AWWA WQTC71541

The goal of this project was to develop a post-treatment oxidation process for removing organics in membrane concentrates. Several technologies capable of oxidizing organics were evaluated, including: Fenton reactions with and without subsequent iron coagulation; ozone with and without hydrogen peroxide; UV irradiation alone, with hydrogen peroxide, or with titanium dioxide; and, wet chemical oxidation. Most of the research was conducted with concentrate from reverse osmosis (RO) of partially denitrified wastewater at the City of Scottsdale Water Campus. The RO concentrate had a dissolved organic carbon (DOC) concentration of 40 to 50 mg/L and total dissolved solids (TDS) concentration of ~ 5500 mg/L. One membrane cleaning solution was also studied. Oxidation experiments were conducted using bench-scale units. In addition to standard laboratory test systems, two proprietary advanced oxidation process (AOP) systems were evaluated. The first system (HiPOx from Applied Technologies Inc.) feeds hydrogen peroxide and ozone. The lab-scale unit supplies ozone as a gas to a rapidly recirculating sample (RO concentrate) spiked with high levels (100 to 1000 mg/L) of hydrogen peroxide. The second system (PhotoCat™ by Purifics Inc.) is an integrated ultraviolet (UV) irradiation and ceramic membrane system that permits the internal recirculation of titanium dioxide. Over the course of the study, RO concentrate was collected and subjected to treatment in the bench-scale reactors. The loss of DOC as a function of chemical dosage and energy input was monitored. Changes in other organic parameters (e.g., UV absorbance at 254 nm, chemical oxygen demand, concentrations of organic acids and biodegradable components) were also monitored. During select experiments, the steady state concentration of hydroxyl radicals was estimated using a probe compound (parachlorobenzoic acid). Includes abstract only.