Patent Publication Number: US-2023150854-A1

Title: Method and apparatus for anaerobic digestion of liquid waste streams

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional patent application of and claims priority to U.S. Provisional Patent Application No. 63/280,888 filed Nov. 18, 2021, which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The disclosure relates to anaerobic digestion of liquid waste streams. 
     BACKGROUND 
     The anaerobic digestion of organic liquid waste streams has been a fundamental part of waste treatment for hundreds of years. Municipal and industrial wastes have been treated utilizing anaerobic digestion techniques for over 100 years in the United States, and within the last thirty years, anaerobic digestion of higher strength animal wastes has also become an accepted practice. However, a limitation of the bacterial-based anaerobic digestion process has been the inability of anaerobic bacteria to grow outside the parameter of a narrow pH range. 
     Anaerobic digestion comprises two main classes of anaerobic bacteria: acid forming bacteria (acid formers) and methanogenic bacterial (methane formers). The acid forming bacteria perform best at a pH of about 6.0 to about 7.0 and the methanogenic bacteria perform bets at a pH of about 6.5 to 8.0. These narrow pH ranges preclude effectively utilizing anaerobic digestion waste treatment technology for the treatment of high-strength organic, liquid waste streams having a pH below about 6.5 or above about 8.0. 
     A high-strength organic liquid waste stream typically has a solids content of about 5% to about 40%. Acidic high-strength organic liquid wastes have a pH of less than about 5.0 Examples of such wastes include acidic cheese whey, with a pH of about 3.5, and the rapidly growing wastes from ethanol plants, with a pH of about 3.5 to 4.0 and a solids content of about 30% to about 35%. When anaerobic digestion has been attempted with acidic high-strength organic liquid wastes in mixed digesters, the traditional response has been to adjust the pH of the acidic wastes to about 7 with either the addition of expensive chemical pH adjusters or the blending of alkaline waste streams with the acidic wastes. Alkaline high-strength organic liquid wastes have a pH greater than about 8.0. Examples of such wastes include the glycerin by-product waste from biodiesel plants that convert animal oils or vegetable oils into biodiesel. Glycerin typically has a pH of about 12 to about 14 and a high solids content of about 20% to about 35%. When anaerobic digestion has been attempted with alkaline high-strength organic liquid wastes in mixed digesters, the traditional response has been the addition of expensive, corrosive acids, such as sulfuric or citric acids, to lower the pH of the entire digester prior to the anaerobic biodegradation so that the influent pH of the waste stream is continually adjusted to a pH of about 7. 
     BRIEF SUMMARY 
     In one embodiment, the disclosure relates to a system for treating liquid waste. In one embodiment, the system for treating liquid waste comprises: an acid forming chamber that at least partially converts carbon molecules in the liquid waste to acids; a plug-flow methanic chamber downstream from the acid forming chamber that at least partially converts the acids in the liquid waste to methane; a weir structure provided between the acid forming chamber and the methanic chamber; a solid-liquid separator downstream from the methanic chamber, the separator separating a portion of the liquid waste into alkaline sludge and effluent; and a first flow path that recycles alkaline sludge to at least one of the acid forming chamber, the methanic chamber, and combinations thereof. 
     In one embodiment, the system for treating waste further comprises a center wall that divides the methanic chamber into a first leg and a second leg. In one embodiment, a portion of the center wall forms a partial division between the acid forming chamber and the methanic chamber. 
     In one embodiment, the system for treating waste further comprises an enclosure surrounding the acid forming chamber, the methanic chamber, the solid-liquid separator and the first flow path. 
     In one embodiment, the weir structure is positioned between the enclosure and the portion of the center wall forming the partial division between the acid forming chamber and the methanic chamber. 
     In one embodiment, the weir structure has a first weir wall at a level below an operating liquid level of both the acid forming chamber and methanic chamber. 
     In one embodiment, the weir structure has a second weir wall at a level approximately equal to the operating liquid level of the acid forming chamber, wherein the operating liquid level of the acid forming chamber is greater than the operating liquid level of the methanic chamber. 
     In another embodiment, the second weir wall is inclined from the methanic chamber to the acid forming chamber. 
     In one embodiment, the disclosure relates to a system comprising: an acid forming chamber that at least partially converts carbon molecules in a liquid waste to acids; a plug-flow methanic chamber downstream from the acid forming chamber that at least partially converts the acids in the liquid waste to methane; and a weir structure provided between the acid forming chamber and the methanic chamber, wherein the weir structure has a first weir wall at a level below an operating liquid level of both the acid forming chamber and methanic chamber. 
     In another embodiment, the disclosure relates to a system comprising an enclosure surrounding an acid forming chamber and a methanic chamber that is downstream from the acid forming chamber, wherein the enclosure has a roof; a center wall that divides the methanic chamber into a first leg and a second leg; wherein a portion of the center wall forms a partial division between the acid forming chamber and the methanic chamber; and a weir structure positioned between the roof of the enclosure and the portion of the center wall forming the partial division between the acid forming chamber and the methanic chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view of a waste treatment system in accordance with embodiments of the present disclosure; 
         FIG.  2    is a partial cross-section elevational view of the methanic chamber of the waste treatment system shown in  FIG.  1   ; 
         FIG.  3    is a partial top plan view of the methanic chamber shown in  FIG.  1   ; 
         FIG.  4    is a partial cross-sectional view of the methanic chamber taken along the  4 - 4  line of  FIG.  1   ; 
         FIGS.  5 A- 5 C  are schematic views of the waste treatment system of  FIG.  1    with an alternative passage from the acid chamber to the methanic chamber; 
         FIG.  6    is a schematic view of an alternative waste treatment system in accordance with embodiments of the present disclosure; 
         FIG.  7    is a partial cross-sectional view of a methanic chamber taken along line  6 - 6  of  FIG.  6   ; 
         FIG.  8    is a partial cross-section elevational view of the digester taken along the  7 - 7  line in  FIG.  6   ; 
         FIG.  9    is a schematic view of a waste treatment system according to embodiments of the present disclosure; and 
         FIG.  10    is a schematic view of a waste treatment system according to embodiments of the present disclosure. 
     
    
    
     Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The methods and apparatuses are capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     DETAILED DESCRIPTION 
     Definitions 
     The numerical ranges in this disclosure are approximate, and thus may include values outside of the range unless otherwise indicated. Numerical ranges include all values from and including the lower and the upper values, in increments of one unit, provided that there is a separation of at least two units between any lower value and any higher value. As an example, if a compositional, physical or other property, such as, for example, molecular weight, viscosity, melt index, etc., is from 100 to 1,000, it is intended that all individual values, such as 100, 101, 102, etc., and sub ranges, such as 100 to 144, 155 to 170, 197 to 200, etc., are expressly enumerated. For ranges containing values which are less than one or containing fractional numbers greater than one (e.g., 1.1, 1.5, etc.), one unit is considered to be 0.0001, 0.001, 0.01 or 0.1, as appropriate. For ranges containing single digit numbers less than ten (e.g., 1 to 5), one unit is typically considered to be 0.1. These are only examples of what is specifically intended, and all possible combinations of numerical values between the lowest value and the highest value enumerated, are to be considered to be expressly stated in this disclosure. Numerical ranges are provided within this disclosure for, among other things, relative amounts of components in a mixture, and various temperature and other parameter ranges recited in the methods. 
     As used herein, the singular forms “a,” “an,” and “the” refer to one or more than one, unless the context clearly dictates otherwise. 
