Robust Evaluation Methodology for the Biogas Utilization Alternatives at the San Francisco Oceanside WPCP

Abstract

San Francisco Public Utilities Commission (SFPUC) Wastewater Enterprise executed a study that targets determination of the best (and highest use of) biogas utilization option(s) for the Oceanside Water Pollution Control Plant (OSP), as the existing cogeneration facility is nearing the end of its useful life. In addition, there are two current projects that will result in an increase in biogas production. One is the digestion system conversion from conventional mesophilic digestion to sequencing batch reactor temperature phased anaerobic digestion. The second project is addition of restaurant grease waste (brown grease) to be co-digested with the wastewater residuals. At OSP, biogas is currently utilized in the existing engine generators and boilers producing combined heat and power. The biogas utilization study includes seven options for biogas utilization. Five of those options include biogas-fueled combined heat and power production and two of the options include scrubbing the carbon dioxide from the biogas to produce natural gas grade quality fuel (a.k.a. biomethane). This paper includes the use of decision making methodology combining quantitative outputs (cost estimates, energy production, and greenhouse gas offsets) with non-financial criteria using a technique called multi-attribute utility analysis (MUA). Given the number of alternatives and the complexities of each for this project and similar projects, it is prudent to have a proven evaluation methodology to ensure there is a robust process for decision-making.A side-by-side analysis of capital, O&M, and life-cycle costs; GHG offset, energy production, and overall system energy efficiency made up the basis of the alternatives evaluation. Internal combustion engines scored the highest in all categories followed by microturbines. Because of the overall efficiency and economics of internal combustion engines, they were recommended by CH2M HILL.