The ozonation of organic halide precursors: effect of bicarbonate

A laboratory study of the effect of bicarbonate on the ozonation of organic halide precursors in fulvic acid solutions and in a raw drinking water was conducted. The experimental variables were bicarbonate concentration, ozone dose and pH of chlorination. Results are expressed in terms of trihalomethane (THM), total organic halide (TOX), trichloracetic acid, dichloroacetic acid, trichloroacetone and dichloroacetonitrile precursor concentrations. Kinetic studies showed that bicarbonate slowed the decomposition of ozone in the presence of fulvic acid, and thereby, led to a greater degree of destruction of u.v.-absorbing substances. Similarly, precursor destruction increased with increasing bicarbonate concentrations in the range of 10−4spd 10−2 M. Precursor destruction was greatest when chlorination was performed at low pH. At high pH's of chlorination, some precursor enhancement was noted, especially in the absence of bicarbonate. Results are interpreted both from a mechanistic standpoint and with respect to their applicability to water treatment practice.