In a guest column for Water Online, CWEA member Melanie Holmer, PE, along with Kati Bell, PhD, PE, BCEE of MWH Global discuss the benefits and barriers of ozone-biologically active filtration for potable reuse in California’s inland communities.
Currently, the state of California allows indirect potable reuse (IPR) by groundwater replenishment; however, in direct injection scenarios, water must be treated with a treatment train that includes reverse osmosis. Typically, this is accomplished using Full Advanced Treatment (FAT), which incorporates microfiltration (MF), reverse osmosis (RO), and ultraviolet (UV) advanced oxidation processes (UV-AOP). Together, these unit processes provide a multi-barrier treatment scenario that provides adequate treatment of secondary effluent such that the finished water can be injected into groundwater supplies for drinking water.
The RO process produces a concentrate waste stream that cannot easily be disposed because of its salinity, toxicity, and high concentrations of trace chemical contaminants, which include compounds such as pharmaceuticals and personal care products (PPCP) and endocrine disrupting compounds. For coastal treatment facilities, this toxic waste stream can be diluted by disposal with other effluent that is discharged through ocean outfalls. For inland communities, the complexity and cost of dealing with brine disposal often renders RO — and therefore potable reuse — out of reach.
Ozone-biologically active filtration (ozone-BAF) offers an appealing alternative to FAT because there is no concentrate stream associated with this process. While there are benefits to ozone-BAF, there are also challenges including barriers to employing ozone-BAF for potable reuse in California’s inland communities.