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PUC engineers outline biosolids, drying and disinfection technologies under SSIP study
Summary
At the July 27 SSIP workshops, PUC engineers summarized technologies under consideration for biosolids handling and treatment—thermal hydrolysis (CAMBI), solar/thermal drying, co‑digestion of fats/oils/grease, biosolids‑to‑fuel, UV disinfection and nutrient recovery—and recommended pilots and strict proof‑of‑operation before large investments.
San Francisco wastewater engineers presented a technology review on July 27 that cataloged alternatives staff and consultants have pilot‑tested or evaluated for inclusion in the Sewer System Improvement Program.
Humphrey Ho, sanitary engineer, reviewed a menu of technologies: thermal hydrolysis pretreatment (CAMBI) for improved digestion and pathogen reduction; novel low‑temperature drying and solar thermal panels; deep‑well injection (studied in Los Angeles); supercritical water oxidation and slurry‑carb processes for biosolids‑to‑fuel; co‑digestion of restaurant grease to boost biogas production; alternative dewatering equipment; UV disinfection as an alternative to chlorine; and nutrient (struvite) recovery for fertilizer production.
Staff position: Ho recommended maintaining anaerobic digestion as the baseline solids‑handling approach because of its reliability while piloting complementary technologies. He emphasized technology maturity differences, operational risks (corrosion, debris wear, high‑pressure reactors), and the need for full‑scale demonstrations before adopting capital programs that would be difficult to abandon.
Planned pilots and procurement: Staff proposed a full‑scale CAMBI pilot at an early stage of the biosolids digester project, an RFP process for a digester project team, and a CEQA path that will evaluate alternatives and mitigation. Commissioners stressed neighbor mitigation (odors, traffic, truck routes) and the need for community outreach and monitoring plans as pilot projects are developed.
Takeaway: The commission asked staff to prioritize pilots and peer reviews and to visit other installations (regional examples include DC and Terminal Island/Los Angeles) before committing program‑level appropriations to novel technologies.
