WO2001087467A1

WO2001087467A1 - Method and system for treating swine manure

Info

Publication number: WO2001087467A1
Application number: PCT/CA2000/000598
Authority: WO
Inventors: Madeleine TÉTRAULT; Denis COTÉ
Original assignee: Purin-Pur Inc.
Priority date: 2000-05-19
Filing date: 2000-05-19
Publication date: 2001-11-22
Also published as: AU4904200A; EP1583602A1

Abstract

A method for treating swine manure comprising mechanically dewatering the manure through a tangential screen having an average pore size between about 200 and 500 microns to obtain a filtrate and a sludge, filtering the filtrate through at least one ultrafiltration membrane to obtain an ultrafiltration permeate and an ultrafiltration concentrate; and filtering the ultrafiltration permeate consecutively through at least one first reverse osmosis membrane and through at least one second reverse osmosis membrane wherein the at least one first reverse osmosis membrane is able to withstand a pressure of between 500 and 1000 psi to obtain a final permeate and a final concentrate whereby the final permeate may safely be returned to the environment. The present invention also provides a system for treating manure comprising the elements of operating the method. The present method and system for treating manure do not require chemical additives during the operation mode.

Description

TITLE OF THE INVENTION

Method and System for Treating Swine Manure

FIELD OF THE INVENTION

The present invention relates to a method and a system for treating swine manure. More specifically, the present invention is concerned with a method and a system for mechanically dewatering swine manure without the use of chemical additives.

BACKGROUND OF THE INVENTION

The creation of large farms for raising domestic animals at the commercial level in large numbers, such as cows, chickens, pigs and swine, has created an increased concern environmentally over the animal waste products, typically liquid and solids, created by such large domestic production of animals. Typical environmental concerns which are each related but different in result include air contamination caused by the odours produced from the waste, ground water and stream contamination from runoffs at the waste site, and soil contamination, particularly for agricultural purposes, resulting form the large volume of waste. Therefore, organic animal waste sludges have become a tremendous environmental problem throughout the United States and throughout the world. The increasing production of agricultural waste, such as swine production and their waste products presents a large problem for both farming soils and the natural environment, which includes streams, water tables, and soils.

Various methods of treating manure involving the mechanical dewatering of manure have been described. Known methods involve the use of polymers and/or coagulating agents. French patent application no. 2,724,922 published on

March 29, 1996 with Raes et al. as inventors describes one method of treating organic wastes that may be adapted for manure. It involves the addition of chemicals such as coagulating agents and flocculating agents to obtain a permeate substantially free from suspended solids. Canadian patent application no. 2,200,164 published

August 7, 1998 with Tetrault and Grandbois as inventors discloses an other method of mechanically dewatering manure also comprising chemical additives. This method involved the use of a rotary press for achieving a first liquid/solid separation of the manure, followed by a liquid treatment involving the use of a separating membrane of the type nanofiltration or reverse osmosis. Chemical additives such as polymers and coagulating agents were necessary to obtain an efficient liquid/solid separation.

The concentration of polymers necessary to obtain an efficient liquid/solid separation in that method varied with the daily characteristics of the manure (pH, water content, etc.) so that the method could not easily be automated: a person was therefore needed everyday to make the necessary adjustments. Furthermore, the use of polymers involved very high costs. Finally, because of the complexity involved in controlling all the factors affecting the action of the polymers, this method failed to produce constant and adequate liquid/solid separations.

In this method, because the filtrate contained remaining suspended solid particles and macromolecules, it could not be sent directly to the nanofiltration/osmosis step: an intermediate step of prescreening was necessary.

OBJECTS OF THE INVENTION

An object of the present invention is therefore to provide a new method of mechanically dewatering swine manure with none of the shortcomings of the prior art. Another object of the present invention is to provide a method of dewatering manure that does not necessitate the use of chemical additives for the operation mode.

Another object of the present invention is to provide a simple method of dewatering manure that can be automated and, more economically interesting, does not necessitate the use of chemical additives.

