Formation of haloacetonitriles and haloacetamides and their precursors during chlorination of secondary effluents.

Abstract The formation of dichloroacetonitrile (DCAN), dichloroacetamide (DCAcAm) and trichloroacetamide (TCAcAm) during chlorination of secondary effluents was evaluated under different conditions. The formation of DCAN and DCAcAm increased, then decreased with increasing contact time and chlorine dose, while TCAcAm formation increased continually, exceeding DCAcAm formation after a relatively long contact time or in response to a relatively high chlorine dose (20–80 mg L −1 ). Increasing the sample pH from 6 to 9 reduced the formation of DCAN and TCAcAm, while DCAcAm formation was highest at pH 8. Precursors in the secondary effluent were characterized by separating the organic matter into several fractions using membrane filtration and XAD resins and then measuring the formation of DCAN, DCAcAm and TCAcAm from each fraction during chlorination. Dissolved organic matter (DOM) with a molecular weight less than 1 kDa dominated the formation of DCAcAm and TCAcAm. However, particle-associated DCAN precursors were detected in addition to potent DCAN precursors in the DOM fractions. Among the XAD fractions of DOM, the hydrophilic neutral fraction prevailed in the secondary effluent and produced the most DCAN, DCAcAm and TCAcAm per volume, and the hydrophilic basic fraction with a low organic content had the highest yields of DCAN, DCAcAm and TCAcAm on a DOC basis, so their dominant precursors were associated with hydrophilic matter.