     As used herein, the term “anaerobic digester effluent” refers to effluent produced at any stage during a manure management lifecycle. Anaerobic digester effluent includes effluent directly removed from the anaerobic digester, effluent removed from the digester and separated from large solids, effluent removed from the digester and separated from fine solids, effluent removed from the digester and separated from large and fine solids; effluent removed from the digester and aerated; effluent removed from the digester and heated; effluent removed from the digester and heated and aerated; effluent removed from the digester heated and aerated and separated from solids; effluent removed from the digester heated, aerated and used to remove H 2 S from a biogas, effluent removed from the digester heated, aerated, separated from solids; used to remove H 2 S from biogas; effluent removed from the digester heated, aerated, used to remove H 2 S from a biogas and regenerated to an alkaline pH; effluent removed from the digester heated, aerated, separated from solids; used to remove H 2 S from biogas, and regenerated to an alkaline pH; effluent removed from the digester heated, aerated, used to remove H 2 S from a biogas, regenerated to an alkaline pH, and used to remove CO 2  from a biogas; and effluent removed from the digester heated, aerated, separated from solids; used to remove H 2 S from biogas, regenerated to an alkaline pH and used to remove CO 2  from biogas. Anaerobic digester effluent and effluent may be used interchangeably unless stated otherwise. 
     As used herein, the term “includes” means “comprises.” For example, a device that includes or comprises “A” and “B” contains “A” and “B” but may optionally contain “C” or other components other than “A” and “B.” A device that includes or comprises “A” or “B” may contain “A” or “B” or “A” and “B,” and optionally one or more other components such as “C.” 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed terms. For example, when used in a phrase such as “A and/or B,” the phrase “and/or” is intended to include both A and B; A or B; A (alone); and B (alone). Likewise, the term “and/or” as used in a phrase such as “A, B and/or C” is intended to encompass each of the following embodiments: A, B and C; A, B, or C; A or C; A or B; B or C; A and C; A and B; B and C; A (alone); B (alone); and C (alone). 
     Spatial terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element&#39;s or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of device in use or operation in addition to the orientation depicted in the figures. For example, if the device is turned over, elements described as “below” or “beneath” other elements or features would then be orientated “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90° or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     As used herein, the term “manure” is meant to refer herein to animal wastes including animal dejections, feed remains and hair. 
     As used herein, the term “treated biogas” refers to biogas that has been in direct or indirect contact with an alkaline effluent. 
     Treatment of Acidic High-Strength Organic Liquid Wastes 
     The present invention allows for the treatment of acidic high-strength organic liquid wastes with little or no chemical pH adjustment and without the requirement of blending with other higher pH liquid wastes. This waste treatment system allows the host waste production facility to treat its own wastes economically, on-site with a small plant footprint, and to utilize the resultant high-energy biogas internally in its plant process. As used herein, the term “acidic high-strength organic liquid waste” (hereinafter “acidic liquid waste”) means a process waste, organic in nature, with a pH of less than about 5.0 and with a solids content of greater than about 5%. 
     The challenge in completing the anaerobic degradation of acidic liquid wastes is an imbalance in the biological system. Anaerobic degradation relies on acid forming bacteria to break down the complex carbon molecular structures of the organic input feed into simpler molecular structures such as acetic acid. Subsequently, methanogenic bacteria break down the simpler acid molecular structures into a biogas consisting primarily of methane and carbon dioxide. Suitable acid forming bacteria and methanogenic bacteria may be found in nature, such as, but not limited to, the bacteria found naturally in a cows stomach. Examples of acid forming bacteria may include, but are not limited to, at least one of  Clostridia, Fibrobacter succinogenes, Ruminococcus albus, Butyrivibrio fibrisolvens, Selenomanas ruminatium, Streptococcuslovis, Eubacterium ruminatium , external enzymes, and combinations thereof. Examples of methanogenic bacteria may include, but are not limited to, at least one of  Methanothrix, Methanosarcina, Methanospirillum, Methanobacterium, Methanococcus, Methanobrevibacterm, Methabnomicrobium - mobile, Methanosaeta, Methanobacterium thermoautotrophicum, Methanobacterium formicicum, Methanobactotrophicum, Methanobacterium formicicum, Methanobacterium thermoalcahphilum, Methanococcus thermolithotrophicus, Methanosarcina thernophila, Methanosaela thermoacetophila  and combinations thereof. The bacteria production of biogas consumes the acids in the liquid waste and creates a higher pH, alkaline solution. In traditional waste such as municipal and animal wastes, the input wastes have a neutral pH of about 7 and possess sufficient natural fiber and alkalinity so that the acid forming and the acid reducing reactions take place concurrently and the pH of the treatment process remains in the range of about 6.0 to about 8.0. This chemically and biologically balanced system allows for unimpeded degradation of the organic wastes and production of energy in the form of biogas. 
     Acidic liquid wastes create a special problem for the traditional anaerobic digestion processes. Acid forming bacteria are much more robust, faster population multipliers, and more tolerant of lower pH conditions than the slower breeding, pH sensitive methanogenic bacteria. When presented with an acidic liquid waste that has very slight natural alkalinity with it, such as ethanol by-product wastes, the acid forming bacteria out-produce the methanogenic bacteria. As a result, the pH of the liquid waste rapidly drops to a pH of about 4.0 or less. The entire digestion process stops and the organic waste becomes “dead” due to bacteria inaction at this low pH level. In the traditional mixed anaerobic digester industry, the response to this type of acidic waste and the resultant problems has been digester technology avoidance or continuous heavy chemical usage for pH balancing with high technology/monitoring and low biogas production. 
     One aspect of the present invention is to modify a plug-flow anaerobic digester system to treat acidic liquid wastes using a two-step anaerobic biodegradation process. In the first step, acid forming bacteria are cultivated to break down the complex carbon molecular structures in the liquid waste into simpler acid molecules. In the second step, methanogenic bacteria are cultivated to subsequently break down the simpler acid molecules into biogas. Examples of plug-flow systems that may be modified for this purpose are disclosed in U.S. Pat. No. 6,451,589 issued to Dvorak on Sep. 17, 2002, U.S. Pat. No. 6,613,562 issued to Dvorak on Sep. 2, 2003, U.S. Pat. No. 7,078,229 issued to Dvorak on Jul. 18, 2006, U.S. application Ser. No. 10/694,244 (U.S. Publication No. 2004/0087011) filed on Oct. 27, 2003, and International Patent Application No. PCT/US2006/045414 entitled “Anaerobic Digester Employing Circular Tank,” GHD, Inc. filed on Nov. 27, 2006 (MBF Case No. 031154-9005) the contents of each of which are hereby fully incorporated by reference. 
       FIGS.  1 - 4    represent various aspects of one embodiment of the present invention. In  FIG.  1   , the waste treatment system  10  comprises an influent pH monitoring station  16  and a digester enclosure  20 . The digester enclosure  20  encompasses an acid forming chamber  30 , a methanic chamber  40 , a sludge pit  60 , and an effluent pit  50 . The acid forming chamber  30  containing the acid forming bacteria and the methanic chamber  40  containing the methanogenic bacteria collectively form an anaerobic digester. The digester enclosure  20  is arranged such that a relatively large methanic chamber  40  may be built in a relatively small space. 
       FIG.  2    illustrates one embodiment of the construction of an outside wall  54  of the digester enclosure  20 . The height of the outer wall  54  of the digester enclosure  20  is about 17 feet, with a liquid depth  58  in the digester enclosure  20  of about 14.5 feet. A footing  62  provides an interface between the wall  54  and the ground  66 , and supports the wall  54  and the edge  50  of the floor  52 . Both the footing  62  and the wall  54  are constructed of poured concrete. The wall  54  is about twelve inches thick at the lower end  78  of the wall  54 , and about eight inches thick at the upper end  82  of the wall. The floor  52  of the digester enclosure  20  is about five inches of concrete. Insulation  86  (optional) with a thickness of about four inches is arranged below the floor  52  and provides an interface between the floor  52  and the ground  66 . 
     The roof  90  of the digester enclosure  20  is located about 16 feet above the floor  52  of the digester enclosure  20 . The roof  90  is constructed of about ten-inch thickness of hollowcore precast concrete panels  98  (e.g., Spancrete® Hollowcore® available from Spancrete, Inc., Green Bay, Wis.) topped by a layer of insulation  94  with a thickness between about four and about eight inches. 
