Bioelectrochemical Denitrification for the Treatment of Saltwater Recirculating Aquaculture Streams

Maintaining low concentrations of nitrogen compounds (ammonium, nitrate and nitrite) in recirculating aquaculture waters is extremely important for a larger and healthier fish production, as well as for water discharge purposes. Although ammonium removal from aquaculture streams is usually done within a nitrifying step, nitrate removal via denitrification is still partially limited by the low organic matter availability. Therefore, an easy-to-operate autotrophic denitrifying bioelectrochemical system is herein proposed for the treatment of seawater aquaculture streams. The nitrate-containing synthetic stream flows sequentially through a biological denitrifying cathode (placed at the lower portion of a tubular reactor) and an abiotic anode (generating electrons and oxygen from water splitting, at the upper portion). Experimental results with synthetic seawater showed that the system reached denitrification rates of 0.13 ± 0.01 kg N m^–3 day^–1, operating with minimum ammonium and nitrite accumulation, as well as minimum chlorine formation in the abiotic anode, despite the high chloride concentration. There results support the technical potential for simultaneous bioelectrochemical denitrification and partial re-oxygenation of aquaculture waters either for recirculation or discharge purposes.