Patent Publication Number: US-2020277212-A1

Title: Brown grease treatment and disposal system

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a U.S. national stage application under 35 USC § 371 of International Application No. PCT/US18/50996 filed on Sep. 14, 2018 and entitled “BROWN GREASE TREATMENT AND DISPOSAL SYSTEM,” which claims priority to U.S. Provisional Application No. 62/558,569 filed on Sep. 14, 2017 and entitled “Brown Grease Treatment and Disposal System for Restaurants and Food Establishments,” the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Today, it is estimated that 495 million gallons of brown or trap grease is generated annually in the U.S. If the trap grease is not properly disposed of, fat, oil, and grease (FOG) can accumulate in downstream sewage pipes causing clogs and sanitary sewer overflows (SSOs). FOGs are sticky and easily accumulate along the inside walls of sewage pipes, eventually hardening to form a concrete-like substance. FOG accumulation is one of the primary causes of SSOs. The resulting cost of cleaning up clogs, SSOs and repairing damage to pumping stations can be quite high. Taxpayers typically bear these costs in the form of increased water and sewage service rates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical components or features. 
         FIG. 1  illustrates a block diagram view of an example resource recovery system for processing wastewater according to some implementations. 
         FIG. 2  illustrates a cross-sectional view of the example the primary circular zoned dissolved air and/or ozone flotation (CZDAOF) unit of  FIG. 1  according to some implementations 
         FIG. 3  illustrates a top view of an example the primary CZDAOF unit of  FIG. 1  with scum scraper assembly removed according to some implementations. 
         FIG. 4  illustrates a top view of an example the primary CZDAOF unit of  FIG. 1  according to some implementations. 
         FIG. 5  illustrates a partial view of an example resource recovery system of  FIG. 1  including the primary CZDAOF unit, the primary gaseous material dissolving system, and the primary weir tank according to some implementations. 
         FIG. 6  illustrates a top view of the example bio-DAF unit of  FIG. 1  according to some implementations. 
         FIG. 7  illustrates a cross-sectional view of the bio-DAF unit of  FIG. 1  according to some implementations. 
         FIG. 8  illustrates a partial view of an example bio-DAF unit of  FIG. 1  according to some implementations. 
         FIG. 9  illustrates an example flow diagram showing a process for forming finished oil and dry solids according to some implementations. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure includes techniques and implementations for cleaning and recovering fat, oil, and grease (FOG) from wastewater. In particular, the system discussed herein is configured to remove and recover organic matter from wastewater produced as part of restaurant food processing. For instance, the system may be used for removing and recovering fat, oil, and grease (FOG) from restaurant brown grease to produce usable biodiesel feedstocks and fertilizer, and further treating the wastewater to meet downstream city sewer, municipal wastewater treatment plants (WWTP), or publicly owned treatment works (POTW) discharge limits for biochemical oxygen demand (BOD) and total suspended solids (TSS). 
     In general, brown grease, also known as trap grease, is collected from grease traps that are typically installed in restaurants, cafeteria, fast-food restaurant chains, and institutional food establishments to separate FOG from kitchen wastewater. Brown grease is a byproduct of cooking and comes from meat fats, lard, oil, shortening, butter, margarine, food scraps, baked goods, sauces, and dairy products. Brown grease is a mixture of FOG, food particulates, water, kitchen waste, grit, rocks and debris that has gone down a drain and been trapped in a grease trap or grease interceptor. 
     A grease trap works by slowing down the flow of warm/hot greasy water and allowing the water to cool. As the water cools, the grease and oil separate and float to the top of the grease trap. The cooler water with less FOG content continues to flow down the pipe to the sewer, WWTP, or other POTW. The FOG is trapped by baffles that cover the inlet and outlet of the grease trap tank, thereby preventing FOG from flowing out of the grease trap. However, if grease traps are not periodically emptied, the grease traps eventually become full, pushing the higher content FOG water downwards and out into the sewer system. FOG is sticky and can easily accumulate along the inside walls of sewage pipes, eventually hardening to form a concrete-like sub stance. 
     In most of states, grease traps or interceptors are mandated to be emptied or cleaned when FOG contents fill up 25% of the grease trap&#39;s working volume, or at least once in every three months. Unfortunately, restaurants often fail to maintain or meet the government imposed cleaning requirements. This failure is a major cause of accumulation of FOGs in downstream sewage pipes. In fact, FOG accumulation is one of the primary causes of sanitary sewer overflows (SSOs). The resulting cost of cleaning up clogs, SSOs and repairing damage to pumping stations is substantial and often the taxpayers bear these costs in the form of increased water and sewage service rates. 
     In addition to causing SSOs, FOG also presents a problem for downstream POTW or WWTP. FOGs can build up in inlet coarse screens and fine screens, settling tanks, digesters, and other surfaces at the plant. Since many WWTPs are not equipped to clean FOG, the FOG build-up results in decreased treatment efficiency, and WWTP must then be upgraded and outfitted with the appropriate equipment. FOG accumulation also contributes to odor generation and hydrogen sulfide problems. 
     Many existing brown grease handling facilities are old and use out-of-date technologies. In many cases, several tanks are connected in series to skim FOG off brown grease. The FOG removal efficiency is usually very poor and the treated wastewater still contains very high FOG, BOD, and TSS loadings. When the treated wastewater is discharged into the sewer, the municipality may apply substantial surcharge fees based on these excessive FOG, BOD, and TSS loadings. If the downstream POTW is not equipped with FOG removal and handling equipment, the brown grease handling facility is often mandated to install pretreatment equipment to meet predetermined discharge criteria. Otherwise, the POTW may refuse to receive wastewater from the brown grease handling facility or restaurant. 
     Thus, the system, discussed herein, provides a sustainable, integrated, compact, modular, environmentally and economically efficient system for removing and recovering FOG from brown grease. In some implementations, the system may be configured to produce biodiesel feedstocks and fertilizer as a byproduct while removing BOD and TSS pollutants to meet the city sewer or downstream POTW discharge limits. 
     In one implementation, the system includes an inlet coarse screen to remove grit, debris, and small rocks, a primary circular zoned dissolved air and/or ozone flotation (CZDAOF) unit to remove and to recover FOG, a bio-dissolved air and/or ozone flotation (bio-DAF) unit to further remove BOD and TSS, and a three-phase centrifuge to process recovered FOG and produce biodiesel feedstocks and fertilizer. 
     In some cases, the primary CZDAOF unit may be configured to receive screened trap grease wastewater. The primary CZDAOF unit may remove and/or recover FOG while removing BOD and TSS contaminants via a series of flotation zones. In some implementations, a gaseous material dissolving system may be in fluid communication with the primary CZDAOF unit to dissolve gases (such as ozone and/or air) into fluid that mixes with the wastewater in the primary CZDAOF unit. When exposed to the atmosphere, the dissolved gases form microbubbles that may attach to and assist with the removal of the FOG. 
     In one implementation, the primary CZDAOF unit may include a central entry column and the series of substantially circular or ring-shaped flotation zones that are arranged in concentric series around the central entry column. In some cases, the central column may receive brown grease or screened trap grease wastewater transferred from a holding tank via a feed pump. In some cases, the flotation zones may be annular or have a conical shaped or sloped exterior/bottom wall(s) to assist with the collection of heavy or solid particles in the brown grease. For example, the depth of each of the consecutive flotation zones may be reduced to allow for the waste sludge to be collected via one or more primary bottom sludge discharge ports. 
     In some implementations, each of the flotation zones as well as the central entry column may include independent pressured dissolved air diffusers that introduce microbubbles into the wastewater and/or effluent. As discussed above, the microbubbles attach on the surface of FOG or suspended solid particles within the wastewater. The attached microbubbles then cause the FOGs or particles to float upward where the FOGs or particles may be extracted from the wastewater. 
