Efficient degradation of inorganic nitrogen in mariculture wastewater by electrochemical methods

The effective treatment of inorganic nitrogen in mariculture wastewater is important to ensure the quality and yield of cultured organisms, and protect the marine environment. The concentration of inorganic nitrogen, i.e. NO3--N, NO2--N and NH4+-N, reaches to the first-level of Water Drainage Standard for Seawater Mariculture (SC/T 9103-2007) after electrochemical treatment with a double-chamber cell (Ti/RuO2-IrO2 anode and Ni cathode) in this study. The results showed that the reductions of NO3--N and NO2--N on Ni cathode are easier than Ti and Pt cathodes. The removal rate and products (NH4+-N and NO2--N) selectivity in degradation of NO3--N using Pt and Ni cathodes are much higher than Ti cathode. However, the energy consumption of Pt cathode is much higher than Ti and Ni cathodes. With the potential shifted to negative using Ni cathode, both the removal rate of NO3--N and the selectivity of NH4+-N increase, while the selectivity of NO2--N decreases. The lowest energy consumption of Ni cathode is achieved under the potential of NO3--N reduction peak, i.e. -1.25 V. Most of NH4+-N is oxidized indirectly on Ti/RuO2-IrO2 anode through active chlorine, and 1.30 V is the optimum potential. NO2--N is oxidized to NO3--N on Ti/RuO2-IrO2 anode, which can be introduced into cathode chamber again for further electrolyzing. The final product is N-2 for treatment of mariculture wastewater in the double-chamber cell with Ni cathode and Ti/RuO2-IrO2 anode.