     A biogas storage chamber  102  (optional) is located above the roof  90 . The primary component of the biogas storage chamber  102  is a liner  106  including an upper liner section  110  and a lower liner section  114 . The liner  106  is preferably constructed from high-density polyethylene (HDPE), but may be any other suitable material. The liner  106  is sealed around the edges  118  of the liner  106  by capturing the edges  118  beneath six-inch channel iron  122 , which is removably attached to the digester enclosure wall  54  using nuts  126  on a plurality of anchor bolts  130  embedded in the digester enclosure wall  54 . A ten-inch PVC pipe  134  is inserted around the periphery of the chamber  102  within the liner  106  to assist in maintaining the seal around the periphery of the liner  106 . The liner  106  is constructed such that it can flexibly fill with biogas as the biogas is produced in the methanic chamber  40 , and can be emptied of biogas as is needed. The biogas storage chamber  102  may be replaced by any other suitable gas storage system including a roofed storage system. 
     As shown in  FIG.  1   , a pH monitoring station  16  measures and adjusts the pH of the influent acidic liquid waste prior to sending the liquid waste to the acid forming chamber  30 . The pH of the influent may be monitored by a pH probe that controls a vari-speed chemical feed pump. If the pH of the influent is too low, the chemical pump delivers an alkaline solution that adjusts the initial pH of the influent to a level that facilitates the growth of acid forming bacteria. Examples of such alkaline solutions include solutions of Ca(OH) 2 , Mg(OH) 2 , NaOH, KOH, alkaline organic materials, or combinations thereof. 
     An influent conduit  18  transfers liquid waste from the pH monitoring station to the acid forming chamber  30 . An internal heating device  22 , such as heat exchanging coils, located within the acid forming chamber  30  maintains the liquid waste at a temperature that facilitates bacterial activity. Stirring mechanisms within the acid forming chamber  30  prevent temperature stratification and promote better bacterial growth. Stirring mechanisms may include, but are not limited to, mechanical stirrers, agitation from recycled biogas, hydraulic agitation with recycled waste liquids, or combinations thereof. A pH monitoring station A in  FIG.  1    measures the pH of the liquid waste within the acid forming chamber  30  and triggers the delivery of alkaline sludge from the sludge pit  60  to the acid forming chamber  30  via flow path  42  to maintain the pH of the liquid waste in the acid forming chamber  30  at about 6.0 to about 7.0. Although  FIG.  1    shows the alkaline sludge being delivered to the pH monitoring station A in the acid forming chamber  30 , it should be understood by one skilled in the art that the alkaline sludge may be delivered to one or more sites located anywhere within the acid forming chamber  30 . The flow path  42  may be defined by any number of devices that may include, but are not limited to, a pipe, tile, a channel, and a tube. In some embodiments, the pH monitoring station A triggers a vari-speed sludge recirculation pump. The pump recycles an appropriate amount of alkaline sludge from the sludge pit  60  at the end of the waste treatment system  10  to the liquid waste in the acid forming chamber  30 . 
     The liquid waste from the acid forming chamber  30  is transferred via horizontal plug-flow movement of the liquid waste to the methanic chamber  40 . As shown in  FIG.  1   , the methanic chamber  40  may be a U-shaped tank with overall horizontal dimensions of about 120 feet long and about 72 feet wide, depending on the volume of liquid wastes to be treated. A center wall  65  divides the methanic chamber  40  into a first leg or passageway  46  and second leg or passageway  48  of the U-shape. One or more partitions  70  may run severally parallel to, and on opposite sides of, the center wall  65 . The partitions  70  may comprise at least one of a rigid board or plank, curtain or drape, tarp, film, and a combination thereof. In addition, the partitions  70  may be constructed of a variety of materials including, without limitation, at least one of a metal, wood, polymer, ceramic, composite, and a combination thereof. As illustrated in  FIG.  4   , the partitions  70  are shorter than the center wall  65  and are raised off the floor of the methanic chamber  40 . This allows liquid waste to flow underneath and then over the partitions  70  as it plug flows through the methanic chamber  40 . In some embodiments, the center wall  65  rises about 16 feet off the floor of the methanic chamber  40 . The partitions  70  are about 10 feet 6 inches high and sit about 2 feet above the floor of the methanic chamber  40 . The partitions  70  are about 2 feet away from the center wall  65 . The digester enclosure  20  is about 36 feet from the center wall  65 . 
     As shown in  FIGS.  3 - 4   , an internal heating device  72  is located within the methanic chamber  40  to maintain the liquid waste at a temperature that facilitates bacterial activity. The heating device  72  may be used for heating or cooling as determined by the influent liquid temperature. In the embodiment shown in  FIGS.  3 - 4   , the heating device  72  comprises a series of heating conduits  74  that run parallel to the center wall  65 . The heating conduits  74  each contain a heating medium. Any variety of heating media may be used including, but not limited to, water and gas. The heating conduits  74  are arranged in a two-by-four grid. However, it should be recognized by those skilled in the art that any number of heating conduits  74  may be arranged in a variety of configurations without departing from the spirit and scope of the present invention. Moreover, other heating devices known to those skilled in the art may be employed including, but not limited to, heating coils. 
     In addition to controlling the temperature within the methanic chamber  40 , the heating device  72  may facilitate the mixing of the liquid waste as it flows through the methanic chamber  40 . The heating device  72  may be used to heat the liquid waste, causing the heated liquid waste to rise up the center wall  65  under convective forces. In embodiments employing one or more partitions  70 , heated waste material flows upwardly in the space created between the partitions  70  and the center wall  65 . At the same time, liquid waste near the inner wall of the relatively cooler digester enclosure  20  falls under convective forces. As a result, the convective forces cause the liquid waste to follow a circular flow path upward along the center wall  65  and downward along the digester enclosure  20 . At the same time, the liquid waste flows along the first leg  46  and second leg  48  of the methanic chamber  40 , resulting in a combined corkscrew-like flow path for the liquid waste. Mixing of the plug flow prevents stratification in the digester. 
     Stirring mechanisms are also located within the methanic chamber  40  and may include mechanical stirrers, agitation from recycled biogas, hydraulic agitation with recycled liquid waste, or combinations thereof. In some embodiments, recycled biogas agitation is maintained for waste mixing in a direction perpendicular to the waste flow direction. As illustrated in  FIGS.  3  and  4   , one or more gas conduits  30  may run parallel to, and in-between, the center wall  65  and the partitions  70 . Air diffuser nozzles  32  located along the gas conduits  30  dispense biogas upward and parallel to the center wall  65 . As liquid waste plug flows through the methanic chamber  40 , liquid waste is drawn underneath the partitions  70  by the vertical rising of the gas and forced back over the top of the partitions  70 , creating a similar corkscrew-like flow path through the methanic chamber  40 . The air diffuser nozzles can be a variety of sizes, including ¾ inch. 
     pH monitoring stations are located at various sites throughout the methanic chamber  40  to maintain the pH of the liquid waste at a level that facilitates bacterial activity.  FIG.  1    shows three such pH monitoring stations (B-D). However, any number of pH monitoring stations can be distributed throughout the methanic chamber  40 . The number of such stations may depend upon such factors as the nature of the liquid waste, activity of the methanogenic bacteria, and system flow rates. When the pH of the liquid waste drops below an acceptable level, pH monitors trigger the delivery of alkaline sludge via one or more flow paths  44  from the sludge pit  60  to the methanic chamber  40 . In some embodiments, the pH monitors trigger a vari-speed sludge recirculation pump that delivers an appropriate amount of alkaline sludge to the methanic chamber  40 . Although  FIG.  1    shows the alkaline sludge being delivered to the pH monitoring stations (B-D) in the methanic chamber  40 , it should be understood by one skilled in the art that the alkaline sludge may be delivered to one or more sites located anywhere within the methanic chamber  40 . The flow paths  44  may be defined by any number of devices that may include, but are not limited to, a pipe, tile, a channel, and a tube. 