     The primary CZDAOF unit may include a primary scum scraper assembly positioned along the top of the primary CZDAOF unit to remove the FOG and solid particle scum from the surface of the wastewater within each of the flotation zones of the primary CZDAOF unit and deposit the FOG and solid particle scum into a scum collection trough. For example, as the microbubbles raise the FOG and solid particle scum to the surface, the primary scum scraper assembly may skim, trap, and remove the FOG from the primary CZDAOF unit. 
     In some cases, the flow direction of the wastewater is reversed in each successive flotation zone. This counter-current flow pattern (known as a “plug flow pattern”) slows the rate of travel of the wastewater through the primary CZDAOF unit, causing increased exposure of the wastewater to the flotation zones, thereby increasing chances for FOG to attach to the microbubbles and be removed by the scrum scraper assembly. 
     In some implementations, the primary CZDAOF unit may be configured to introduce the microbubbles into the system via recirculated effluent. For example, the primary CZDAOF unit may dissolve the microbubbles into effluent produced by the system and then reintroduce the effluent into the flotation zones via the independent pressure dissolved air diffusers. For example, the primary CZDAOF unit may include an effluent reservoir (such as via a weir tank) coupled to an exit port of the exterior flotation zone (e.g., the final flotation zone or the polishing zone) to collect the effluent after the sludge and the FOGs have been removed. 
     The primary CZDAOF unit may also include a gaseous material dissolving system coupled to the effluent weir tank such that the gaseous material dissolving system may receive at least a portion of the effluent produced by the primary CZDAOF unit. The gaseous material dissolving system may include one or more pumps to dissolve the gaseous material into the effluent. 
     The bio-DAF unit may be an integrated physiochemical and biochemical wastewater treatment system that includes a central entry column, an aerobic bio-media reactor (such as a four-stage aerobic bio-media reactor), and a secondary DAF unit. The central entry column of the bio-DAF unit maximizes FOG and light particulates removals due to the lower uprising velocities of particulates and FOG. The bio-media reactors may be used to biodegrade and remove organic matter and nutrients. For example, each stage of the aerobic bio-media reactor develops and accumulates optimized bacteria species and/or microorganisms systems based on BOD and nutrient levels in the wastewater. The bio-media treatment process is based on attached growth biofilm principles by eliminating the returning activated sludge. Floating plastic media are kept inside the reactors to provide a place for bacteria and/or microorganism growth. 
     In some implementations, aeration may be supplied to the aerobic reactors to provide oxygen for microbial growth and cause mixing to fully disperse the plastic media throughout the reactors. Mixing also serves as a measure to control the biofilm thickness on the plastic media. Aeration and turbulence help to maintain a desired biofilm thickness, as the turbulence causes extra or excess biomass to be stripped from the plastic media and flow out of the bio-media reactors along with the treated effluent. 
     In some instances, suspended solid mixtures are captured and removed in the downstream secondary DAF unit of the bio-DAF unit. For example, the secondary DAF unit may be used to separate suspended solids, stripped biomass and small particulates from the bio-media reactor effluent in a manner similar to the primary CZDAOF unit. The effluent discharged from the secondary DAF effluent meets the downstream city sewer or POTWs discharge requirements for BOD and TSS and, thus, reduces the costs associated with BOD and TSS discharge surcharges. In some situations, the system, discussed herein, may also be installed near metropolitan areas to be closer to the points of brown or trap grease generation and, thereby, save transportation and disposal costs. 
     In one particular example, a secondary scum collection assembly may be positioned over the secondary DAF unit to collect and remove additional FOG prior to discharging the effluent to the downstream sewer system. The secondary scum collection assembly, similar to the primary scum collection assembly, may be configured to skim FOGs and solid particles from the surface of the wastewater in the secondary DAF unit and discharge the collected FOG into a scum collection chute. 
     Thus, the system provides a sustainable brown grease treatment and disposal system for removing and recovering FOG from restaurant trap grease wastewater to produce usable biodiesel feedstocks and fertilizer. In some implementations, a three-phase centrifuge can be used to produce biodiesel feedstocks and fertilizer from the recovered FOG. 
     In some cases, the units of the system may be configured to have a modular design. The modular design of units enables each of the units to be split into smaller modular components for easier shipping and allows for a unit of any desired diameter or number of flotation zones to be constructed on-site. Additionally, the circular walls between the flotation zones may be formed from thinner material, due to the inherent strength provided by cylindrical symmetry. For example, allowing the use of thinner stainless steel provides a cheaper manufacturing alternative and lower maintenance costs than conventional designs. 
       FIG. 1  illustrates a block diagram view of an example resource recovery system  100  for processing wastewater according to some implementations. The system  100  includes an inlet coarse screen  102 , an equalization (EQ) tank  104 , a primary CZDAOF unit  106 , a FOG preheat tank  108 , a pick heater  110 , a boiler  112 , a three-phase centrifuge  114 , finished oil tank  116 , bio-DAF feed tank  118 , bio-DAF unit  120 , blower  122 , a primary gaseous material dissolving system  124 , a secondary gaseous material dissolving system  126  as well as other equipment that will be discussed in more detail below. 
     In general, brown or trap grease wastewater can contain trash, grit, small rocks, and/or debris. These materials must be caught and removed to protect subsequent pumps, pipelines, and tanks of the system  100  from damage. As depicted in  FIG. 1 , a hauling truck  128  initially dumps trap grease wastewater  130  into the inlet coarse screen  102 . The inlet coarse screen  102  operates to remove trash, debris, grit, and small rocks (e.g., larger debris) from the brown or trap grease wastewater  130 . In some cases, the inlet coarse screen  102  is designed to remove large debris and objects to protect the subsequent pumps and piping operations without removing significant amounts of FOG from the brown trap grease wastewater  130 . For example, the inlet coarse screen  102  may include one or more coarse screens, one or more screw conveyors, and/or one or more steam spray washing systems. In some cases, the coarse screens may be a heavy-duty industrial screen for handling wastewater having a high FOG content. In some situations, steam may be applied or used to spray and wash the inlet coarse screen  102  to prevent FOG attaching on the surface of equipment. 
     After screening by the inlet coarse screen  102 , the screened trap grease wastewater  132  is transferred into the EQ tank  104  by a pump  134 . Since trap grease wastewater hauling trucks  128  usually work during daytime to collect and transport the trap grease wastewater  130  from restaurants, fast-food chains, and other establishments, the EQ tank  104  is configured with sufficient volume to hold half of the design flow capacity of the brown grease treatment and disposal system  100 . While the screened trap grease wastewater  132  is within the EQ tank  104 , steam may be injected to maintain a desired temperature to avoid FOG sticking on the walls and pipes. 
     A feed pump  136  may be used to transfer the screened trap grease wastewater  132  from the EQ tank  104  to the primary CZDAOF unit  106 . The primary CZDAOF unit  106  is configured to remove and recover FOG from the screened trap grease wastewater  130  as well as to remove BOD and TSS contaminants. For example, the primary CZDAOF unit  106  may utilize one or more flotation zones, each of which may introduce microbubbles to attach and float the FOG to the surface. For instance, the flotation zones may be in fluid communication with the primary gaseous material dissolving system  124  to receive fluid containing dissolved gases that form the microbubbles when exposed to the atmosphere in the primary CZDAOF unit  106 . 
     In some implementations, the primary gaseous material dissolving system  124  may include one or more ozone generators, as well as additional equipment, generally indicated by  144  (e.g., one or more oxygen generators, one or more chillers, one or more air compressors, and/or one or more microbubble generators). The primary gaseous material dissolving system  124  may draw primary CZDAOF unit effluent  138  from a fill chamber of a primary CZDAOF weir tank  146 . 
