Impacts of drinking water pretreatments on the formation of nitrogenous disinfection by-products

The formation of disinfection by-products (DBPs), including both nitrogenous DBPs (N-DBPs) and carbonaceous DBPs (C-DBPs), was investigated by analyzing chlorinated water samples following the application of three pretreatment processes: (i) powdered activated carbon (PAC) adsorption; (ii) KMnO4 oxidation and (iii) biological contact oxidation (BCO), coupled with conventional water treatment processes. PAC adsorption can remove effectively the precursors of chloroform (42.7%), dichloroacetonitrile (28.6%), dichloroacetamide (DCAcAm) (27.2%) and trichloronitromethane (35.7%), which were higher than that pretreated by KMnO4 oxidation and/or BCO process. The removal efficiency of dissolved organic carbon by BCO process (76.5%) -was superior to that by PAC adsorption (69.9%) and KMnO4 oxidation (61.4%). However, BCO increased the dissolved organic nitrogen (DON) concentration which caused more N-DBPs to be formed during subsequent chlorination. Soluble microbial products including numerous DON compounds were produced in the BCO process and were observed to play an essential role in the formation of DCAcAm in particular.

► BCO pretreatment process increased DON levels and halogenated N-DBPs formation.
► More N-DBP precursors were removed by PAC adsorption itself than KMnO4 oxidation.
► KMnO4 can improve conventional process performance on removing N-DBP precursors.
► Hydrophilic organics played a critical role in the halogenated N-DBPs formation.
► DON compounds produced from BCO process is a class of important N-DBP precursors.