Disinfection by-product formation from the monochloramination of chironomid larvae

Abstract

Formation of disinfection by-products (DBPs), including dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), chloroform (TCM), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), chloropicrin (TCNM) and chloral hydrate (CH), from monochloramination of chironomid larvae was investigated at different contact times, pH levels and temperatures. Increased monochloramine dosage and prolonged reaction time resulted in an increase in most DBPs. Furthermore, the concentrations of TCAN, DCAN and CH initially increased over time before reaching a plateau. This is because of the hydrolysis of functional groups and the function of NH2Cl. The concentrations of DCAA, TCAA and TCM decreased as pH was increased from 5 to 10, and TCAN, DCAN and CH were not detected when the pH exceeded 8. As for TCNM, their concentration increased as the pH increased from 5 to 7, following a subsequent decrease at higher pH values. High temperatures led to higher DCAN and TCAN concentrations, while low temperatures resulted in higher TCNM and DCAA concentrations. Both high and low temperatures reduced the concentrations of TCAN and CH. Finally, concentrations of the four predominant DBPs (TCM, DCAN of DCAA and TCAA) all decreased as Cl/N ratio declined.