     In the illustrated example, coagulant and/or flocculant  184  may be added to one or more of the flotation zones of the primary CZDAOF unit  106  by a chemical feed system  182 . For instance, in some cases, FOG recovery may be enhanced by adding the coagulant and/or flocculant  184 . 
     The remaining primary CZDAOF unit effluent  138  not recirculated into the primary CZDAOF unit  106  by the primary gaseous material dissolving system  124  is transferred from the primary CZDAOF unit  106  to the bio-DAF feed tank  118 . The bio-DAF unit  120  is fed with the primary CZDAOF effluent  138  by a pump  140 . In general, the bio-DAF unit  120  has a central column for receiving the primary CZDAOF effluent  138 , a four-stage aerobic bio-media reactor, and a secondary DAF unit for final polishing of the cleaned effluent  142 . The bio-media treatment process is based on attached growth biofilm principles by eliminating the recycling activated sludge. For example, floating plastic media may be kept inside each of the reactors to provide a place for bacteria and microorganism growth. Aeration is supplied to the aerobic reactors by the blower  122  to provide the necessary oxygen for microbial growth as well as to cause turbulence to fully disperse the plastic media throughout the reactors. In some cases, the mixing also serves as a measure to control the biofilm thickness on the plastic media. For instance, when the biomass on the plastic media becomes too thick and heavy, the biomass detaches from the plastic media and may cause damage to the biological treatment system  100  or even system failure. In the present bio-media reactor, aeration and turbulence make the biofilm thin and fresh, because extra biomass is stripped from the plastic media and flows out with the treated effluent. These suspended solid mixtures are captured and removed in the downstream secondary DAF unit. 
     In some cases, the bio-media is made of high density polyethylene (HDPE) and formed in a cylindrical shape. The specific gravity of the bio-media is close to one (such as between approximately 0.97 and 1.01), so that the bio-media can be easily moved around in the reactors with biofilms attached. In some cases, the dry weight of the bio-media is about 105 kilograms per cubic meter (or in a range between 102 and 107 kilograms per cubic meter) to assure a strong media structure and that the media are not broken during aeration. The specific surface area of the bio-media is larger than approximately 500 m 2 /m 3  to provide more surface area for bacteria and microorganism growth and multiplication. 
     In some cases, the bio-media treatment system  100  uses variable frequency drives (VFD) for automated speed control of the blowers  122  based on dissolved oxygen (DO) levels that are continuously monitored by a DO sensor installed in the aerobic reactors. The ability to automatically speed up, slow down or even turn off the blowers  122  based on real-time DO measurements provides greater control over the system process, allowing the system  100  to conserve energy and save money thereby improving system performance. 
     In some implementations, the bio-DAF unit  120  may include a secondary DAF-unit, as will be discussed in more detail below. The secondary DAF unit may be used to remove suspended solids, stripped biofilm and biomass, and small particulates introduced by the bio-media reactors, as a final stage in processing before supplying the bio-media reactor effluent  142  to the downstream sewer system. In the illustrated example, the secondary DAF unit is physically incorporated into the bio-DAF unit  120 . In other cases, the secondary DAF unit may be a standalone DAF similar to the primary CZDAOF unit  106 . 
     Similar, to the primary CZDAOF unit  106 , the secondary DAF unit of the bio-DAF unit  120  may utilize microbubbles to float remaining FOG, the suspended solids, stripped biofilm and biomass, and remaining small particulates to the surface for removal from the system  100 . For instance, the secondary DAF unit may include one or more flotation zones in fluid communication with the secondary gaseous material dissolving system  126  to receive fluid containing dissolved gases (such as air and/or ozone) that form the microbubbles when exposed to the atmosphere in the secondary DAF unit. In some cases, when ozone is utilized as the dissolved gas, the ozone may assist in disinfecting the bio-media reactor effluent  142  and eliminate odor in the secondary DAF unit. 
     In some implementations, the secondary gaseous material dissolving system  126  may include one or more ozone generator, as well as additional equipment, such as one or more oxygen generators, one or more chillers, one or more air compressors, and/or one or more microbubble generators. The secondary gaseous material dissolving system  126  may draw the bio-media reactor effluent  142  from a fill chamber of a secondary DAF unit weir tank  148  for dissolving gases and recycling back into the secondary DAF unit. 
     As discussed above, scum is collected from the surface of the flotation zones of the primary CZDAOF unit  106  and the flotation zones of the secondary DAF unit and sludge is collected from the bottom of the flotation zones of the primary CZDAOF unit  106  and the flotation zones of the secondary DAF unit, generally indicated as scum and sludge  150 . The collected scum and sludge  150  is transferred to the FOG preheating tank  108  via respective pumps  152 - 160 . In some cases, when ozone is used as a dissolved gas in the primary CZDAOF unit  106  and/or the secondary DAF unit, the ozone helps to increase FOG recovery efficiency and control odors from the system  100 . 
     The scum and sludge  150  stored in the FOG tank  108  is preheated to a first desired temperature (or temperature range) and then transferred by a pump  162  through a constant-flow steam heater  110  to the three-phase centrifuge decanter  114 . The constant-flow steam heater  110  may apply steam from the boiler  112  to achieve a second desired temperature (or temperature range) within the scum and sludge  150 . In some specific examples, boiler  112  may also provide steam for the inlet coarse screen  102  washing and EQ tank  104  operational demands. 
     The three-phase centrifuge decanter  114  may process the preheated scum and sludge  164  on a batch basis for both FOG and sludge dewatering. Oil  166  from the three-phase centrifuge decanter  114  is collected and transferred to the finished oil tank  116  by a pump  168 . After decanting the water in the finished oil tank  116 , the finished oil  170  can be sold as biodiesel feedstock and loaded to an oil tanker for shipment by pump  172  through a flow and mass recording meter  174 . In some cases, in addition to the finished oil  170 , the system  100  via the three-stage centrifuge decanter  114  may output dry solids  176  that may be used to make organic fertilizer for agricultural applications. 
     In some cases, excess water or centrate  178  may be generated in addition to the dry solids  176  and the finished oil  170 . In these cases, the excess water or centrate  178  may be transferred back to the primary CZDAOF unit  106  for processing by the primary CZDAOF unit  106  and the bio-DAF unit  120  prior to discharging into the downstream sewer system. 
       FIG. 2  illustrates a cross-sectional view of the example primary CZDAOF unit  106  of  FIG. 1  according to some implementations. As discussed above, the raw wastewater is received by the CZDAOF system  106  at the central inlet column  202  via an inlet pipe  204 . In one example, the central inlet column  202  may be sealed to prevent the formation of the microbubbles in the received screened trap grease wastewater until the screened trap grease wastewater including the dissolved gaseous material, such as air, ozone, chemicals, and/or other dissolved gaseous elements, is exposed to the atmosphere in the first flotation zone  214 . In still other cases, the central inlet column  202  may receive the screened trap grease wastewater but not the fluid containing the dissolved gaseous materials. 
     In some alternative implementations, a mixture of dissolved gases (such as air and/or ozone) is introduced into the central column  202  via a diffuser  206  and mixes with the raw screened trap grease wastewater. Upon release to the atmosphere, the dissolved gases generate numerous micro-size bubbles or microbubbles. The microbubbles attach on the surface of FOG and/or suspended solid particles and cause the FOG and/or suspended solid particles to float upward. An angular guide plate  208  is mounted within the central inlet column  202  to change the flow direction and eliminate any FOG or particle accumulation on the surface of the central inlet column  202 . Further, as illustrated, the central inlet column  202  may be exposed to the atmosphere, via at least openings  210  between a scum collection assembly  212  and a top surface of the central inlet column  202 . 
