TRIHALOMETHANES FORMATION IN WATER TREATED WITH CHLORINE DIOXIDE

Formation of trihalomethanes (THMs) was investigated in water treated with chlorine dioxide (ClO2) and/or chlorine (Cl-2) where humic acid ( HA) was used as THMs precursors. When ClO2 was used as the only disinf ectant, no THMs were detected in bromide-free water; while only CHBr3 was formed in water containing bromide ion because ClO2 could oxide br omide to form hydrobromous acid which subsequently reacted with HA, an d the yield CHBr3 increased with bromide concentration and ClO2 dosing . When water was treated with ClO2 combined with Cl-2, only CHCl3 was formed in the absence of bromide, however, all four species of THMs we re formed in the presence of bromide; the THMs formation potential dec reased gradually with an increase in the ratio of ClO2 to Cl-2 because ClO2 reacted with HA to render them unreactive or unavailable for THM s production. When water (with or without bromide ion) was irradiated by light, the yield of THMs was increased as a function of irradiation time to a maximum, and thereafter decreased markedly; the possible me chanism is that irradiation could activate the THMs precursors in HA, and at the same time destroy the reactivity of ClO2 or Cl-2. The same results could be collected from natural water treated by ClO2 with or without irradiation. Copyright (C) 1996 Elsevier Science Ltd