Anacortes shortlists five biosolids treatment alternatives to replace aging incinerator

Anacortes shortlists five biosolids treatment alternatives to replace aging incineratorThe Washington municipality is advancing a comprehensive planning process to overhaul its wastewater solids handling system, evaluating options that range from upgraded incineration to pyrolysis.

City staff and consultant Brown and Caldwell have narrowed 14 potential biosolids management options down to a shortlist of five.

The shortlisted alternatives include rehabilitating the existing fluidized bed incinerator, building a new incinerator, autothermal thermophilic aerobic digestion (ATAD), biodrying, and biodrying paired with pyrolysis.

Council members raised concerns about potential odors from digestion and biodrying options, contrasting with the odor-destroying high temperatures of incineration.

High-heat options like incineration and pyrolysis destroy PFAS compounds, while standard biodrying leaves PFAS in the final Class A product.

A final technical memo recommending a single alternative is expected in the first quarter of 2027.

The City of Anacortes, Washington, is advancing a comprehensive planning process to overhaul the solids handling system at its wastewater treatment plant. During a July 27, 2026 meeting, consultant Brown and Caldwell presented five shortlisted alternatives to replace or upgrade the city's aging fluidized bed incinerator. The city narrowed the list from 14 initial options following a screening process that prioritized physical footprint, commercial viability, regulatory adaptability, and operational reliability. The five remaining alternatives represent a mix of traditional and alternative stabilization technologies: • Alternative 1: Rehabilitating the existing incinerator to meet new, more stringent "Quad L" federal air emission requirements. • Alternative 2: Constructing a new Quad L fluidized bed incinerator. • Alternative 6: Autothermal Thermophilic Aerobic Digestion (ATAD), an aerobic process producing a Class A biosolid. • Alternative 8: Biodrying, utilizing low-temperature tumbling systems to produce a Class A product. • Alternative 9: Biodrying paired with pyrolysis, which converts dry biosolids into a PFAS-free biochar suitable for concrete admixture. A major point of discussion among council members centered on the public impact of the new facility, particularly regarding odor. While the high-temperature incineration options naturally destroy odor-causing compounds, the digestion and biodrying alternatives carry a higher risk of odor generation. Brown and Caldwell representative Greg Makos noted that any non-incinerator option would include specific odor control systems, such as chemical scrubbers and carbon filters. Regulatory compliance, specifically concerning PFAS, was also highlighted as a differentiator. Makos explained that while the biochar and ash produced by the incinerator and pyrolysis options are PFAS-free due to thermal oxidation, the dry biosolids produced by standard biodrying would retain PFAS compounds. While Anacortes' biosolids currently test below anticipated numeric limits, future regulatory shifts remain a consideration. The project team will spend the coming months refining layouts and developing lifecycle cost models using their BC:SWEET tool. A workshop in September will narrow the field to three alternatives, followed by a multi-criteria decision analysis in November. A final technical memo detailing the recommended alternative is slated for the first quarter of 2027. In separate water infrastructure business, the council approved a $61,505 contract award to Hargis Engineers for mechanical and electrical engineering design services related to HVAC improvements at the Water Treatment Plant High Service Pump Station.