     In addition to producing activated sludge, the anaerobic digestion in the methanic chamber  40  also produces biogas in the form of methane gas, which is collected above the liquid level  58  and can be stored in the biogas storage chamber  102 , or utilized directly as a bio-fuel. Liquid that condenses within the chamber  102  may be directed through an effluent conduit to a liquid storage lagoon. The collected biogas may be used to fuel an internal combustion engine that, in combination with an electric generator, may be used to produce electricity that is used within the waste treatment system  10 , sold to a power utility, or a combination thereof. The cooling system of the internal combustion engine may also produce hot coolant that may be used to heat liquid waste in the acid forming chamber  30  and/or to heat and agitate the liquid waste in the methanic chamber  40 . Hot water from the engine may pass through an air/water cooler to reduce the temperature of the water from the about 180° F. temperature at the exit of the engine to about 160° F. for use in the acid forming chamber  30  and the methanic chamber  40 . 
     The effluent pit  50  is located adjacent to the sludge pit  60 . The liquid waste plug flows sequentially from the acid forming chamber  30  into the methanic chamber  40  into the sludge pit  60  and into the effluent chamber  50 . At least a portion of the sludge may be recirculated via one or more flow paths  42 ,  44  to the acid forming chamber  30  and methanic chamber  40 . In some embodiments, a sump conduit from the effluent chamber  50  leads to a standard solids press to separate the digested liquid from the digested solids. The liquid from the solids press may be recycled to the acid forming chamber  30  for further processing. The solids from the solid press may be sent to a composter and bagged for commercial sale. 
     A natural gravity system may be used to separate solids from liquids in the sludge pit  60  at the end of the waste treatment system  10 . However, it should be understood by one skilled in the art that any solid-liquid separator may be used in place of, or in addition to, the gravity system. Any solid-liquid separator that separates solids from liquids by gravity, differential settling velocity, or size-exclusion may be employed. Examples of additional solid-liquid separators include settling ponds, hydrocyclones, centrifuges, and membrane filters or separators. 
     In operation of the waste treatment system  10 , as illustrated in  FIG.  1   , acidic liquid waste is transported to the waste treatment site. Prior to entering the acid forming chamber  30 , the pH of the liquid waste influent is measured and, if necessary, the pH of the influent is adjusted to a range of between about 6.0 and about 7.0 to start the acid forming bacterial growth. In one embodiment, a pH probe that controls a vari-speed chemical feed pump is utilized to monitor and adjust the initial pH of the influent. Agents used to adjust the pH may include a variety of alkaline substances, such as solutions of Ca(OH) 2 , Mg(OH) 2 , NaOH, KOH, alkaline organic materials, or combinations thereof. 
     The liquid waste is transferred from the pH monitoring station  16  via the influent conduit  18  to the acid forming chamber  30 . In the acid forming chamber  30 , the internal heating device  22  adjusts the temperature of the influent to facilitate the growth of acid forming bacteria. Temperature control is important for methanogenic bacteria (less so for acid forming bacteria) and the temperature is closely regulated in the acid forming chamber  30  so that the temperature is kept constant as the liquid “plug flows” from the acid forming chamber  30  into the methanic chamber  40 . The temperature can be site determined to be about 97° F. to about 103° F. for a mesophilic operating digester or about 132° F. to about 138° F. for a thermophilic digester. The liquid waste in the acid forming chamber  30  is continuously stirred to eliminate temperature stratification in the liquid waste and to promote better bacterial growth. In one embodiment, the contents of the acid forming chamber are continuously stirred with recycled biogas agitation. 
     Within the acid forming chamber  30 , acid forming bacteria convert complex carbon molecules into simpler acids. These acids in turn lower the pH of the liquid waste in the acid forming chamber  30 . In order to prevent the pH from dropping too low to sustain bacterial activity, the pH of the liquid waste must be frequently adjusted upward. Rather than add additional pH adjusters from outside the waste treatment system, the pH can be adjusted internally by mixing alkaline sludge from the sludge pit  60  at the end of the waste treatment system  10  with the existing influent in the acid forming chamber  30  to maintain the pH of the influent at about 6.0 to about 7.0 for maximum acid-forming bacteria growth rates and efficiency. The pH of the sludge in the sludge pit is typically between about 7.0 to about 8.0. In addition to changing pH, the sludge can also “seed” the influent in the acid forming chamber  30  with mature acid forming bacteria and methanogenic bacteria. In some embodiments, a roof mounted pH monitor identified by station A in  FIG.  1    controls a vari-speed sludge recirculation pump to recycle sludge from the sludge pit  60  at the end of the waste treatment system  10  to the influent in the acid forming chamber  30 . The flow rate of recycled sludge is determined by the need for pH blending, which is ultimately determined by the growth rate of the acid forming bacteria. 
     As new influent enters the acid forming chamber  30 , the treated liquid waste within the acid forming chamber  30  will plug flow into the methanic chamber  40 . In the methanic chamber  40 , an environment to foster the growth of the methanogenic bacteria is maintained. The pH of the liquid waste in the methanic chamber  40  is maintained at a pH of about 6.5 to about 8.0, and particularly at a pH of about 7.5 to about 8.0. To accomplish this, pH monitoring stations (B-D) are located throughout the methanic chamber  40 . If the drops below a set value, such as 6.5, at any of these stations, the pH monitors will activate one or more vari-speed sludge recirculation pumps to add alkaline sludge from the sludge pit  60  to the liquid waste in the methanic chamber  40 . The corkscrew mixing of the liquid waste in the methanic chamber  40  by the utilization of the recirculated biogas and/or heating ensures a homogeneous pH mix and prevents pH stratification within the vessel. Heat exchanging coils within the methanic chamber  40  maintain the temperature of the liquid waste within a range of about 1 to about 2 degrees of the set point temperature. The set point temperature for a mesophilic temperature digester will be about 100° F. and about 134° F. for a thermophilic digester. The heating coils can be utilized for heating or cooling as determined by the influent liquid temperature. The liquid waste within the methanic chamber  40  is continuously mixed with recycled biogas jetted into the liquid waste in a direction perpendicular to the waste flow direction. Mixing prevents stratification within the methanic chamber and enhances biodegradation. 
     As the waste stream plug flows through the methanic chamber  40 , it is not mixed with the newer incoming waste material and is, therefore, allowed to biodegrade in multiple sections as it travels in a horizontal corkscrew-like pathway through the first leg  46  and the second leg  48  of the methanic chamber  40 . As the methanogenic bacteria function, they consume the acids created in the acid forming chamber  30  and effectively raise the pH of the liquid waste stream and increase the alkalinity of the liquid waste. At the end of the methanic chamber  40 , with properly engineered hydraulic retention times based on influent characteristics, the acid forming bacteria will have long completed their function and the methanogenic bacteria will have consumed the bacteria-produced acids. This results in a waste effluent of high pH and alkalinity in comparison to the influent. The greatest alkalinity and bacteria population at the very end of the waste treatment system  10  will be in the bacteria “sludge” that is allowed to settle in the sludge pit  60  located at the end of the waste treatment system  10 . The sludge pit  60  does not have mixing and thus the sludge is allowed to settle to the bottom. This sludge, with its higher alkalinity, pH, and bacteria population, is the recirculated sludge utilized at the various points (stations A, B, C and D) throughout the waste treatment system  10  for pH control and bacterial seeding. 
     The biodegraded effluent may be further treated or disposed of by the generating facility as required. Biogas generated by the anaerobic biological process may be collected in the gas collection space above the liquid level and under the ceiling of the methanic chamber  40 . The biogas may be utilized as a “BTU replacement” in the production of electricity or natural gas. 
