Santa Rosa turns industrial food waste into energy and savings

Ken Kolp used to start his workday with a two-hour trip to the East Bay to dispose of thousands of gallons of slimy slop sucked out of area grease traps.

Now, he just drives his tanker truck over to Santa Rosa’s Laguna Road wastewater treatment plant, pumps the oily ooze into one of four new holding tanks, and is back on his route in a matter of minutes.

The process saves time, money and environmental impacts for local businesses like his, North Bay Restaurant Service, as well as bigger players such as Lagunitas Brewing Co., Amy’s Kitchen and Cowgirl Creamery.

“It’s a great big help because instead of having a 70-mile trip, we now have a 7-mile trip,” said Ryan Neal, sales manager of the Santa Rosa-based hauler.

Since Santa Rosa began operating its new $3 million high-strength waste receiving station in August, the project is proving to be an environmental success story, said Adam Ross, an engineer at consulting firm Brown and Caldwell, which helped design the facility.

“It’s already achieving all of the project goals that we set out for it,” Ross said.

To date, the treatment plant has received ?2.3 million gallons of liquid waste from area businesses. Having a local disposal option has so far saved ?609 trips out of county, most to the East Bay Municipal Utility’s District’s facility in Oakland.

At about 20 gallons of diesel saved per trip, that’s 12,180 gallons of fuel local businesses didn’t have to buy and burn. Add to that lower personnel costs and less wear and tear on vehicles and area roads, and the savings to local businesses is clear.

But are the people who bankrolled the project - the 230,000 water and sewer users in Santa Rosa, Sebastopol, Rohnert Park and Cotati - getting a return on their investment?

It turns out that this tough-to-treat waste is proving to be a valuable fuel for the plant, boosting its production of biogas, and allowing the power-hungry facility to generate new revenue and lower its energy bills.

The combination of new income and cheaper energy means the project is on track to pay for itself in a few years and curb the need for rate increases.

“Projects like this help us keep rate increases as low as possible,” said Mike Prinz, deputy director in charge of the plant.

The plant already turns the solid waste collected from local sewer systems into methane. This is done by collecting the sludge into four 1-million gallon digesters, where trillions of microbes break down the organic material in a warm, oxygen-free environment.

The byproduct methane is captured and fed into massive engines that generate electricity and heat for the plant.

Engineers hoped that by gradually adding nutrient-rich wastes from local businesses to the sludge, they could turbocharge the biologic process in the digesters, boosting biogas production and shrinking the plant’s power bills even further. Initial results have been promising, with biogas production up ?40 percent in the first three months of operation. This has allowed the plant to start up a second gas generator and shave about $29,000 per month off its ?$3 million annual PG&E bill.

Engineers started adding the new material in August. It included watery cheese waste from Cowgirl Creamery, vegetable slurry from Amy’s Kitchen in Santa Rosa, and fats, oils and grease from area restaurants. Each was tested to see how it affected gas production.

“The thickest stuff we get is the consistency of a melted milkshake, but you definitely would not want to drink this,” Prinz said.

As plant operators accept new materials, they closely monitor the chemistry inside the digesters to make sure the biological processes remain robust, Prinz said.

“We’re asking a lot of that microbiological community, and we don’t want to throw the balance of bacteria in the digesters out of whack,” he said.

So far, the process has gone smoothly, he said.

It turns out that one of the best boosters to the digester process is chicken blood and guts from Petaluma Poultry Processors, which is now taking several tanker trucks a week to the plant. The material is so potent that Prinz has taken to calling that delivery the “hot sauce.”

Lagunitas is also a big contributor. The brewery, whenever its own treatment system is maxed out, sends truckloads of the nutrient-rich wastewater left over after workers hose down huge brewing tanks.

Plant operators are finding, however, that the brewery wastewater is fairly diluted compared to the potent poultry waste.

“Those are the two extremes of what we are getting,” Prinz said.

The challenge now is to maximize not only the volume of material the plant receives, but also its biogas production.

The station is currently operating at about ?75 percent of its 40,000 gallon storage capacity. At fees to haulers of 4 cents per gallon, the operation is generating about $27,000 per month. When combined with the power savings, the project - in addition to providing numerous environmental benefits - is well on its way to paying for itself within four years Prinz said. If volumes can be boosted to maximize use of material with the best potency, then the benefits to the ratepayers could be even greater, Prinz said.

Ross attributes Santa Rosa’s success in part to the outreach it did beforehand to make sure enough businesses would use the new service. If the plant gets to the point where demand for the service exceeds the plant’s capacity, operators will be more selective of what they take. That would be a nice problem to have, Ross said.

“Doing everything for the right reasons and doing it the right way and then seeing it come to fruition just they way we drew it up is really satisfying,” Ross said.

Editor’s Note: This story has been updated to note that East Bay MUD’s industrial food waste facility is located in Oakland.

You can reach Staff Writer Kevin McCallum at 707-521-5207.