Process for thermophilic aerobic fermentation of organic waste

A thermophilic, aerobic fermentation process is disclosed for conversion of a wide variety of organic waste materials to useful end products. The fermentation process is initiated over a period of from about 2 to 6 days by application of external heat to an uninoculated, oxygenated aqueous mixture of the waste material, and thus utilizes thermophilic microorganisms naturally present in the waste material to initiate the fermentation. After initiation of an active fermentation, additional amounts of waste material are added to the fermenting mixture on a continuous or intermittent basis to maintain the fermentation in an active state. Therefore, the process can be conducted on a continuous or semi-continuous basis, requiring about 24 to 48 hours for waste to be completely converted to end product. The process is capable of being operated over a wide pH range and can ferment acidic waste materials without the need for pH adjustment. The process converts waste matter such as food waste and fecal matter into a protein enriched end product suitable for use as an animal feed, feed supplement or fertilizer, fertilizer ingredient, soil amendment or soil conditioner free of pathogens, biological contaminants and chemical contaminants such as antibiotics.

FIELD OF THE INVENTION 
This invention relates to a commercially viable process for converting 
organic waste from various sources to useful end products by a 
thermophilic, aerobic microbiological fermentation process, more 
particularly a fermentation process which is initiated without inoculation 
with thermophilic microorganisms and in which external heat is applied to 
achieve and maintain thermophilic temperatures. 
BACKGROUND OF THE INVENTION 
It is well known that the disposal of organic waste materials, for example 
animal and food wastes, is becoming increasingly difficult and expensive. 
As a way to avoid the difficulties in disposal of organic waste materials, 
fermentation processes have been developed to chemically modify these 
wastes into useful end products, such as animal feeds, feed supplements 
and fertilizers. 
In general, such fermentation processes are conducted in the presence of 
oxygen at elevated temperatures, preferably in the range of from about 
50.degree. C. to about 80.degree. C. Microorganisms which grow and 
proliferate in this temperature range and which preferably are largely 
responsible for fermenting the waste material are known as "thermophilic" 
microorganisms or "thermophiles". Aside from chemical modification of the 
waste material by the thermophilic microorganisms, it is generally known 
that the heat generated by fermentation processes conducted in this 
temperature range is capable of providing a "pasteurization" effect by 
destroying pathogens and other undesirable biological contaminants present 
in the waste material. This pasteurization effect is desirable since it 
increases the safety of the end product, whether used as a fertilizer or 
food stuff. 
One example of a known process for thermophilic fermentation of animal 
waste is disclosed in U.S. Pat. No. 3,462,275, issued to W. D. Bellamy. In 
the Bellamy process, animal fecal matter is inoculated with 
thermophilically active microorganisms obtained from sources such as 
compost piles or hot springs, and is then heated by an external heat 
source to thermophilic fermentation temperatures in a thermophilic aerobic 
growth chamber. After fermentation of the inoculated waste by the 
thermophilic microorganisms, a fermented product is obtained which is 
separated into solid and liquid components by centrifuging and filtering. 
The liquid is disposed of by conventional means while the solid portion is 
dried and packaged for use as an animal food stuff. 
One disadvantage of the Bellamy process is that inoculation of the waste 
material with thermophilic microorganisms may be problematic. For example, 
microorganisms obtained from external sources for the purpose of 
inoculation may not be compatible with the waste matter being fermented, 
thus requiring careful process control. For example, pH adjustment of the 
fermenting mixture to within a narrow range at which the microorganisms 
proliferate and/or nutrient supplementation may be required. Also, 
inoculation requires the addition of one or more steps to the overall 
process. 
Therefore, inoculation of the waste material with thermophilic 
microorganisms is preferably avoided. However, it has generally been 
accepted that thermophilic microorganisms are not naturally present in 
waste materials in sufficient quantities to initiate or sustain 
thermophilic fermentation. 
Another known fermentation process is described in U.S. Pat. No. 4,292,328, 
issued to Coulthard et al. The Coulthard patent describes a thermophilic, 
aerobic fermentation process for converting a wide range of organic waste 
materials into animal feeds, feed supplements and fertilizers. Although, 
like the Bellamy process, inoculation is fundamental to the Coulthard 
process, it is disclosed in Coulthard that microorganisms naturally 
present in the waste material may be used to initiate and maintain an 
active fermentation. 
Since the waste material is at ambient temperature before initiation of the 
fermentation, the microorganisms naturally present in the waste material 
in the greatest number are those which grow and proliferate at 
temperatures of from about 0.degree. C. to about 30.degree. C. These 
microorganisms are referred to as "psychrophilic" microorganisms or 
"psychrophiles". The Coulthard process initiates the fermentation by 
introducing the waste material into a thermally insulated fermenter as an 
aqueous slurry, and vigorously agitating and oxygenating the mixture at 
ambient temperatures to promote the growth of aerobic, psychrophilic 
microorganisms. 
As fermentation begins at ambient temperature, psychrophilic microorganisms 
metabolize substrates present in the waste material and liberate heat, 
thereby gradually raising the temperature of the fermenting mixture out of 
the ambient temperature range to slightly elevated temperatures between 
ambient temperatures and thermophilic temperatures. As the temperature 
increases, the psychrophilic microorganisms are gradually replaced by 
"mesophilic" microorganisms or "mesophiles" which grow and proliferate at 
temperatures of from about 20.degree. to about 50.degree. C. 
Fermentation by the mesophilic microorganisms gradually raises the 
temperature into the thermophilic range of from about 50.degree. to about 
80.degree. C., at which thermophilic microorganisms proliferate. 
