Palo Alto staff recommend keeping current biosolids practice, reserving Measure E land for future processing

City of Palo Alto staff presented an update to the city’s biosolids facility plan and recommended continuing the city’s current approach — dewatering biosolids and hauling them offsite for composting or thermochemical processing — while reserving a portion of the Measure E strip adjacent to the treatment plant for possible future solids processing.

Tina, a city staff presenter, told the meeting the plant’s long‑range planning work evaluates options through 2055 and that Measure E (voter action in 2014) gave the city the option to use about 10 acres adjacent to the plant for future solids processing. Tina said staff’s near‑term recommendation is to continue the baseline practice and “reserve a portion of the Measure E site” for flexibility if regulations, technology, or regional partnerships change.

Corollo consultants presented the technical and financial analysis that underpins the recommendation. The Palo Alto Regional Water Quality Control Plant sits on roughly 25 acres and serves more than half a million people across six partner agencies; its dry‑weather capacity is 39 million gallons per day and peak wet‑weather capacity is 80 million gallons per day, and recent average daily dry‑weather flow was about 18 million gallons per day. Consultants noted the plant’s tight footprint and ongoing capital program — described in the presentation as roughly $400 million of improvements to meet future regulatory requirements.

The consulting team screened 15 alternatives plus the baseline and carried six forward for detailed study: (1) baseline (continue current dewater/haul practice), (2) an undefined San Jose/Santa Clara regional partnership, (3) mesophilic anaerobic digestion (MAD), (4) MAD with thermal hydrolysis (THP), (5) belt thermal drying, and (6) drying plus pyrolysis (for undigested material). Corollo’s Christine said on‑site options were difficult to site and would require substantial capital investment; she said the on‑site digestion and drying alternatives each had capital estimates in the $250–$350 million range, while the drying+pyrolysis option was roughly $630 million.

“Drying and pyrolysis is about $630 million,” Corollo consultant Christine said during the presentation.

Consultants combined capital and 20‑year O&M into net present value and applied eight evaluation criteria weighted with public input. Because capital costs dominate, the baseline and the off‑site partnership scored best on net present value; among on‑site alternatives, mesophilic anaerobic digestion scored highest. Christine emphasized that while drying+pyrolysis performed well on greenhouse‑gas metrics (largely because biochar sequesters carbon in soils), its very high capital cost kept it from being competitive in the weighted scoring.

“Drying and pyrolysis has negative greenhouse gas emissions” in the BEAM model results, the consultant said, explaining that biochar application drives substantial sequestration that can outweigh emissions from drier fuel use.

Consultants also ran sensitivity tests (doubling or halving weights for net present value and for greenhouse‑gas criteria) and reported that the baseline and the off‑site partnership remain most competitive under a range of plausible assumptions. The team described hypothetical contingencies: if off‑site hauling costs rose markedly, the city could build MAD (~$250 million); if future PFAS regulations require on‑site destruction, adding a full pyrolysis solution could increase capital needs substantially.

Public commenters pressed technical and land‑use questions in the Q&A. Carbon Free Palo Alto’s Bruce Hodgej asked why drying+pyrolysis shows a net negative greenhouse‑gas result despite sizable positive emissions from natural gas used in drying; the consultant replied that the BEAM model accounts for both the natural‑gas emissions from drying and the large carbon‑sequestration credit when biochar is used in agriculture. Several residents asked about the Silicon Valley Clean Water pyrolysis pilot; staff and consultants said that pilot is capacity‑limited and has faced operational issues, and they will monitor such pilots as technologies evolve.

Residents also raised sea‑level‑rise and wildlife concerns for Measure E. Staff said that the city is running a Measure E wetland/wildlife corridor feasibility study and will present those findings to the Parks & Recreation Commission and the Climate Action and Sustainability Committee later in the year. Public works director Brad (present at the meeting) and other speakers emphasized the competing demands: limited plant footprint, the plant’s future liquids infrastructure needs, and community interest in parkland or wildlife connectivity.

Staff said the next steps are to continue monitoring PFAS (referred to in the meeting as PAS), technology maturity and potential regional partnerships, finish the Measure E ecological analysis, seek committee feedback, and return to city council for plan acceptance by year‑end.

The meeting did not include any formal votes. Staff presented their recommendation for council consideration: retain the baseline approach in the near term and reserve a portion of Measure E adjacent to the plant so the city can adapt if regulatory or market conditions change.