     As the screened trap grease wastewater exits the central inlet column  202 , the screened trap grease wastewater is processed via a series of flotation zones, such as flotation zones  214 - 218 . In each of the flotation zones  214 - 218 , additional microbubbles may be introduced to the screened trap grease wastewater to remove additional FOGs and solid particles via the respective diffuser  220 - 224 . In some cases, the microbubbles attach to and raise the FOGs and solid particles to the surface. The scum collection assembly  212  then skims the surface of the screened trap grease wastewater to collect the floated FOGs and solid particles into a scum collection trough  226  and out via the discharge ports  228 (A)-(C). For example, the discharge port  228 (A) may collect the FOG and particles from the first flotation zone  214 . The discharge port  228 (B) may collect the FOG and particles from the second flotation zone  216 . The discharge port  228 (C) may collect the FOG and particles from the third flotation zone  218 . As shown in  FIG. 1 , the collected FOG and particles may be provided to the FOG tank  108  for further processing. In some specific examples, the FOG and particles collected from each individual flotation zones  212 - 216  may be stored in separate tanks. 
     The scum collection assembly  212  may include a drive motor  230  configured to rotate a scum collection assembly  212 . The drive motor  230  as well as the assembly  212  may be mounted on a central drive mounting pad  232 . In the illustrated example, the scum collection assembly  212  also includes at least one scraper mounting arm  234 , at least one corresponding side wall wheel assembly  236 , and one or more scum scrapers  238  mounted below the at least one scum scraper mounting arm  234 . In general, as the scum collection assembly  212  is rotated by the drive motor  230 , the assembly  212  rotates over flotation zones  214 - 218 . In some cases, the drive motor  230  may be equipped with a variable frequency drive (VFD), such that the drive motor  230  may be operable at variable speeds. In other cases, the rotation of the scum collection assembly  212  may be periodic, such that the scum collection assembly  212  may rotate for a first predefined period of time and then halt for a second predefined period of time. In some cases, the scum collection assembly  212  may rotate in the clockwise direction. During the rotations, the scum scrapers  238  mounted below the scum scraper mounting arms  234  push the scum (e.g., the floated FOGs and solid particles) accumulated on the surface of the screened trap grease wastewater into the scum collection trough  226 . 
     The scum collection trough  226  may include a screw convey unit  240  to push the FOGs and solid particles towards the discharge ports  228 (A)-(C). In some cases, a drive motor  242  may be mechanically coupled to the screw convey unit  240 . The screw convey unit  240  may include one or more fin plates  244  coupled to a screw beam  246 . In this example, the drive motor  242  may rotate the screw convey unit  240  to move the FOGs and solid particles deposited in the scum collection trough  226  towards the discharge port  228 (A)-(C). The collected FOGs and solid particles may then be used or processed, such as when the FOGs include commercially desirable products (e.g., the finished oil and dry solids), as discussed above with respect to  FIG. 1 . 
     In the illustrated example, the bottom plate of each of the flotation zones  214 - 218  are sloped to collect bottom sludge and heavy particles that is included in the wastewater received via the inlet pipe  204 . In each of the flotation zones  214 - 218  a bottom sludge assembly  248  is configured to with several sludge discharge ports  250 (A)-(C) ports evenly spaced along the circumference of each of the flotation zones  214 - 218  to collect and discharge the heavy solids and sludge that accumulates on the bottom of each flotation zone  214 - 218 , as discussed above. For example, the bottom plate of each flotation zone  214 - 218  may be sloped toward the inner zone wall to help heavy solid particles slide toward the sludge discharge ports  250 (A)-(C). In one implementation, the bottom sludge discharge assembly  248  consists of a number of sludge discharge ports  250 (A)-(C) and a circular sludge pipe manifold (not shown). In some implementations, each flotation zone  214 - 218  may have a separate bottom sludge discharge ports  250 (A)-(C), as illustrated. For instance, the sludge discharge ports  250 (A)-(C) may be in fluid communication with the FOG tank  108  as discussed above with respect to  FIG. 1 . 
     In the current example, the primary CZDAOF unit  106  is in fluid communication with the primary effluent weir tank  146 . For instance, the third flotation zone  218  may be in fluid communication with the effluent weir tank  146  via a channel  254 , such that the primary CZDAOF unit effluent exiting the third flotation zone  218  enters the primary effluent weir tank  146 . The primary effluent weir tank  146  may include a weir gate  256  that is adjustable via a control handwheel  258  to control the primary CZDAOF unit effluent level in the weir tank  146 . The primary CZDAOF unit effluent passes through an opening in the weir gate and is discharged through a discharge port  260  to the bio-DAF feed tank  118 . 
     In some cases, the FOG and colloidal particulates remaining in the screened trap grease wastewater after exiting the first flotation zone  214  are further agglomerated and flocculated to form larger particulates with the help of coagulant and flocculant  262  added to the screened trap grease wastewater in the first flotation zone  214 , the second flotation zone  216  and/or the third flotation zone  218 . 
       FIG. 3  illustrates a top view of an example primary CZDOAF unit  106  of  FIG. 1  with scum scraper assembly removed according to some implementations. As discussed above, the primary CZDOAF unit  106  may be configured to clean screened trap grease wastewater prior to discharging the screened trap grease wastewater into a downstream sewer system. In some examples, the primary CZDOAF unit  106  may be used to recover FOG from wastewater. In the illustrated example, the example primary CZDOAF unit  106  includes a central column  202  and the series of flotation zones  214 - 218 . 
     In the current example, the screened trap grease wastewater is received from a source (not shown) at the lower or bottom portion of the central column  202 . As discussed above, the central column  202  may be configured to introduce microbubbles, via pressurized recirculated primary CZDOAF unit effluent, into the screened trap grease wastewater. For instance, in one example, the pressurized recirculated primary CZDOAF unit effluent containing the mixture of dissolved gases (such as air and/or ozone) is introduced to the screened trap grease wastewater via a diffuser pipe  206 . Upon release to the atmosphere within the first flotation zone  204 , the dissolved gases in the pressurized recirculated primary CZDOAF unit effluent generates numerous microbubbles. The microbubbles attach on the surface of the FOG or suspended solid particles and cause the FOG and the particles to float upward. The FOG and the particles may then be removed from the surface the primary scum scraper assembly (not shown) and the scum collection trough  226 . 
     The first flotation zone  214  extends radially around the central column  202  and is in fluid communication with the central column  202 . Similar to the central column  202 , the first flotation zone  204  may introduce microbubbles into the screened trap grease wastewater by introducing additional pressurized recirculated primary CZDOAF unit effluent via at least one diffuser  220 . In the illustrated example, the diffusers  220  are a circular dissolved air diffuser, however, in other examples, the diffuser  220  may be multiple dissolved diffusers evenly distributed around the first flotation zone  214 . 
     The second flotation zone  216  extends radially outward around the first flotation zone  214  and is configured in fluid communication with the first flotation zone  214 , such that when the screened trap grease wastewater exits the first flotation zone  214 , the screened trap grease wastewater enters the second flotation zone  216 . In various implementations, the primary CZDOAF unit  106  may be configured with baffles, generally indicated by  302 (A)-(C), that allow the wastewater within the flotation zones  214 - 218  to flow in different directions. For instance, in some examples, the baffles  302 (A)-(C) may be configured such that the screened trap grease wastewater within the first flotation zone  214  flows in a first direction, generally indicated by  304 , opposite a second direction, generally indicated by  306 , to the screened trap grease wastewater within the second flotation zone  216 . For instance, in the illustrated example, the screened trap grease wastewater in the first flotation zone  214  flows in a clockwise direction while the screened trap grease wastewater in the second flotation zone  216  flows in a counter-clockwise direction. 
