WO2005095009A1

WO2005095009A1 - Manure treatment process

Info

Publication number: WO2005095009A1
Application number: PCT/CA2004/000488
Authority: WO
Inventors: Robert Monteith
Original assignee: Nutrient Management Technologies Ltd.
Priority date: 2004-03-30
Filing date: 2004-03-30
Publication date: 2005-10-13

Abstract

An improved process for the remediation of animal manure, particularly hog manure, is disclosed. The improved process for remediation of animal manure includes the step of continuous acidification of manure prior to passing the manure or animal waste through a bioreactor for the removal of ammonia from the manure.

Description

MANURETREATMENTPROCESS

Field of the Invention . The present invention relates to a process for the treatment and remediation of animal waste and more specifically to a process for the treatment and remediation of manure.

Background of the Invention A major problem in animal farming, particularly hog farming, is the production of manure by those animals. The manure produced presents an environmental problem. One problem presented by hog manure is the presence of pathogens. These pathogens can be hazardous if allowed to proliferate in the environment where the animals are reared. In addition these pathogens can present a contamination problem in the environment if not treated before disposal.

Another environmental problem for the disposal of manure is the presence of harmful compounds. In manure, particularly hog manure, nitrogen and phosphorous are the primary chemical components of environmental concern. In hog manure the nitrogen content is mostly in the form of ammonia. The phosphorous is generally associated with solid material in the manure. If spread manure runs off into streams or reaches groundwater, the resulting nitrogen or phosphorous contamination can adversely affect the receiving waters. It is therefore becoming necessary to remove or reduce these chemical components from manure to neutralize the threat and to help the farmer stay within his environmental management guidelines.

A further environmental problem presented by hog manure is the strong unpleasant odour. These odours are associated with particular compounds in the manure, the soluble organic matter. Accordingly, a treatment is needed which can reduce the odours by reduction or elimination of the compounds responsible for the odour from the manure. It is known that hog manure is particularly amenable to biological treatment because of its high water content.

In response to the potential environmental problems posed by large animal, particularly hog, farming operations processes have been developed for the biological treatment of hog manure. There are two principal factors to consider in the treatment of biological wastewater (that is wastewater containing animal waste) using bioreactor systems. The first of these factors is the hydraulic retention time ("HRT"). The hydraulic retention time is a measure of bioreactor efficiency since a short HRT means that a relatively small reactor volume is required to treat a given flow of wastewater. The second factor is the microbial solids retention time ("SRT"). The microbial solids retention time is a factor which determines the concentration and thus efficiency of biocatalysis within the bioreactor. A relatively long SRT means there is a high concentration of biomass within the bioreactor which promotes high rates of organics destruction. In addition, a relatively long SRT promotes microbial stability and shock resistance to variations in the organic mass loading to the bioreactor. Further a relatively long SRT also causes lower sludge, or biomass yields per volume of biological wastewater treated. Lower sludge yields per volume of biological wastewater treated are preferred since this means lower sludge disposal costs. Conventional bioreactor systems are known for the treatment of animal waste. In such conventional bioreactor systems a stirred tank is used with activated sludge to treat wastewater. Such activated sludge apparatus is often found in municipal sewage treatment plants. One of the problems with these conventional bioreactor systems is that the biomass is either carried out with the treated water or extensive settling operations to recover the biomass are required. If biomass is washed away a relatively long HRT is required increasing the size of the bioreactor system. Further, if settling is required to recover the biomass a large footprint for the bioreactor system will be required. Usually a large footprint translates to a relatively expensive system that is usually more complicated to operate. One of the problems of existing bioreactors is improper mass transfer and distribution of air and water through the packed beds of the bioreactors. This improper mass transfer leads to the problem of clogging. When a bioreactor that is packed and completely colonized and extensive biofilm begins to fill or clog the gaps between the packing, clogging can occur. This clogging reduces the effective volume of the bioreactor by creating dead zones with minimal mass transfer and minimal biocatalytic activity.

Accordingly there is a need for an improved process for the treatment of manure. In particular an improved process for the remediation of the manure, including the lcilling of pathogens, removal of enviromnentally harmful compounds and removal of soluble organic solids is needed.

Summary of the Invention The present invention provides an improved process for the remediation of animal manure, particularly hog manure, in which there is improved ammonia removal in a bioreactor, improved sedimentation of solids from manure, enhanced killing of pathogens in the manure and producing a final effluent that has a pH of approximately 7 for safe use in irrigation or flushing of barns. In one embodiment the present invention provides continuous acidification of manure prior to passing the manure or animal waste through a bioreactor for the removal of ammonia from the manure.

