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Biogas Enhancement Pilot Test at Sacramento Regional Wastewater Treatment Plant Proves Feasibility and Value of Co-digestion Using High Strength Organic Wastes
Author: Lance Hershman, Bob Witzgall, Jose R. Ramirez, Jeremy Boyce, John Nurmi
Date: 6/311
Preprint, WEF/AWWA Joint Residuals and Biosolids Management Conference 2011 May 22-25, 2011, Sacramento, CA

The Sacramento Municipal Utility District (SMUD) currently generates electricity at a cogeneration plant located adjacent to the Sacramento Regional Wastewater Treatment Plant (SRWTP), which is owned and operated by the Sacramento Regional County Sanitation District (SRCSD). Biogas produced by the SRWTP anaerobic digesters currently represents a small portion of the fuel used at the cogeneration plant, with natural gas supplying the bulk of the needed energy. Technical and economic feasibility studies completed between 2006 and 2008 concluded that the SRWTP could increase the production of biogas from 1,400 standard cubic feet per minute (SCFM) to 2,000 CFM, by co-digesting high strength organic wastes (such as restaurant grease and food processing wastes) with the municipal sludge in the anaerobic digesters (Brown and Caldwell, 2006-2008). However, before proceeding to full-scale, SRCSD required proof of concept through successful completion of a small-scale pilot test facility. The Biogas Enhancement Pilot Test was conducted at the SRWTP in 2009. The objectives for the pilot project included: Monitor digester process parameters to assess impacts on digester biology Monitor foam levels in digester to assess impact of biogas enhancement feedstock materials Monitor O&M activities and costs which may impact economics of a full-scale system Monitor biogas output to determine changes as a result of adding feedstock materials Monitor changes in biosolids characteristics affecting suitability for recycling and disposal Monitor receiving station for significant odors or other nuisances that can not be mitigated Assess any fatal flaws that would prevent implementation of a full-scale system Obtain data on economic factors required to reassess the full scale life-cycle analysis. The pilot facilities were designed to receive, store, and pump high strength organic waste to a test digester, while a separate control digester was also monitored. Both digesters were equal in size, and design features (heating, mixing, etc.), and received essentially equal quantities of municipal sludge during the pilot test. Therefore, any incremental differences in performance between the two digesters could be attributed to the addition of high strength organic waste.