Clean Water Act (CWA) Technology-Based Effluent Limitations Guidelines for MPP

July 10, 2025

The Clean Water Act (CWA) specifies various technology-based Effluent Limitations Guidelines (ELGs) for direct and indirect dischargers. These ELGs include:

• Best Practicable Control Technology Currently Available (BPT): Applies to all pollutants and is based on the best performance of facilities within the industry.
• Best Conventional Pollutant Control Technology (BCT): Targets conventional pollutants and involves a cost-reasonableness test.
• Best Available Technology Economically Achievable (BAT): Focuses on toxic and nonconventional pollutants, representing the highest performance in the industry.
• New Source Performance Standards (NSPS): Applies to new sources and reflects the most stringent controls attainable.
• Pretreatment Standards for Existing Sources (PSES): Designed to prevent pollutants from interfering with Publicly Owned Treatment Works (POTWs).
• Pretreatment Standards for New Sources (PSNS): Similar to PSES but applies to new indirect dischargers.

EPA evaluated available technologies to treat or remove meat and poultry (MPP) pollutants individually and in treatment trains, as shown below in subsections, based on the type of pollutant removal, including conventional pollutants, phosphorus, nitrogen, pathogens, and chlorides.

Conventional Pollutant Removal
MPP process wastewater contains oil & grease, TSS, and BOD, all conventional pollutants removed with primary treatment, which removes floating and settle-able solids. Typical treatment technologies include screening and DAF.

Facilities may add polymers, flocculants, and phosphorus-precipitating chemicals to or before the DAF. The chemical addition increases the removal of pollutants from the wastewater. Adding chemicals to remove phosphorus can help facilities meet phosphorus effluent limits. Chemical addition may not be possible for facilities that recycle materials from the DAF to the facility, as this would contaminate the raw material.

Biological/Organic Pollutant Removal an Attractive Option
Biological, physical, and chemical processes remove BOD, nitrogen, and phosphorus. Biological processes are useful to achieve low levels of BOD and nitrogen and are common at MPP facilities. Microorganisms in biological wastewater treatment require phosphorus for cell synthesis and energy transport, typically removing 10 to 30 percent of influent phosphorus. Through biological treatment, organic compounds break down with bacteria into water, CO2, N2, and CH4 products.

1. Anaerobic biological treatment: Facultative and anaerobic microorganisms in anaerobic digesters reduce organic matter and Biochemical Oxygen Demand (BOD) into gaseous methane and carbon dioxide in anaerobic wastewater treatment. The gas may be reused as biogas, offsetting energy costs. Anaerobic treatment systems have negligible energy requirements and can treat high-strength wastewater. Anaerobic lagoons are a typical anaerobic system used at MPP facilities. Due to the detention time, these lagoons also equalize wastewater flow. The lagoons are not mixed to maintain anaerobic conditions. Anaerobic lagoons can reduce BOD by 95 percent and suspended solids by 95 percent. (Johns. 1995; [4] USEPA. 1974; [5] USEPA. 1975).[6]
2. Aerobic biological treatment: In aerobic wastewater treatment, microorganisms require oxygen to degrade organic material into water, carbon dioxide, and organic compounds. Aerobic degradation is faster than anaerobic degradation. Soluble BOD reductions up to 95 percent are possible. Aerated lagoons have fixed, floating, or diffused air systems to aerate the water. Aerobic lagoons (naturally aerated systems) use algae to aerate the system through photosynthesis.
3. Anoxic biological treatment: Anoxic wastewater treatment systems are oxygen-deficient; bacteria break down nitrogenous compounds into nitrogen gas and oxygen.
4. Activated sludge: This system includes an aeration tank followed by a settling tank. Settled solids from the second tank are recycled back into the aeration tank. Under optimal conditions, this process can achieve 95 percent reductions in BOD, suspended solids, and ammonia.
5. Sequencing batch reactor (SBR): An SBR completes the activated sludge process in a single reactor. The system first fills with wastewater, and then the reaction in which bacteria break down organic compounds in the presence of oxygen occurs for some time. The system needs time to settle and separate the microorganisms from the treated effluent, and then the tank is discharged. SBR systems provide high removal rates of BOD and suspended solids, can be designed for nitrification, and can remove nitrogen and phosphorus. SBRs are ideal for low-flow processes as they do not need to run continuously, and the systems allow for operational and loading flexibility.
6. Multistage biological treatment for nitrogen removal: Nitrogen removal is a two-step process: nitrification and denitrification.
7. Nitrification is a two-step aerobic process. First, Nitrosomonas bacteria oxidize ammonia into nitrite. Then, Nitrobacter bacteria oxidize nitrite into nitrate.
8. Denitrification: This process reduces nitrite and nitrate produced by heterotrophic bacteria into nitrogen gas in anaerobic conditions. A carbon source, such as methanol, may need to be added to keep the microbes healthy.

