Degradation of atrazine by manganese-catalysed ozonation: Influence of humic substances

A bench-scale, laboratory study has been undertaken on the ozonation of atr azine in the presence of manganese using a conventional gas bubble-contacti ng column. Manganese was present in solution either as Mn(II) or as in situ formed Mn(IV). The experimental results indicate that the presence of humi c substances has a substantial influence on the Mn-catalysed ozonation of a trazine. In the presence of a small amount of humic substances (e.g. 1 mg/l as DOG), the Mn-catalysed ozonation is obviously enhanced. However, with t he further increase of humic substance concentration, a negative effect of humic substances on the catalytic oxidation of atrazine is observed for bot h the cases of Mn(ll) and Mn(IV). It is proposed that Mn-catalysed ozonatio n of atrazine follows a radical-type mechanism. At low concentrations of hu mic substances, both the manganese species and the humic substances may ini tiate and promote the formation of hydroxyl radicals during ozonation which enhance the destruction of atrazine. However, at higher concentrations, hu mic substances may scavenge these highly reactive hydroxyl radicals, thus d ecreasing the oxidation efficiency of atrazine. (C) 1998 Elsevier Science L td. All rights reserved.