Like many small water utilities in California, the Sunny Slope Water Company in Pasadena has a nitrate pollution problem. The chemical, a legacy of fertilizers used in the state’s huge agriculture industry, has been linked to birth defects and cancer at high levels.
To meet California’s drinking water standards for nitrates, Sunny Slope had to blend water across its five wells, which serve 38,000 homes. But when one of those wells reached nitrate levels that forced its closure, the company had to tap into a more expensive reservoir, says its general manager Ken Tcheng.
The experience sent Tcheng searching for a cheaper solution. Existing technologies for filtering out nitrates were off the table because they produce waste that is expensive to dispose. “We didn’t have the infrastructure that was cost-effective to truck the waste,” Tcheng says. So he started looking into newer, alternative technologies harnessing the water-cleaning power of microbes that naturally dwell in soil and water.
Tcheng turned to a a San Francisco Bay Area–based company called Microvi, which has landed on a unique way to handle water-cleaning microbes to minimize waste and—if its technology can scale up—potentially reduce costs for small outfits and disadvantaged California communities where nitrate pollution is most acute. “If it works, it would be a magic wand,” says Jeannie Darby, an environmental engineer at the University of California, Davis, who is not involved with the company.
The industry standard for removing nitrates from drinking water is a process called ion exchange, in which water flows through a special resin designed to attract nitrates. Salt ions attached to the resin are exchanged for the nitrates in the water, releasing the salt and creating a brine that has strict—and thus expensive—disposal requirements.
In the quest to avoid this waste and cost, several companies have recently developed treatment systems that use microbes. Such systems are the standard for treating wastewater, but their use in cleaning drinking water is new. Although these systems do not generate brine, they do produce a sludge formed by the spent microbes as they multiply and die. This waste must itself be managed, usually by sending it to a wastewater-treatment facility—which can also be costly.
But Microvi says it has found a way to prevent sludge formation in a system that uses microbes to clean drinking water. It houses the microbes in water-permeable, jelly bean–sized beads made of plastic composites that create the right conditions for a process called cryptic growth, which stops organisms from reproducing but lets them remain viable enough to clean water. These “biocatalysts” (the company’s name for the beads) keep the microbes in a phase in which their growth and death rates are equal, and living microbes digest dead ones—keeping the overall population stable for five to 10 years. “We don’t change the microorganisms. We just put them in an environment where we’ve discovered they will go into that nongrowing but metabolically active phase,” says Ameen Razavi, director of innovation at Microvi.
Microvi’s setup looks something like a giant vat of bubble tea. Raw water is pumped into a continuously stirred reactor vessel containing millions of biocatalyst beads. Each one is packed with billions of microbes selected from hundreds of kinds the company tested to see which of them best remove pollutants. When the water flows through the beads, the microbes convert the nitrates into nitrogen gas (which is harmless and can be released to the atmosphere) with the help of acetic acid pumped into the reactor.
Strict third-party testing, which secured the California state government’s approval for the technology, found it reduced nitrates to five milligrams per liter or less—competitive with ion-exchange treatment and well below the Environmental Protection Agency’s standard of 10 milligrams per liter. Later testing by the nonprofit Water Research Foundation confirmed those results and calculated that over a 20-year period, the Microvi system would be roughly one third less expensive than ion exchange.
When the biocatalysts degrade and are no longer functional (expected at five to 10 years), the company will dispose of them for water districts and can recycle some of the plastics for future use, Razavi says. The rest will likely go into a landfill. Microvi claims the use of its technology at Sunny Slope has produced 10 times less solid waste than other treatments would; experts are waiting to see if these savings can be replicated with larger systems.
“No Silver Bullet”
So far Microvi has also adapted its technology to remove ammonia, phosphorus and several other pollutants from drinking water and wastewater, but it does not handle the full water-treatment process. Its reactors are modular components designed to be plugged into larger facilities that conduct the other phases, from filtration to chlorination.
That modularity has lower costs than building a full plant, which makes it attractive to municipalities, says Arthur Umble, global practice leader for wastewater at an international design firm called Stantec.
In terms of gaining a foothold in the market, Microvi’s biocatalyst system “would be scalable probably within five years,” says Umble, who is an unpaid adviser to the company. The project at Sunny Slope has been running for more than two years, and Razavi says Microvi has a bigger system—with three 38,000-liter reactors capable of together processing 5.3 million liters of water per day. That system is slated to open this summer as part of a larger project involving other companies at the Cucamonga Valley Water District outside Los Angeles. The company also has facilities in Australia and England and two more planned for California’s Central Valley, an epicenter of nitrate pollution in the state.
Kurt Souza, principal engineer at the California State Water Resources Control Board, says the new system is “pretty slick.” But when looking for alternative ways to address nitrate pollution, “there’s no silver bullet,” he says. “We have a bunch of [companies] that are talking to water systems. They all have their pros and cons,” with Microvi potentially being a good fit for smaller water systems or those too far from the coast to make brine disposal economical.
“One of our biggest goals is to change the reliance of this country on using only chemical or physical processes to treat drinking water,” because of such methods’ large energy and waste footprints, Razavi says.
In Pasadena, Sunny Slope’s Tcheng is pleased to help turn the tide. “We partnered with Microvi to help bring the technology to market,” he says. “We’re the first one in California to have it approved. We’re happy with that.”