Resilient Nitrate Removal by a Biological Nitrate-Selective Ion Exchange (BIO-NIX) Process

Abstract

Nitrate violation is increasing globally due to substantial fertilization to feed the growing population. Biological denitrification (BIO) represents one of the major techniques in addressing nitrate contamination, but it lacks resiliency in handling system fluctuations. To improve the resiliency, we have demonstrated a biological nitrate-selective ion exchange (BIO-NIX) process for resilient nitrate removal, which differentiates from typical biologically regenerated ion exchange that requires intermittent interruption of regeneration. BIO-NIX combines a fixed-bed BIO column and a nitrate-selective ion exchange (NIX) column. Efficient denitrification (over 90%) was enabled by biofilms attached to a highly porous ceramic host material in the BIO column, and the effluent was polished by the NIX column to handle system fluctuations. To enable efficient denitrification, we designed a self-adjusted carbon-releasing system using a citrateloaded ion exchange column. The whole system operated for over two months under conditions of carbon shortage, influent nitrate surge, and flow rate jump; resilient nitrate removal to below 45 mg/L (MCL as NO 3 − ) was achieved without intermittent regeneration of the nitrate-selective resin. The BIO-NIX system is also retrofittable to a biologically regenerated NIX process (BIO-RNIX) to fully restore resin capacity if necessary. The demonstrated resiliency enables BIO-NIX to be deployed in various applications, especially in decentralized, rural areas.