Another object of the present invention is to provide a method of dewatering manure wherein the liquid output produced therewith can safely be returned to the environment. A further object of the present invention is to provide a method of treating manure that substantially reduces the volume of animal wastes to be disposed of by increasing the percentage of water recovered from the initial manure.

SUMMARY OF THE INVENTION

More specifically, in accordance with the present invention, there is provided a method for treating swine manure comprising mechanically dewatering the manure through a tangential screen having an average pore size between about 200 and 500 microns to obtain a filtrate and a sludge, filtering the filtrate through at least one ultrafiltration membrane to obtain an ultrafiltration permeate and an ultrafiltration concentrate, and filtering the ultrafiltration permeate consecutively through at least one first reverse osmosis membrane and through at least one second reverse osmosis membrane wherein the at least one first reverse osmosis membrane is able to withstand a pressure of between 500 and 1000 psi to obtain a final permeate and a final concentrate whereby the final permeate may safely be returned to the environment.

In accordance with a preferred method of the present invention the method above-described further comprises treating the sludge through a press means for separating the sludge into a solid portion containing at least about 25 to 30% of dry solid and a liquid portion. The press means is preferably a screw press but any equivalent may be used.

In accordance with preferred methods and systems of the present invention, the tangential screen preferably has an average pore size of about 300 microns, and the at least one ultrafiltration membrane used is at least one tubular ultrafiltration membrane.

In accordance with preferred methods and systems of the present invention, the ultrafiltration permeate is maintained at a temperature not above about 35°C and most preferably at about 20°C.

According to preferred methods of the present invention, a further step of disinfecting may be added to the above-described methods for treating the final permeate. This step is preferably selected from the group consisting of ozonation and chlorination. It may also be followed by a treatment in an activated coal bed. According to the present invention, there is provided a system for treating manure comprising a tangential screen having an average pore size between about 200 and 500 microns for separating the manure into a filtrate and a sludge, at least one ultrafiltration membrane substantially removing suspended solids and macromolecules from the filtrate thereby producing an ultrafiltration permeate substantially devoid of suspended solids and macromolecules and an ultrafiltration concentrate, at least one first reverse osmosis membrane able to withstand a pressure of between about 500 and about 1000 psi substantially removing dissolved salts from the first permeate thereby producing a first osmosis permeate and a first osmosis concentrate; and at least one second reverse osmosis membrane substantially removing nitrogen containing molecules from the first osmosis permeate thereby producing a final permeate that may safely be returned to the environment and a second osmosis concentrate.

Preferred systems according to the present invention, comprise a chiller maintaining the ultrafiltration permeate at 35°C or less.

Other preferred systems according to the present invention further comprise a press means for separating the sludge into a solid portion containing between about 25 to about 30% of dry solid and a liquid portion. There is also provided a system wherein the final permeate constitutes at least 55% of the original manure.

As provided herein, the expression "raw manure" is meant to refer to the manure produced by swine before it is subjected to any treatment. It comprises liquid and solid wastes produced by swine.

As provided herein, the expression "operation mode" is used herein in opposition to the expression "cleaning mode". The expression "operation mode" is meant to refer to the manner in which the system described herein is operated during the manure treatment whereas the expression "cleaning mode" is used to refer to the manner in which the system is cleaned.

Other objects, advantages and features of the present invention will become more apparent upon reading of the following non- restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

In the appended drawing:

Figure 1 schematically illustrates the steps of a preferred method according to the present invention;

DESCRIPTION OF PREFERRED EMBODIMENTS

The overall invention deals essentially with two major phases. The first phase involves the separation of liquids from the swine waste product, to get the driest sludge available, while separating the water for further treatment. This greatly reduces the volume of the sludge once an important portion of the liquid has been removed.

The second phase involves the treatment of water and liquid removed from the swine manure. This water is treated by a pressure-driven membrane separation technology so that it is adequately clean environmentally to return to the natural water supply. One of the important features of the invention is that it limits the use of additional chemicals that have been traditionally used to treat sludge to further prevent environmental harm. Thus, the invention does not use chemicals, such as chlorine, flocculating or coagulating agents, to obtain an environmentally safe liquid output. In preferred methods according to the present invention, chlorine may be used to disinfect the liquid output when it is intended for human consumption.