Biological treatment systems are often used in series to achieve high nitrogen removal rates. Wastewater flows from one system to the next, with recycle streams and returned activated sludge returning to various system locations. Some examples include:

1. Modified Ludzack-Ettinger (MLE): The MLE is a two-stage system in which an aerobic stage follows an anoxic stage before wastewater goes to a clarifier. Mixed liquor with high nitrate levels is recycled from the aerobic stage back to the influent. Activated sludge from the clarifier is also recycled back into the influent. The MLE process removes most of the BOD and can achieve a nitrogen removal of 80 percent.
2. Bardenpho: This is a four-stage process: anoxic, aerobic, anoxic, aerobic, followed by a secondary clarifier. Mixed liquor with high nitrate levels is recycled from the first aerobic stage back to the first anoxic stage. Activated sludge from the clarifier is recycled back to the influent. Nitrification occurs primarily in the second stage (aerobic). Denitrification occurs in the first and third stages (anoxic). The final aeration stage removes nitrogen gas from the system and increases dissolved oxygen concentration. The four-stage Bardenpho process achieves higher nitrogen removal rates than the two-stage MLE process.

iii. Modified Bardenpho: This is a five-stage process: anaerobic, anoxic, aerobic, anoxic, aerobic, followed by a secondary clarifier. As in the Bardenpho process, mixed liquor with high nitrate levels is recycled from the first aerobic stage to the first anoxic stage, and activated sludge from the clarifier is recycled back to the influent. The anaerobic stage at the beginning of the system results in biological phosphorus removal. Phosphate-accumulating organisms (PAOs) are recycled from the aerobic stage in the mixed liquor to the anaerobic stage. In the following aerobic stages, PAOs uptake large amounts of phosphorus.

1. Other: Many other processes use multiple stages of treatment to remove nitrogen. These include A2/O, step feed, University of Capetown (UCT) processes, oxidation ditches, and Schreiber processes (USEPA, 2004, EPA-821-R-04-011).
2. Membrane bioreactor (MBR): MBRs use membranes to separate liquids and solids. The liquid stream then passes through anoxic and aerobic zones, similar to the biological treatment systems described above. As the membranes greatly reduce the suspended solids in the liquid stream, MBR removes nitrogen and phosphorus.
3. Enhanced Biological Phosphorus Removal: Microorganisms used in biological wastewater treatment require phosphorus for cell synthesis and energy transport. In treating typical domestic wastewater, between 10 and 30 percent of influent phosphorus is removed by microbial assimilation, followed by clarification or filtration. However, phosphorus assimilation above requirements for cell maintenance and growth, known as luxury uptake, can be induced by a sequence of anaerobic and aerobic conditions (Metcalf & Eddy, Inc., 1991). As explained above, the modified Bardenpho process removes phosphorus biologically.

Phosphorus Removal
As mentioned in the biological/organic pollutant removal section, some phosphorus is removed in biological treatment processes. Chemical addition and/or tertiary filters achieve low phosphorus levels.

1. Chemical addition: Phosphorus can be removed from wastewater by precipitation using metal salts [ferric chloride, aluminum sulfate (alum)] or lime. Add polymers to increase the removal efficiency. The chemicals may be added before or in the DAF, in primary clarifier effluent, or in the biological treatment processes before or after secondary clarification. The precipitated phosphorus is removed with other biosolids.
2. Tertiary Filters: Filters are used to achieve high phosphorus removal rates following chemical phosphorus removal. Tertiary filtration may include sand filters, ion exchange, membranes, etc.

