Removal of neutral chloroacetamide herbicide degradates during simulated unit processes for drinking water treatment.

ABSTRACT

Four chloroacetamide herbicides and 20 neutral chloroacetamide derivatives (known to occur as their environmental degradates) were subjected to simulated drinking water treatment (coagulation, oxidation and adsorption). Coagulation with alum and ferric chloride, at doses for optimum turbidity removal, provided little to no (<10%) removal of parent herbicides or neutral degradates. Chlorination with 6 mg/L applied free chlorine for 6 h was able to achieve 100% removal of those degradates lacking an acetanilide substituent; compounds possessing this functional group exhibited low (0-16%) removal efficiencies. Products were generally not identified, except in the case of dimethenamid and its deschloro degradate, both of which formed a single ring-chlorination product on their ready reaction (84% and 96% removal, respectively) with aqueous chlorine species. Treatment with ozone at an applied dose of 3 mg/L for 30 min proved effective (60-100%) at transforming all of the compounds under investigation to unidentified products. The parent herbicides and neutral degradates underwent adsorption by powdered activated carbon (PAC). Adsorption capacities (Freundlich K constants) correlated with K(ow) values.