Therefore, the Coulthard fermentation process is dependent on a succession 
of microorganisms to slowly raise the temperature over a period of about 
two or more days from ambient to thermophilic temperatures in which the 
desired thermophilic microorganisms grow and proliferate. This succession 
of microorganisms involves a progressive and successive change in the 
profile of the microorganisms from mainly psychrophiles to mesophiles, and 
then to thermophiles, effected by simultaneous aeration and agitation of 
the fermenting waste. 
It would be expected that using an external heat source to rapidly heat 
uninoculated waste matter to thermophilic temperatures would preclude this 
succession of microorganisms and would result in the thermophilic 
fermentation process being initiated either very slowly or not at all. 
Raising the temperature to the thermophilic range would permit growth 
primarily only of thermophiles, which as discussed above are generally 
considered to be present in the unfermented waste material in much smaller 
numbers than psychrophiles. 
The inventors have found that promoting a succession of microorganisms as 
in the Coulthard process is disadvantageous in that the waste material is 
at least partially fermented by microorganisms other than thermophilic 
microorganisms, primarily during the initial stages of the process before 
the temperature has risen into the thermophilic range. Some of the 
microorganisms which proliferate at lower temperatures may cause 
contamination and/or poisoning of the waste material. Furthermore, 
fermentation at lower temperatures allows the continued growth and 
proliferation of pathogens present in the waste material. 
Specifically, control over the fermentation in the Coulthard process is 
minimal, particularly during the initial stages. For example, the 
Coulthard process may not lead to establishment of thermophilic conditions 
at all or maintenance of a thermophilic fermentation if initiation is 
achieved. This is at least partially due to the fact that fermentable 
substrates may be completely utilized prior to establishment of 
thermophilic conditions. Furthermore, the fermentable substrates may be 
utilized by psychrophilic or mesophilic microorganisms which may preclude 
the growth of thermophilic microorganisms through production and 
liberation of toxins or poisons, such as growth inhibitors and 
antibiotics, in the fermentation medium. 
Therefore, the disadvantage exists that no thermophilic, aerobic 
fermentation process is known which avoids the use of inoculation with 
thermophilic microorganisms and which promotes growth and proliferation 
only of thermophilic organisms. 
Even though the Coulthard fermentation process utilizes microorganisms 
occurring naturally in the waste matter, it is still somewhat pH 
sensitive. For example, in order to ferment acidic waste materials such as 
wastes from fruit and vegetable processing, which typically have a pH in 
the range of about 3.8 to about 4.4, Coulthard teaches the addition of a 
pH adjusting agent to raise the pH into a more neutral range. 
Therefore, the additional disadvantage exists that no aerobic, thermophilic 
fermentation processes are known which do not require careful monitoring 
of process pH and the addition of pH adjusting agents. 
SUMMARY OF THE INVENTION 
To overcome the disadvantages of the prior art discussed above, the present 
invention provides a process for thermophilic, aerobic fermentation of 
organic waste which is initiated by application of external heat to an 
oxygenated aqueous mixture of uninoculated waste matter. 
The inventors have surprisingly found that a thermophilic fermentation can 
be initiated by application of heat to an uninoculated aqueous mixture of 
waste matter, thus promoting the growth and proliferation primarily only 
of thermophilic microorganisms in the waste matter. Although external 
heating of the uninoculated waste matter precludes a succession of 
microorganisms from being produced, the inventors have found that the 
thermophilic fermentation may be completely initiated in a period of from 
about 2 to about 6 days. 
Subsequent to initiation, the present invention preferably also provides a 
semi-continuous or continuous process for fermentation of waste matter 
which is capable of fermenting a wide range of waste materials over a wide 
pH range. In the semi-continuous or continuous fermentation of the present 
invention, relatively small volumes of uninoculated waste matter is fed 
intermittently or continuously into an active fermentation, and fermented 
product is removed intermittently or continuously from the active 
fermentation. Preferably, the volume of the active fermentation is 
completely turned over once about every 24 to 48 hours. 
Furthermore, because the fermentation process of the present invention is 
not initiated by inoculation, it utilizes thermophilic microorganisms 
naturally present in the waste material, which are more compatible with 
the waste material than microorganisms introduced by inoculation. 
The inventors have also surprisingly found that the process of the present 
invention is relatively insensitive to the pH of the waste material and 
operates over a wide pH range. In fact, the inventors have found that 
almost all types of food, animal and lignocellulosic wastes may be 
fermented by the process of the present invention without the addition of 
pH adjusting agents. 
In particular, the inventors have found that the present process does not 
require the neutralization of acidic waste matter, such as fruit and 
vegetable processing waste, thus making it adaptable to fermentation of a 
wide variety of waste materials without the need to carefully monitor and 
adjust pH. 
By reason of the improvements of the process of the present invention over 
previously known processes, the process of the present invention may be 
used on a commercial basis to quickly and efficiently convert a wide range 
of waste matter into a useable end product, such as animal feed, animal 
feed supplements, fertilizers, fertilizer ingredients, soil conditioners 
or soil amendments. 
Preferably, when used as a commercial process, the process of the present 
invention is operated on a continuous or semi-continuous basis. The 
inventors have found that operation of the process on a continuous or 
semi-continuous basis provides improved control over the fermentation. 
Specifically, operation on a continuous or semi-continuous basis ensures 
that a thermophilic fermentation will be maintained by supplementation of 
the active fermentation with a continuous or semi-continuous supply of 
fresh substrate to preferably maintain the fermentation in a steady state. 