     Alternately, the screened trap grease wastewater in the first flotation zone  214  flows in a counter-clockwise direction while the wastewater in the second flotation zone  216  flows in a clockwise direction. By changing the direction of flow of the screened trap grease wastewater using baffles  302 (A)-(C) within each flotation zone  214 - 218 , the primary CZDOAF unit  106  can slow the rate of flow of the screened trap grease wastewater and, thereby, increase the time the screened trap grease wastewater is within each flotation zone  214 - 218 . In some cases, the baffles  302 (A)-(C) may include textures, protrusions, or other configurations that may cause the screened trap grease wastewater to be disturbed and/or slow. 
     Within the second flotation zone  216 , microbubbles of dissolved gases, such as air and/or ozone, are again injected through a number of dissolved air diffusers  222 . Again, the microbubbles may attach to additional FOGs and suspended solid particles not removed in the central column  202  or the first flotation zone  214 . The FOGs and particles attached to the microbubbles in the wastewater again raise to the surface and may be collected in the scum collection trough  226  by the primary scum collection assembly  212 . 
     In the illustrated example, a third flotation zone  218  extends radially outward around the second flotation zone  216  and is configured in fluid communication with the second flotation zone  216 , such that when the screened trap grease wastewater exits the second flotation zone  216 , the screened trap grease wastewater enters the third flotation zone  218 . The primary CZDOAF unit  106  is further configured such that the screened trap grease wastewater within the third flotation zone  218  flows in the first direction  304  opposite the second direction  306  of the screened trap grease wastewater within the second flotation zone  216  (e.g., the screened trap grease wastewater in the third flotation zone  218  flows in the same direction as the screened trap grease wastewater within the first flotation zone  214 ). 
     Within the third flotation zone  218 , microbubbles of dissolved gases, such as air and/or ozone, are again injected through a number of dissolved air diffusers  224 . Again, the microbubbles may attach to additional FOGs and suspended solid particles not removed in the central column  202 , the first flotation zone  214 , or the second flotation zone  216 . The FOGs and particles attached to the microbubbles in the wastewater again raise to the surface and may be collected in the scum collection trough  226  by the primary scum collection assembly  212 . 
     In some cases, the FOG and colloidal particulates remaining in the screened trap grease wastewater after exiting the first flotation zone  214  may be further agglomerated and flocculated to form larger particulates with the help of coagulant and flocculant added to the screened trap grease wastewater in the second flotation zone  216  and/or the third flotation zone  218 . The addition of the coagulant and flocculant, in the second flotation zone  216  and/or third flotation zone  218  assist in significantly reducing the BOD and TSS loadings in the primary CZDOAF unit effluent. 
     In the various implementations discussed herein, the relative sizes of each of the flotation zones  214 - 218  may vary and may be determined based on process requirements of the wastewater. In some cases, the flotation zones  214 - 208  may be separated by vertical zone walls  308  that are arranged in concentric configuration. Additionally, while the primary CZDOAF unit  106  is shown having three substantially circular flotation zones  214 - 218 , it should be understood that the number of flotation zones as well as the shape may vary from implementation to implementation. Thus, in various implementations, the primary CZDOAF unit  106  may be configured with one or more flotation zones. 
       FIG. 4  illustrates another top view of the example the primary CZDAOF unit  106  of  FIG. 1  according to some implementations. As discussed above in  FIG. 1 , the primary CZDAOF unit  106  may include a central inlet column (shown as sealed to the atmosphere by a central drive mounting pad  232 ) and a series of flotation zones, such as flotation zones  214 - 218 , arranged about the central inlet column. 
     In the current example, the screened trap grease wastewater is received from a source (such as a hauler truck) at the lower or bottom portion of the central inlet column. In the current example, the scum collection assembly  212  is shown positioned over the primary CZDAOF unit  106 . The scum collection assembly  212  may be configured to skim FOGs and solid particles from the surface of the wastewater within each of the flotation zones  214 - 218  and deposit the FOG and solid particles into the scum collection trough  226 . The scum collection trough  226  may then push the collected FOG and solid particles out of the primary CZDAOF unit  106  via one or more discharge ports, generally indicated by  228 (A)-(C). For example, the scum collection trough  226  may discharge FOG and solid particles from the first flotation zone  214  via discharge port  228 (A), FOG and solid particles from the second flotation zone  216  via discharge port  228 (B), and FOG and solid particles from the third flotation zone  218  via discharge port  228 (C). 
     The scum collection assembly  212  may include a drive motor  230  configured to rotate a scum collection assembly  212 . The drive motor  230  as well as the assembly  212  may be mounted on a central drive mounting pad  232 . In the illustrated example, the scum collection assembly  212  also includes four scraper mounting arms, generally indicated by  402 , four inner structural beams, generally indicated by  404 , four outer structural beams, generally indicated by  406 , four side wall wheel assemblies, generally indicated by  408 , and a scum scraper (not shown) coupled to each of the scum scraper mounting arms  402 . While the illustrated example has four scarper mounting arms  402 , four inner structural beams  404 , and four outer structural beams  406 , it should be understood that in other implementations, different numbers of scarper mounting arms  402 , inner structural beams  404 , and outer structural beams  406  may be used, such as two or six. 
     In general, as the scum collection assembly  212  is rotated by the drive motor  230 , the assembly  232  rotates over flotation zones  214 - 218  via the four side wall wheel assemblies  408 . During the rotations, the scum scrapers mounted below the scum scraper mounting arms  402  push the scum (e.g., the floated FOGs and solid particles) accumulated on the surface of the screened trap grease wastewater into the scum collection trough  226 . For example, as the scum collection assembly  232  rotates one or more scum scrapers within each of the flotation zones  214 - 218  may be positioned to push the FOGs and solid particles floated by the microbubbles into the scum collection trough  226  where the collected FOG and solid particles may be provided to the FOG tank  108  via the respective discharge ports  228 (A)-(C). 
     As discussed above, each of the flotation zones  214 - 218  may include diffusers, such as illustrated diffusers  220 - 224 , to introduce fluid or recirculated primary CZDOAF unit effluent having dissolved gases (such as air and/or ozone) that produce microbubbles when exposed to the atmosphere after exiting the diffusers  220 - 224 . In the current example, the primary CZDOAF effluent exits out of the third flotation zone  218  into the primary weir tank  146 . Thus, the third flotation zone  218  and the primary weir tank  146  are in fluid communication. 
     In the current example, the primary CZDAOF unit  106  may be configured to be fabricated using 304L or 316L, stainless steel, or a series of duplex stainless. For instance, stainless steel does not need to be painted or coated in some manner, and therefore can be more economical. Further, the circular shape of the CZDAOF unit  106  allows the side zone walls to be in hoop stress, enabling the CZDAOF unit  106  to be built to almost any diameter using lighter, thinner materials than conventional rectangular CZDAOF units. Additionally, to address potential shipping problems due to size, the CZDAOF unit  106  may be fabricated in a number of flanged sections or modules that can be easily transported in pieces and assembled at the construction site. This allows the CZDAOF unit  106  to be of any desired diameter to be built and shipped to meet the requirements of the project at hand, and also reduces transportation costs when compared to conventional units. 