Preferred methods according to the present invention comprise two distinct phases: a liquid/solid separation phase and a liquid treatment phase.

The liquid/solid separation phase preferably involves a first screening of the manure with a tangential screen and a screw press. Any press able to produce a solid having a dry solid content of about 25 to 30% can be used without departing from the spirit of this invention. Alternatively, a centrifuge could be used for the liquid/solid separation phase instead of the tangential screen combined with the press when the manure does not contain a high level of swine hair. The size of the pores is selected so that it is able to efficiently screen swine hair and suspended particles and macromolecules. The average size of the pores is about between 250 and 500μm depending on the nature of the swine manure to be treated. Preferably, it is about 300 μm in size. The separated liquid treatment phase involves a number of steps. The filtrate is first conveyed to an ultrafiltration system that removes suspended particles and macromolecules. The resulting permeate contains dissolved organic and inorganic solids.

Although any type of ultrafiltration membrane may be used in accordance with the present invention, it was found advantageous to use the tubular type of ultrafiltration membrane for a number of reasons. First, the tubular membrane was determined to be more efficient in screening suspended particles and macromolecules that have a tendency to foul other types of ultrafiltration membranes. The tubular ultrafiltration membrane has the further advantages of being space efficient, compact and of relatively low cost. After the ultrafiltration step, a high operating pressure is preferably used for treating the ultrafiltration permeate which contains a high concentration of dissolved solids (between 10 000 and 20 000mg/l). For this reason, it was found advantageous according to the methods of the present invention to use reverse osmosis membranes able to withstand the high pressures (500-1 OOOpsi) necessary to substantially remove these high concentration of dissolved solids in the permeate. Indeed, preferred methods of the present invention have shown that these membranes are able to produce a first osmosis permeate constituting about 75% of the ultrafiltration permeate. The average concentration of dissolved solid in the first osmosis concentrate according to the present invention may be at the most about 40 000 to 45 000 mg/L.

The ultrafiltration permeate is therefore preferably conveyed through a first reverse osmosis membrane for a substantial removal of the remaining dissolved ammoniacal nitrogen and other dissolved solids.

Although Figure 1 described below illustrates four first osmosis membranes, the methods of the present invention may use one or more first osmosis membrane without departing from the spirit of the present invention depending on the flow of ultrafiltration permeate to treat. Although the first osmosis permeate obtained according to a preferred method of the present invention could not be immediately rejected in the environment because of the residual amount of nitrogen that it still contains, it could be used as wash-water for the piggery or for general agricultural purposes.

The first osmosis permeate is therefore subjected to a second reverse osmosis step to grant the final permeate an improved quality .

The operating pressure used during the second osmosis may be between about 200 to 500psi depending on the flow of liquid going through. Under this pressure, about 80 % to 90 % of the flow is able to pass through the second osmosis membrane. The remaining 10 % to 20 % constitutes the second osmosis concentrate, which is returned upstream from the first osmosis.

The resulting final permeate constitutes water that is suitable for feeding the swine or may be safely returned to the environment. Although this final permeate is initially free from adverse bacteria, contamination may occur in the water storage tank which suggests that it may be advisable to disinfect the final permeate taken from the tank before it is fed to swine. The concentrates produced during the treatment (ultrafiltration concentrate, osmosis first concentrate) can safely be spread as fertilizer. The separated solid retained by the tangential screen can also be conveyed used as a fertilizer. However, due to its high dryness, this solid is very light so that it is preferably mixed with the ultrafiltration or the first osmosis concentrate before it is spread. This solid may also be used for composting.

The final permeate produced pursuant to preferred methods according to the present invention may retain a weak odour that is probably due to the small concentration of H₂S and amino acids that it may still contains. This final permeate is therefore preferably disinfected (chlorination or ozonation followed by an activated coal bed treatment) if it were intended for human consumption to prevent contamination that may have occurred in the water storage tank and to eliminate this odour. Preliminary tests with preferred methods of the present invention have indicated that the use of preferred methods according to the present invention is able to significantly reduce undesirable gaseous emanations produced by swine wastes.