     The waste treatment system  10  will treat acidic liquid wastes with a solids percentage varying between about 5% and about 40%. It does this by monitoring and closely controlling the pH in the liquid waste and by utilizing the naturally generated alkalinity and pH rise associated with the two-step anaerobic biodegradation process of acid forming bacteria followed by methanogenic bacteria and their resultant biological waste products. Use of a mixed plug flow is preferred. Additionally, the plug-flow separation of the processed wastes over the designed hydraulic retention time enables the natural increase in pH and alkalinity, thus allowing for the production of the returned sludge. Mixing of the plug flow prevents stratification in the acid forming chamber  30  and methanic chamber  40 . Eliminating stratification in the acid forming chamber  30  and methanic chamber  40  prevents buildup of acid forming bacteria colonies and the resultant high acidic liquid (low pH) “dead” spots, facilitates better methanogenic bacteria growth to achieve better and faster acid neutralization and alkalinity production, and provides for more uniform hydraulic retention time in the waste treatment system  10  by preventing “short circuiting” of the liquid pathflow. 
       FIG.  5 A  is a schematic showing the general waste treatment system  10  of  FIG.  1    with a modification at the transition from the acid forming chamber  30  and methanic chamber  40 . In particular, in the embodiment shown in  FIG.  1   , a portion  65   a  of the center wall  65  extends between the acid forming chamber  30  and the methanic chamber  40  to partially separate the two chambers  30 ,  40 . The wall portion  65   a  provides an airtight division between the two chambers  30 ,  40  except for at the weir structure  67 . 
     As shown in  FIG.  5 B , the portion  65   a  does not extend completely to the roof  98 . Rather, the weir structure  67  is provided between the wall portion  65   a  and the roof  98 . The first weir wall portion  67   a  of the weir structure  67  is shown below the liquid levels  30   a ,  40   a  of both the acid forming chamber  30  and methanic chamber  40 , respectively. A second weir wall portion  67   b  is provided near the operating liquid level  30   a  of the acid chamber  30  which is notably greater than the operating liquid level  40   a  of the methanic chamber  40 . Further, the second weir wall portion  67   b  is cut at an incline. 
     It will be appreciated that, with the described structures, liquid from the acid forming chamber  30  is able to flow over the wall portion  65   a  and into the methanic chamber  40 . Reverse flow from the methanic chamber  40  into the acid forming chamber  30 , however, is prevented. Similarly, the weir structure  67  acts as a double sewer trap to prevent gases from escaping the methanic chamber  40 . 
     In a particular embodiment, the height difference between the first weir wall portion  67   a  and the second weir wall portion  67   b  is from 3 inches, or 4 inches, or 5 inches, or 6 inches to 7 inches, or 8 inches, or 9 inches, or 10 inches. In a further embodiment, the height difference between the first weir wall portion  67   a  and the second weir wall portion  67   b  is from 5.0 inches, or 5.2 inches, or 5.4 inches, or 5.6 inches, or 5.8 inches or 6.0 inches to 6.2 inches, or 6.4 inches, or 6.6 inches, or 6.8 inches, or 7.0 inches. In still a further embodiment, the height difference between the first weir wall portion  67   a  and the second weir wall portion  67   b  is from 5.7 inches, or 5.8 inches, or 5.9 inches, or 6.0 inches to 6.1 inches, or 6.2 inches, or 6.3 inches, or 6.4 inches. In a specific embodiment, the height difference between the first and second weir wall portions  67   a ,  67   b  is approximately 6 inches. 
     By providing the weir structure  65 , it is easy to isolate the acid forming chamber  30  from the methanic chamber  40  by simply decreasing the liquid level in the acid forming chamber. The ability to completely seal the acid forming chamber  30  from the methanic chamber  40  is beneficial to permit flow adjustments to drive biogas production. It also allows for the cleaning of the acid forming chamber  30  and continued operation of the methanic chamber  40  during that cleaning. 
       FIGS.  6 - 8    illustrate an alternate embodiment of a waste treatment system according to the present invention. The waste treatment system  310  shown in  FIGS.  6 - 8    is similar in many ways to the illustrated embodiments of  FIGS.  1 - 5    described above. Accordingly, with the exception of mutually inconsistent features and elements between the embodiment of  FIGS.  6 - 8    and the embodiment of  FIGS.  1 - 5   , reference is hereby made to the description above accompanying the embodiment of  FIGS.  1 - 5    for a more complete description of the features and elements (and the alternatives to the features and elements) of the embodiment of  FIGS.  6 - 8   . Features and elements in the embodiment of  FIGS.  6 - 8    corresponding to features and elements in the embodiment of  FIGS.  1 - 5    are numbered in the 300 series. 
     As shown in  FIG.  6   , the waste treatment system  310  includes a digester enclosure  320 , an acid forming chamber  330 , a methanic chamber  340 , a sludge pit  360  and an effluent pit  350 . pH monitoring stations A-D adjust the pH of the liquid waste in the acid forming chamber  330  and methanic chamber  340  by recycling alkaline sludge from the sludge pit  360  via one or more flow paths  342 ,  344 . The system  310 , or portions of the system  310 , may be anaerobic. A center wall  365  divides the methanic chamber  340  into a first leg or passageway  346  and a second leg or passageway  348 . The liquid waste can therefore move from the acid forming chamber  330  into the methanic chamber  340  along the first leg  346  in a first direction, and toward the sludge pit  360  along the second leg  348  of the methanic chamber  340  in a second direction opposite the first direction. 
     The first leg  346  and the second leg  348 , as illustrated in  FIG.  6   , each include a partition  370  positioned relative to the center wall  365  such that a space  380  is created between the partitions  370  and the center wall  365 . The partitions  370  may comprise at least one of a rigid board or plank, curtain or drape, tarp, film, and a combination thereof. In addition, the partitions  370  may be constructed of a variety of materials including, without limitation, at least one of metal, wood, polymer, ceramic, composite, and a combination thereof. The first leg  346  and the second leg  348  each further include a heating device  372  positioned within the space  380  between the partitions  370  and the center wall  365  such that liquid waste is heated as it contacts the heating device  372 . Heated liquid waste rises relative to cooler liquid waste by free convection and is allowed to rise upwardly within the space  380 . 
     The heating device(s)  372  and the partition(s)  370  are shown in greater detail in  FIGS.  7  and  8   . For simplicity, one of the heating devices  372  and one of the partitions  370  will be described in greater detail, but it should be noted that the description may equally apply to the other heating device  372  and partition  370 . As shown in  FIGS.  7  and  8   , the heating device  372  includes a series of conduits  374 , each containing a heating medium. A variety of heating media may be used with the present invention, including at least one of water and a gas. The conduits  374  do not all need to contain the same heating medium. That is, some of the conduits  374  may contain a gas, while others contain a liquid, such as water. 
     As illustrated in  FIGS.  7  and  8   , the waste treatment system  310  may further include at least one conduit  378 , which contains a compressed, recycled biogas from the biogas storage area (not shown) and has nozzles  376 . The nozzles  376  are gas outlets. The compressed biogas contained in the conduit  378  flows through the conduit  378  and out the nozzles  376 , such that as the gas escapes the conduit  378  via the nozzles  376 , the gas is propelled upwardly in the space  380  to promote the liquid waste to move upwardly through the principle of air/water lifting.  FIGS.  7  and  8    illustrate one conduit  378  having nozzles  376 . Any number of conduits  378  having nozzles  376  can be used without departing from the spirit and scope of the present invention. The nozzles  376  may be simple holes drilled into conduit  378  or may be specialized nozzles attached to conduit  378  via welding or tapping. 
     Referring to  FIGS.  7  and  8   , a frame  364  is positioned within the space  380  to support the heating device  372  and conduit  378 . The frame  364  is illustrated as comprising a plurality of ladder-like units  363  and a connecting bar  369  running generally parallel to the center wall  365  to connect the units  363 . Each unit  363 , as illustrated in  FIGS.  7  and  8   , is formed of two vertical columns  366  positioned on opposite sides of the space  380  and a plurality of crossbeams  368  connecting the two vertical columns  366  across the space  380 . The frame  364  is illustrated by way of example only, and the present invention is in no way limited to the illustrated support structure. A variety of frame elements can be used to support the heating device  372 , conduit  378 , and/or other components of the waste treatment system  310  within the space  380  without departing from the spirit and scope of the present invention. 