       FIG. 5  illustrates a partial view of an example resource recovery system  100  of  FIG. 1  including the primary CZDAOF unit  106 , the primary gaseous material dissolving system  124 , the primary weir tank  146 , and the equipment  144  according to some implementations. As discussed above, screened trap grease wastewater  132  enters the CZDAOF unit  106  via the inlet pipe  204  coupled to the central inlet column  202 , as discussed above. Likewise, the primary CZDAOF unit effluent  138  exits the primary CZDAOF unit  106  via a channel  254  and into the primary weir tank  146 . In some implementations, some portion of the primary CZDAOF unit effluent  138  may be recirculated to the gaseous material dissolving system  124 , as shown. In the illustrated example, the gaseous material dissolving system  124  and additional equipment  144  includes an ozone generator  502 , oxygen generator  504 , chiller  506 , air compressor  508 , and one or more microbubble generators  510 . The gaseous material dissolving system  104  may draw cleaned effluent  138  from the outfall chamber  514  of the weir tank  146 . The primary weir tank  146  may include an adjustable weir gate that controls the water level in the primary CZDAOF system  106 . When this filling chamber  512  is full (e.g., more cleaned effluent  138  is in the filling chamber  512  than the gaseous material dissolving system  124  may consume), the excess primary CZDAOF unit effluent  138  overflows the adjustable weir  256  into the outfall chamber  514  and is discharged through the discharge port  260  to the bio-DAF feed tank. 
     In general, the microbubble generators  510  may cause the air, ozone and/or other gases (e.g., nitrogen) to be dissolved into the primary CZDAOF unit effluent  138  under high pressure. The primary CZDAOF unit effluent  138  including the dissolved gases may then be provided via fluid communication to corresponding dissolved air diffuser, such as diffusers  206 ,  220 ,  222 , and  224 . In the illustrated example, each of the microbubble generators  510  are in fluid communication with each of the central inlet column  202  and the flotation zones  214 - 218 . However, in alternative implementations, each of the microbubble generators  510  may dissolve gases into cleaned effluent  138  being supplied to select ones of the diffusers  206 ,  220 ,  222 , or  224 , such as when different gases are dissolved for use in different flotation zones  214 - 218 . 
       FIG. 6  illustrates a top view of the example bio-DAF unit  120  according to some implementations. As discussed above, the bio-DAF unit  120  may be used to remove organic matter, suspended solids, and nutrient removal from the primary CZDAOF unit effluent  132 . The bio-DAF unit  120  includes a central column (not shown), multiple-stage aerobic bio-media reactors including aerobic bio-media reactor  602 - 608 , and a secondary DAF unit  610 . The bio-DAF unit  120  may also be coupled to ancillary equipment, such as a gaseous material dissolving system and blowers, as discussed above with respect to  FIG. 1 . 
     In general, the primary CZDAOF unit effluent  138  is received via an inlet pipe  612  at the central column  600 . In some implementations, the primary CZDAOF unit effluent  132  is mixed with secondary DAF effluent having dissolved gases (such as ozone and/or air). The primary CZDAOF unit effluent  138  transfers into first stage aerobic bio-media reactor  602  from the central column  600 . For instance, an screen cage  614 . A screen cage may cover the central column effluent pipe  614  exit to stop bio-media from the bio-media reactor  602  back into the central column  600 . 
     Within the first stage bio-media reactor zone  602 , air and/or oxygen is provided by an aeration system including the blowers  122 . The air and/or oxygen may be distributed through a diffuser assembly (e.g., a coarse bubble diffuser)  616 (A). Bio-media in the first stage aerobic bio-media reactor zone  602  may be loaded in at a first pre-designated filling ratio. Since the influent organic loading may be high in the primary CZDAOF unit effluent  138 , fast-growing bacteria species may be selected to dominate in the first stage aerobic bio-media reactor zone  602 . Thus, the organic matter and BOD can be oxidized and biodegraded into carbon dioxide and water through metabolism of the microorganism system. The air and/or oxygen provided by the diffuser assembly  616 (A) provides for microorganism growth as well as causes water flow for moving and rotating the bio-media within the reactor to avoid biofilm soaring on the surface of the bio-media. 
     First stage aerobic bio-media reactor effluent  618  enters the second stage aerobic bio-media reactor zone  604 , for instance, through a second screen cage  620 . The incoming organic loading of the effluent  618  may be significantly reduced, as the effluent  618  has been processed by the first stage aerobic bio-media reactor  602 . Again, a microorganism system suitable for the available organic matter level is developed within the second stage aerobic bio-media reactor zone  604  and dominating bacteria species may be built up. Again, air and/or oxygen is provided by the blowers  122  and distributed in the second stage aerobic bio-media reactor zone  604  through a diffuser assembly  616 (B), such as a coarse bubble diffuser assembly. In the second stage aerobic bio-media reactor  604 , bio-media may be loaded at a second pre-designated filling ratio. In the second stage aerobic bio-media reactor  604 , the organic matter and BOD can be further biodegraded and oxidized into carbon dioxide and water through metabolism of microorganisms. Again, the air and/or oxygen provided via the diffuser  616 (B) acts to cause water flow to move and rotate the bio-media within the reactor and to, thus, avoid biofilm soaring on the surface of bio-media. 
     Second stage aerobic bio-media reactor effluent  624  enters the third stage aerobic bio-media reactor zone  606  through a third screen cage  624 . The incoming organic loading of the effluent  624  may be significantly reduced, as the effluent  624  has been processed by the first and second stage aerobic bio-media reactor  602  and  604 . Again, a microorganism system suitable for the available organic matter level is developed within the third stage aerobic bio-media reactor zone  606  and dominating bacteria species may be built up. Again, air and/or oxygen is provided by the blowers  122  and is distributed in the third stage aerobic bio-media reactor  606  through a diffuser assembly  616 (C), such as a coarse bubble diffuser assembly. Bio-media may be loaded in the third stage aerobic bio-media reactor  606  based on a third pre-designated filling ratio. Again, the air and/or oxygen provided via the diffuser  616 (C) acts to cause water flow to move and rotate the bio-media within the reactor  606  and to, thus, avoid biofilm soaring on the surface of bio-media. 
     In some cases, the third stage aerobic bio-media reactor effluent  626  enters the fourth stage aerobic bio-media reactor zone  608  through a fourth standard screen cage  628 . Through biodegradation in the first, second, and third stage aerobic bio-media reactors  602 - 606 , the majority of BOD has been consumed and removed. In one example, aerobic autotrophic bacteria species may become the dominating species in the third stage aerobic bio-media reactor  608 . Again, air and/or oxygen is provided by the blowers  122  and is distributed in the third stage aerobic bio-media reactor  606  through a diffuser assembly  616 (D), such as a coarse bubble diffuser assembly. Bio-media may be loaded in the third stage aerobic bio-media reactor  606  based on a fourth pre-designated filling ratio. Again, the air and/or oxygen provided via the diffuser  616 (D) acts to cause water flow to move and rotate the bio-media within the reactor  608  and to, thus, avoid biofilm soaring on the surface of bio-media. In some cases, the fourth stage aerobic bio-media reactor effluent  630  enters the secondary DAF unit  610  through a standard screen cage  632  (and, in some cases, a pipe) to further separate biomass and TSS from effluent  630 . 
     In the illustrated example, the aerobic bio-media reactor  602 - 608  of the bio-DAF unit  120  are formed as four sections. Each reactor  602 - 608  may be configured to propagate and accumulate specific bacteria and microorganisms based upon the food source, nutrient level, air supply, and environmental conditions. As discussed above, screen cages  614 ,  620 ,  624 , and/or  632  may be installed at the exit/entrance of each reactor  602 - 608  to retain the bio-media, bacteria, and microorganisms in their respective reactor  602 - 608 . Thus, the bio-media, bacteria, and microorganisms within each of the reactor  602 - 608  are maintained in an environment that is configured to maximize biomass production rates. 
