Statistical analysis and optimization of ammonia removal from landfill leachate by sequential microwave/aeration process using factorial design and response surface methodology

The application of microwave (MW) radiation followed by aeration (A) for the purpose of ammonia removal from both synthetic solutions and landfill leachate was investigated in this study. 100 mL of synthetic solution or landfill leachate was subjected to MW radiation for 30, 45, 60, 90 and 120 s under 50 and 100% power output level and a pH of 10, 10.5 and 11. The samples were then aerated for 10 min. The initial, after MW application and final total ammonia nitrogen (TAN) were measured. Results confirmed that the sequential microwave/aeration process was an effective approach for removal of ammonia from aqueous systems. Maximum ammonia removal of 81.7% for 100 mL synthetic solution and 70% for 100 mL landfill leachate was achieved by applying 78 KJ microwave energy output and 10 min aeration. Factorial design and response surface methodology were applied to evaluate and optimize the effects of pH, MW energy level and microwave power output. When applying the same energy output to the batch tests, the effect of varying MW power output is negligible. For 100 mL synthetic ammonia solution, the optimum pH and MW energy output level for ammonia removal were 11 and 78 KJ and the maximum ammonia removal efficiency predicted for the synthetic solution is 76.3%. R2 of 0.941 indicates that the observed results fitted well with the model prediction.