"Here and there the grease and filth have caked solid, and the creek looks like a bed of lava; chickens walk about on it, feeding, and many times an unwary stranger has started to stroll across, and vanished temporarily.” Upton Sinclair wrote this passage in 1906 in The Jungle describing the waste discharges from the Chicago stockyards to the Chicago River. Ever since, renderers have been under pressure to properly manage their wastewaters. Following is a brief summary of the evolution of the government regulations and wastewater treatment technologies available for renderers to maintain constant environmental compliance.
Regulations
Federal regulation of point source discharges from meat processors and renderers became widespread with the passage of the Federal Water Pollution Control Act of 1972. Sections 304 and 306 of this legislation set guidelines for best available control technologies to remove pollutants from wastewaters before direct discharge to waterways.(1) Municipalities and sewerage authorities also become empowered to implement pretreatment standards controlling the discharges to local sewers. These regulations have forced the rendering industry to make significant investments in wastewater treatment systems and labor. Although the initial regulations were primarily concerned with conventional pollutants, namely, total suspended solids (TSS) and biochemical oxygen demand (BOD), today’s regulations now stipulate additional treatment for nitrogen and phosphorus, air emissions, chlorides, and fecal coliforms.
Treatment Challenges
Separation of grease, protein, and by-products from offal unavoidably produces wastewater. This wastewater is chemically complex and contains high concentrations of fats, oil, and grease (FOG), BOD, and TSS. Renderers desire fresh offal since FOG and proteins have had less time to break down during transport and storage. Offal breakdown impacts rendering wastewater in several ways; for instance, decomposed FOG produces volatile fatty acids (VFAs). VFAs increase the BOD concentration of wastewater and complicate its biological treatment by stimulating undesirable filamentous bacteria, causing foaming and poor discharge quality. Another source of BOD at some rendering plants is dissolved air flotation (DAF) sludge they accept from slaughter and processing clients for by-product recovery. Rapid putrefaction of DAF sludge during storage and transportation can drastically increase the wastewater flow rates and BOD loadings at rendering plants.
Rendering operational issues that impact wastewater flow and characteristics include process design, equipment age, blowdowns, sidestreams, process malfunctions, and cleanup procedures. Savvy managers institute best management practices including dry cleanup, waste minimization, and water conservation; however, the nature of the “beast” is that wastewater is unavoidable during rendering.
Conventional Treatment Technologies
Rendering wastewater must be treated before discharge onto land or into surface waters or local sewers. Historically, screens, gravity DAF, and crude anaerobic (capped with grease) and aerobic lagoons have been used to reduce BOD, FOG, and TSS. Renderers are now upgrading their anaerobic lagoons with mixing to improve BOD removal and with plastic covers to capture methane-rich “biogas.” For example, American Proteins, Inc., in Cumming, GA, employs a covered anaerobic lagoon followed by aerobic polishing, and the biogas from the former process is collected for fuel, saving the facility nearly $400,000 per year. Central Bi-Products Co., Redwood Falls, MN, efficiently uses an anaerobic lagoon to mix wastewater effluent to reduce BOD before aerobic polishing, providing their operation with high-quality water suitable for reuse in their operation.
Emerging Treatment Technologies
The latest federal and state environmental regulations impose discharge limits for ammonia and total nitrogen, phosphorus, fecal coliforms, and other pollutants. Accordingly, renderers are forced to seek new, improved treatment technologies to meet these stringent regulations. Promising technologies include the following:
• High-Rate Dissolved Air Flotation: Conventional DAF systems are based on gravity clarification and operated at low efficiency for removal of TSS, FOG, and BOD. Newer innovative technologies use smaller tanks, internal plates and in-line flocculating mixers, and highly efficient pumps that directly dissolve air into the feed and recycle streams. These smaller systems are typically constructed out of stainless steel, extending their lifespan and improving the quality of the recovered float sludge. Another benefit of high-rate DAF treatment over conventional systems is significant reduction or elimination of chemicals such as ferric chloride and polymers. DAF chemicals are costly, and their residues contaminate DAF sludge that may be rendered back into the finished products.
• Enhanced Anaerobic Treatment: By incorporating mixing, heating, and biomass recycle into anaerobic systems, renderers are able to increase BOD and TSS removal, biogas production, and treatment efficiency.
• Aerobic Biological Nutrient Removal: Subsequent to DAF and anaerobic treatment, further polishing is required to substantially reduce BOD and nutrient levels. Sequence batch reactors (SBRs) using air have been proven to be effective for removal of different forms of nitrogen and phosphorus in addition to BOD, and their use is expected to grow in the future. Furthermore, pure oxygen-based SBRs are shown to reduce foaming, filamentous growth, and odors generated by aerosols.
• Membrane Treatment: Membrane separation systems such as ultrafiltration and reverse osmosis are increasingly used by renderers for many reasons, including improved by-product recovery and water conservation. Membrane systems have become more attractive because of their decreasing costs in recent years. However, they have certain limitations; for example, wastewater abrasives and chemicals can destroy the delicate membranes. The most appropriate applications are for specific sidestreams such as serum waters, brines, stick water, and hydrolysates. Membranes are also being coupled with bioreactors to improve biomass separation and removal of BOD and fine suspended solids that contribute to turbidity.
• Online Respirometry and Automation: A great need exists for renderers to increase sophistication of their operations in order to maintain constant compliance and reduce operating costs. Several proven technologies and tools from other industries (e.g., pharmaceuticals, refining, chemicals) can easily be applied in rendering wastewater treatment. Continuous online respirometry provides wastewater operators with early-warning capability in case of spills within the plant or high BOD surge loadings that can damage biological treatment processes. Automation of wastewater treatment systems using technologies like SCADAR (Supervisory Control and Data Acquisition with Response) offer instantaneous information on process variables so that the process performance is closely monitored for potential failure and optimized for cost savings.
Summary
Renderers continuously seek to comply with federal, state, and local wastewater regulations. As the regulations impose stricter limits with more pollutants brought under the purview, renderers have no choice but to embrace new, innovative technologies to improve wastewater process ef-ficiencies enhancing product recovery at the same time.
Reference:
1. U.S. Environmental Protection Agency. 1974. Development Document, Meat Products Category. EPA 440/1-74/031.
Charles R. Stack, M.P.H., and Prasad S. Kodukula, Ph.D., P.M.P., are vice president and president, respectively, at Constant Compliance, Inc., a company specializing in industrial wastewater treatment and management.
December 2003 Render