Update on Edmonds

The City of Edmonds currently owns and operates a regional wastewater treatment plant (WWTP) at 2nd Ave S and SR104. The plant contains a complex system of pumps, tanks, and mechanical systems to clean, disinfect, and ultimately discharge clean water into Puget Sound. 

Starting in 2013 the staff at the WWTP began to implement a “Pathway to Sustainability” that would reduce the plant’s energy consumption and reduce its carbon emissions. Three significant efficiency upgrade projects have been completed: 1) Replacing several lower efficiency blowers with smaller, more efficient ones, 2) replacing and repairing the aeration system piping and delivery nozzles as well as several remaining blowers, and 3) replacing the biosolids dewatering equipment. These three projects have resulted in electricity cost savings of over $200,000 per year, and the reduction of greenhouse gas emissions (primarily carbon dioxide) of 1,146 tons per year. Now the WWTP has begun a Carbon Recovery project that will achieve another significant step on the WWTP’s Pathway to Sustainability.                                   
WWTP Pathway to snip

During the process of treating wastewater, solids are removed, concentrated, and burned in a high temperature furnace (incinerator). The incinerator is not only expensive to operate in terms of electrical use and significant maintenance costs, but the residual ash must also be transported to the landfill for disposal. This process does not recover heat nor create valuable by-products for reuse. Further, the incinerator is nearing the point in time when it must be replaced in order to meet new regulatory standards.

In 2018 the Edmonds City Council authorized the evaluation of alternative technologies and a cost/benefit comparison to replace the inefficient and aging incinerator with alternative biosolids disposal methods that are energy neutral or energy positive. After a thorough evaluation of modern technologies, staff at the plant identified pyrolysis as the best method to use because it will reduce operation and maintenance costs and also reduce the plant’s energy costs and its environmental impact. With this innovative approach, rather than sending truckloads of ash to the landfill, the pyrolysis system will generate biochar which will further benefit the community and set a benchmark of sustainability within the wastewater industry.

What are pyrolysis and biochar? “Pyrolysis is a naturally occurring phenomenon that can be defined as the thermal decomposition of organic material through the controlled application of heat in the absence of abundant air or oxygen.” Through this process, that takes place at temperatures between 660 and 1,650 degrees F, three co-products may be obtained: syngas, bio-oil, and biochar. Syngas and bio-oil are recoverable sources of energy that will be used within the process to reduce energy consumption. Biochar is a valuable, charcoal-like material with numerous beneficial uses from industrial filtration to soil remediation.

Using this technology will further reduce the treatment plant’s electricity, natural gas, and even our diesel fuel usage while at the same time producing an end product that can be used locally by the City or sold. Another beneficial aspect of Biochar is it eliminates any remaining hormones and pathogens (disease causing bacteria and viruses) from biosolids, reduces pollutants released into the environment. Heavy metals from the wastewater stream are sequestered into the biochar where they remain and are not released into soil. The graphic below shows Pyrolysis and biochar in the biochar Cycle. (Courtesy of Carbon Washington, www.carbonwa.org)
WWTP Carbon Biochar                    

Biochar is garnering more and more attention among the business community, environmentalists, foresters, Washington State University researchers, and the Washington State Legislature, which recently passed Senate Joint Memorial 8005 supporting research efforts to produce and use biochar. The City of Edmonds is proud to participate with these groups and to be a leader with our “Pathway to Sustainability” at the wastewater treatment plant.

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