Any number of screens, ultrafiltration membranes, osmosis membranes depending on the flow of manure to be treated may be used without departing from the present invention. For instance, for a farm of 5000 growing-finishing pigs bred in the Province of Quebec, 1 tangential screen, 1 screw press, four ultrafiltration membranes, four first osmosis membranes and one second osmosis membrane are preferably used. It is to be understood that the volume and quality of the manure produced by pigs in different parts of the world varies depending on the temperature and the nature the food that they are being given. For this reason, the number of screens, presses and membranes necessary to treat the manure produced a fixed number of pigs may vary according to the place of the world where are grown. Each of the above-described steps will be further described below with reference to Figure 1 in accordance with preferred embodiments of the present invention, which is a schematic view of a preferred method according to the present invention illustrating this method from the liquid/solid separation to the second reverse osmosis step.

Example 1 : liquid/solid separation of the swine manure

As is illustrated in Figure 1 , raw manure is pumped out of a temporary manure storage tank (1 ) and poured onto a tangential screen (2) having an average pore size of 300 μm. A portion of the liquid contained in the manure thereby filtrates through the screen so as to produce a concentrated manure portion on the bottom of the screen, a sludge, and a filtrate (5). The sludge is then pressed through a screw press (3) so as to obtain a solid portion (4) and a liquid portion. The liquid portion may be returned to the temporary manure storage tank (1 ). A screw-conveyor (6) then transports the solid portion (4) constituting about two to three percent of the raw manure to storage facilities (not shown). Two final outputs are then produced by the tangential screen/screw press mechanical dewatering system: a flocculent solid portion (4) having between about twenty-five to thirty percent of dry solid content and a filtrate (5) having between about two to four percent of dry solid content. It may then be used as fertilizer as it is or mixed with concentrates produced later in the treatment to produce a heavier fertilizer. If a surplus of solid is produced thereby, it can be transferred to an appropriate solid manure treatment center where it may be dried for later exportation. The solid portion can also be used for composting. Example 2: Ultrafiltration

As is illustrated in Figure 1 , the filtrate (5) is then conducted to a filtrate storing tank (34) from which it is led (7) to a tubular ultrafiltration membrane system. Although a preferred embodiment of the present method uses tubular ultrafiltration membranes for the purpose of substantially removing suspended solids and macromolecules, any type of ultrafiltration membranes may be used without departing from the spirit of the present invention. Four tubular ultrafiltration membranes are separately illustrated and respectively identified as (8a), (8b), (8c) and (8d). As indicated earlier, the number of membranes used depends on the flow to be treated: for a farm of 5000 pigs, four ultrafiltration membranes are preferably used. This ultrafiltration step produces two principal flows: an ultrafiltration concentrate (10) containing suspended solids and macromolecules strained by the membranes and an ultrafiltration permeate (11 ). For farms producing flows of seven gallons per minute, the filtrate (7) is preferably divided into two streams (7a) and (7b). Each stream (7a) and (7b) follows a separate but identical path to the other. For instance, stream (7a) goes through the ultrafiltration membrane (8a), the ultrafiltration concentrated portion produced thereby goes through a second ultrafiltration membrane (8b) through (7a'). The final ultrafiltration concentrate (10) is brought (10") to a manure storage tank (42) to be used as a fertilizer depending on the level of liquid in the storing tank (6). The ultrafiltration system operates in a semi-batch mode: the ultrafiltration concentrate (10) of the last membrane is returned to the filtrate storing tank (34) so that it is subjected again to the ultrafiltration cycle. The level of liquid in the filtrate storing tank (34) varies during the cycle and sensors (not shown) measure and indicate when the level is high and when it is low. The return of the ultrafiltration concentrate (10) back into the ultrafiltration cycle continues until the level of the filtrate storing tank (34) is high. At that point, the ultrafiltration concentrate (10) is brought to (10") to a manure storage tank (42) to be used as fertilizer. The ultrafiltration concentrate (10) is sent to the manure storage tank (42) until the level of the filtrate storing tank (34) is low: at that point, the cycle starts again and the ultrafiltration concentrate (10) is returned to the filtrate storing tank (34).

