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MWMC FACILITIES PLAN projected flows and loads indicate that additional digestion and FSL capacity may be needed during this study period. The BMF historically was not able to keep up with solids production from the WPCF. Construction of the dewatering facility has increased biosolids processing capacity but the FSLs still have a solids inventory above optimal levels. A study has been conducted to analyze the capacity of the biosolids stabilization processes and to develop alternatives that provide the necessary capacity and optimal operating conditions. The primary purpose of sludge stabilization is to reduce pathogens and vector attractions (VSS destruction) in the use and disposal of treated sewage sludge (biosolids). Both pathogen and vector attraction reduction are regulated primarily by federal requirements set forth in EPA's 40 CFR Part 503. Subpart D of Part 503 includes criteria to classify biosolids as Class A or Class B with respect to pathogens. These classifications are based on the level of pathogens present in biosolids that are used or disposed. Biosolids produced by MWMC's solids treatment processes are classified as Class B. The following text will focus on Class B products and requirements. Pathogen Reduction Pathogen reduction alternatives are identified in 40 CFR Part 503 and are intended to ensure that pathogen levels in biosolids are reduced to levels considered safe for biosolids to be land-applied or surface-disposed. To meet Class B biosolids pathogen requirements, one of the following three alternatives can be used: · Alternative 1: Monitor indicator organisms. A test of fecal coliform density is required as an indicator for all pathogens. The geometric mean of seven samples shall be less than 2 million MPN (Mean Probable Number) per gram of total solids. · Alternative 2: Treat biosolids in a process to significantly reduce pathogens (PSRP). PSRPs include aerobic digestion, air drying, anaerobic digestion, composting, and lime stabilization. · Alternative 3: Treat biosolids in a process equivalent to a PSRP. Anaerobic digestion is a PSRP as defined in 40 CFR Part 503.32(b)(3) if the solids are retained in the digesters for at least 15 days at a minimum temperature of 35 °C. Currently, MWMC's anaerobic digesters meet these criteria and produce Class B biosolids. The liquid biosolids are further processed in the FSLs, where additional solids stabilization occurs. Vector Attraction Reduction It is critical to reduce the potential for exposing humans or other susceptible hosts (plants or animals) to pathogens contained in biosolids. Exposure may be initiated through vectors (ffles, mosquitoes, fleas, rodents, and birds) that can potentially transmit pathogens to humans and other hosts through physical contact or by playing a specific role in the life cycle of pathogens. Reducing the attractiveness of biosolids to vectors is regulated through twelve options identified in the Part 503 rule. The first of the twelve options is to achieve 38 percent reduction in volatile solids content. MWMC biosolids have consistently met vector attraction reduction requirements by achieving greater than 38 percent volatile solids reduction through both anaerobic digestion and additional treatment in the FSLs. Anaerobic digestion alone achieves greater than 6-32 MWMC_6.0_REV11.DOC