Total halogenated organic (TOX) measurement in ground waters treated with hypochlorite and with chlorine dioxide. Initial results of an experiment carried out in Emilia-Romagna (Italy)

We examined ground waters (from wells) which feed the distribution systems of some municipalities in the provinces of Parma and Reggio Emilia (Italy), before and after treatment with hypochlorite and chlorine dioxide. During our tests, THMs, TOX, free and combined chlorine, chlorine dioxide and chlorite were measured according to the American Standard Methods. These parameters were also measured in the waters of wells treated with known concentrations of hypochlorite and chlorine dioxide under the same experimental conditions in our labs. Before treatment THMs were always absent, while very low levels of TOX were always measured. THMs were not constantly present in treated waters: 54% in waters treated with hypochlorite, 4% after treatment with chlorine dioxide. Mean concentrations of THMs were 0.34 μg/l with hypochlorite and 0.073 μg/l with dioxide. TOX showed a fourfold increase with hypochlorite, from 5.9 to 22.7 μg/l and a twofold increase with dioxide, from 6.8 to 14.5 μg/l. Experimental tests conducted under controlled conditions confirmed this trend. TOX measurement, together with THMs measurement, seems to be a useful parameter for a more complete assessment of water quality of ground waters and for a more complete control of water disinfection processes.