Nitrate removal using a mixed-culture entrapped microbial cell immobilization process under high salt conditions

Brine wastes resulting from the regeneration of exhausted ion exchange resins require further treatment for final disposal. In this study, a mixed-culture entrapped microbial cell immobilization (EMCI) process for nitrate removal from brine wastes was examined. Because of the presence of elevated concentrations of sodium chloride or sodium bicarbonate in the brine waste, the effects of high salt concentrations on the mixed-culture EMCI process and sludge production were investigated. Denitrification capacity of the mixed-culture EMCI process was found to be slightly affected at sodium chloride or sodium bicarbonate concentrations up to 20 g/l. The process generally performs better than other biodenitrification processes in the presence of salt concentration typically required for the regeneration of ion exchange resins. The cell yields were estimated to be 0.11 gSS produced/g COD removal or 0.36 g SS produced/g nitrate-N removed. The mixed-culture EMCI process was found to be an economical alternative for treatment of brine wastes and exhibits a great potential to be coupled with an ion exchange process for complete nitrate removal. The proposed coupling represents a closed-loop treatment in which the brine waste from ion exchange processing is denitrified by the mixed-culture EMCI process and the denitrified effluent is recycled to regenerate exhausted resins, resulting in the reduction of salt requirements for regeneration.