From black water to flushing water: potential applications of chlorine-mediated indirect electrooxidation for ammonia removal

Removing ammonia from black water is one of the most urgent issues before it can be recycled as flushing water. In this study, an electrochemical oxidation (EO) process with commercial Ti/IrO2-RuO2 anodes to treat black water could remove 100% of different concentrations of ammonia by adjusting the dosage of chloride. Through the relationship between ammonia, chloride, and corresponding the pseudo-first-order degradation rate constant (K-obs), we could determine the chloride dosage and predict the kinetics of ammonia oxidation based on initial ammonia concentration in black water. The optimal N/Cl molar ratio was 1:1.8. The difference between black water and the model solution in terms of ammonia removal efficiency and oxidation products was explored. A higher chloride dosage was beneficial for removing ammonia and shortening the treatment cycle, but it also led to the generation of toxic by-products. Especially HClO and ClO3- generated in black water were 1.2 and 1.5 times more than the synthesized model solution under 40 mA cm(-2). Through SEM characterization of electrodes and repeated experiments, the electrodes always maintained a high treatment efficiency. These results demonstrated the potential of the electrochemical process as a treatment method for black water.

Automated summary

In this study, an electrochemical oxidation (EO) process using commercial Ti/IrO2-RuO2 anodes was employed to remove ammonia from black water. By adjusting the dosage of chloride, 100% removal of ammonia was achieved. The relationship between ammonia, chloride, and the degradation rate constant (K-obs) was used to determine the optimal chloride dosage and predict ammonia oxidation kinetics. The electrochemical process showed potential as a treatment method for black water, but the high chloride dosage also resulted in the generation of toxic by-products.