     As illustrated in  FIGS.  7  and  8   , the partition  370  has a top edge  371  and a bottom edge  373 . In addition, the illustrated partition  370  is substantially vertical and shorter in height than the methanic chamber  340 , such that heated liquid waste can move over the top edge  371  of the partition  370  and out of the space  380  between the partition  370  and the center wall  365 , and cooled liquid waste can move under the bottom edge  373  of the partition  370  and into the space  380 . Therefore, as illustrated by the arrows in  FIGS.  7  and  8   , the partition  370 , in conjunction with the heating device  372 , promotes upward and downward movement of the liquid waste. This upward and downward movement of the liquid waste results in an overall corkscrew-like movement of the liquid waste as the liquid waste is moved along the first and second legs  346 ,  348  of the methanic chamber  340 . Further promoting this corkscrew-like flowpath is conduit  378  with nozzles  376 , which is located beneath the series of conduits  374  of the heating device  372  closest to the center wall  365  in  FIGS.  7  and  8   . The corkscrew-like flowpath of the liquid waste throughout the methanic chamber  340  promotes thermal mixing of the liquid waste. 
     The series of conduits  374 ,  378  illustrated in  FIG.  7    is formed by having a two-by-six configuration within the space  380  (i.e. two conduits  374 ,  378  across and five conduits  374 ,  378  up and down), with the conduits  374 ,  378  running generally parallel to the center wall  365 . Another example is a two-by-five configuration, as shown in  FIG.  8   . As illustrated in  FIGS.  7  and  8   , one of the conduits  378  having nozzles  376  transports compressed biogas and the remaining conduits  374  transport heating media. It should be noted, however, that any number of conduits  374  containing heating media and any number of conduits  378  having nozzles  376  can be combined in a variety of configurations without departing from the spirit and scope of the present invention. The series of conduits  374  and the conduit  378  having nozzles  376  depicted in  FIGS.  6 - 8    are shown by way of example only. 
       FIG.  9    illustrates an alternate embodiment of a waste treatment system according to the present invention. The waste treatment system  410  shown in  FIG.  9    is similar in many ways to the illustrated embodiments of  FIGS.  1 - 8    described above. Accordingly, with the exception of mutually inconsistent features and elements between the embodiment of  FIG.  9    and the embodiments of  FIGS.  1 - 8   , reference is hereby made to the description above accompanying the embodiments of  FIGS.  1 - 8    for a more complete description of the features and elements (and the alternatives to the features and elements) of the embodiment of  FIG.  9   . Features and elements in the embodiment of  FIG.  9    corresponding to features and elements in the embodiments of  FIGS.  1 - 8    are numbered in the 400 series. 
       FIG.  9    illustrates a waste treatment system  410  which includes a pH monitoring station  416 , a digester enclosure  420 , an acid forming chamber  430 , a methanic chamber  440 , a sludge pit  460  and an effluent pit  450 . The system  410 , or portions of the system  410 , may be anaerobic. The digester enclosure  420  is arranged such that a relatively large methanic chamber  440  may be built in a relatively small space. 
     As illustrated in  FIG.  9   , an outer wall  454  of the digester enclosure  420  is generally circular, such that an outer perimeter of the digester enclosure  420  is generally circular as well. Furthermore, the outer wall  454  forms at least a portion of the outer perimeter of the acid forming chamber  430 , methanic chamber  440 , sludge pit  460  and effluent pit  450 . In other words, each of the acid forming chamber  430 , methanic chamber  440 , sludge pit  460  and effluent pit  450  has an outer perimeter defined by the generally circular outer wall  454  of the digester enclosure  420 . 
     The acid forming chamber  430  includes an influent conduit  418  for receiving liquid waste from the pH monitoring station  416  into the acid forming chamber  430 . A cutout  459  is formed in a wall  461  between the acid forming chamber  430  and the methanic chamber  440  to allow liquid waste to flow from the acid forming chamber  430  into the methanic chamber  440 . The acid forming chamber  430  also includes a heating device  422  for heating the liquid waste as it flows through the acid forming chamber  430 . The heating device  422  may, for example, be a heating conduit or other conduit containing a liquid or gas. The heating device  422  may include discharge nozzles (not shown) to further agitate the liquid waste. Additionally, a pH monitoring station A measures the pH of the liquid waste within the acid forming chamber  430  and triggers the delivery of alkaline sludge from the sludge pit  460  to the acid forming chamber  430  via flow path  442  to maintain the pH of the liquid waste in the acid forming chamber  430  at about 6.0 to about 7.0. 
     The methanic chamber  440  includes a first leg or passageway  441 , a second leg or passageway  443  and a third leg or passageway  445 . The first and second legs  441 ,  443  are separated from one another by a first divider  447 , while the second and third legs  443 ,  445  are separated from one another by a second divider  449 . The first leg  441  has a first end  441   a  and a second end  441   b , the second leg  443  has a first end  443   a  and a second end  443   b , and the third leg  445  has a first end  445   a  and a second end  445   b . The first end  441   a  of the first leg  441  is adjacent the cutout  459 , which thus also serves as an inlet for receiving liquid waste into the methanic chamber  440 . The second end  441   b  of the first leg  441  is adjacent the first end  443   a  of the second leg  443 . The second end  443   b  of the second leg  443  is adjacent the first end  445   a  of the third leg  445 . The second end  445   b  of the third leg  445  is adjacent the sludge pit  460 . The first divider  447  has an end  447   a  around which the liquid waste flows from the first leg  441  to the second leg  443 . Likewise, the second divider  449  has an end  449   a  around which the liquid waste flows from the second leg  443  to the third leg  445 . From the methanic chamber  440 , the liquid waste flows into the optional sludge pit  460 . 
     The methanic chamber  440  forms a flow path for the liquid waste that is generally S-shaped. It should be noted, however, that additional dividers could be employed to increase the length of the flow path, by adding additional legs or passageways. The methanic chamber  440  provides a relatively long flow path for the liquid waste within the relatively small area enclosed by the outer wall  454 . 
     The methanic chamber  440  may optionally include one or more partitions  470  positioned relative to the first divider  447  and the second divider  449  such that a space  480  is created between the partition  470  and the respective divider. The partitions  470  may comprise at least one of a rigid board or plank, curtain or drape, tarp, film, and a combination thereof. In addition, the partition  470  may be constructed of a variety of materials including, without limitation, at least one of metal, wood, polymer, ceramic, composite, and a combination thereof. The illustrated partition  470  is substantially vertical and shorter in height than the methanic chamber  440 , such that heated liquid waste can move over the top edge of the partition  470  and out of the space  480  between the partition  470  and the divider  447 , and cooled liquid waste can move under the bottom edge of the partition  470  and into the space  480 . 
     The waste treatment system  410  as illustrated in  FIG.  9    may include any of the features discussed with respect to the previous embodiments. For example, the methanic chamber  440  may include a heating device  472  for heating the liquid waste as it flows through the methanic chamber  440 . In one embodiment, the heating device  472  includes one or more heating conduits (not shown) arranged along one or both of the dividers  447 ,  449  within the first leg  441 , the second leg  443 , the third leg  445 , or a combination thereof. The heating conduits locally heat the liquid waste using, for example, hot water or gas, causing the heated mixed liquid waste to rise under convective forces. The convective forces cause the heated liquid waste to rise near the first and second dividers  447 ,  449 . At the same time, liquid waste near the relatively cooler outer wall  454  falls under convective forces. As a result, the convective forces cause the liquid waste to follow a circular flow path through the first leg  441  upward along the divider  447  and downward along the outer wall  454 . Likewise, the convective forces cause the liquid waste to follow a circular flow path through the third leg  445  upward along the second divider  449  and downward along the outer wall  454 . At the same time, the liquid waste flows along the first, second and third legs  441 ,  443 ,  445 , resulting in a combined corkscrew-like flow path for the liquid waste. The heating conduits may include jet nozzles to dispense water or gas into the liquid waste. In another embodiment, hot gas injection jets using heated gases from the output of the engine (not shown) replace the hot water heating conduits as a heating and current-generating source. The injection of hot gases circulates the liquid waste through both natural and forced convection. A similar corkscrew-like flow path is thereby developed in the methanic chamber  440 . In a further embodiment, at least one conduit containing compressed, recycled biogas is used in combination with the heating device  472 . The compressed biogas contained in the conduit is forced out of the conduit and propelled upwardly to promote the liquid waste to move upwardly through the principle of air/water lifting. The released gas may also facilitate the corkscrew-like flow path of liquid waste through the methanic chamber  440 . 
