Effect Of Coagulation And Adsorption On Don Removal And Dbps Formation Potential In Municipal Wastewater Effluent

Municipal wastewater effluent has increasingly been used as reclaimed water and a source of water for downstream communities. Dissolved organic nitrogen (DON) in wastewater effluent can be a precursor of nitrogen disinfection by-products (N-DBPs), which has garnered recent attention. Our results indicated that: (1) the concentration of DON in the effluent was 1.95 mg/L, and the DON was primarily composed of soluble microbial products (SMPs) resulting from the process of biological treatment of sewage. (2) Approximately 20% of the DON could be removed using coagulants at a dosage of 120 mg/L, and almost 80% of the DON was eliminated by adsorption with activated carbon at a dosage of 0.5 g/L. Small molecular weight DON compounds (<6 kDa) comprised most of the DON and accounted for 74.34% of the total. After coagulation, the percent fraction of <6 kDa DON increased, while the fraction of >20 kDa DON decreased. However, adsorption resulted in an opposite trend, with large molecular weight DON increasing and small molecular weight DON decreasing. (3) Hydrophilic and hydrophobic DON comprised most of the DON, and accounted for 58.5% and 30.8% of the DON, respectively. The removal of hydrophilic DON (mean 12%) was lower than that of hydrophobic DON (mean 76%) after coagulation. In contrast, adsorption resulted in a greater removal of hydrophilic DON (mean 83%) than that of hydrophobic DON (mean 49%). (4) Coupling coagulation with adsorption prior to chlorination was the most effective means to lower the formation potential of disinfection by-products (DBPs). The formation potential of monochloro bromoacetonitrile was highest (41.3 mu g/L), while that of trichloroacetonitrile was the lowest (1.3 mu g/L). (5) Normalized excitation-emission area volumes (empty set(i,n)) were used to quantify 3-DEEM fluorescence. empty set(2,n) and empty set(4,n) of fluorescence regions II and IV were highest, and accounted for 23.38% and 46.83% of the total, respectively. SMPs were effectively removed by coagulation or adsorption, which was highlighted by the highest removal rate for empty set(4,n) compared with the other four empty set(i,n).