A California treatment plant joins a US Department of Energy program, expands its cogeneration system and makes progress toward net zero energy.
The Victor Valley Wastewater Reclamation Authority saves about $40,000 per month by using biogas to displace some natural gas for generating electricity.
With a biogas cogeneration system that went online in September, the plant now produces 93 percent of its power. “We’re nearing a goal where we can say we are energy neutral,” says Logan Olds, general manager.
Victor Valley was the first wastewater treatment plant to join the U.S. Department of Energy Better Buildings, Better Plants program in December 2014. Many more plants have since joined the program, which has 160 members representing more than 2,400 industrial facilities.
Those in the program pledge to reduce energy use by 25 percent over 10 years and share their solutions to help others. “We are trained to meet water-quality regulatory requirements,” notes Olds. “We are not trained on electrical production and energy efficiency. Better Buildings, Better Plants helps educate me and the staff about how we monitor, track and project our energy efficiencies and savings. It’s helping us develop the same programmatic approach for energy that we have for water quality.”
The opportunity came when Anaergia, looking to demonstrate technology it has used for years overseas, applied for a grant from the California Energy Commission to install its Omnivore anaerobic digestion system at a wastewater treatment plant in the state. The company had 1,600 Omnivore installations worldwide but none in North America.
The commission provided a $2 million grant for the Omnivore project, and Anaergia contributed $600,000. The company used the money to retrofit a decommissioned VVWRA anaerobic digester for its process, which triples biogas production. The authority had saved three old digesters instead of tearing them out when two larger digesters were built in 2008.
VVWRA entered a 20-year power purchase agreement with Anaergia for the biogas-to-energy project. “Anaergia provided the equipment, retrofitted the tanks and installed the mixing technology,” says Olds.
The Omnivore process thickens and mixes solids to increase biogas production. “I’ve always been told you can’t reliably mix more than 2.5 percent solids in anaerobic digesters,” says Olds. “We are mixing 6 percent day in and day out. They’ve also demonstrated the decoupling of the hydraulic and solids retention time. So the water goes away, but the solids remain in the digester so we can generate additional gas.”
Looking to export
The biogas is stored in a double-membrane gas holder installed by Anaergia and is burned in a pair of 800 kW engine-generators (2G Energy).
One improvement being considered is battery-based energy storage. “One issue with power production is that you have varying loads and the generators can’t always ramp up fast enough, or you get frequency variations in the voltage,” says Olds. “With a battery system and a microgrid controller, we can handle those variable loads. Once we demonstrate that ability, we could export up to 400 kW to the utility grid.” Olds will pursue a grant from the Energy Commission for that project.
The ability to export power would make it possible to co-digest FOG and food processing waste and produce more fuel, export more power and generate revenue. “We still have two digesters offline, so I’d like to find a private partner to find a use for them and provide some benefit to our facility,” Olds says.
Learning from others
VVWRA serves about 300,000 people across 216 square miles in the Mojave Desert. Its activated sludge plant (18 mgd design, 12.3 mgd average) uses biological nutrient removal, AquaDiamond cloth-media tertiary filters (Aqua-Aerobic Systems) and UV disinfection.
“It’s kind of unusual,” says Olds. “We are required to release a little more than 8 mgd for reuse by downstream communities and for habitat maintenance in the Mojave River. The remainder is used in a local power plant’s cooling towers or sent to percolation ponds and eventually goes back to the aquifer.”
As a member of the DOE program, Olds hopes to learn from industries that have been treating water for other uses and with less energy intensity. “If you look at other places where water is scarce, our industrial partners have already done some of this work on the pretreatment side for creating potable water for their product,” he says. “Some of the big ones are bottled water and soda. We need to do the same in cleaning up the water before releasing it to the environment.”
The authority is now building two 1 mgd regional plants that will reclaim some wastewater for irrigating landscapes and golf courses and send the remaining wastewater and the solids to the main plant for further treatment. They are to be operational in mid-2017. Olds is also considering solar energy to help meet those plants’ energy needs.