     Although the above embodiments were described in the context of treating acidic liquid wastes, it should be understood by those skilled in the art that the same embodiments may also be used to treat high-strength organic liquid wastes having an influent pH of about 7. 
     Treatment of Alkaline High-Strength Organic Liquid Wastes 
     Another aspect of the present invention is to modify a plug-flow anaerobic digester system to treat alkaline high-strength organic liquid wastes. As used herein, the term “alkaline high-strength organic liquid waste” (hereinafter “alkaline liquid waste”) means a process waste, organic in nature, with a pH greater than about 8.0 and with a solids content greater than about 5%. 
       FIG.  10    illustrates one embodiment of an alkaline waste treatment system according to the present invention. The waste treatment system  610  shown in  FIG.  10    is similar in many ways to the acidic waste treatment system illustrated in the embodiment of  FIGS.  1 - 5 B  described above. With the exception of mutually inconsistent features and elements between the embodiment of  FIG.  10    and the embodiment of  FIGS.  1 - 5 B , reference is hereby made to the description above accompanying the embodiment of  FIGS.  1 - 5 B  for a more complete description of the features and elements (and the alternatives to the features and elements) of the embodiment of  FIG.  10   . Features and elements in the embodiment of  FIG.  10    corresponding to features and elements in the embodiment of  FIGS.  1 - 4    are numbered in the 600 series. 
     As shown in  FIG.  10   , the waste treatment system  610  includes a digester enclosure  620 , an acid forming chamber  630 , a methanic chamber  640 , a sludge pit  660  and an effluent pit  650 . The system  610 , or portions of the system  610 , may be anaerobic. An optional pH monitoring station  616  may be used to adjust the pH of the influent liquid waste prior to sending the liquid waste to the acid forming chamber  630 . If the liquid waste is alkaline, the pH of the liquid waste may be adjusted to a pH of about 7.0 with the addition of acidic material. Acidic material may include, but is not limited to, industrial acids (e.g., H 2 SO 4 ), acidic liquid animal wastes, or acidic organic liquid wastes. 
     The acid forming chamber  630  includes an influent conduit  618  for receiving liquid waste from outside the digester enclosure  620  into the acid forming chamber  630 . The acid forming chamber  630  has an upstream end  630   a  and a downstream end  630   b . Liquid waste enters the acid forming chamber  630  at the upstream end  630   a  and exits the acid forming chamber  630  at the downstream end  630   b . A cutout  659  is formed in a wall  661  between the acid forming chamber  630  and the methanic chamber  640  to allow liquid waste to plug flow from the acid forming chamber  630  into the methanic chamber  640 . The acid forming chamber  630  used to treat alkaline liquid waste is typically larger than the acid forming chambers used to treat acidic liquid waste. In some embodiments, the acid forming chamber  630  is about four times larger than those used to treat acidic liquid waste. 
     As the liquid waste flows through the acid forming chamber  630 , acid forming bacteria convert complex carbon molecules into simpler acids. As a result, the pH of the liquid waste in the acid forming chamber  630  is lowest at the downstream end  630   b  and highest at the upstream end  630   a . A pH monitoring station E in the acid forming chamber  630  measures the pH of the influent liquid waste. When the pH of the influent waste becomes too high to support the acid forming bacteria, liquid waste from the downstream end  630   b  of the acid forming chamber  630  is recycled via flow path  693  to the upstream end  630   a  of the acid forming chamber  630  to reduce the pH of the influent alkaline liquid waste. The flow path  693  may be defined by any number of devices that may include, but are not limited to, a pipe, tile, a channel, and a tube. In some embodiments, the pH monitoring station E triggers a vari-speed recirculation pump. The pump recycles an appropriate amount of liquid waste from the downstream end  630   b  of the acid forming chamber  630  to the upstream end  630   a  of the acid forming chamber  630  to adjust the influent alkaline liquid waste to a neutral pH of about 6.5 to about 7.5. 
     The recirculation of the lower pH liquid waste enables the waste treatment system  610  to self-regulate the pH of the influent liquid waste to a level that is within the range of bacteria acceptance and reduce or eliminate the need for outside acid addition. This recirculation of the lower pH liquid waste also serves to reseed liquid waste at the upstream end  630   a  of the acid forming chamber  630  with acid forming bacteria. Reseeding may increase bacterial action on liquid waste, particularly bacteria sterile influent wastes, such as glycerin waste. The amount of liquid waste recycled from the downstream end  630   b  of the acid forming chamber  630  to the upstream end  630   a  of the acid forming chamber  630  will be reflected in the increased hydraulic retention time sizing of the acid portion of the waste treatment system  610 . The liquid waste, upon entering the methanic chamber  640 , contains the proper pH and simple acid components for efficient conversion into methane biogas and the reduction of organic compounds, and will be processed in the established pattern of the waste treatment system  610 . 
     The acid forming chamber  630  includes a heating device  622  for heating the liquid waste as it flows through the acid forming chamber  630 . The heating device  622  may, for example, be a heating conduit (not shown) or other conduit containing a liquid or gas. The heating  622  device may include discharge nozzles to further agitate the liquid waste. 
     The liquid waste from the acid forming chamber  630  is transferred via horizontal plug-flow movement of the liquid waste to the methanic chamber  640 . As shown in  FIG.  10   , the methanic chamber  640  may be a U-shaped tank. A center wall  665  divides the methanic chamber  640  into a first leg or passageway  646  and second leg or passageway  648  of the U-shape. The liquid waste moves from the acid forming chamber  630  into the methanic chamber  640  along the first leg  646  in a first direction, and toward the sludge pit  660  along the second leg  648  of the methanic chamber  640  in a second direction opposite the first direction. 
     One or more partitions  670  may run severally parallel to, and on opposite sides of, the center wall  665 . The partitions  670  may comprise at least one of a rigid board or plank, curtain or drape, tarp, film, and a combination thereof. In addition, the partitions  670  may be constructed of a variety of materials including, without limitation, at least one of metal, wood, polymer, ceramic, composite, and a combination thereof. The partitions  670  are shorter than the center wall  665  and are raised off the floor of the methanic chamber  640 . This allows liquid waste to flow underneath and then over the partitions  670  as it plug flows through the methanic chamber  640 . 
     The methanic chamber  640  illustrated in  FIG.  10    may include any of the features discussed with respect to the previous embodiments illustrated in  FIGS.  1 - 8   . For example, pH monitoring stations B-D may adjust the pH of the liquid waste in the methanic chamber  640  by recycling alkaline sludge from the sludge pit  660  via one or more flow paths  644 . Additionally, the methanic chamber  640  may include a heating device  672  located within the methanic chamber  640  and adjacent to the center wall  665  to maintain the liquid waste at a temperature that facilitates bacterial activity. The heating device  672  locally heats the liquid waste using, for example, hot water or gas, causing the heated mixed liquid waste to rise under convective forces. The convective forces cause the heated liquid waste to rise up the center wall  665 . At the same time, liquid waste near the relatively cooler outer wall  654  falls under convective forces. As a result, the convective forces cause the liquid waste to follow a circular flow path through the first and second legs  646 ,  648  upward along the center wall  665  and downward along the outer wall  654 . At the same time, the liquid waste flows along the first and second legs  646 ,  648 , resulting in a combined corkscrew-like flow path for the liquid waste. The heating device  672  may include heating conduits having jet nozzles to dispense water or gas into the liquid waste. In another embodiment, hot gas injection jets using heated gases from the output of the engine (not shown) replace the hot water heating conduits as a heating and current-generating source. The injection of hot gases circulates the liquid waste through both natural and forced convection. A similar corkscrew-like flow path is thereby developed in the methanic chamber  640 . In a further embodiment, at least one conduit containing compressed, recycled biogas is used in combination with the heating device  672 . The compressed biogas contained in the conduit is forced out of the conduit and propelled upwardly between the conduits  670  and center wall  665  to promote the liquid waste to move upwardly through the principle of air/water lifting. The released gas may also facilitate the corkscrew-like flow path of liquid waste through the methanic chamber  640 . 