Maintaining the thermophilic fermentation in a steady state ensures that 
there will be minimal competition for fermentable substrates by other 
competing microorganisms, thereby reducing the chance that the 
fermentation will be suppressed or inhibited by competing microorganisms. 
It is one object of the present invention to provide initiation of a 
process for conversion of waste matter to a useful end product by 
thermophilic, aerobic fermentation of the waste matter wherein external 
heat is applied to uninoculated waste matter, such that the process is 
initiated by thermophilic microorganisms naturally occurring in the waste 
matter. 
It is another object of the present invention to provide a process for 
conversion of waste matter to a useful end product by thermophilic, 
aerobic fermentation of waste matter, the process being initiated by 
application of heat to uninoculated waste matter, such that the process is 
initiated by thermophilic microorganisms naturally occurring in the waste 
matter. 
It is yet another object of the present invention to provide continuous and 
semi-continuous processes for conversion of waste matter to a useful end 
product by thermophilic aerobic fermentation of the waste matter. 
It is yet another object of the present invention to provide a process for 
conversion of waste matter to a useful end product by thermophilic aerobic 
fermentation of the waste matter, the process being operated at acidic pH. 
It is yet another object of the present invention to provide a process for 
conversion of waste matter to a useful end product by thermophilic aerobic 
fermentation of the waste matter, wherein the process is capable of 
destroying chemical contaminants present in the waste material. 
In one aspect, the present invention provides a process for conversion of 
organic waste matter to an end product by thermophilic, aerobic 
fermentation of the waste matter by thermophilic microorganisms naturally 
occurring in the waste matter, the process being initiated by steps of: 
forming an aqueous mixture of the waste matter; heating the mixture, with 
heat from an external heat source, to a temperature suitable for growth 
and proliferation of the thermophilic microorganisms; and oxygenating the 
mixture at the temperature by continuously introducing oxygen into the 
mixture to maintain an oxygen concentration in the mixture sufficient for 
growth and proliferation of the thermophilic microorganisms. 
Preferably, the waste matter is selected from the group comprising animal 
fecal matter, bakery product waste, waste derived from fruits and 
vegetables, food wastes derived from animals, tannery waste, leaves, 
weeds, trees, shrubs, and wood refuse. 
Preferably, the end product is selected from the group comprising animal 
feeds, animal feed supplements, and fertilizers, fertilizer ingredients, 
soil conditioners and soil amendments. 
Preferably, the waste matter is mechanically macerated to a particle size 
of from less than about 1 mm to about 5 mm prior to or during the step of 
forming the aqueous mixture, and the aqueous mixture contains from about 5 
percent to about 20 percent total solids by weight. 
Preferably, the process is initiated over a period of from about 2 to about 
6 days at a temperature of from about 55.degree. to about 80.degree. C. 
and an oxygen concentration maintained at about 0.2 ppm or higher. 
Preferably, the initiation is complete when the fermentation reaches a 
steady state at which a rate of the fermentation is substantially constant 
and a portion of the waste matter has been converted to the end product. 
In another aspect, the present invention provides a process for conversion 
of organic waste matter to an end product by thermophilic, aerobic 
fermentation of the waste matter by thermophilic microorganisms naturally 
occurring in the waste matter, the process comprising: (a) initiation of 
the fermentation by steps of: (i) heating an aqueous mixture containing 
the waste matter in a fermentation vessel, with heat from an external heat 
source, to a temperature suitable for growth and proliferation of the 
thermophilic microorganisms; (ii) oxygenating the aqueous mixture at the 
temperature by continuously introducing oxygen into the mixture to 
maintain an oxygen concentration in the mixture sufficient for growth and 
proliferation of the thermophilic microorganisms, the initiation being 
continued until the fermentation reaches a steady state at which a rate of 
the fermentation is substantially constant and a portion of the waste 
matter in the aqueous mixture has been converted to the end product; (b) 
continuing the heating and the oxygenating of the aqueous mixture; (c) 
adding to the fermentation vessel additional quantities of an aqueous 
mixture of the waste matter; and (d) removing from the fermentation vessel 
quantities of the aqueous mixture containing the end product, such that 
growth and proliferation of the thermophilic microorganisms is maintained 
in the fermentation vessel during steps (b), (c) and (d). 
Preferably, the steady state of the fermentation is maintained during steps 
(b), (c) and (d), at a temperature maintained in the range of from about 
55.degree. C. to about 80.degree. C., and an oxygen concentration is 
maintained in a range of from about 1 ppm to about 5 ppm during steps (b), 
(c) and (d). 
Preferably, step (c) comprises intermittently adding to the fermentation 
vessel additional quantities of an aqueous mixture of the waste matter, 
and step (d) comprises intermittently removing from the fermentation 
vessel quantities of the aqueous mixture containing the end product. 
Preferably, the fermentation vessel comprises a primary fermentation vessel 
which is connected to a secondary fermentation vessel, and step (d) 
comprises transferring quantities of the aqueous mixture containing both 
the waste matter and the end product to the secondary fermentation vessel, 
and substantially completing the fermentation in the secondary 
fermentation vessel, the process additionally comprising: (e) heating the 
aqueous mixture in the secondary fermentation vessel, with heat from an 
external heat source, to maintain a temperature therein suitable for 
growth and proliferation of the thermophilic microorganisms; (f) 
oxygenating the aqueous mixture in the secondary fermentation vessel by 
continuously introducing oxygen into the mixture to maintain an oxygen 
concentration therein sufficient for growth and proliferation of the 
thermophilic microorganisms; and (g) removing from the secondary 
fermentation vessel quantities of the aqueous mixture containing the end 
product and containing substantially no unfermented waste material, 
wherein the fermentation in the secondary fermentation vessel is 
maintained at a steady state at which a rate of the fermentation is 
substantially constant. 
