Breaking through limits of technology: Nitrate removal using membrane biofilm reactor

Breaking through limits of technology: Nitrate removal using membrane biofilm reactor
Richard Buday takes daily reads, recording information from the C-More HMI (Automation Direct) for final product nitrate level, final product turbidity, final product Cl2, pH and temperature to ensure they are meeting required limitations. The system has safeguards built into the programming so if they are not on spec water is diverted to the sewer until the system corrects itself. (Photos by Dustin Hochreiter)

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What do the Fighting Irish of Notre Dame University in South Bend, Ind., have to do with Rancho Cucamonga, a growing suburban community seated in the foothills of Southern California’s Angeles National Forest? In a word: Nitrates. 

Rancho Cucamonga was once home to dozens of orchards and vineyards whose citrus and grape crops thrived in the arid soil. But, like many suburban settings in the 1970s, this desert community, located 40 miles east of Los Angeles, experienced rapid growth. Real estate prices soared, enticing many of the old-time farmers and vintners to sell their lands and move on. The city has replaced most of its citrus groves and grape arbors with warehouses, industry, and residential neighborhoods. 

More than a century of agricultural soil enhancement left behind residual nitrates that, over time, seeped through the sandy soil and penetrated the water table — hundreds of feet below the surface. One after another, the Cucamonga Valley Water District (CVWD) has had to abandon wells whose nitrate levels exceed 1974 Safe Drinking Water Act raw water standards limits of 10 ppm. Citrus had a big impact on the current nitrate levels found in the groundwater tables today, says Rob Hills, CVWD water treatment superintendent. 

Novel nitrogen removal process

Enter Psomas Engineering. They were looking for a pilot site to test one of the novel nitrogen removal processes developed by Dr. Robert Nerenberg, associate professor, Department of Civil & Environment Engineering & Earth Sciences at the University of Notre Dame, and Bruce Rittmann, Regents’ Professor of Environmental Engineering and Director of the Swette Center for Environmental Biotechnology at Arizona State University. This technology was originally developed by Rittmann at Northwestern University, where Nerenberg was his doctoral student. Since then, Nerenberg has expanded his interest in developing nitrate removal solutions that would conserve space and energy, while reducing the impact and safety issues of conventional remediation byproducts to the environment. 

In 2007, Nerenberg and Rittmann partnered with APTwater, Inc., which develops and commercializes advanced water treatment process technologies for water reuse and environmental remediation by using technologies that are based on renewable resources and minimize or eliminate production residuals or waste byproducts. Through licensing from Northwestern, APTwater has developed a proprietary membrane biofilm reactor (MBfR) called ARoNite (Autotrophic Reduction of Nitrate) to remove nitrates from groundwater. The test site is a Cucamonga Valley Water District well taken out of service in 1985 when raw water nitrate levels exceeded 10 ppm, making it prohibited for human consumption. 

How does MBfR work?

MBfR falls under an umbrella of membrane filters that are finding increasing presence in water and wastewater treatment. MBfR is not used to separate biomass from effluent water, like that of its better known cousin, the membrane bioreactor (MBR), a process that makes MBRs susceptible to fouling by biofilms and other materials that collect and accumulate on membrane surfaces. Instead, an MBfR system uses membranes to supply dissolved gas directly to a biofilm. These autotrophic bacteria use inorganic compounds such as hydrogen (electron donors) or light as an energy source to do what they do best — break the bonds between nitrogen and oxygen (electron acceptors) in nitrate molecules, making the oxygen available for their own metabolism, releasing byproducts of H2O into the water and nitrogen gas to the air. 

David Friese, ARoNite technology director, describes the ARoNite system as using hollow-core, hydrophobic membranes, measured in microns — about the diameter of fishing line — tiny little pipes that, when filled under pressure, leak hydrogen gas out to the biofilm on the membrane surface. The hollow membranes are weaved together and rolled into a 6-foot-by-1-foot-diameter cloth jellyroll. Each end of the roll is dipped into a resin, capping one end and placing a manifold — a tap — on the other end through which pressurized hydrogen is forced. After the roll is installed in the reactor, beneficial bacteria then grow on the outside of the membrane, across surface area, allowing for population sizes in a compact space, a fraction of the area of a traditional suspended solids basin. 

Testing the theory

Friese, a chemical engineer who worked in process development for a chemical company for two decades was recruited by APTwater to develop and manage the project from the beginning. To ensure its success, Friese has worked closely with Nerenberg’s group, as well as with Hills, and the California Department of Public Health, the state water regulating authority. 

Richard Buday, a licensed water operator since 2006 and APTwater employee, operates the system, answers alarms on nights and weekends, monitors progress, and maintains the records. He has nurtured the ARoNite test site from the start. With a degree in business, he has the entrepreneurial spirit that a prototype like this benefits from. When nearly a decade ago, a friend in the industry suggested that working with public water supplies would give him a reliable career path to upper management, he listened. So, Buday sold his business and began his new career with a municipal water supply, eventually attracting the attention of Friese. 

Buday regularly travels to the test well site in Rancho Cucamonga for site inspections, listening for rough pump bearings or air compressors cycling out of sync. He checks for leaks and looks at the C-More HMI screen (Automation Direct) on the ARoNite pump skid, checking for different operating parameters such as hydrogen gas or nitrate, pH, and turbidity levels in the final effluent. 

Turbidity, caused when biofilm breaks away from the membrane surface, is a natural process in the life of beneficial bacteria. Filter media traps breakaway biofilm in the water effluent; the media is backwashed about every eight to 12 hours. Buday, using Allen-Bradley PLCs (Rockwell Automation), can control and monitor the ARoNite system 24/7 from his smartphone. “I rarely get alarm notifications these days,” he says, as he continually strives to improve the system’s reliability and performance. 

The future is here – now

The MBfR technology works. ARoNite takes nitrates down to well below the 10 ppm limit. Buday says that they can get down to nondetectable levels in the water effluent — below 1 ppm. That’s enough to satisfy the California Department of Public Health, who is close to permitting the process for public use — hopefully this year. If they do, Friese says the CDPH permit would be one of the first ever to allow bacteria to purposefully be added to raw drinking water. Hills says it could mean returning 12 CVWD wells that were taken out of service due to excessive nitrate levels with a potential recovered capacity of 9 mgd — a circumstance that could meet much of the CVWD water customers’ current demand for drinking water. 

Removal of nitrates and other impurities from raw water may be just the beginning of what membrane biofilm reactors are capable of. Nerenberg and his group are busy developing creative ways to apply this promising new science to agricultural runoff and wastewater treatment, among other things. There seems to be no limit to benefits of MBfR technology. “It’s exciting technology that could change how we deal with contaminants like nitrates,” says Hills.



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