title: Elucidating competitive adsorption mechanisms of atrazine and NOM using model compounds.
abstract: Based on the relative adsorbability of natural organic matter (NOM) fractions with different molecular weights (MWs), two model compounds, poly(styrene sulfonate) (PSS) (nominal MW=1800 Dalton) and p-dichlorobenzene (DCB), were chosen to study the competitive effect of large and small NOM molecules on atrazine adsorption by two powdered activated carbons (PACs) with different pore size distributions. Both isotherm and kinetic tests of atrazine adsorption were conducted using fresh PAC and PAC preloaded with the model compounds. 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 was found to significantly reduce atrazine adsorption capacity but to have no effect on atrazine adsorption kinetics. In contrast, the effect of PSS-1.8k on atrazine adsorption capacity was very small. Furthermore, during simultaneous adsorption, PSS-1.8k had no effect on atrazine surface diffusion. However, preloading PAC with PSS-1.8k lowered the atrazine surface diffusion coefficient, D(s), by more than three orders of magnitude; D(s) decreased with increasing solid phase PSS-1.8k concentration. 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.
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 N Mathews Avenue, Urbana, IL 61801, USA.
authors.forename: Qilin
authors.initials: Q
authors.lastname: Li
authors.forename: Vernon L
authors.initials: VL
authors.lastname: Snoeyink
authors.forename: Benito J
authors.initials: BJ
authors.lastname: Mariãas
authors.forename: Carlos
authors.initials: C
authors.lastname: Campos
mesh_terms: D000327:Adsorption; D001280:Atrazine / Q000737:chemistry*; D002606:Charcoal / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D008970:Molecular Weight; D009930:Organic Chemicals / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*
chemical_list: D009930:Organic Chemicals; D014874:Water Pollutants, Chemical; D014867:Water; D002606:Charcoal; D001280:Atrazine