Portland’s Columbia Boulevard Wastewater Treatment Plant serves over 600,000 residential and commercial customers. In 2009, the plant began capturing methane, a greenhouse gas (GHG) produced by the bacterial decomposition of solid waste. The plant generates about 600 million cubic feet of digester gas (biogas) every year, of which 60 percent is methane, a renewable natural gas.
Up until now, the technologies used to collect the biogas only allowed for 77 percent of the methane to be captured, leaving the remaining 23 percent to be flared off, adding climate-changing GHGs to the atmosphere. But last month, City Council unanimously voted to construct a $9 million facility to convert the remaining methane gas into marketable natural gas, according to Oregon Live.
produces 600 million cubic feet of biogas every year. Biogas is a wastewater
treatment by-product.
City commissioner Nick Fish said in a statement, “We are creating a triple win for the public in terms of revenue, climate action, and cleaner air. The renewable natural gas we will produce is truly local and homegrown, a by-product of the waste from every Portland household that we can now repurpose.”
How big a deal will this be? The captured methane gas will replace 1.34 million gallons of diesel fuel, according to the city, with 154 garbage trucks expected to run on that amount a year. So getting rid of diesel fuel, which is one of the biggest contributors to environmental pollution is a win for everyone. Diesel emissions have been linked to cancer, cardiovascular and respiratory issues, smog and global climate change
Bureau of Planning and Sustainability Director Susan Anderson said the new project will significantly reduce Portland’s carbon footprint, adding, “From an environmental point of view, it’s not just about our local air quality. It’s about reducing carbon emissions. We need to walk our talk.”
Portland’s beneficial reuse of biogas
Environmental Services installed two 850 kilowatt GE/Jenbacher engine-generators with a total generating capacity of 1.7 megawatts at the wastewater treatment plant in 2009. A pretreatment system first removes hydrogen sulfide, siloxane and moisture to prepare the biogas to be used as fuel.
Using the engine-generators, the plant recovers heat from water and engine exhaust to use in its anaerobic digesters. The engine-generators supply about 40 percent of the plant’s electrical needs, another money-saving benefit. Additionally, the plant compresses almost 20 percent of the biogas and this is piped to a nearby industrial facility to be used in process heating.
