Ammonia removal by air stripping for reject water from advanced sludge dewatering process

Reject water from advanced sludge dewatering process was characterized by high concentrations of ammonia nitrogen, high pH and high alkalinity. The effects of air-liquid ratio, temperature and stripping time on the removal of ammonia nitrogen from the reject water were investigated, and the phenomena of pH decrease and scaling during the stripping process were analyzed. High pH and high alkalinity of the reject water were conducive to the progress of stripping, while the increase of air-liquid ratio and temperature could both improve the stripping efficiency. Ammonia air stripping also results in the simultaneous decrease of pH and Ca²⁺ concentration. The decrease of pH was in favor of subsequent biological treatment of the reject water, while the latter decrease caused the precipitation of CaCO₃ in the stripping equipment.