In another embodiment the invention provides a process for the remediation of animal manure by continuously acidifying the manure for remediation and separating solids from the manure to generate a substantially liquid animal waste prior to passing the liquid animal waste into a bioreactor for the removal of ammonia. In a further embodiment the invention provides a process for the remediation of manure by continuously acidifying the manure for remediation prior to passing the manure into an anaerobic portion of a bioreactor, separating solids from the manure to generate a substantially liquid animal waste and passing the substantially liquid animal waste through a bioreactor having at least two bioreactive compartments for the removal of phosphorous and ammonia. In this embodiment the first bioreactive compartment is an anaerobic compartment and the last bioreactive compartment is an aerobic compartment to produce a liquid effluent. In another embodiment this liquid effluent can be safely used for irrigation or flushing of barns. In a further embodiment the invention provides a process for the remediation of animal manure by continuously acidifying the manure for remediation and enhanced separation of solids from the manure. In this embodiment the separated solids are fed to worms to create worm castings which can be used as fertilizer.

Brief Description of the Drawings In drawings which illustrate by way of example only a preferred embodiment of the invention,

Figure 1 shows a side view of a serpentine bioreactor used in a preferred embodiment of the invention.

Detailed Description of the Invention One of the primary goals of the present invention is to treat manure, particularly hog manure to reduce odours and render the treated effluent to such a quality that it can be recycled back into the hog barns and also used for irrigation on the crop fields. In order to achieve this certain compounds must be reduced or eliminated from the manure. The primary components that it is desirable to remove in a preferred embodiment of the invention are soluble organic matter, nitrogen primarily in the form of ammonia or ammonium, phosphorous which is generally associated with the solids in the manure, and potentially harmful pathogens. Soluble organic matter is measured or quantified in terms of biological oxidation demand or BOD. Reduction of BOD will decrease many of the odours associated with hog manure. Nitrogen, primarily in the form of ammonia or ammonium when the manure of liquid animal waste enters the bioreactor in a preferred embodiment is removed through a cycle of nitrification and denitrifϊcation. Phosphorous removal is achieved through removal of solids from the manure to generate a substantially liquid animal waste. In the present invention, removal of the solids is achieved through the acidification of the manure. The steady pH for acidification in a preferred embodiment of the invention is from pH 4 to 4.5. The passage of manure, or substantially liquid animal waste derived from that manure, through a bioreactor usually results in a significant increase in the pH. The resulting effluent from a bioreactor treatment of manure can be as alkaline as pH 10 if the initial manure was not acidified. Acidification of the manure to a generally acidic pH also reduces the pH of the final effluent. For example, it has been found that acidification to pH 4.0 prior to passage of the manure or substantially liquid animal waste into the bioreactive compartments of a bioreactor can result in a final effluent pH of approximately 7. Since the effluent produced by this process can be substantially free of environmental contaminants such as nitrogen and phosphorous is of an approximately neutral pH, the resulting effluent may be recycled for use in the barn for flushing or for irrigation.

In addition, to changing the final pH of the effluent, initial acidification can promote the separation of solids from the manure resulting in solids deposits and a substantially liquid animal waste which can proceed to be treated in bioreactive compartments of a bioreactor. Since phosphorous as well as the unpleasant odour of manure generally remains with the solids in the manure the acidification of the manure leading to enhanced separation of solids from the substantially liquid animal waste also enhances the removal of phosphorous and odour from the substantially liquid animal waste. The cells of normally occurring bacteria contain about 1.5% phosphorous. Under ideal conditions there are bacteria known in the art that can be encouraged to accumulate 10 - 20 times more. It is these bacteria that are responsible for the biological removal of any phosphorous from liquid in the manure. The acidification of the manure prior to passing through the bioreactor improves the efficiency and ability of these bacteria to remove phosphorous. In addition to removal of solids, phosphorous removal is accomplished using an anaerobic compartment followed by aerobic or conditions.

Acidification of manure to an acidic or low pH also improves the killing of pathogens in the manure since many pathogens are intolerant of low pH conditions, particularly where the pH is reduced relatively quickly. In one embodiment of the invention the pH is reduced to 3 in order to kill most pathogens. Accordingly, acidification prior to bioreactions of the manure results in reduced pathogens in the final effluent. Further, as the effluent has passed through a bioreactor containing bacteria which break down contaminants in manure some of these bacteria will pass into the effluent. This provides a further advantage since the flushing of barns with this effluent will result in reduced counts of harmful pathogens due to competition with the bacteria in the effluent capable of breaking down contaminants.

