Gravity-Based, Low-Energy Biofilter With Low Backwash Rate for Nitrate Removal in Groundwater
December 22, 2020
Energy Research and Development (500)
Electric Program Investment Charge - EPIC
Edgar Kim, Ph.D.
Groundwater is an essential component of California’s water supply. However, in the past 10 years, more than 6,934 wells and 1,149 wells statewide have been contaminated by nitrate and perchlorate, respectively. In this project, the recipient, Tomorrow Water, tested an energy-saving groundwater treatment system, Tomorrow Water Biofiltration, that can decontaminate groundwater to drinking-water standards. From the project site in the City of Barstow in Southern California, the project team performed tests required by the State Water Resources Control Board to secure conditional acceptance as a Title 22 drinking water treatment technology for perchlorate and nitrate removal. During this testing, influent nitrate and perchlorate concentrations were measured as 4 to 15 milligrams per liter (mg/L) and 4 to 30 micrograms per liter (ug/L), respectively. The Tomorrow Water Biofiltration system simultaneously removed nitrate, perchlorate, and turbidity from groundwater to bellow state-mandated maximum contaminate levels. At the same time, the system reduced energy consumption by 70 percent when compared with a conventional fluidized bed reactor. Both contaminants were treated until each maximum contamination level reached the project goals of 10 mg/L for nitrate and 6 ug/L for perchlorate based on California’s Title 22 drinking water standard. The maximum level of influent water quality for this demonstration was 15 mg /L of nitrate and 53 ug/L of perchlorate. Empty bed contact time was between 45 minutes and 120 minutes depending on the influent groundwater quality, but the Tomorrow Water Biofiltration system showcased capabilities to treat both contaminants under Title 22 drinking water standard maximum contaminant level while saving 70 percent of energy. While the project did not achieve a Title 22 certification, Tomorrow Water continues to seek approval and is working with the Regional Water Board to solve the issue regarding real-time perchlorate data.The Tomorrow Water Biofiltration system also implemented advanced operational and control measures to mitigate the risk of incidental contaminant discharge. The safety logic was automatic once the system detected contaminants in effluent, such as during the high-nitrate and perchlorate-loading tests and during the carbon source failure test.