Preferably, step (c) comprises continuously adding to the primary 
fermentation vessel additional quantities of an aqueous mixture of the 
waste matter, and step (d) comprises continuously transferring the aqueous 
mixture from the primary fermentation vessel to the secondary fermentation 
vessel. 
Preferably, step (g) comprises continuously removing from the secondary 
fermentation vessel quantities of the aqueous mixture containing the end 
product and containing substantially no unfermented waste material. 
Preferably, the retention time of the aqueous mixture in the primary and 
secondary fermentation vessels from step (b) to (g) is sufficient that the 
aqueous mixture removed from the secondary fermentation vessel in step (g) 
contains no unfermented waste matter and no biological contaminants 
present in the waste material prior to the fermentation, and wherein the 
biological contaminants are one or more members selected from the group 
comprising pathogens, insect eggs, larvae, worms, and viruses. 
Preferably, the waste material prior to fermentation contains chemical 
contaminants, and wherein a retention time of the aqueous mixture in the 
primary and secondary fermentation vessels from step (b) to (g) is 
sufficient that the aqueous mixture removed from the secondary 
fermentation vessel in step (g) contains no unfermented waste matter and 
none of the chemical contaminants, and wherein the chemical contaminants 
are selected from the group comprising herbicides, pesticides and 
pharmaceuticals selected from one or more members of the group comprising 
chlortetracycline, sulfamethazine and penicillin. 
Preferably, the pH in the primary and secondary fermentation vessels is in 
a range of from about 3.8 to about 4.4, and wherein the waste matter 
comprises food waste.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred process of the present invention preferably comprises 
initiation of an active fermentation followed by continuous or 
semi-continuous processing of wastes, and is now described below with 
reference to FIG. 1. 
The process of the present invention may be used to ferment a wide variety 
of organic materials, which are normally considered wastes and treated as 
disposal problems. Typical waste materials include tannery waste, 
municipal or yard waste, food waste, animal waste and sludges from 
biological processes. Animal waste includes fecal matter or manure 
produced as a byproduct of an animal's digestion of food, for example 
manure from cattle, swine, sheep, horses, mink, chicken or human fecal 
matter which may be in the form of sewage sludge (.about.5% solids), 
dewatered sewage sludge (.about.25-30% solids) or septage. 
Food waste includes bakery product waste, all fruit and vegetable 
processing waste, for example potato and tomato processing wastes, all 
fruit and vegetable trim and peeling wastes, and food wastes derived from 
animals such as meats and meat trimmings, cheese whey, fish processing 
wastes, and slaughterhouse waste such as blood. Food wastes may be 
obtained from a wide variety of sources, including retail and wholesale 
grocery operations, restaurants, institutions, food processors/preparers, 
and "wet" household garbage. 
Municipal or yard waste includes leaves and weeds, as well as materials 
containing lignocellulosic complexes, for example woody plants such as 
trees, shrubs and wood refuse derived therefrom. Lignocellulosic materials 
may also be obtained as by-products of wood processing industries. Tannery 
wastes include hides, bones, cartilage and animal trimmings. 
Furthermore, the process of the present invention is capable of either 
fermenting mixtures of various types of waste materials or "pure" waste 
materials comprising only one type of waste. 
Therefore, the process of the present invention is capable of fermenting a 
wide range of waste materials of plant or animal origins. In general, any 
organic substances comprised of protein, simple and/or complex 
carbohydrates and lipids are fermentable according to the process of the 
present invention, including those disclosed in the Coulthard patent. 
The first step in the process is the formation of an aqueous mixture of the 
organic waste matter. Because the fermentation of the waste matter occurs 
at its surface, it is preferred to maximize the surface area of the waste 
material available to the microorganisms by mechanically macerating the 
waste material prior to commencement of the fermentation. 
Since different types of waste matter differ in water content, it may be 
necessary to add water to the waste matter prior to commencement of the 
fermentation process to reduce the viscosity of the aqueous mixture, 
thereby avoiding use of large amounts of energy to agitate the mixture 
during fermentation. The reduced viscosity also serves to increase the 
dissolution of oxygen in the fermentation medium. Preferably, the aqueous 
mixture of waste matter contains from about 5% to about 20% total solids 
by weight, more preferably from about 12% to about 18% by weight. 
In the preferred process of the present invention shown in FIG. 1, a 
hydropulper 12 having a blade 13 is used to macerate the waste matter. The 
capacity of hydropulper 12 may preferably be about 12,000 to 16,000 
litres. If necessary, water may be added to the waste matter in the 
hydropulper 12. However, it is to be appreciated that water may also be 
added to the waste matter during the fermentation process. Preferably, the 
waste matter is reduced to a particle size as small as possible, generally 
from less than about 1 mm to about 5 mm. 
The aqueous mixture of hydropulped, macerated waste matter is preferably 
subjected to fermentation shortly after being formed. However, the aqueous 
mixture may be stored prior to fermentation, preferably not longer than 
about 24 hours. Preferably, the aqueous mixture is oxygenated during 
storage by aeration and agitation, thereby avoiding substantial anaerobic 
fermentation during storage. 
