EDR generates a contaminantconcentrated residual stream that, under current EPA regulations, could be discharged to the sewer system. However, Magna, in partnership with the local industry responsible for the original perchlorate contamination, opted to seek a method that would remove perchlorate from the brine stream prior to sewer discharge, thereby eliminating future environmental contamination.
A novel approach to treating perchlorate-laden residuals streams, developed by Carollo, involves blending the residuals stream with scalped municipal wastewater followed by treatment in a fixed-bed bioreactor (Biodestruction of Blended Residual Oxidants or BIOBROx). The BIOBROx process eliminates perchlorate (or any other oxidant such as nitrate, bromate, or selenate) from the residuals stream prior to sewer discharge.

In effect, blending the residuals stream with municipal wastewater decreases the dissolved oxygen (DO) concentration and salinity of the untreated stream (i.e., increases degradation kinetics) and eliminates the need to add substrate or a bacterial seed to the bioreactor system. As a result, reactor volumes and consumable costs are minimized and process stability improves.
The US EPA funded a seven-month pilot study at Magna’s Barton Well Field in 2004-2005 to demonstrate the efficacy of the BIOBROx process for removing perchlorate from an EDR concentrate stream. An EDR pilot plant was operated to remove perchlorate, arsenic, and TDS from groundwater, and the resulting concentrate stream was blended with scalped municipal wastewater and treated in a fixed-bed bioreactor.

Testing showed that using an empty-bed contact time (EBCT) of 10 minutes and a 1.5:1 wastewater flow to EDR concentrate flow blend ratio, sustained perchlorate removal to below detection was achieved in the fixed-bed bioreactor. The associated required reactor volume would be a small fraction of the volume required by “conventional” biological residuals treatment systems, and no consumables would be required. The data also demonstrated that the system was robust with respect to process upsets and seasonal temperature variation.
Based on the success of the pilotscale study, Magna has chosen to build a 4.5-mgd EDR + BIOBROx facility to treat their groundwater. Carollo has been retained for design and construction management for this project, which began in December 2005.
This work has shown that the BIOBROx process provides an efficient alternative to residuals disposal that can be considered for post-treatment of separationbased oxidant treatment processes such as EDR, ion exchange, and reverse osmosis.