[Competitive sorption of mixed organic pollutants by soils]

Binary sorption equilibria were measured using three different loading methods: METHOD (1): Naphthalene loaded before phenanthrene; Method (2): Both Solutes loaded simultaneously; Method (3): Naphthalene loaded after phenanthrene. Each having 110 reactors and 10 levels of initial concentrations for both tested organic solutes. This is very different from previous studies which employed one single initial concentration of the primary solute and multiple concentration levels of the competitor and loaded both solutes simultaneously. Results indicate that the adsorption behavior of the same solute on the same sorbent with competing solute is distinctly different from its single adsorption behaviors. Naphthalene isotherm becomes more linear as phenanthrene concentration increases in the binary systems tested using all three loading methods. In contrast, phenanthrene isotherm remains nonlinear when it was loaded after or loaded simultaneously with naphthalene. It becomes more linear as a function of naphthalene concentration only when phenanthrene was loaded before naphthalene. The Koc values decrease as a function of competing solute concentration (c(e)), and approach to the lowest value when this c, is about 0.5 Sw. IAST provides better predictions for the sorption only when the competing solute is at lower c(e)(< 0.01 Sw). Large-size and more hydrophobic phenanthrene competes favorably with the small-size and relatively less hydrophobic naphthalene, and the heterogeneity of natural organic matter associated with the soil may have strong influence on the competitive phenomena between the tested solutes.