Dissolved organic nitrogen removal from reclaimed water by enhanced coagulation, ozonation, and biodegradation

Abstract

The presence of dissolved organic nitrogen (DON) in reclaimed water can pose adverse effects in water reuse practices, serving as a precursor of carcinogenic nitrogenous disinfection by-products (N-DBPs) and promoting membrane fouling. This study investigated DON removal by enhanced coagulation, ozonation, and ozonation/biodegradation at the lab and pilot scales. In the lab, enhanced coagulation by polyaluminum chloride (PACl) (60 mg/L) resulted in 46 ± 4 % DON removal. Lab-scale ozonation resulted in about 50 % reduction in DON over 2 h with a constant total nitrogen concentration. Biodegradation studies revealed <15 % DON removal, but ozonation combined with biodegradation achieved >30 % DON removal. At the pilot scale, enhanced coagulation by 56 mg/L of PACl plus 4 mg/L aluminum chlorohydrate resulted in 36 ± 8 % and 27 ± 9 % DON removal from secondary and filter effluent, respectively. Pilot-scale ozonation followed by biological active carbon (BAC) removed DON by 40 ± 6 % and 42 ± 5 %, respectively, from secondary and filter effluent. Dissolved organic carbon was also significantly removed by enhanced coagulation (23 ± 7 % and 20 ± 13 % from secondary and filter effluent, respectively) and by ozonation/BAC (39 ± 6 % and 39 ± 3 % from secondary and filter effluent, respectively) treatment.