The ultrafiltration permeate (11) may then be directed to a chiller (15) where it may be cooled to avoid its temperature reaching 35°C to avoid the passage of dissolved salts and nitrogen through the membranes. It is preferably cooled to 20 °C for optimum results. The cooled ultrafiltration permeate (35) is then directed to the first reverse osmosis step.

Example 3: Reverse Osmosis

As is illustrated in Figure 1 , before a first osmosis takes place, the ultrafiltration permeate may first be conducted (35) to an ultrafiltration permeate storing tank (16). The ultrafiltration permeate storing tank (16) and the osmosis storing tank (22) described below act during the operation mode as temporary tanks for receiving the liquid from the preceding step, respectively the ultrafiltration step and the first reverse osmosis step, ensuring that sufficient liquid will be sent to the next step, respectively the first osmosis and the second osmosis steps. In specific methods of the present invention for which results are presented hereinbelow, spiral wound polymer membranes of 20,32 cm of diameter are used for the reverse osmosis. Other types of reverse osmosis membranes are encompassed by the present invention. Any other type of reverse osmosis membrane able to withstand pressures of 500 to 10OOpsi could be used without departing from the spirit of the invention. The operating pressure was about 5,52 Mpa (800 psi). Tubular reverse osmosis membranes may also be used according to the present invention but they are generally more expensive and are more space consuming.

From the ultrafiltration permeate storing tank (16), the ultrafiltration permeate is then directed (18) to the first reverse osmosis step.

The ultrafiltration permeate goes through a first reverse osmosis membrane (19a) whereby a first osmosis concentrate (20a) and a first osmosis permeate (21a) are produced. The first osmosis concentrate (20a) is then directed to additional concentration steps through additional first osmosis membranes. Depending on the flow of permeate to treat, the number of first osmosis membranes may vary. In Figure 1 , four first osmosis membranes are independently identified as (19a), (19b), (19c) and (19d). After going through all the first osmosis membranes, the final first osmosis concentrate (20) is directed to the manure storage tank (42) to be used as fertilizer or mixed with other concentrates produced by methods of the present invention. Four streams of first osmosis permeate are illustrated, each one produced by one of the four illustrated first osmosis membranes. The four streams of first osmosis permeate, which are each separately identified as (21a), (21 b), (21c) and (21d), are merged and the merged flow (21 ) is led to a reverse osmosis storing tank (22) from which it is directed (24) to the second reverse osmosis step.

Figure 1 shows that the first osmosis permeate (24) is then conducted through a second reverse osmosis membrane (26) to produce a second osmosis concentrate (28) and a final permeate (27). The second osmosis concentrate (28) is returned (29) upstream to the ultrafiltration permeate storing tank (16).

The final permeate (27) can then be safely returned to the environment or can be led to a water storage tank (33) to be used as wash-water for the piggery, for feeding the swine after a cautionary disinfecting step, or for agricultural purposes.

Example 4: Results

The specific system of the present invention the performance of which was presented in the above examples possesses 1 screen, 1 press, 4 ultrafiltration membranes, 4 first osmosis membranes and 1 second osmosis membrane. It has a capacity of treatment of about 9290 m³ per year with a variation of about 25%. This performance is calculated on the basis of an operating time of 16 hours per day and of 365 days a year. This system is thereby able to treat efficiently up to 1 ,6 m³ of manure per hour and 25 m³ of manure per day. An additional capacity of 25% remains (i.e. six hours each day) and is designed as a safety margin for unforeseeable increases in the manure production and for washing the membranes when necessary. The system may also be adapted for larger farms by increasing the number of membranes operating and/or by using several of the systems presented herein installed in parallel. This specific system was tested on a farm having a manure production of 4736 m³ per year.

