Evaluation and reduction of THMs, DCAN and TCNM formation potential from chlorination and chloramination of verapamil

Abstract

Verapamil (VRPM) is a kind of pharmaceuticals that widely used over the world and frequently detected in wastewater treatment plants effluents and downstream river waters. VRPM also can be a kind of precursor for carbonaceous (C-) and nitrogenous (N-) disinfection by-products (DBPs) during disinfection in water treatment. The formation of trihalomethanes, dichloroacetonitrile (DCAN) and trichloronitromethane (TCNM) from chlorination and chloramination of VRPM was firstly examined and compared in this study. The impacts of chlorine or monochloramine dose, contact time, pH, bromide, chloramination mode, temperature, and pre-oxidation were evaluated as well. It was found that chloroform (CF) was the major DBPs during chlorination, while N-DBPs became dominant in chloramination.The yields of CF, DCAN and TCNM were increased significantly with increasing monochloramine dose. Unlike CF and DCAN, the yield of TCNM increased firstly and then deceased with contact time. The effect of pH on DBPs formation was significant both for chlorination and chloramination of VRPM. Bromide was proposed to play an important role in DBPs formation during disinfection. Compared to ultraviolet/persulfate, ultraviolet/hydrogen peroxide was a better pre-oxidation to not only efficiently oxidize VRPM, but also significantly reduce DBPs formation.