ABSTRACT
Preloading of Background Organic Matter (BOM) onto Granular Activated Carbon (GAC) is commonly found to reduce the adsorption of target compounds, such as pesticides. Preloading of BOM is the adsorption of these compounds onto GAC before the adsorption of target compounds. Ozonation of filter influent may reduce this preloading, because it enhances biodegradability, and reduces adsorbability and molecular mass of an important part of BOM compounds.
In this study, the breakthrough of atrazine was determined from the Short Fixed Bed (SFB) tests done with virgin and preloaded GAC. Adsorption capacity of (pulverized) activated carbon for atrazine was determined from adsorption isotherms. Rate-coefficients for atrazine’s external and internal mass transfer were determined by fitting the breakthrough of atrazine in the SFB tests with the Plug Flow Homogenous Surface Diffusion model. To allow comparisons, all tests were done in the same ultra-pure water.
The SFB tests confirmed that preloading of BOM from pretreated Rhine River water speeds up the breakthrough of atrazine. Ozonation reduces this adverse effect of preloading: delayed breakthrough of atrazine was observed in the tests with GAC preloaded with ozonated rather than non-ozonated water.
All three parameters that govern the adsorption of atrazine, i.e. the adsorption capacity of activated carbon for atrazine, and the external as well as the internal mass transfer rate of atrazine, are reduced due to preloading. Ozonation reduces this adverse effect of preloading: each of these three parameters was found higher for GAC preloaded with ozonated rather than non-ozonated water.