Table 1 below presents the concentration of various substances of the manure before its treatment and in various outputs of the treatment according to a preferred method of the present invention. Table 1

These results show that 71% of the total manure treated is recoverable by methods of the present invention in the form of environmentally safe water. In other words it reduces the volume of animal waste generated by 71%. Out of the remaining 29%, about 3 % (the solid portion) may serve as composting or as fertilizer and the remaining 26% is preferably stored and may be used as fertilizer.

These results also show that methods of the present invention are able to significantly reduce concentrations of deleterious substances without the use of any chemical additives during the operation mode.

Table 2 presents the mineral contents of the final permeate obtained by the preferred method presented in the examples 1 to 3 presented above.

Table 2

Description Maximum Maximum Final acceptable acceptable permeat concentration concentration for

These results show that the final permeate (27) after treatment on a simple activated coal bed contains very low concentrations of deleterious substances. It then satisfies, in the case of Canada, the Health Canada norms for the maximum acceptable concentration of various substances for the rainwater sewage and for the maximum acceptable concentration of these substances for drinking water. Additional treatments may be effected to remove the substances that are still over the norms. The phenols may be removed by chlorination or ozonation and the sulfides may be removed with the use of a filter comprising a metal and activated coal.

The value of fertilizers can be measured in terms of their nitrogen, phosphorus and potassium content: this criterion can be referred to as the N-P-K value.

Table 3 below presents the N-P-K value of the outputs of the present invention

Table 3

(1 ) Before spread loss.

(2) Average values for swine manure.

These results show that the fertilizing value of each residue produced according to the preferred method of the present invention presented in examples 1 to 3 may be higher than that of raw manure. Although the phosphorus content of the first osmosis concentrate and the nitrogen content of the solid portion are lower than that of the raw manure itself, when all the residues are mixed together, the resulting fertilizing value is equivalent or higher to that of the raw manure.

Example 5: cleaning mode

For an optimum performance of the preferred method presented in examples 1 to 4, it is suggested to clean the system when the osmosis and ultrafiltration membranes performance noticeably decreases.

For the same reason, the osmosis and ultrafiltration membranes will be preferably changed every 3 to 5 years. The final permeate (27) is used as wash water for cleaning the ultrafiltration and reverse osmosis membranes. The cleaning mode is conducted countercurrent to the operating mode: the final permeate (27) that is used to clean the second osmosis membrane (26) is reused to clean the first osmosis membranes and this water is then used again to clean the ultrafiltration membrane. The lines (9a), (9b), (9c) and (9d) illustrate how the wash water goes through the ultrafiltration membranes (8a), (8b), (8c) and (8d) in a direction that is countercurrent to the operating mode direction of the liquid to be treated. The pH of the final permeate (27) may be adjusted when it is used as wash water. Any strong acid and strong base may be used to adjust the pH, hydrochloric acid and sodium hydroxide are preferably used because of their low cost and availability. In preferred embodiments of the present invention presented in examples 1 to 3 above, three tanks are used for during the cleaning mode. One of them is used exclusively during the cleaning mode: the filtrate storing tank (34) located upstream from the ultrafiltration receives the filtrate (5) that is still filled with suspended solid and macromolecules. To avoid having to wash this tank before each cleaning mode, a separate tank (12) is preferably used for washing the ultrafiltration membranes (8a), (8b), (8c) and (8d). The storing tanks (16) and (22) have a double function. During the operation mode, these storing tanks (16) and (22) act as buffer tanks that ensure that a sufficient amount of liquid from the previous step has accumulated before respectively the first osmosis and the second osmosis step begins. They also act as buffer tanks during the cleaning mode ensuring that a sufficient amount of liquid accumulated before the cleaning of the first reverse osmosis membranes and of the ultrafiltration membranes starts. The washing liquid may be adjusted with various chemical additives to clean the membranes more efficiently. The double function of these storing tanks (16) and (22) reduces the space that would otherwise have been required to locate additional washing tanks. Valves are appropriately located on elements of the system so as to adequately direct the.flow of liquid during the operating mode and the cleaning mode. Hence, the line (17) and other lines illustrated in Figure 1 that have not been referred to in the above examples show the direction of the liquid during the cleaning mode.

