inoculation of bacterial seed. Normal sludge apparently possesses sufficient thermophilic bacteria requiring only aeration and thorough, continuous agitation. The temperature rise of the mixed liquor and suspended solids (MLSS) was rapid in the initial stages of fermentation. It is important at this stage to provide ample aeration to satisfy the high demand for dissolved oxygen in the oxidation process.
The biochemical oxygen demand (BOD5) and the chemical oxygen demand (COD) show a rapid oxidation rate during the first ten to twelve days of fermentation. This sludge may reach a temperature of from 60C. to about 75C.
;~

^~: 10~73~3~

During the fermentation process the microorganism5 create an alkaline condition with a corresponding increase ln pH value. An attempt to control the pH by the addition of hydrochloric acid was carried out when the substrate reached an 8.7 pH value. The pH was lowered but the bacterial activity was also reduced for several days.
The results of such treatment on diluted sewage sludge are shown ; below in Table VI:

TABLE VI
CONCENTRATED SLUDGE
Raw Sewage ll days 25 days initial Temp. ~C. 56C. 23 ~C.
p~ 6.1 8.39 3.20 .

,.

17 ``

:

.
~.

~ . . . . .

~ 3'73~
BOD5 ~14,000 mg/l 2,600 mg/l 1,300 mg/l COD 60,698 mg/l 32,642 mg/l 18,320 mg/l Total Res. 45,690 mg/l 38,280 mg/l 19110 mg/l Vol. Sol. 29,620 mg/l 2~,740 mg/l 13,760 mg/l Fxd. Res. 16,070 mg/l 13,540 mg/l 5,350 mg/l Total P. 310 ppm 330 ppm 270 ppm Total N. 1,140 ppm 700 ppm 990 ppm Cr. Protein %* 14.34 13.5 12.89 Organic N 980 ppm 295 ppm 495 ppm N03-N ~ 2 ppm - <2 ppm NH3-N 200 ppm 455 ppm 495 ppm Pb 3.0 ppm - 3.8 ppm Zn 2.5 ppm - 4.2 ppm Cu 3.1 ppm - 4.4 ppm * Crude Protein; calculated as T-N X 6.25 Substrates with a high content of oxidizable organic matter are suit-able for biological stabilization by aerobic bacteria may yield 7.87 KCal per ~;
gm of carbon oxidized to C02. The oxidation of hydrogen to water may yield 34.15 KCal per gm of hydrogen oxidized to H20. A part of the energy is ut-ilized by the bacteria for the assimilation of new cell substance while the remainder raises the temperature of the substrate medium. The increased temp- -erature accelerates the biochemical reaction necessary for biological stabil-ization.
At the completion of the fermentation period the MLSS was pumped out and sieved by a "Sweco" screen. The solids were divided into those retained on a 30 mesh and 150 mesh screens, respectively. The liquid passing through the 150 mesh screen was subjected to a force of 2755XG in a basket centrifuge to obtain the residual solids.
Each of the solids separated was oven dried to obtain the yield of material. The size of particles in each case were determined by microscopic analyses to eveluate the efficiency of the separation processes.

` ,~

~'7373~
TABLE VlI

YIELD OF_PROCESSED SLUDGE

Sieve Si~e % Wet Wt. % Dry Wt.% Cr Prvtein .
Dr~J Wt.

15.05 1.27 9.2 150 1.82 0.62 4.0 ~150 (CentriEuged - 0.167 26.0 Solids) Supernatant - 0.12 41.0 Particle Size u .

150 15-200 ,u C150 15-150 ~
The solids recovered from the screening and centrifuging processes are suitable for incorporation into animal feed rations.
It is clear therefore that municipal sludge can be processed satis-factorily by the process of an aspect of this invention using aerobic therm-ophilic bacteria. The resulting product may be used for an animal feed sup-plement. The processed sludge is substantially odorless, fine grained, and is substantially free from pathogenic organisms. It is not necessary to intro-duce an inoculum and a continuous fermentation process maintains a more rapid oxidation of the carbonaceous substrate. The thermophilic process of an aspect of this invention provides a suitable solution to the disposal of mun-icipal sludge materials.
By this invention, therefore, the fermentatlon of organic sewage sludge produces single cell protein. The aerobic thermophilic bacterial process dis-closed herein provides a route to achieve single cell protein production from such waste material. The process, due to its high operating temperature, (55 to about 75 C.) permits a sterilizing effect on pathogenic organisms, and re-duces the processing detention time considerably.
The invention has been described with reference to the illustrations and presently preferred embodiment thereof. It is not intended that the in-~9 ~

~, ~ - ' ' :

~0'~ 3~

vention be unduly restricted by the steps and reagents, and their obvious ; equivalents, set forth in the following claims:

~ ' .

,, . . .:~
~0 ~'.

.' ;"~.

:' ... , . .. . . . . ~ .

Claims (12)

What Is Claimed Is:

1. A method for the treatment of animal wastes which comprises contacting an aqueous suspension of from 40 to about 75 weight percent animal wastes solids with air, with an aeration rate of from 0.01 to about 0.2 volumes air per minute per volume of aqueous suspension while main-taining said suspension under substantially adiabatic condi-tions to obtain a maximum autothermic increase in temperature of the suspension and achieve a temperature of from 50° to about 88° C. over a processing period of from 10 to about 18 days, and withdrawing from the process a liquid suspension of thermophilic bacteria suitable for drying and processing as an animal feed supplement.

2. The method of Claim 1 wherein air is introduced at an aeration rate of from 0.02 to 0.1 volumes per minute per volume of suspension.

3. The method of Claim 1 wherein said liquid sus-pension is subjected to rapid agitation during said contact-ing.

4. The method of Claim 1 wherein the temperature of said suspension increases to a value from 60° to 70° C.
during said processing.

5. The method of Claim 1 wherein said product of said digestion is dewatered to obtain a solid having a moisture content no greater than about 75 weight percent which is dried for production of a dried solid therefrom.

6. The method of Claim 1 wherein said suspension contains from 50 to about 70 weight percent solid animal wastes.

7. The method of Claim 1 including the step of adjusting the pH of said suspension to a value from 6 to about 8 prior to said contacting.

8. The method of Claim 1 including the step of adding a defoaming agent to said suspension.

CLAIMS SUPPORTED BY SUPPLEMENTARY DISCLOSURE

9. A method for the treatment of sewage sludge containing a high content of oxidizable organic matter which comprises; aerating said sludge, in the presence of thermophilic bacteria normally occurring therein, under thorough continuous agitation, with sufficient air to satisfy the high BOD5 and COD demands of the sludge, while allowing the sludge to achieve and main-tain a temperature of from 50°C. to about 80°C. over a processing period of from 10 to 25 days; separating solid material suitable for use as a protein-aceous animal feed supplement.

10. The method of Claim 9 wherein the temperature is from 55° to 75°C., sufficient to permit a sterilizing effect on pathogenic organisms.

11. The method of Claim 9 including the step of maintaining the pH
below 8.7.

12. The method of Claim 9 including the final steps of screening the fermented medium; centrifuging the screened product to obtain residual solids;
and drying solids; thereby to provide substantially colourless fine grained particles substantially free from pathogenic bacteria.