Preferably, the aqueous mixture is pumped from hydropulper 12 through 
conduit 14 to a holding vessel 15, where the aqueous mixture may be stored 
with constant agitation by mixing blade 40 and aeration through air supply 
23, and without application of heat. The holding vessel 15 is merely a 
reservoir of "raw", unfermented waste matter, from which the aqueous 
mixture of waste matter is drawn intermittently or continuously, and 
pumped through conduit 17 to a fermentation apparatus. Different waste 
materials may also be blended in the holding vessel. It is to be 
appreciated that more than one holding vessel 15 may be provided. The 
capacity of holding vessel 15 may preferably be about 50,000 to 55,000 
litres. 
The fermentation apparatus comprises at least one fermenter, and preferably 
comprises at least two fermenters connected in series. In a more preferred 
embodiment shown in FIG. 1, the fermentation apparatus comprises primary 
fermenter 16, having a mixing blade 42 and connected through conduit 18 to 
a secondary fermenter 20, which has a mixing blade 44 and is connected 
through conduit 22 to a tertiary fermenter, or wet product storage tank, 
24 which has a mixing blade 46. Fermenters 16, 20 and 24 are preferably 
highly insulated and similar to the fermenters described in the Coulthard 
patent, each fermenter preferably having a capacity of about 30,000 
litres. However, for purposes of temperature control and air quality 
management, the fermenters 16, 20 and 24 are preferably covered to 
substantially completely enclose the aqueous mixtures fermenting therein. 
Furthermore, each of the fermenters 16, 20 and 24 is provided with a 
source of external heat (not shown). 
Initiation of the preferred fermentation process of the present invention 
is now described with reference to FIG. 1. 
Initiation of the fermentation process of the present invention may be 
viewed as a batch process. Firstly, a quantity of the aqueous mixture of 
waste material is pumped through conduit 17 from holding vessel 15 to 
primary fermenter 16. Preferably, the quantity of aqueous mixture 
transferred from holding vessel 15 is sufficient to substantially fill 
primary fermenter 16. More preferably, both primary fermenter 16 and 
secondary fermenter 20 are completely filled with the aqueous mixture, 
with secondary fermenter 20 preferably being filled through primary 
fermenter 16 by conduit 18. The preferred initiation process will be 
described as having both primary fermenter 16 and secondary fermenter 20 
filled with the aqueous mixture of waste matter. 
The aqueous mixture pumped from holding vessel 15 to primary fermenter 16 
and secondary fermenter 20 is preferably at ambient temperature, typically 
from about 10.degree. to about 30.degree. C. 
Once inside primary fermenter 16 and secondary fermenter 20, external heat 
is applied to the aqueous mixture, preferably rapidly increasing its 
temperature from ambient temperature to a thermophilic temperature. The 
term "thermophilic temperature" as used herein means a temperature 
sufficient to promote growth and proliferation of thermophilic 
microorganisms. Thermophilic temperatures typically range from about 
50.degree. C. to about 85.degree. C. The thermophilic temperature at which 
the process is initiated, and at which the fermentation is carried out, is 
at least partially dependent on the substrate and the desired 
characteristics of the end product. 
The term "thermophilic microorganism" means any microorganism which is 
capable of growing and proliferating at above-defined thermophilic 
temperatures. Therefore, the term "thermophilic microorganism" as used 
herein includes thermophilic microorganisms and facultative mesophilic 
microorganisms, that is a mesophilic microorganism which can adapt its 
metabolism to grow and proliferate at thermophilic temperatures. 
The term "external heat" as used herein means heat generated by a source 
other than the fermentation process, which is exothermic. For example, 
external heat may be generated by a heating coil located either inside or 
outside fermenters 16 and 20. 
In addition to being heated, the aqueous mixture of waste matter is also 
oxygenated, preferably by vigorous agitation by the mixing blades 42 and 
44 and aeration within fermenters 16 and 20 provided by air supply 23. 
This ensures that the aqueous mixture is supplied with sufficient oxygen 
to encourage the proliferation of aerobic, thermophilic microorganisms and 
to prevent the proliferation of anaerobic microorganisms. The inventors 
have found that oxygen demand is greatest during the initial start-up of 
the process, and dissolved oxygen concentrations on the order of about 0.2 
ppm are typically observed. Once the process is initiated, oxygen demand 
drops and dissolved oxygen concentration is typically observed to rise 
above about 1 ppm. 
Although injection of air into the fermenters 16 and 20 is the preferred 
form of oxygenation, it is to be appreciated that air enriched with oxygen 
or oxygen in any other form, including pure or substantially pure oxygen, 
may be used to aerate the aqueous mixture of waste matter. 
The inventors have also found that the maintenance of a sufficiently high 
dissolved oxygen concentration requires high shear rates within the 
fermenter 16 effective to disperse air bubbles throughout the aqueous 
mixture, but not in excess of shear rates at which microbial cells are 
damaged or destroyed. 
Once the aqueous mixture reaches thermophilic temperatures and is 
oxygenated in the fermenters 16 and 20, a time of from about 2 to about 6 
days is typically required for thermophilic fermentation to be achieved. 
Preferably, the initiation is continued until the fermentation reaches a 
steady state at which the rate of fermentation is substantially constant 
and the waste matter in fermenters 16 and 20 has been partially converted 
to the end product. Most preferably, the steady state is the maximum rate 
at which the fermentation will proceed at any given temperature and oxygen 
concentration. 