In one embodiment of the invention a bioreactor unit 1 is divided into several compartments. The compartments allow for individual sub-environments - aerobic, anoxic or anaerobic - to exist in one bioreactor. Different compounds in manure require different environments in which to be broken down or removed. The compartmentalized bioreactor process is able to provide these different environments and achieve contaminant reduction and removal. In an embodiment of the invention the process for the remediation of manure involves the steps of continuously acidifying the manure for remediation prior to passing the manure into an anaerobic portion of a bioreactor, separating solids from the manure to generate a substantially liquid animal waste, and passing the substantially liquid animal waste through a bioreactor having four bioreactive compartments for the removal of phosphorous and ammonia. The bioreactor system used in this embodiment of the invention is known as a serpentine, plug-flow packed bed reactor. Serpentine refers to the way the liquid flows through the reactor from top to bottom to top. Plug flow means the liquid particles exit from the reactor in the same sequence in which they entered. Fluid particles remain in the reactor for a time essentially equal to the theoretical detention time. Packed bed means the reactor is filled with some type of packing material. In this embodiment of the invention three different mediums are used.

In an embodiment of the invention acid is added to one or more of the anaerobic compartments to lower redox potential and enhance anaerobic activity, which reduces TSS and TDS. Sulphuric acid can be used as the acid in this process to stimulate the bacteria on the front end of the reactor and also to lower the pH.

The purpose of the compartments is to allow increased and simpler control of the environments under which the breakdown of the individual manure compounds occurs. In many cases biological treatment requires a sequential series of reactions and the compartments allow the user to have more control over environments which foster the reactions.

In this embodiment the bioreactor unit comprises four compartments though the first compartment 3 should not be considered a bioreactive compartment. The first compartment 3 contains no medium. It is in the first cell that the acidification takes place. The desired acid, preferably sulphuric acid is mixed with the manure for remediation. The acid is added to ensure a continuous pH is maintained in this manure in the range of pH 4 - 4.5. The addition of the acid should be made with a continuous mixing action to prevent separation of the liquid manure from the acid used. This acidification enhances sedimentation of solids from the manure. Accordingly the first compartment 3 also acts as a settling zone for the solids in the manure. The solids can be allowed to separate in this first compartment 3 leaving a substantially liquid animal waste. This first cell will usually be in an anaerobic state and could be considered an anaerobic compartment. In this embodiment of the invention the second compartment 4 4 is packed with a material known as Biocord™, supplied by Fukui. This material comprises a core strand covered with large amounts of rings of thread. The thread is made of a polymer such as polypropylene. When in use, six to eight foot sections are stretched vertically between pairs of horizontally laid poles in the reactor, spaced 10 cm apart. The biocord is used in the second cell simply for the fact that it will not plug up with particulate matter and provides the qualities needed in a packed-bed growing medium such as high surface area. This second compartment 4 is also anaerobic or anoxia It is in this compartment, and the first compartment 3 that the process of denitrification occurs. Denitrification is the process of converting nitrate to nitrogen gas. This involves the biological oxidation of many organic substrates in the manure using nitrate or nitrite as the electron acceptor. As a result of the biological oxidation of organic compounds, BOD is reduced.

The third and fourth compartment 6s of the bioreactor used in this embodiment of the invention are aerobic. These compartments contain a mixed medium of polystyrene foam and plastic rings or tubes. This mixed medium preferably comprises polystyrene sponges in the shape of 2 inch by 2 inch cubes and hollow plastic tubes with a diameter of three inches and a length of 6 inches. This mixture of packing material serves at least two functions. First, the mixed packing provides ideal spacing within the compartment and prevents clogging due to excessive biofilm growth. Second, the mixed medium also prevents compaction of the medium. This prevents the formation of dead-zones where distribution of air and biocatalytic activity would be negatively impacted.

The third and fourth compartment 6s also contain about 10 fine bubble air diffusers 9, 10 each of which are spaced evenly along the floor of the compartment. The air diffusers 9, 10 are fed compressed air from an electric blower which is run above the reactor. It is in the third compartment 5 that the remaining organic components are oxidized and nitrification of the ammonia begins. The ammonia initially present in the manure remains unchanged as it passes through the first and second compartment 4s. It is in the third compartment 5 that the conversion of the ammonia to nitrite and nitrate begins. In the fourth compartment 6 most of the remaining ammonia is converted to nitrite and nitrate. In a first pass of the substantially liquid animal waste through the bioreactor, 100% of the liquid input into the reactor is recycled through a recycling tube 7 from the fourth compartment 6 back through into the first compartment 3. The nitrite and nitrate in this recycled stream is then converted to nitrogen gas under the anaerobic or anoxic conditions of the first and second compartments 3 and 4 respectively. The nitrogen gas is then harmlessly released to the atmosphere.