Pathogen Removal
Disinfection destroys remaining pathogenic microorganisms and is generally required for all MPP wastewater discharged to surface waters. Chlorination/dechlorination, Ultra-Violet (UV), and some filters can meet effluent limits for pathogens and inactivate pathogenic microorganisms before discharge to surface waters.

1. Chlorination/dechlorination: Chlorine disinfects wastewater through oxidation reactions with cellular material, which destroys pathogens. Mixing and contact time in a chlorine contact chamber are critical to ensure proper disinfection. The chlorine compounds commonly used for wastewater disinfection are chlorine gas, calcium hypochlorite, sodium hypochlorite, and chlorine dioxide (Metcalf & Eddy, Inc. 1991). Chlorine residuals are toxic to aquatic life, so dechlorination is often necessary. Add sulfur dioxide as it reacts with free chlorine and chloramines with chloride ions, lowering chlorine residuals (USEPA, 1999, EPA 832-F-99-062).
2. Ultra-Violet (UV): Radiation emitted from UV light is an effective bactericide and virucide and does not generate toxic compounds. Wavelengths between 250 and 270 nm inactivate cells (USEPA, 1999, EPA 832-F-99-064). UV lamps can be submerged in the wastewater or suspended outside the wastewater.
3. Tertiary Filtration: Filters and membranes with pore sizes smaller than pathogens can be useful in removing pathogens from wastewater. Ultrafiltration, membranes, and reverse osmosis are options.

Chloride Removal
Some MPP processes, including hides processing, meat and poultry koshering, and further processing techniques, such as curing, brining, and pickling, commonly produce wastewater streams with high levels of chlorides. Some facilities use water softening, which can also produce high chloride wastestreams. Wastewater treatment technologies commonly found at POTWs and many MPP facilities do not remove chlorides. The optimal chloride treatment technologies for a facility depend on wastewater strength, climate, land availability, and cost. High chloride wastestreams may be able to be separated from other wastestreams, which can reduce costs and energy required for treatment.

1. Hauling: Facilities may haul high chloride wastewater (brine) offsite in tanker trucks. The wastewater may be taken to a renderer where it may be used for production purposes, transported to a facility equipped to treat and/or dispose of brine, or taken offsite for deep-well injection or other means of disposal. Hauling can be costly compared to other options, especially for large amounts of wastewater.
2. Evaporation ponds: Brine wastewater flows into shallow ponds exposed to the sun. The water evaporates, leaving salt. Empty the salt from the ponds occasionally to allow for reuse. This technology relies on solar evaporation and is best in dry/semi-dry climates. Land space for the ponds is also necessary. Due to the potential for groundwater pollution, line the ponds.
3. Evaporation systems/Crystallizers: Concentrate brine water to near saturation, which results in salt crystallization. Heat evaporates the water. The systems are often costly compared to other options, and corrosion is common when not using proper construction materials.
4. Deep-well injection: Fluids such as brine or salt water can be injected underground into porous geological formations. A Class I well is normally 1,700 to more than 10,000 feet deep. Constructing a well can be costly, and deep-well injection is not allowed in all states, but the permit is valid for years.

Solids Handling
Some wastewater treatment technologies produce industrial sludge. In the MPP industry, DAF and clarifiers primarily generate sludge. The sludge contains oil & grease, organic materials, nitrogen, phosphorus, and chemicals/polymers added in the treatment system. The sludge may have a high water content, which can be reduced to reduce volume and save on hauling and landfilling costs. Common dewatering technologies include gravity thickening units and the belt filter press. The sludge may be incinerated, land applied, or landfilled, depending on state, local, and federal regulations and disposal method availability. 

Additional Information About PFAS Removal – Foam fractionation is a separation process that leverages the affinity of certain molecules for the air-liquid interface to isolate and concentrate them. It works by bubbling gas through a liquid, causing the target molecules to adsorb onto the surface of the bubbles and rise to the top, forming a foam that is removed. This process is useful for removing and concentrating per- and polyfluoroalkyl substances (PFAS) from water and wastewater.

• Additional Information About Wastewater Treatment
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