It is to be emphasized that the thermophilic fermentation is initiated 
without the need for inoculation, utilizing only thermophilic and 
facultative mesophilic microorganisms which are naturally present in the 
waste materials. 
As discussed above, rapid heating of the aqueous mixture to thermophilic 
temperatures precludes the microbial succession disclosed in the Coulthard 
patent, and permits the proliferation only of thermophilic and facultative 
mesophilic microorganisms in the aqueous mixture. This has the effect of 
reducing competition for waste material among the microorganisms, 
consequently reducing the chance of contamination and/or poisoning by 
opportunistic microorganisms and/or pathogens that might proliferate at 
lower temperatures. 
Once an active fermentation has been initiated by the above initiation 
process, continuous or semi-continuous processing of waste material 
according to the present invention may preferably begin. However, it is to 
be understood that the initiation process of the present invention may be 
used on its own as a batch fermentation process having distinct advantages 
over the above-discussed prior art processes. 
As in the initiation of the process, the aqueous mixtures in the fermenters 
16 and 20 are heated by an external heat source and oxygenated to promote 
and sustain growth and proliferation of thermophilic and facultative 
microorganisms. The temperature is preferably maintained within the 
thermophilic ranges disclosed above. The oxygenation is preferably the 
same as that described above with the exception that the inventors have 
found that dissolved oxygen concentrations of from about 1 ppm to about 5 
ppm are sufficient to maintain an active fermentation in fermenters 16 and 
20. 
Once an active thermophilic fermentation is initiated, it is preferred that 
steady state fermentation conditions, and more preferably optimum 
fermentation conditions, be maintained within fermenters 16 and 20. 
Therefore, a small amount of fresh aqueous mixture of waste matter at 
ambient temperature is pumped from holding vessel 15 into primary 
fermenter 16. This provides additional fermentation substrates in the form 
of fresh waste matter to maintain a steady state, active fermentation in 
primary fermenter 16. 
Since both primary and secondary fermenters 16 and 20 are preferably 
maintained in a full condition and are connected in series, adding fresh 
aqueous mixture to primary fermenter 16 preferably results in the 
displacement of a corresponding volume of aqueous end product from 
secondary fermenter 20. Furthermore, a steady state fermentation is 
preferably also maintained in secondary fermenter 20 by discharge thereto 
of partially fermented aqueous mixture from primary fermenter 16. 
In a preferred continuous process of the present invention, fresh aqueous 
mixture of waste matter is continuously supplied to primary fermenter 16, 
preferably at a rate of from about 20 to about 50 litres per minute. 
Consequently, the aqueous mixture of end product is preferably 
continuously discharged from secondary fermenter 20 at substantially the 
same rate. In a continuous process, the provision of secondary fermenter 
20 ensures that substantially no unfermented waste matter may pass through 
the fermentation apparatus. 
In a semi-continuous process, fresh aqueous mixture of waste matter is 
intermittently supplied to primary fermenter 16, preferably at a constant 
and average rate of from about 20 to about 50 litres per minute. These 
intermittent additions preferably occur at a set flow rate for about 5 to 
about 15 minutes every one half hour. Preferably, the aqueous mixture of 
end product is intermittently discharged from secondary fermenter 20 at 
substantially the same rate. It is to be understood that a semi-continuous 
fermentation process could be conducted without secondary fermenter 20. 
However, secondary fermenter 20 is preferably provided to improve the 
efficiency of the process. 
In the process of the present invention, it is preferred that substantially 
the entire fermentation occurs in the primary and secondary fermenters 16 
and 20. The fermentation time, defined as the time required for volume of 
the active fermentation medium to be turned over, or the time required for 
the aqueous mixture to pass through the fermenters 16 and 20, is 
preferably from about 24 to about 48 hours. 
Typically, in an apparatus as shown in FIG. 1 wherein the waste matter is 
completely or substantially completely fermented in primary and secondary 
fermenters 16 and 20, the degree of fermentation of material passing from 
primary fermenter 16 to secondary fermenter 20 is typically about 50% 
complete. However, it is to be appreciated that the degree of fermentation 
in the primary fermenter 16 is dependent both on the processing time and 
the number of fermenters connected in series. 
A fermentation time of at least about 24 hours ensures the waste matter has 
a residence time in fermenters 16 and 20 sufficient to completely destroy 
pathogenic organisms and other undesirable biological contaminants present 
in the waste matter prior to fermentation. Typical pathogens include 
bacteria such as salmonella and coliform bacteria, and other biological 
contaminants include insect eggs, larvae, worms and viruses. 
Given that the minimum time-temperature conditions for complete destruction 
of the above contaminants is about 10 minutes at 65.degree. C., a 
fermentation time of about 24 hours is more than sufficient to ensure that 
contaminants are destroyed completely and that the end product is 
completely safe. Although it may be possible to provide a completely 
fermented product with a fermentation time of less than about 24 hours, it 
is preferred that the fermentation time not be shorter than about 24 hours 
to ensure the complete safety of the end product. 
Also to ensure the safety of the end product, the process of the present 
invention is preferably operated in the upper end of the above-mentioned 
thermophilic temperature range. Preferred operating temperatures for the 
process of the present invention, including initiation, are above about 
55.degree. C. and no higher than about 80.degree. C., more preferably at 
least about 65.degree. C., and most preferably within the range of from 
about 65.degree. C. to about 75.degree. C. 
It is to be appreciated that destruction of contaminants is dependent on 
both temperature and time of fermentation. Therefore, minimum 
time-temperature conditions may be achieved with longer fermentation times 
at a relatively low temperature, or short fermentation times at a 
relatively high temperature. However, in the process of the present 
invention, it is preferred to use higher temperatures as discussed above 
to achieve complete destruction of contaminants in a relatively short 
time. 
