Abstract:The simultaneous removal of ammonia and nitrate nitrogen is a challenging process in the treatment of recirculating aquaculture systems. This study first analyzed the effects of current density, plate area ratio, plate spacing, and initial pH on the removal rates of ammonia and nitrate nitrogen by a single-factor experiment. To understand the effects of different influencing factors on the efficiency of nitrogen removal, four-factor and three-level response surface experiments were designed on the basis of the central combination principle of Box-Behnken in Design-Expert software. Subsequently, the reaction conditions for the simultaneous removal of ammonia and nitrate nitrogen were optimized using a response surface model. Finally, the optimized reaction conditions were evaluated using verification experiments. In the single-factor experiments, we found that the changes in the current density, plate area ratio, plate spacing, and initial pH had little effect on ammonia and nitrate nitrogen removal. The removal rate of ammonia is always > 80% in the given reaction conditions, whereas the changes in reaction conditions significantly affected the removal rate of nitrate nitrogen, which ranges from 29.8% to 80.9%. The constructed response surface model showed that the regression coefficient (R2) was 0.9340 and the correction coefficient (R2) was 0.8681, which showed that the model has good accuracy. We obtained the optimal reaction conditions using the response surface model: current density was 25.6 mA/cm2, plate area ratio between cathode and anode was 1.6:1, plate spacing was 2.5 cm, and initial pH was 6.6. Experimental verification under the reaction conditions proved that the removal rate of nitrate nitrogen could reach up to 81.5% and the removal rate of ammonia up to 87.3%. This experiment showed that electrochemical treatment can effectively achieve the simultaneous removal of ammonia and nitrate nitrogen and that application of the response surface model can improve the nitrogen removal efficiency of electrochemical treatment in aquaculture wastewater.
