Biogas Benefits

Anaerobic digestion project in Washington’s Tualco Valley is paying off.
By Bryan Sims | February 22, 2011

In Washington’s Tualco Valley, the Qualco Energy Corp. anaerobic digester in Snohomish County has come a long way since the project was conceived in 2003.

Qualco Energy Corp., a nonprofit organization formed by representatives from the Sno/Sky Agricultural Alliance, Northwest Chinook Recovery and the Tulalip Tribes, began operating the digester in 2008. The digester was first proposed to help consume waste from local dairy operations and to prevent runoff into salmon streams on land that formerly housed a correctional facility.

According to Daryl Williams, environmental liaison for the Tulalip Tribes, Qualco uses a modified mixed plug flow mesophyllic digester capable of producing 600 cubic feet per minute of biogas that powers its 450-kilowatt generator. Manure is collected from Werkhoven Dairy’s three farms and piped to Qualco’s 2 million gallon digester tank.

Qualco sells electricity to Puget Sound Energy Corp. and is negotiating a power-purchase agreement with the Snohomish County Public Utility District.

The solids left over from the anaerobic digestion process are used as compost material, Williams said. Qualco currently gives its digestate material away for free, but they will charge a fee once a market for it is found. “We’ll hopefully sell the solids for about $10 per yard,” Williams said.

Waste liquid from the digester gets piped to a nearby lagoon and is utilized for irrigation.

Qualco was awarded a $500,000 grant from the U.S. DOE to conduct an environmental assessment and feasibility study in 2005, and received $500,000 from the USDA to help pay for the digester.
Williams said the economic and environmental impact of the anaerobic digester has been a boon for the county, adding that Qualco intends to expand operations to include more generators and solar panels.

—Bryan Sims