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Consultants present five‑option biosolids alternatives analysis; council schedules workshops
Summary
Consultants from Brown & Caldwell presented a biosolids alternatives analysis that narrowed technology choices to five options (rehab incinerator, new incinerator, ATAD digestion, bio‑drying, and bio‑drying plus pyrolysis). Council and staff emphasized odor mitigation, PFAS sampling, site footprint and lifecycle cost modeling; a September workshop will refine alternatives and a November MCDA session will weigh tradeoffs.
Brown & Caldwell consultant Greg Makos presented the biosolids alternatives analysis and a recommended process for narrowing options. After nine months of work, the team screened an initial universe of technologies down to five end‑to‑end alternatives: rehabilitate the existing fluidized‑bed incinerator (with added air pollution controls), build a new incinerator, adopt ATAD (thermophilic aerobic digestion), use a low‑temperature bio‑dryer package system, or use bio‑drying supplemented by pyrolysis to produce biochar.
Makos explained the city’s mandatory goals for technologies: must fit on the existing treatment plant site, have a commercial U.S. installation of similar size, be adaptable to future regulations (PFAS noted as a key regulatory area), avoid proprietary dependencies for critical components, and not require 24/7 staffing. The team’s screening eliminated options that were too large to fit on site, overly complex to operate, or unproven at the city’s scale.
Council members and staff focused questions on odor control, PFAS handling, construction phasing and sequencing (including truck traffic if incineration is offline), lifecycle cost modeling, and how alternatives might be phased in over time. Makos said options that could produce a marketable product (class A biosolid or biochar) create new management needs and potential outlets, but also present regulatory and operational tradeoffs.
The consultants outlined next steps: September workshop to refine and pare alternatives to three, development of phasing/implementation plans and life‑cycle cost modeling, and a November live MCDA workshop where council staff will test priorities (cost vs. odor vs. operational reliability) to identify a recommended alternative in a technical memo early next year.
What happens next: staff and consultants will hold a September workshop to refine alternatives, develop phasing and cost models, and present a live multi‑criteria decision analysis (MCDA) with council participation in November.
