Biosolids Digester Facilities Project/ Biogas Utilization System

Biosolids Digester Facilities Project/ Biogas Utilization System

On March 8, 2018, the San Francisco Planning Commission certified the Final Environmental Impact Report (FEIR) for the San Francisco Public Utilities Commission's (SFPUC) Biosolids Digester Facilities Project (Biosolids project or approved project) at the Southeast Water Pollution Control Plant (Southeast Plant), located in the southeast part of San Francisco. Originally built in 1952 with major upgrades in 1982 and 1996, the Southeast Plant is the City's largest wastewater treatment facility, treating approximately 80 percent of San Francisco's sewage and stormwater flows. The approved project includes the construction and operation of a new solids treatment process, odor control, energy recovery, and associated facilities to replace outdated existing facilities with more reliable, efficient, and modern technologies. Biosolids are the recyclable solid materials removed from the wastewater during the wastewater treatment process and digesters are the major facility used in the solids treatment process. The SFPUC proposes to modify the approved project to construct the Biogas Utilization System to achieve the project's objective of beneficially reusing the digester gas (or biogas) generated by the solids treatment process instead of the originally planned energy recovery system. Instead of building an energy recovery/cogeneration facility in which boilers and a turbine generator would convert the digester gas into energy (heat, steam, and electricity) for on-site use, the digester gas would be upgraded to pipeline-quality, renewable natural gas (energy) for injection into the existing natural gas pipeline running along Quint Street adjacent to the Southeast Plant for distribution to end users. 1 The biogas utilization system components would include a biogas upgrading facility, an Interconnection Station to be constructed and operated by Pacific Gas & Electric (PG&E), and various buried pipelines connecting new and existing facilities. The proposed components would be built within the same boundaries as the approved project site and would be less substantial than the energy recovery facilities. The proposed modification would require importing more natural gas and possibly some electricity from PG&E to operate the biogas utilization system, as well as the steam boilers and other approved Biosolids project facilities. Like the approved project, should issues occur during operation of the biogas utilization system, the digester gas would need to be flared. As with the approved project, the modified project would not change the overall treatment capacity of the Southeast Plant. Lastly, the SFPUC proposes to extend the construction period an additional 1.5 years due to construction taking longer than initially envisioned. The overall Biosolids project would therefore be completed in Summer 2028, including facilities construction, testing, start-up, and full commissioning.

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