AWWA WQTC55210

Two model compounds, poly(styrene sulfonate) (MW = 1,800 Dalton) (PSS- 1.8k) and p-dichlorobenzene (DCB), were selected to simulate the competitive effects of two important molecular weight fractions of natural organic matter (NOM) on atrazine adsorption. Two types of powdered activated carbon (PAC) were used. The effects of both simultaneous adsorption and preloading with model compounds on adsorption equilibrium and kinetics were investigated. The model compounds were found to affect atrazine adsorption through two different mechanisms due to their size difference: direct competition for sites by p-DCB, and pore constriction/blockage by PSS-1.8k. p-DCB significantly reduced atrazine adsorption capacity but had no effect on atrazine surface diffusion rate. The effect of PSS-1.8k on atrazine adsorption capacity was very small, but preloading PAC with PSS-1.8k lowered the atrazine surface diffusion coefficient by several orders of magnitude. The pore size distribution of the PAC was found to play an important role in competitive adsorption. A high mesopore surface area could alleviate pore blockage significantly. Includes 11 references, table, figures.