Transformation of Trace Organic Contaminants from Reverse Osmosis Concentrate by Open-Water Unit-Process Wetlands with and without Ozone Pretreatment.

Abstract

Reverse osmosis (RO) treatment of municipal wastewater effluent is becoming more common as water reuse is implemented in water-stressed regions. Where RO concentrate is discharged with limited dilution, concentrations of trace organic contaminants could pose risks to aquatic ecosystems. To provide a low-cost option for removing trace organic compounds from RO concentrate, a pilot-scale treatment system comprising open-water unit-process wetlands with and without ozone pretreatment was studied over a 2-year period. A suite of ecotoxicologically relevant organic contaminants was partially removed via photo- and bio-transformations, including β-adrenergic blockers, antivirals, antibiotics, and pesticides. Biotransformation rates were as fast as or up to approximately 50% faster than model predictions based upon data from open-water wetlands that treated municipal wastewater effluent. Phototransformation rates were comparable to or as much as 60% slower than those predicted by models that accounted for light penetration and scavenging of reactive oxygen species. Several compounds were transformed during ozone pretreatment that were poorly removed in the open-water wetland. The combined treatment system resulted in a decrease in the risk quotients of trace organic contaminants in the RO concentrate, but still dilution may be required to protect sensitive species from urban-use pesticides with low environmental effect concentrations.