     In operation of the waste treatment system  610 , as illustrated in  FIG.  10   , alkaline liquid waste is transported to the waste treatment site. Prior to entering the acid forming chamber  630 , the pH of the liquid waste influent may optionally be adjusted to a range of between about 6.0 and about 7.0 to start the acid forming bacterial growth. In one embodiment, a pH probe that controls a vari-speed chemical feed pump is utilized to monitor and adjust the initial pH of the influent. Agents used to adjust the pH may include a variety of acidic substances, such as industrial acids (e.g., H 2 SO 4 ), acidic liquid animal wastes, or acidic organic liquid wastes. 
     The liquid waste enters the acid forming chamber  630  via the influent conduit  618 . In the acid forming chamber  630 , the internal heating device  622  adjusts the temperature of the influent to facilitate the growth of acid forming bacteria. Temperature control is important for methanogenic bacteria (less so for acid forming bacteria). The temperature is closely regulated in the acid forming chamber  630  so that the temperature is kept constant as the liquid “plug flows” from the acid forming chamber  630  into the methanic chamber  640 . The temperature can be site determined to be about 97° F. to about 103° F. for a mesophilic operating digester or about 132° F. to about 138° F. for a thermophilic digester. The liquid waste in the acid forming chamber  630  is continuously stirred to eliminate temperature stratification in the liquid waste and to promote better bacterial growth. In one embodiment, the contents of the acid forming chamber are continuously stirred with recycled biogas agitation. 
     Within the acid forming chamber  30 , acid forming bacteria convert complex carbon molecules into simpler acids. These acids in turn lower the pH of the liquid waste in the acid forming chamber  30 . As a result, the pH of the liquid waste at the downstream end  630   b  of the acid forming chamber  630  is lower than the pH of the influent liquid waste at the upstream end  630   a  of the acid forming chamber  630 . In some embodiments, the pH of the liquid waste at the downstream end  630   b  of the acid forming chamber  630  is about 6.0. 
     A pH monitoring station E measures the pH of influent alkaline waste as it enters the upstream end  630   a  of the acid forming chamber  630 . If the pH of the influent liquid waste is greater than about 7, an appropriate amount of liquid waste from the downstream end  630   b  of the acid forming chamber  630  is recycled to the upstream end  630   a  of the acid forming chamber to reduce the pH of the influent liquid waste to about neutral. This insures that the pH of the influent liquid waste will be maintained at a level that fosters acid-forming bacteria growth rates and efficiency. In some embodiments, a roof mounted pH monitor identified by pH monitoring station E controls a vari-speed sludge recirculation pump to recycle liquid waste from the downstream end  630   b  to the upstream end  630   a  of the acid forming chamber  630 . 
     As new influent enters the acid forming chamber  630 , the treated liquid waste within the acid forming chamber  630  will plug flow into the methanic chamber  640 . In the methanic chamber  640 , an environment to foster the growth of the methanogenic bacteria is maintained. The pH of the liquid waste in the methanic chamber  640  is maintained at a pH of about 6.5 to about 8.0, and particularly at a pH of about 7.5 to about 8.0. To accomplish this, pH monitoring stations (B-D) are located throughout the methanic chamber  640 . If the pH drops below a set value, such as 6.5, at any of these stations, the pH monitors will activate one or more vari-speed sludge recirculation pumps to add alkaline sludge from the sludge pit  660  to the liquid waste in the methanic chamber  640 . The corkscrew mixing of the liquid waste in the methanic chamber  640  by the utilization of the recirculated biogas and/or heating ensures a homogeneous pH mix and prevents pH stratification within the vessel. A heating device  672  within the methanic chamber  640  maintains the temperature of the liquid waste within a range of about 1 to about 2 degrees of the set point temperature. The set point temperature for a mesophilic temperature digester will be about 100° F. and about 134° F. for a thermophilic digester. The heating device  672  can be utilized for heating or cooling as determined by the influent liquid temperature. The liquid waste within the methanic chamber  640  is continuously mixed with recycled biogas jetted into the liquid waste in a direction perpendicular to the waste flow direction. Mixing prevents stratification within the methanic chamber and enhances biodegradation. 
     As the waste stream plug flows through the methanic chamber  640 , it is allowed to biodegrade in multiple sections as it travels in a horizontal corkscrew-like pathway through the first leg  646  and the second leg  648  of the methanic chamber  640 . In one embodiment, the waste stream is not mixed with the newer incoming waste material. As the methanogenic bacteria function, they consume the acids created in the acid forming chamber  630  and effectively raise the pH of the liquid waste stream and increase the alkalinity of the liquid waste. At the end of the methanic chamber  640 , with properly engineered hydraulic retention times based on influent characteristics, the acid forming bacteria will have long completed their function and the methanogenic bacteria will have consumed the bacteria-produced acids. This results in a waste effluent of high pH and alkalinity in comparison to the liquid waste exiting the acid forming chamber  630 . The greatest alkalinity and bacteria population at the very end of the waste treatment system  610  will be in the bacteria “sludge” that is allowed to settle in the sludge pit  660  located at the end of the waste treatment system  610 . The sludge pit  660  may not have mixing and thus the sludge is allowed to settle to the bottom. This sludge, with its higher alkalinity, pH, and bacteria population, is the recirculated sludge utilized at the various points (stations B, C and D) throughout the waste treatment system  610  for pH control and bacterial seeding. 
     The waste treatment system  610  will treat alkaline liquid wastes with a solids percentage varying between about 5 and about 40%. It does this by monitoring and closely controlling the pH in the liquid waste and by utilizing the naturally generated alkalinity and pH rise associated with the two-step anaerobic biodegradation process of acid forming bacteria followed by methanogenic bacteria and their resultant biological waste products. Use of a mixed plug flow is preferred. Additionally, the plug-flow separation of the processed wastes over the designed hydraulic retention time enables the natural increase in pH and alkalinity, thus allowing for the production of the returned sludge. Mixing of the plug flow prevents stratification in the acid forming chamber  630  and methanic chamber  640 . Eliminating stratification in the acid forming chamber  630  and methanic chamber  640  prevents buildup of acid forming bacteria colonies and the resultant high acidic liquid (low pH) “dead” spots, facilitates better methanogenic bacteria growth to achieve better and faster acid neutralization and alkalinity production, and provides for more uniform hydraulic retention time in the waste treatment system  610  by preventing “short circuiting” of the liquid path flow. 
     The biodegraded effluent may be further treated or disposed of by the generating facility as required. Biogas generated by the anaerobic biological process may be collected in the gas collection space above the liquid level and under the ceiling of the methanic chamber  640 . The biogas may be utilized as a “BTU replacement” in the production of electricity or natural gas. 
     It will be appreciated that, while the embodiments of  FIGS.  5 A and  5 B  is shown only in relation to the waste treatment system  10  of  FIGS.  1 - 4   , the use of such a valve is applicable to the systems provided in  FIGS.  6 - 10    as well. 
     Although the above embodiment was described in the context of treating alkaline liquid wastes, it should be understood by those skilled in the art the same embodiment may also be used to treat high-strength organic liquid wastes having an influent pH of about 7. 
     Thus, the invention provides, among other things, a system and method for treating high-strength organic liquid wastes. Various features and advantages of the invention are set forth in the following claims.