Many publications have stated that use of anaerobic processes for liquid treatment at wastewater treatment plants can provide several significant advantages over aerobic treatment. These advantages include lower operating costs, reduced energy demands, increased biogas production with potential for power generation, lower sludge production, simpler operation, and a smaller footprint. However, few of these publications have attempted to quantify these advantages and compare them to conventional aerobic processes, particularly for the treatment of municipal strength wastewaters. This paper compares several anaerobic technologies to a traditional aerobic municipal wastewater plant designed to remove carbon, solids, and nutrients to quantify and compare sludge production, footprint, energy requirements, costs, and green house gas production. It is shown that anaerobic technologies do offer advantages of reduced footprint, reduced sludge production, and reduced energy requirements. However, in terms of cost, the traditional aerobic process is most attractive when having to meet nutrient limits.

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Full-scale validation of the Waste Activated Sludge Anaerobic Contact (WASAC) process was conducted at the City of Chico Water Pollution Control Plant (Chico WPCP). The WASAC process removes chemical oxygen demand (COD) without air, and stores the COD in the waste sludge resulting in increased energy recovery during co-generation. The goals of the project were to successfully operate the WASAC process at full-scale, define operational boundary conditions, and quantify treatment benefits and process kinetics. The data collected demonstrated the WASAC process had no adverse effects on plant effluent quality; removed approximately 40% of the soluble BOD (sBOD) sent to the WASAC process and 20% of the sBOD overall; greater than 90% of the sBOD uptake in the WASAC process occurred within the first 30 minutes. The volatile suspended solids (VSS) content in the WASAC process was consistently higher than the VSS content of the secondary process.

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