A multi-attribute utility analysis was used to facilitate decision-making for a biogas utilization alternatives study at the Oceanside Water Pollution Control Plant in San Francisco.

By: Dru Whitlock, P.E. CH2M HILL

Dru Whitlock will present his paper “Robust Evaluation Methodology for the Biogas Utilization Alternatives at the San Francisco Oceanside WPCP” on Tuesday, October 8 at 1:30 p.m. in TS414, during the Water Environment Federation Technical Exhibition and Conference (WEFTEC), in Chicago, Illinois. Learn more about CH2M HILL’s WEFTEC 2013 participation and technical sessions.

The City of San Francisco owns and operates three wastewater treatment facilities, including the Oceanside Water Pollution Control Plant (OSP). The City’s water infrastructure is aging, and despite the fact that OSP is the newest of San Francisco’s treatment plants, the effects of deferred maintenance and a corrosive near-ocean environment are beginning to show. As part of a larger Sewer System Master Plan, the City is investing in wastewater treatment and biosolids management modifications.

Treating wastewater results in a wastewater residual byproduct that can be converted to biosolids for beneficial reuse. Like many wastewater facilities, OSP uses anaerobic digestion to convert wastewater residuals to biosolids, which results in the production of methane-rich biogas that can be used for production of renewable energy. Recently, the San Francisco Public Utilities Commission (SFPUC) and CH2M HILL completed a study to determine the highest and best use of the biogas, and, therefore, the optimal solution for replacing SFPUC’s aging cogeneration facility at OSP.

Taking into consideration capital, operations and maintenance (O&M), and life cycle costs, energy production, greenhouse gas offsets, and overall system energy efficiency, the biogas utilization study identified 7 alternatives—5 of which include biogas-fueled combined heat and power production and 2 of which include scrubbing the carbon dioxide from the biogas to produce biomethane (also known as renewable natural gas).

  • Combined Heat and Power Alternatives:
    • Alternative 1: Refurbishment of existing cogeneration system, with additional gas cleanup (baseline alternative)
    • Alternative 2: Gas cleanup and new internal combustion engines
    • Alternative 3A: Gas cleanup and microturbines
    • Alternative 3B: Flex fuel turbines
    • Alternative 5: Gas cleanup and onsite fuel cell
  • Biomethane (Renewable Natural Gas) Alternatives:
    • Alternative 6: Gas cleanup and CO2 removal for injection to the natural gas pipeline
    • Alternative 7A: Gas cleanup and CO2 removal and compression for offsite existing natural gas fueling station for City of San Francisco fleet vehicles
    • Alternative 7B: Gas cleanup and CO2 removal and compression for onsite natural gas fueling station for City of San Francisco fleet vehicles

After analyzing the alternatives using a multi-attribute utility analysis approach to evaluate the benefits of the alternatives against social, environmental, and economic criteria, Alternative 2: Gas cleanup and new internal combustion engines was recommended to SFPUC as the best option because it delivers the highest overall system efficiency; significant power savings; lower O&M costs; and the highest achievable carbon offset credit.

Dru Whitlock is the U.S. West Residuals Resource Recovery Technology Leader for CH2M HILL, with more than 15 years of wastewater engineering experience and more than 20 years of combined science and engineering experience. Dru holds degrees in science, engineering, and business administration. He has been working with San Francisco Public Utilities Commission at the Oceanside Plant on the anaerobic digestion system as well as the biogas utilization since 2009. He is the president of the Water Environment Association of Utah and Vice-Chair of the Bioenergy Subcommittee of the WEF Residuals and Biosolids Committee. Dru is a member of the Salt Lake City Energy and Carbon Advisory Committee, and on the board of the Salt Lake City Community Development and Capital Improvement Advisory. Dru enjoys cycling and Nordic skiing with his wife and two children in the beautiful Wasatch Mountains of Utah.