The packing materials used in the second to fourth compartment 6s address the problem of improper mass transfer and distribution of air and water through the packed bed as well as the related problem of clogging since the packing materials are relatively large porous material with very high internal surface area but also relatively large spacing between the packing. This ensures good distribution of both gas and water throughout the packed bed of the bioreactor. The growing medium used in this embodiment of the invention immobilizes the biomass and gives a much greater solids retention time as the bacteria are prevented from being washed away in the treated effluent. The highly increased retention of biomass allows for decreased HRT which produces a reactor that is compact, efficient and generates very little sludge. Further, the growing medium used in this embodiment of the invention allows generated biomass to be recycled in the bioreactor and prevents the formation of sludge in the effluent. Within the packing material, localized metabolic zones are created that aid in the utilization of excess biomass. In the localized oxic zones organics are adsorbed and degraded and particulate biomass is formed. Within the same bioreactor there are localized anoxic zones where a significant proportion of biomass is converted to volatile fatty acids (VFAs). The VFAs migrate back to the oxic zones and are aerobically metabolized to CO₂ and water. The embodiment of the invention allows the system to recycle most of the biomass and generate very little sludge.

Using the process of this invention a typical final effluent will have the appearance of light tea and very minimal odour. With initial solids separation at the front end of the bioreactor the following results are typical (though a person skilled in the art will appreciate that the initial manure will also influence the results):

BOD: < 100 mg/L

Pathogens: < 10²

Ammonia: < 90 mg/L

Phosphorous: 80% Reduction TSS: < 40 mg/L

The improved packing materials in addition to the solids separation which is enhanced by the acidification steps allows for a smaller and more efficient bioreactor system to be used. This allows for less expensive disposal of the animal manure often at the site of its production. In addition, the present invention allows the use of packing material as a growing medium which allows the bacteria in the reactor to remain in a concentrated and steady state. A further benefit of the steady state environment promoted by the initial acidification is the promotion of autolytic or self digesting reactions by the bacteria in the bioreactor. These bacteria will actually consume and recycle their own biomass and sludge in different zones of the growing medium, thereby further reducing sludge production.

In a further embodiment of the invention, the manure can be subject to acidification separately from a bioreactor unit. The acidification can take place either before or after solids separation from the manure leaving a substantially liquid animal waste. In these embodiments the solids can be separated from the manure using a stand alone separator. However, it is preferable to perform solids separation contemporaneously with or subsequent to acidification since the acidification can facilitate separation of the solids from the manure. In yet a further embodiment of the invention the solids separated from the manure can be fed to worms which create worm castings. Worm castings from manure, and particularly hog manure are an excellent natural fertilizer and marketable product, the sale of which can reduce or offset the costs of disposal of the manure.

Various embodiments of the present invention having been thus described in detail by way of example, it will be apparent to those skilled in the art that variations and modifications may be made without departing from the invention. The invention includes all such variations and modifications as fall within the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A process for the remediation of manure including the step of continuously acidifying the manure for remediation prior to passing the manure into a bioreactor for the removal of ammonia from the manure.

2. A process for the remediation of manure including the steps of:

(a) continuously acidifying the manure for remediation; and

(b) separating solids from the manure to generate a substantially liquid animal waste prior to passing the liquid animal waste into a bioreactor for the removal of ammonia. /

3. A process for the remediation of manure comprising the steps of:

(a) continuously acidifying the manure for remediation prior to passing the manure into an anaerobic portion of a bioreactor;

(b) separating solids from the manure to generate a substantially liquid animal waste;

(c) passing the substantially liquid animal waste through a bioreactor having at least two bioreactive compartments for the removal of phosphorous and ammonia, wherein the first bioreactive compartment is an anaerobic compartment and wherein the last bioreactive compartment is an aerobic compartment to produce a liquid effluent.

4. The process of any of claims 2 to 3 wherein the separated solids are fed to worms to create worm castings.

5. A process for the remediation of manure of any of claims 1 to 4 wherein the step of continuously acidifying the manure for remediation maintains a manure pH of from 4 to 4.5 prior to passing the manure into a bioreactor for the removal of ammonia from the manure.

6. The process of any of claims 1 to 5 wherein sulphuric acid is used to continuously acidify the manure for remediation.

7. The process of claim 3 wherein the substantially liquid animal waste passes through a bioreactor having three bioreactive compartments, wherein the first bioreactive compartment is an anaerobic compartment, the second bioreactive compartment is an anaerobic compartment, and the last bioreactive compartment is an aerobic compartment.

8. The process of any of claims 3 and 7 wherein the aerobic compartment is ventilated.