     Partition walls, such as partition walls  634 (A)-(D), may be used to divide the aerobic bio-media reactor  602 - 608  of the bio-DAF unit  120  into the four different functional zones. In some situations, to address potential shipping problems due to size, the reactor  602 - 608  may be fabricated as individual flanged sections that may be more easily transported in pieces and assembled at a construction or operational site. Thus, of the bio-DAF unit  120  of any desired diameter maybe fabricated, shipped to a location, and assembled on site to meet the requirements of the project at hand while still reducing overall transportation costs when compared with conventional systems. 
     In the illustrated example, the secondary DAF unit  610  is used to remove any combination of suspended solids, stripped biofilm, TP and small particulates from the bio-media reactor effluent  630 . In cases in which TP removal is necessary, alum and a small amount of flocculant can also be added in the secondary DAF unit  610 . In particular, the secondary DAF unit  610  extends radially outward around the central column  600 , as shown. Biomass and TSS in the aerobic bio-media reactor effluent  630  may be floated by dissolved gasses (such as, air and/or ozone) introduced into the secondary DAF unit  610 . For example, gases may be dissolved in recycled bio-DAF effluent  142  by the secondary gaseous material dissolving system  126 . The recirculated effluent containing the dissolved gases may be injected through several diffuser pipes (not shown) above the bottom of the secondary DAF unit  610 . Upon exposure to the atmosphere within the secondary DAF unit  610 , the dissolved gases form microbubbles that may attach and float the remaining biomass and TSS and raise them to the surface where the remaining biomass and TSS may be removed via a secondary scum collection assembly  634 . 
     In the current example, the secondary scum collection assembly  634  is shown positioned over the secondary DAF unit  610 . The secondary scum collection assembly  634  may be configured to skim FOGs and solid particles from the surface of the secondary DAF units  610  and discharge the FOG and solid particles  150  into the scum collection trough or chute  638 . The scum collection assembly  634  may include a drive motor  640  configured to rotate a scum collection assembly  634 . The drive motor  640  as well as the assembly  634  may be mounted on a central drive mounting pad  642 . In some implementations, the central drive motor  640  may be equipped with a VFD. In some cases, the central drive motor  640  may cause the assembly  634  to continuously rotate in a clockwise direction. In other cases, the central drive motor  640  may cause the assembly  634  to continuously rotate in a counter-clockwise direction. 
     In the illustrated example, the scum collection assembly  634  also includes four scraper mounting arms  642  coupled to four side wall wheel assemblies  646 . The four side wall wheel assemblies  646  may be configured to mount over the secondary DAF unit wall  648 , such that the drive motor  640  may cause the assembly  634  to rotate on over the primary and secondary DAF units  610  as the wheel assemblies  646  rotate about the secondary DAF unit wall  648 . 
     The scum collection assembly  634  includes a scum scraper mounted to the scraper mounting arms  644  to collect floated scum from the secondary DAF unit  610 . Scum  150  collected in the chute  638  may be discharged using gravity and transferred to the FOG tank via a pump, as discussed above. The bio-DAF effluent  142  is then provided to the secondary DAF unit weir tank  148  after exiting the secondary DAF unit  610  via outlet pipe  650 . In some cases, the bio-DAF effluent  142  may be recycled back into the secondary DAF unit  610 . For example, the bio-DAF effluent  142  may be used to dissolve gases which are then mixed with the bio-DAF effluent  142  and re-introduced into the secondary DAF unit  610  to form the microbubbles. 
       FIG. 7  illustrates a cross-sectional view of the bio-DAF unit  120  of  FIG. 1  according to some implementations. The bio-DAF unit  120  includes a central column  702 , the multiple-stage aerobic bio-media reactors  704 , and secondary DAF unit  610 . The multiple-stage aerobic bio-media reactors  704  may be divided into multiple independent reactors, such as the bio-media reactors  602 - 608  discussed above with respect to  FIG. 6 . 
     In some implementations, the central column  702  may be used to introduce and distribute primary CZDAOF effluent  138  into the bio-DAF unit  120 . As discussed above, the primary CZDAOF effluent  138  may be received via an inlet pipe  612  such that the primary CZDAOF effluent  138  enters the central column  702  near the bottom. The central column  702  provides FOG and light particulate removal based on the lower uprising velocities of particulates and FOG. Contemporaneously, a mixture of effluent containing dissolved gases (such as air and/or ozone) recycled from the secondary DAF unit  610  may be introduced into the central column  702 . To prevent FOG accumulation on the surface of the central column  702 , an angular guide plate  706  may be mounted within the central column  702 . For example, the central column  702  may change the flow direction. In one implementation, the angular guide plate  706  may be mounted on the top of or near the top of the central column  702 . In some examples, the central column  702  may be exposed to the atmosphere, via at least openings between a scum collection assembly  634  and a top surface of the central column  702 . In an alternative implementation, the central column  702  may be sealed to prevent the formation of the microbubbles. 
     As discussed above, the multiple-stage aerobic bio-media reactors  704  are divided into four relatively independent functional zones. In general, the bio-media treatment process is based on attached growth biofilm principles to eliminate the returned activated sludge. In some cases, floating plastic media are kept inside the various reactors to provide a place for bacteria and microorganism growth. Aeration is supplied to the aerobic reactors to provide the necessary oxygen for the microbial growth and sufficient mixing to fully disperse the plastic media throughout the reactors. The mixing also serves as a measure to control the biofilm thickness on the plastic media. When the biomass becomes too thick and heavy to hold onto the plastic media, it is sloughed or stripped off from the plastic media. For example, the multiple-stage aerobic bio-media reactors  704  may include an aeration and turbulence introduction process. The aeration and turbulence within the multiple-stage aerobic bio-media reactors  704  keeps the biofilm thin and fresh, because extra biomass is stripped from the plastic media by the turbulence and floated by the coarse air bubbles. The extra biomass may then be captured and removed in the downstream secondary DAF unit  610 . Air may be provided by the blowers and is distributed in the zones of the multiple-stage aerobic bio-media reactors  704  through one or more diffuser assemblies  708 . 
     In the illustrated example, the secondary DAF unit  610  is used to remove suspended solids, stripped biofilm, and small particulates from the bio-media reactor effluent. In particular, the secondary DAF unit  610  extends radially outward around the central column  702  as shown. Biomass and TSS in the third stage aerobic bio-media reactor zone effluent may be floated by dissolved gasses (such as, air and/or ozone) introduced into the secondary DAF unit  610 . For example, gases may be dissolved in recycled effluent by the secondary gaseous material dissolving system  126 . The effluent containing the dissolved gases may be injected through several diffuser pipes, generally indicated by  710 , above the bottom of the secondary DAF unit  610 . Upon exposure to the atmosphere within the secondary DAF unit  610 , the dissolved gases form microbubbles that may attach and float the remaining biomass and TSS. In some cases, the diffusers  710  may be individual or separate diffusers designated to the secondary DAF unit  610 . The bio-DAF effluent  142  may exit from the secondary DAF unit  610  via an exit pipe  650 . 
     In some cases, the central column  702  may also be configured to trap large solids or heavies to protect the screen cages between each of the reactors. For example, the large solids or heavy sludge  150  may collect on a bottom surface of the central column  702  where the large solids or heavy sludge  150  may be removed and/or collected by a sludge discharge assembly  712 . In some cases, the sludge discharge assembly  712  may include one or more discharge ports to discharge the sludge  150  from the unit  120 . In some cases, the sludge discharge assembly  712  may run along the bottom of the central column  702 , the secondary DAF unit  610 , and the reactors  704  to remove sludge  150  collecting on the bottom surface of each of the central column  702 , the secondary DAF unit  610 , and the reactors  704 . The removed sludge  150  may be transferred to the FOG tank by one or more pumps. 
