Electrochemical Treatment of Recirculating Aquaculture Wastewater Using a Ti/RuO2-IrO2 Anode for Synergetic Total Ammonia Nitrogen and Nitrite Removal and Disinfection

Abstract

Wastewater treatment and biosecurity are essential for intensive recirculating aquaculture system (RAS) production. In this study, the viability of the electrochemical process using a Ti/RuO2-IrO2 anode for synergetic total ammonia nitrogen (TAN) and nitrite removal and disinfection of semi-commercial RAS wastewater was evaluated. During the electrochemical oxidation process, the effects of the applied current density, sodium chloride concentration, and initial pH on the removal of TAN and nitrite were investigated. Experiment results indicated that under the conditions of 1.7 g L-1 sodium chloride concentration and 60 min electrolysis time, TAN removal efficiencies reached 78% at a current density of 60 mA cm-2, while nitrite removal efficiencies reached more than 95% at a current density of 30 mA cm-2. TAN removal due to an indirect oxidation mechanism followed second-order kinetics, while nitrite removal was described by pseudo-first-order kinetics in low-salt water (1.7 g L-1). The kinetics for electro-oxidation of TAN and nitrite affected by the current density were expressed as kTAN = 1.0 x 10-5 J-0.0002 and kNO2- = 1.9 x 10-3 J-0.0041, respectively. For disinfection, the active chlorine in situ generated by electrochemical treatment caused and inactivation. The results showed that the two objective pathogens can be sterilized rapidly, which indicated that no extra treatment for disinfection was needed. Finally, a comparison was made of the energy consumption in this study with those in the literature. This study showed that the Ti/RuO2-IrO2 anodic oxidation process has a potential for sustainable RAS wastewater treatment.