Both the concentrate and the permeate produced by the membranes during the cleaning mode are sent to the tank (12), (16) or (22) that is situated downstream from them (i.e. during the cleaning mode, the ultrafiltration is located downstream from the osmosis membranes). After the cleaning, the washing water coming out of the ultrafiltration membranes (8a), (8b), (8c) and (8d) is sent to the temporary manure storage (1 ).

Although the present invention has been described hereinabove by way of preferred embodiments thereof, it can be modified without departing from the spirit and nature of the subject invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method for treating swine manure comprising mechanically dewatering the manure through a tangential screen having an average pore size between about 200 and 500 microns to obtain a filtrate and a sludge; filtering the filtrate through at least one ultrafiltration membrane to obtain an ultrafiltration permeate and an ultrafiltration concentrate; and filtering the ultrafiltration permeate consecutively through at least one first reverse osmosis membrane and through at least one second reverse osmosis membrane wherein the at least one first reverse osmosis membrane is able to withstand a pressure of between 500 and 1000 psi to obtain a final permeate and a final concentrate; whereby the final permeate may safely be returned to the environment.

2. A method as recited in claim 1 wherein the sludge is further treated through a press means for separating the sludge into a solid portion containing at least about 25 to 30% of dry solid and a liquid portion.

3. A method as recited in claim 2 wherein the press means treating step is done with a screw press.

4. A method as recited in claim 1 wherein the dewatering step is performed through a tangential screen having an average pore size of about 300 microns.

5. A method as recited in claim 1 wherein the filtering through the at least one ultrafiltration membrane is performed through at least one tubular ultrafiltration membrane.

6. A method as recited in claim 1 wherein the ultrafiltration permeate is maintained at a temperature not above about 35°C.

7. A method as recited in claim 6 wherein the ultrafiltration permeate is maintained at a temperature of about 20°C.

8. A method as recited in claim 1 further comprising a disinfecting step for treating the final permeate wherein the disinfecting step is selected from the group consisting of ozonation and chlorination.

9. A method as recited in claim 8 wherein the disinfecting step is followed by a treatment in an activated coal bed.

10. A method for treating swine manure comprising mechanically dewatering the manure through a tangential screen having an average pore size of about 300 microns to obtain a filtrate and a sludge; filtering the filtrate through at least one ultrafiltration membrane to obtain an ultrafiltration permeate and an ultrafiltration concentrate; maintaining the temperature of the ultrafiltration permeate not above 35°C; and filtering the ultrafiltration permeate consecutively through at least one first reverse osmosis membrane able to withstand a pressure of between 500 and 1000 psi and through at least one second reverse osmosis membrane to obtain a final permeate and a final concentrate; whereby the final permeate may safely be returned to the environment.

11. A system for treating manure comprising a) a tangential screen having an average pore size between about 200 and 500 microns for separating the manure into a filtrate and a sludge, b) at least one ultrafiltration membrane substantially removing suspended solids and macromolecules from the filtrate thereby producing an ultrafiltration permeate substantially devoid of suspended solids and macromolecules and an ultrafiltration concentrate; c) at least one first reverse osmosis membrane able to withstand a pressure of between about 500 and about 1000 psi substantially removing dissolved salts from the first permeate thereby producing a first osmosis permeate and a first osmosis concentrate; and d) at least one second reverse osmosis membrane substantially removing nitrogen containing molecules from the first osmosis permeate thereby producing a final permeate that may safely be returned to the environment and a second osmosis concentrate.

12. A system as recited in claim 11 further comprising a chiller maintaining the ultrafiltration permeate at 35°C or less.

13. A system as recited in claim 11 further comprising a press means for separating the sludge into a solid portion containing between about 25 to about 30% of dry solid and a liquid portion.

14. A system as recited in claim 11 whereby the at least one ultrafiltration membrane is of the tubular type.

15. A system as recited in claim 11 wherein the final permeate constitutes at least 55% of the original manure.