     In the current example, a scum collection assembly  634  is shown positioned over the secondary DAF unit  610 . The scum collection assembly  634  may be configured to skim floated FOGs and solid particles from the surface of the effluent within the secondary DAF unit  610  and discharge the FOG and solid particles into the scum collection chute  638 . The scum collection chute  638  may then push the collected FOG and solid particles  150  out of the system  120  where the FOG and solid particles  150  may be transferred to the FOG tank by one or more pumps. 
     As discussed above, the scum collection assembly  634  may include a drive motor  640  configured to rotate a scum collection assembly  634 . In the illustrated example, the scum collection assembly  634  also includes scraper mounting arms, generally indicated by  642 , side wall wheel assemblies, generally indicated by  646 , and one or more scum scrapers  714  coupled to the scum scraper mounting arms  644 . It should be understood that in other implementations, different numbers of scarper mounting arms  644  may be used and various structural beams (not shown) may be associated with the assembly  634 . 
       FIG. 8  illustrates a partial view of an example bio-DAF unit  120  of  FIG. 1  according to some implementations. As discussed above, the bio-DAF effluent  142  may exit the bio-DAF unit  120  from the secondary DAF unit  610  via an exit pipe  650 . The bio-DAF effluent  142  may exit the secondary DAF unit  610  and enter the secondary weir tank  148 . The secondary weir tank  148  may include a filling chamber  802  and outfall chamber  804 . In some cases, the gaseous dissolving systems  126  may draw bio-DAF effluent  142  from the fill chamber  802 . An adjustable weir gate  806  is installed to control the water level in the bio-DAF unit  120 . When this filling chamber  802  is full, water overflows the adjustable weir gate  806  into the outfall chamber  804 . The bio-DAF effluent  142  is discharged through a discharge port  808 . 
     The secondary gaseous material dissolving system  126  is used to provide dissolved gases (e.g., air and/or ozone) to the secondary DAF unit  610 . The secondary gaseous material dissolving system  126  may include one or more microbubble generators  810  and an ozone generator  812  with associated valves and controls. The suction line of the microbubble generator  810  may be connected to the fill chamber  802  of the secondary weir tank  128  such that, for example, a mixture of air and/or ozone is injected in the suction line of the microbubble generators  810  and is dissolved into effluent  142  under high pressure. The bio-DAF effluent  142  having dissolved gases, generally indicated by  814 , is then provided to the central column  702 , the secondary DAF unit  610 , and/or one or more of the reactors  704 . 
       FIG. 9  is a flow diagram illustrating example processes associated with the system  100  according to some implementations. The processes are illustrated as a collection of blocks in a logical flow diagram, which represent a sequence of operations. The order in which the operations are described should not be construed as a limitation. Any number of the described blocks can be combined in any order and/or in parallel to implement the process, or alternative processes, and not all of the blocks need be executed. 
       FIG. 9  illustrates an example flow diagram showing a process  900  for forming finished oil and dry solids according to some implementations. As discussed above, brown grease or trap grease wastewater is collected from grease traps that are typically installed in restaurants, cafeteria, fast-food restaurant chains, and institutional food establishments to separate FOG from kitchen wastewater. Brown grease is a byproduct of cooking and comes from meat fats, lard, oil, shortening, butter, margarine, food scraps, baked goods, sauces, and dairy products. Brown grease is a mixture of FOG, food particulates, water, and kitchen waste, grit, rocks and debris that has gone down a drain and been trapped in a grease trap or grease interceptor. Brown grease in downstream sewers, WWTP, or other POTW are a leading cause of clogs, SSOs and damage to pumping stations. 
     The system discussed above provides a sustainable, integrated, compact, modular, environmentally and economically efficient system for removing and recovering FOG from brown grease. In some implementations, the system may be configured to produce biodiesel feedstocks and fertilizer as a byproduct while removing BOD and TSS pollutants to meet the city sewer or downstream POTW discharge limits. 
     At  902 , the system may receive brown or trap grease wastewater from a hauling truck. For example, the truck may transport the brown or trap grease wastewater from restraints or other establishment to the processing system. Alternatively, for large facilities, the system may be established between the grease trap and the downstream sewer system. 
     At  904 , the system may process the brown or trap grease wastewater via an inlet coarse screen. In general, brown or trap grease wastewater can contain of trash, grit, small rocks, debris. These materials must be caught and removed to protect subsequent pumps, pipeline, and tanks of the system from damage. As depicted in  FIG. 1 , the hauling truck initially dumps trap grease wastewater into the inlet coarse screen and the inlet coarse screen operates to remove trash, debris, grit, and small rocks (e.g., larger debris) from the brown or trap grease wastewater. In some cases, the inlet coarse screen may include one or more coarse screens, one or more screw conveyors, and/or one or more steam spray washing systems to assist with removing the larger debris. 
     At  906 , after screening by the inlet coarse screen, the screened trap grease wastewater is transferred into the EQ tank by a pump. The EQ tank may be configured with sufficient volume to hold half of the design flow capacity of the brown grease treatment and disposal system. While the screened trap grease wastewater is within the EQ tank, steam may be injected to maintain a desired temperature to avoid FOG sticking on the walls and pipes. 
     At  908 , the heated screened trap grease wastewater is transferred to the primary CZDAOF unit. The primary CZDAOF unit is configured to remove and recover FOG from the screened trap grease wastewater as well as to remove BOD and TSS contaminants. For example, the primary CZDAOF unit may utilize one or more flotation zones, each of which may introduce microbubbles to attach and float the FOG to the surface. For instance, the flotation zones may be in fluid communication with the primary gaseous material dissolving system to receive fluid containing dissolved gases that form the microbubbles when exposed to the atmosphere in the primary CZDAOF unit. In some cases, coagulant and/or flocculant may be added to one or more of the flotation zones of the primary CZDAOF unit by a chemical feed system. 
     At  910 , the system transfers the primary CZDAOF unit effluent to the bio-DAF unit. For example, the bio-DAF unit may be fed with the primary CZDAOF effluent from a bio-DAF tank by a pump. In general, the bio-DAF unit has a multi-stage aerobic bio-media reactor and a secondary DAF unit for final polishing of the effluent. In some cases, the bio-media treatment process is based on attached growth biofilm principles by eliminating the recycling activated sludge. For example, floating plastic media may be kept inside each of the reactors to provide a place for bacteria and microorganism growth. Aeration is supplied to the aerobic reactors by the blower and the second to provide the necessary oxygen for microbial growth as well as to cause turbulence to fully disperse the plastic media throughout the reactors. 
     At  912 , scum is collected from the surface of the flotation zones of the primary CZDAOF unit and the flotation zones of the secondary DAF unit and sludge is collected from the bottom of the flotation zones of the primary CZDAOF unit and the flotation zones of the secondary DAF unit. 
     At  914 , the collected scum and sludge is transferred to the FOG preheating tank. The scum and sludge stored in the FOG tank  108  is preheated to a first desired temperature (or temperature range) and then transferred by a pump through a constant-flow steam heater to the three-phase centrifuge decanter. The constant-flow steam heater may apply steam from the boiler to achieve a second desired temperature (or temperature range) within the scum and sludge. 
     At  916 , the three-phase centrifuge decanter may process the heated scum and sludge on a batch basis for both FOG and sludge dewatering. Oil from the three-phase centrifuge decanter is collected and transferred to the finished oil tank by a pump. After decanting the water in the finished oil tank, the finished oil can be sold as biodiesel feedstock. In some cases, in addition to the finished oil, the three-phase centrifuge decanter may output dry solids that may be used to make organic fertilizer for agricultural applications. 
     Although the subject matter has been described in language specific to structural features, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features described. Rather, the specific features are disclosed as illustrative forms of implementing the claims.