Producing Clean Energy by Reducing Waste – City of Millbrae Waste Water Treatment Plant

The City of Millbrae’s Water Pollution Control Plant provides a valuable, sustainable service to the community by ensuring that its wastewater is free of contaminants. In November of 2006 the plant became even more ecologically friendly following construction of an on-site energy cogeneration facility. The innovative new system, engineered by Chevron Energy Solutions, supplies 80% of the plant’s electricity with clean energy produced from inedible kitchen grease – a common urban waste – that would otherwise be sent to landfills and decompose into methane, a formidable greenhouse gas. The on-site energy production at the plant reduces carbon emissions by nearly 1.2 million pounds annually, having the same effect as planting 166 acres of trees or not driving 116 cars for a year.

WHAT IS COGENERATION?
The first of its kind, the cogeneration facility functions by converting over 3,000 gallons of kitchen grease into biogas each day in its anaerobic digester tanks. The tanks contain microorganisms that digest the grease and other organic matter, naturally producing methane gas. The methane then fuels the plant’s 250-kilowatt microturbine generator which provides electricity to run the water treatment system. The system is known as a “cogeneration” facility because it captures the waste heat produced by the microturbine, using what would otherwise be wasted energy to keep the digester tanks at a temperature favorable to methane production.

HOW IS THE WATER POLLUTION CONTROL PLANT SUSTAINABLE?
Through restaurants alone, The United States produces almost 4.2 billion pounds of kitchen grease each year, or roughly 14 pounds per person. If not diverted to innovative facilities such as Millbrae’s Water Pollution Control Plant, the grease ends up in landfills where it naturally decomposes into methane. The methane is then absorbed by Earth’s atmosphere, accounting for nine percent of grease sent to landfills, consequently reducing their greenhouse gas emissions. An even greater sustainable benefit comes from the on-site energy production that reduces carbon emissions by nearly 1.2 millions pounds annually.

FINANCIAL BENEFITS
The upgrade to the plant provides annual savings and revenues of $366,000 for the city. Through the energy cost savings, the disposal fees paid by grease hauling companies, and a $200,000 grant from the Pacific Gas and Electric Company through California’s Self Generation Incentive Program, the $5.5 million upgrade to the plant completely pays for itself, thereby having no effect on wastewater treatment rates.

WHAT IS A SUSTAINABLE STATE?
Former superintendent of the WPCP, Richard York, said at the opening of the facility, “This is the only wastewater treatment plant in the U.S. to receive and process inedible grease in a self-funding, purpose-built system that successfully addresses so may challenges simultaneously. It’s a complete solution that could be adopted in many cities around the country.” Since the opening in late 2006, other cities have indeed followed suit. In Southern California, the cities of Riverside and Rialto have adopted the same technology, and many landfills worldwide capture methane, using it to produce power in a similar process. In a sustainable state, wastewater treatment plants around the world would adopt similar technology, drastically reducing carbon emissions into the atmosphere.

FURTHER RESOURCES

Millbrae Wastewater Treatment
Chevron Energy Solutions
Wikipedia: Cogeneration
How is Kitchen Grease Collected?