The inventors have surprisingly found that the thermophilic fermentation 
process of the present invention is also capable of destroying a wide 
range of chemical contaminants which may be present in residual amounts in 
certain types of waste matter. Such chemical contaminants include a wide 
range of organic compounds, such as pharmaceuticals, pesticides, 
herbicides, and other organic chemicals present in waste matter. 
Pharmaceuticals include antibiotics for veterinary and/or human use. In 
particular, antibiotics are commonly added to animal feeds and can be 
found in the manure or muscle tissues of farm animals which may comprise 
raw waste matter to be fermented in the process of the present invention. 
The inventors have confirmed, in challenge tests conducted with waste 
matter contaminated with selected agricultural antibiotics, complete 
destruction of these antibiotics by the process of the present invention. 
In a particular challenge test conducted by the inventors, 110 g each of 
chlortetracycline and sulfamethazine, and 55 g of penicillin, commonly 
used as veterinary antibiotics, were added to an active fermentation at 
70.degree. C. This level of antibiotics is comparable to that which may be 
present in a finished animal feed in a concentration of 220 g per tonne. 
Samples were taken from the fermentation for evaluation of antibiotic 
content using standard methods before addition, after 30 minutes, and at 
8, 12, 24, 32, 48, 56 and 72 hours. Antibiotic was detected only in the 
sample collected after 30 minutes, at an equivalent concentration of 16.4 
g per tonne. Therefore, more than 95% of the antibiotics were destroyed 
within the first 30 minutes of the test, and the balance within the first 
8 hours. 
It is believed that the destruction of chemical contaminants in the 
fermentation process of the present invention may be caused by thermal 
destruction or through metabolization of the chemical contaminants by 
thermophilic microorganisms, or a combination of both. Due to the length 
of the fermentation process, i.e. 24 to 48 hours, it would be expected 
that the process of the present invention would be capable of thermal 
destruction of heat sensitive chemical contaminants as well as 
contaminants normally considered to be relatively heat resistant. 
In the example of penicillin, it is understood that an extracellularly 
produced enzyme is ultimately responsible for penicillin destruction. 
Therefore, it is possible that even compounds which are highly heat 
resistant may be destroyed by the process of the present invention through 
metabolization by thermophilic microorganisms. 
Although the destruction of antibiotics has been specifically described, it 
is to be appreciated that the process of the present invention is not 
restricted to destruction of antibiotics, and is capable of destroying a 
wide range of chemical contaminants which may be present in waste 
materials. 
One surprising advantage of the process of the present invention is its 
adaptability to a wide pH range, ranging from about 3.5 to about 9.0. This 
is to be contrasted with the pH range disclosed in the Coulthard patent of 
between about 5.0 and about 8.5, with a most preferred pH on the order of 
from 5.9 to 7.5. In the Coulthard process, a pH adjusting agent is added 
to acidic waste materials to raise their pH to an acceptable level, 
approaching neutral. The inventors of the present process have found that 
addition of a pH adjusting agent to acidic food wastes only raises the pH 
temporarily and that addition of the pH adjusting agent must be continued 
throughout the fermentation process to maintain the elevated pH. 
Furthermore, the inventors have found that operation of the process at the 
acidic pH of many food wastes, i.e. from about 3.5 to about 4.5, more 
typically 3.8 to 4.4, is not only possible but is also preferred, without 
the addition of any pH adjusting agent. In fact, operation of the process 
at an acidic pH enhances the thermal destruction of contaminants, thereby 
increasing the safety of the end product. When the process is applied to 
acidic wastes, it is believed that low pH is maintained in the process by 
encouraging the growth only of acidophilic thermophiles. These 
microorganisms themselves are more effective at destruction of many 
contaminants and readily produce organic acids that maintain a low pH and 
thereby preclude the growth of microorganisms which are otherwise active 
at higher pH. 
From secondary fermenter 20, the substantially completely fermented aqueous 
mixture is intermittently or continuously discharged through conduit 22 to 
wet product storage tank 24. As in fermenters 16 and 20, the aqueous 
mixture in product storage tank 24 is preferably vigorously agitated by 
mixing blade 46 and aerated by air supply at a thermophilic temperature, 
as in fermenters 16 and 20. Therefore, wet product storage tank 24 is also 
referred to herein as "tertiary fermenter 24". However, it is to be 
appreciated that the aqueous mixture entering tank 24 has been completely 
or substantially completely fermented in fermenters 16 and 20. 
Therefore, any small amounts of unfermented waste matter remaining in the 
product mixture will be fermented in product storage tank 24. However, it 
is to be appreciated that all or substantially all of the waste matter in 
the aqueous mixture discharged from secondary fermenter 20 has been 
fermented. Therefore, the primary function of product storage tank 24 is 
that of a surge tank, or storage tank, for accumulation of the fermented 
aqueous mixture prior to further processing, such as drying. 
Typically, wet product is collected until tank 24 is filled to about 80% of 
its capacity, after which the wet product is pumped from tank 24. 
In an alternative process not shown in FIG. 1, wet product storage tank 24 
is eliminated and the wet end product comprising the aqueous mixture of 
fermented waste matter discharged from secondary fermenter 20 is used 
without further processing. It is also possible to use the wet product 
from tank 24 without further processing. The inventors have found that 
such wet products may for example be directly fed to animals or used as 
liquid fertilizers, soil conditioners or soil amendments. 
