Recent regulatory changes have necessitated the development and evaluation of technologies used to treat perchlorate and nitrate in drinking water. Currently, the most widely used and accepted treatment technologies for removal of these contaminants involve the generation of a concentrated waste stream, which must be further treated or disposed. Carollo took part in an AWWA sponsored study to investigate innovative biological treatment alternatives for perchlorate and nitrate brine.

One portion of this study investigated the feasibility of utilizing wastewater plant oxidation ditches to treat perchlorate residuals (i.e., residuals discharged to the sewer). A bench-scale batch reactor was used to simulate the oxidation ditches at Magna Water Company’s WWTP, and wastewater from the plant was spiked with perchlorate for testing. The data showed that organisms indigenous to Magna’s WWTP can reduce perchlorate while using the natural organic matter present in the wastewater as substrate.

A subsequent portion of this study evaluated the use of a fixed-film reactor upstream of the oxidation ditches to treat perchlorate residuals. Wastewater from Magna’s WWTP was used to biologically acclimate virgin granular activated carbon in a 2-inch-diameter fixed-bed bioreactor. Perchlorate was spiked to the feed at 1-2 mg/L using a syringe pump. Seeded only with microorganisms indigenous to the raw wastewater, the fixed-bed biological reactor demonstrated efficient perchlorate removal while utilizing only background organics as substrate.

Perchlorate removal to below detection (i.e., 4 μg/L) was achieved and sustained at empty-bed contact times as low as 30 minutes. This work demonstrated that blending concentrate streams with municipal wastewater and treating the blended stream in a dedicated biological reactor can be an effective approach for destroying concentrated oxidants.

The results of this work indicate that perchlorate-laden concentrates combined with municipal wastewater may effectively be treated using a fixed-bed biological process.