Dissolved Organic Nitrogen (DON) Transformations in Typical Orbal Oxidation Ditch

Dissolved organic nitrogen (DON) can form toxic nitrogenous disinfection byproducts (N-DBPs) relatively readily. In this way, DON content can have profound effects on the effluent of wastewater treatment plants (WWTP). This study describes a comprehensive investigation of variations in dissolved organic nitrogen levels in orbal oxidation ditches. The results showed that DON was increased gradually from 0.71 to 1.14 mg/l along anaerobic zone, anoxic zone, aerobic zone 1 and aerobic 2. We performed molecular weight fractionation of DON in one anaerobic zone and one aerobic zone (aerobic zone 2). We found far fewer small-molecular-weight DONs (20 kDa). This variation may have been caused by the release of different types of soluble microbial products (SMPs) during biological processes might be a main reason for the DON variation in orbal oxidation ditch. These SMPs contained both tryptophan-like and aromatic protein substances, as indicated by three-dimensional excitation-emission matrix (EEM) analysis.