For several years, the City of Edmonds has been talking about a replacement system for the aging sludge incinerator at the city’s wastewater treatment plant. The city has been faced with a choice of buying a new incinerator that could meet more stringent federal air quality regulations or turning to a biosolids management system.

Public works staff last year began investigating the feasibility of a pyrolysis system that thermally decomposes organic materials at high heat with little to no oxygen. But during Tuesday night’s city council meeting, Public Works Director Phil Williams shared a new idea that could save money and offer the city greater flexibility when it comes to managing its wastewater solids.

Williams explained that the original pyrolysis proposal, labeled Project A, created a dried pelletized “biochar,” which is sterile and has the appearance of charcoal, and can be sold as a soil conditioner or amendment. Now, the city is looking at another solids management option — Project B — that would produce three different byproducts: biosolids that could be applied directly on the land, biochar through pyrolysis, and a gasification of solids that produces a minimal ash-like residue — about 10% of the incoming volume.

The city determined that Project B would give the city more flexibility, Williams said, and it would also be cheaper and more energy efficient than Project A.

The city would save more than $341,000 by going with Project B, he added. Project A would require the construction of a new building to house the equipment, while Project B “uses our existing footprint,” Williams said.

“It’s the most flexible of the technologies we’ve looked at, the most efficient and the most affordable approach to implement, as well as having the lowest operational costs,” he added.

The company that would provide the system, Ecoremedy, conducted an initial design effort to determine if the technology could be successfully deployed in Edmonds. The city had already prepared initial regulatory reports, modeling, engineering reports and design work for Project A, and much of that information applied to Project B.

The estimated cost for the entire system would be between $25 million and $27 million, but staff plans to come back to the council soon with final cost numbers. Williams said staff is also recommending use of an Energy Savings Performance contract through the state’s Department of Enterprise Services to deliver the project. It’s likely the council will be asked to consider later in 2020 the option of selling revenue bonds to support the project, Williams said.

In other action, the council:

– adopted an interim flood damage prevention ordinance that will allow the city to remain in the National Flood Insurance Program. Once Open Public Meetings Act restrictions related to COVID-19 are lifted and public hearings can resume, the plan is to bring the matter back to the council for consideration as a permanent ordinance.

– agreed to participate in a public service message — proposed by Councilmembers Laura Johnson and Vivian Olson — promoting the use of face coverings.

– discussed a contract renewal with the city’s public defender, Snohomish County Public Defender Association, that includes a 12.5% increase in 2020 and an additional 7.5% increase in 2021. The organization noted that its costs have risen due to additional and higher overhead. The contract will come back to the council for approval at a future meeting.

— By Teresa Wippel