Ozonation and Competitive Adsorption of Background Organic Matter 1

The general aim of the research presented in this chapter is to quantify the extent to which ozonation increases GAC’s adsorption capacity for atrazine, due to reduced adsorbability of ozonated Background Organic Matter (BOM). GAC’s capacity for atrazine was determined in ozonated and non-ozonated pretreated Rhine River water, both from the experiments and by modeling the competitive adsorption of BOM and atrazine. Experiments were conducted for the range of initial atrazine concentrations that allow accurate performance of an isotherm test (C₀ > 3 μg/l). These concentrations are much higher than the concentration of 0.3 μg/l, which is the highest atrazine concentration observed in pretreated Rhine River water in the period 1991–1995. Therefore, the Ideal Adsorbed Solution Theory (IAST) was applied to predict the capacity for C₀ of 0.3 μg/l. The adsorption parameters of BOM required to model its competitive adsorption by the IAST were determined by the Fictive Component Adsorption Analysis (FCAA) method and by the Equivalent Background Compound (EBC) method.

Atrazine adsorption isotherms (C₀ of 3 μg/l and 30 μg/l), determined in ozonated and non-ozonated pretreated Rhine River water, clearly proved that GAC’s capacity for atrazine significantly increases due to reduced adsorbability of BOM. No significant difference was found between atrazine isotherms determined for ozone doses from 1 mg/l to 4 mg/l. The IAST-EBC and the IAST-FCAA methods predict that the equilibrium (C = 0.1 μg/l) adsorption capacity for atrazine in non-ozonated pretreated Rhine River water for C₀ of 0.3 μg/l is between 25% and 50% of the capacity obtained from the experiments done for the initial atrazine concentration of 3 μg/l.

The IAST-FCAA method, based on the analysis of DOC isotherms, was found not applicable for the prediction of the adsorption capacity for atrazine in ozonated water. The IAST-EBC method predicts that the equilibrium (C = 0.1 μg/l) adsorption capacity for atrazine is about two times higher in ozonated rather than non-ozonated pretreated Rhine River water.