Furthermore, it is possible to operate the process on a semi-continuous 
basis using only one fermenter. However, it is preferred to provide at 
least a primary and a secondary fermenter to ensure the safety of the end 
product. Further, the process may be operated with more than three 
fermenters to further ensure the complete destruction of contaminants in 
the end product. 
In the preferred process shown in FIG. 1, the aqueous mixture of fermented 
waste matter is stored in fermenter 24 until it may be subjected to 
drying. Most preferably, the aqueous mixture of fermented waste matter is 
pumped from tertiary fermenter 24 through conduit 26 to centrifuge 28 
where the water content of the fermented product is reduced to obtain a 
wet product comprising about 35% by weight solids. It is to be appreciated 
that the initial removal of water may be accomplished by other means, such 
as decanting and filtering. 
It is to be appreciated that initial removal of water, for example by 
centrifuging or filtering, may not be necessary or desirable and, as shown 
in FIG. 1, the wet product from tank 24 may be directly pumped through 
conduit 27 to a dryer 32. Initial water removal is not desirable, for 
example, when the wet product contains a high content of water soluble 
and/or miscible solids which would remain in the liquid fraction, but are 
otherwise recoverable. 
The water removed from the aqueous mixture of fermented waste matter by 
centrifuge 28 is preferably recirculated to hydropulper 12 through conduit 
30 to be slurried with waste matter being macerated in hydropulper 12. 
Recirculation of the liquid fraction to be slurried with fresh waste 
matter is a convenient way to avoid discharge of water containing solids 
into the environment and allow full recovery of solids from the liquid 
fraction. 
The wet product obtained after centrifuging is typically in the form of a 
wet cake and may either be used directly as an end product or subjected to 
further drying. As shown in FIG. 1, the wet product is transferred to a 
dryer 32, for example by an auger, where it is preferably dried to a water 
content of from less than about 10 to about 15% by weight. The water 
vapour from the dryer 32 is preferably exhausted to the environment, as 
through vent 33, or used as a source of heat energy in the process. The 
use of a dryer 32 allows full recovery of solids from the wet product. 
It is to be appreciated that many types of drying systems are available 
which can dry wet products having a variety of forms. For example dryers 
are available which can dry liquid slurries, as obtained from secondary 
fermenter 20 or storage tank 24, or dewatered cake as obtained from 
centrifuge 28. However, as discussed above, drying is not an essential 
step of the process of the present invention. 
The dried product obtained from dryer 32 is typically a granular, powdery 
or somewhat fibrous solid. Although the dried end product may be used in 
the form in which it is removed from dryer 32, it may preferably be shaped 
into any convenient form, such as pellets, which may for example be used 
as animal feed, animal feed supplement, fertilizer, soil conditioner or 
soil amendment. 
In overview, the fermentation process converts organic waste matter into an 
end product comprising biomass derived from the cells of thermophilic 
microorganisms such as bacteria, yeast and/or fungi, as well as 
unfermented proteins, lipids, carbohydrates, and breakdown products 
thereof arising from fermentation, and water. The product may also contain 
some amount of carbon dioxide which would however be largely liberated 
through aeration during the fermentation process. The end product has a 
significantly higher protein content and nutritional value than the 
unfermented waste matter and is therefore of value as an animal feed, 
animal feed component or ingredient, or as an organic fertilizer, 
fertilizer component, soil amendment or soil conditioner. The specific end 
use may be at least partially dependent on the type of waste matter being 
fermented. For example, it is preferred that the end product obtained by 
fermentation of fecal matter be used as a soil amendment, soil conditioner 
or organic fertilizer, rather than as an animal feed or feed component. 
However, it is to be appreciated that end products derived from fecal 
matter may be suitable for use as an animal feed or feed component. 
One of the benefits of using aerobic fermentation is its oxidizing effect, 
which both destroys odorous compounds and promotes biological pathways 
that preclude the formation of compounds typical of anaerobic 
fermentations. Therefore, the process of the present invention is 
naturally less odorous than an anaerobic fermentation process. 
Further, the entire apparatus used in the process of the present invention 
is preferably contained in a single plant building which is equipped to 
treat all air released into the surrounding environment, thereby 
minimizing unpleasant odours escaping the plant. In order to accomplish 
this, the plant building is preferably under a negative pressure 
throughout to prevent the unintentional escape of air, and all air and 
water vapour exhausted from the plant must preferably pass through a 
thermal oxidizer or other scrubbing device to destroy any odour-producing 
compounds. 
Furthermore, steps are preferably also taken to control odours within the 
plant, to protect plant workers. When waste materials are delivered to the 
plant building, they are dumped onto a tipping floor 10 inside the plant. 
Air from the tipping floor 10, as well as from the fermenters 16, 20 and 
24, is preferably prevented from mingling with general plant air to 
prevent plant workers from being exposed to unpleasant odours. 
Although preferred capacities of hydropulper 12, holding vessel 15 and 
fermenters 16, 20 and 24 have been disclosed herein, it is to be 
appreciated that these capacities may be varied without departing from the 
process of the present invention. 
Although this disclosure has described and illustrated certain preferred 
embodiments of the invention, it is to be understood that the invention is 
not restricted to these particular embodiments. Rather, the invention 
includes all embodiments which are functional or mechanical equivalents of 
the specific embodiments and features that have been described and 
illustrated herein. Furthermore, it is intended that the invention cover 
all alternate embodiments as may be within the scope of the following 
claims.