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Environment Economy


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A Partner in Sustainability

Putting Waste to Work!

How a wastewater treatment plant generates 100% of its own renewable energy.

California is a renowned leader in renewable energy and environmental stewardship, and now the SoCal city of Thousand Oaks has merged those attributes in an innovative public-private infrastructure project. The site is the municipal Hill Canyon Wastewater Treatment Plant (HCTP), nestled in the area’s woodsy canyon country. The facility serves a population of nearly 130,000, treating 8.5 million gallons of sewage water each day.

A few years ago, the city council set a bold goal for HCTP: to generate 100% of its energy from renewable sources on-site, completely bypassing the public utility’s grid. As of September 2014, by combining the electricity output of a 1 MW biogas cogeneration plant and a 584 kWh solar farm, the facility has hit the mark. And as a bonus to the community, the HCTP project is saving utility rate–payers nearly $300,000 a year in energy costs and tallying an average of $700,000 annually from the sale of recycled effluent for local irrigation needs, all while keeping sewer-service rates low.

Pulling together this energy-efficient and cost-effective system was no easy task, though, requiring collaboration among several entities. “The project posed a number of logistical and technical challenges,” says Tom Moore, president and CEO of BioSpark, a Boston-based company that HCTP contracted to construct and manage the cogeneration plant, which supplies about 85% of the treatment facility’s power. The solar array’s 2,783 motorized panels deliver the balance. “[HCTP is] located in a canyon, up a long road, and the footprint is tight. That’s where Siemens came in,” he says, referring to the industrial manufacturer that signed on as an integral partner in the project.

“The cost to the city is zero, and we are saving $300,000 annually over regular grid-purchased energy.”

—John Brooks, senior environmental analyst, City of Thousand Oaks, CA

The heart of the cogeneration plant is a massive Siemens engine. It’s fueled by renewable biogas, specifically purified methane produced inside an airtight, heated anaerobic digester, which decomposes organic, biodegradable waste materials. The waste emanates from local food and beverage processors and farms. Haulers transport the materials to HCTP and pay tipping fees, adding another $400,000 a year to Thousand Oaks’ coffers. What’s more, the biogas-to-energy system annually reduces carbon emissions by 1,600 metric tons, the equivalent of planting 1,659 acres of forest or taking 1,037 cars off the road every year.

Another creative element of the HCTP project is its financing. Both the solar farm and the cogeneration plant are privately owned and operated, each under a separate power purchase agreement (PPA). With a typical PPA, a private developer designs, builds and finances an energy system and sells the electricity to a public utility at a fixed rate usually lower than the utility’s retail rate.

In this case, BioSpark created a sister company, CHP Clean Energy LLC (CHP is an acronym for combined heat and power, a type of renewable energy system). Under a 15-year PPA, CHP Clean Energy sells its biogas-generated electricity to the city for 7.2 cents per kWh, with an annual 2% escalation clause. MMA Renewable Ventures owns the solar plant, and SunPower Corp. operates it through a 20-year PPA that prices its electricity at 16.8 cents per kWh, with no escalation clause. Funding assistance for both developers came from Self-Generation Incentive Program (SGIP) grants from the California Public Utilities Commission totaling $2 million. Another $1.5 million SGIP grant was issued for the new Siemens cogeneration engine.

This kind of public-private partnership is an ideal solution for HCTP, Moore contends, unburdening the plant operators—as well as taxpayers—from the laborious process of constructing and financing the project. “Also, with our PPA,” he adds, “every kilowatt-hour of energy we sell them at a discount to the utility rate is money in their pocket. We have a really symbiotic relationship.”

John Brooks, senior environmental analyst for the city of Thousand Oaks, concurs: “The cost to the city is zero, and we are saving $300,000 annually over regular grid-purchased energy.”

So exemplary is HCTP’s renewable energy project, it was recently cited as a best practice by the U.S. Conference of Mayors Business Council. “This is a scalable solution that could be replicated at wastewater treatment plants across the country,” concludes Moore. “A reliable, efficient source of energy that reduces costs and emissions—it’s a win-win-win.”

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