Ambitious efforts in biogas-to-energy and solar power help a California clean-water plant achieve its goal of generating all its electricity on site.


Since mid-September 2014, all electricity at the Hill Canyon Wastewater Treatment Plant has come from on-site sources. With about 1 MW of biogas cogeneration capacity and a 584 kW solar array, the 14 mgd (design) plant saves money while achieving its goal of electric power self-sufficiency.

Chuck Rogers, superintendent of the plant in Thousand Oaks, California, thanks his staff members who have embraced sustainability, power purchase agreements (PPAs) that make renewable energy feasible, and a city council that set a challenging goal.

The 54-year-old advanced tertiary plant has an average flow of 8.5 mgd. Serving a population of 120,000 people, it earns $700,000 in revenue annually by selling 90 percent of its effluent for farm, golf course and landscape irrigation. The rest supports natural habitat for plants and animals at a nearby lagoon.

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Renewable energy

In 2007, Thousand Oaks pursued two renewable energy projects that led to many years of guaranteed electric rates with zero capital investment. The developers funded construction and operate the generating facilities.

CHP Clean Energy owns the cogeneration system and consumes biogas that used to be flared. The facility includes two engine-generators and a gas treatment system. In 2014, one of the original 250 kW Mann engines was replaced with a 700 kW Ingersoll Rand unit. Actual outputs average 240 kW and 600 kW.

Under a 15-year PPA, the plant provides the biogas and pays 7.2 cents per kWh for the electricity, with an annual 2 percent escalation clause. The arrangement saves about $200,000 a year over rates from Southern California Edison (SCE). “As electrical costs continue to go up, the spread between what we buy it for compared to increases at SCE will be very favorable to the city,” says Rogers.

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The solar plant is owned by MMA Renewable Ventures and operated by SunPower Corporation through a 20-year PPA. The 2,783 panels are motorized to follow the sun, maximizing their output. “The solar is more expensive than the cogeneration, but it serves us well,” Rogers says. The solar electricity is priced at 16.8 cents per kWh with no escalation clause.

Funding assistance for the developers came from California Public Utility Self Generation Incentive Program (SGIP) grants totaling $2 million. Another $1.5 million SGIP grant was issued for the new cogeneration engine.

Putting FOG to work

Hill Canyon’s average electric demand has dropped from 1.2 MW 15 years ago to just 680 kW, largely through use of modern equipment such as variable-frequency drives, energy-efficient motors and LED lighting. “Our goal is to get down to 600 kW,” says Rogers. “Everywhere I turn, I can say we optimized that.

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We looked at the textbook digester mixing and decided we didn’t have to mix them as frequently and vigorously. We turned it way down and it works fine. We try to run things off-peak, and we have a new SCADA system coming on that will give us more opportunity for automation.”

To make sure the cogeneration system has enough fuel, Hill Canyon increased its FOG (fats, oil and grease) program over the years and recruited sources of other high BOD waste. The plant generates 450,000 to 600,000 cubic feet of gas daily.

In 2014, the plant took in about $400,000 from local haulers delivering between 15,000 to 30,000 gallons of waste per day. “We take FOG, coffee waste and beer waste,” says Rogers. “We’ve taken yogurt and biodiesel waste in the past, and are currently taking a Russian dressing waste.

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“FOG is nasty stuff, so we had to learn about controlling the digesters, which are being fed like a buffet every day. We had to increase our level of understanding so we weren’t just foaming out of them. We’ve overfed them and overmixed them. It’s understanding holistically everything that happens at the treatment plant. We just didn’t know until we knew. We’re trying to optimize this all the time.”

One thing that has helped is software a local company developed to automate the feeding of variable Btu waste into the digesters. “It sets a target and then looks at how much gas a certain volume of material creates,” says Rogers. “It’s constantly balancing up and down from that target.”

There was skepticism at first, but the software has been effective. “That’s something a lot of people struggle with,” says Rogers. “This stuff has wild variability. Some FOG loads are great, some are OK, and some are worthless for gas production.” Next up is exploring options with locally generated food waste.

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Infrastructure matters

Rogers has worked at Hill Canyon for 18 years and says Thousand Oaks is an example of what happens when a community pays attention to public works.

“Affluence and wealth follow,” he says. “We have beautiful streets and sidewalks, great water and wastewater systems. When you add them up, we have a community attractive to people and companies like Amgen (a global biopharmaceutical company) and Baxter International (a global biotechnology and health care company).”

He credits leadership for the plant achieving self-sufficiency in its electricity supply. “Our city council really drove it,” says Rogers. “It was very challenging. If it hadn’t been for our city council making a big deal about it, it probably wouldn’t have happened. God bless difficult goals and objectives.”


Lights, camera, action

The Hill Canyon treatment plant tries to operate as a business. The plant rents some land to a farmer who grows peppers for sriracha sauce, and some to California’s film industry. It also hosts numerous bee colonies and aims to turn that into a revenue stream.

“We’ve opened the door to public-private partnerships,” says Chuck Rogers, plant superintendent. “We’re constantly looking for good partners — ways to keep our costs down and make things a little bit better for everybody.”

Just an hour from Los Angeles and Hollywood, the plant has hosted many commercial and video shoots. The Speed Channel shot a program about the Toyota Prius featuring Adam Carolla, and Intel used the plant as a setting for a training video. The first feature-length production was a 2014 low-budget movie, The Big One that Went Direct to DVD. “We got a call from HBO recently, but nothing has happened yet,” says Rogers.

Thousand Oaks lies in the heart of Conejo Valley, site for dozens of popular movies and TV shows since the 1940s, from Tarzan and Old Yeller to Friday Night Lights and Sleepless in Seattle. The Bonanza opening credits scene showing the Cartwrights riding down a dirt road was shot at a farm near the plant.

Working with artists can be a bit challenging but also fun: “Hollywood people are just like they are portrayed in the media. There’s never enough time in the day to not ask for another favor.” 


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