Adsorption of Phthalates onto Nanofiltration Membranes: Effect of Solution Chemistry

Adsorption is ubiquitous during nanofiltration filtering which leading to overestimation of retention with adsorption interpreted as some of the initial retention. The adsorption of four phthalates (PAEs) (dietyl (DEP), di-n-butyl (DBP), dicyclohexyl (DCHP) and di-2-ethylohexyle (DEHP)), in different water matrices (Milli-Q water, simulated water and river water) by nanofiltration (NF) was examined using two types of nanofiltration membranes (NF90 and NF70). PAEs was added to different water matrices with concentration of 100 mu g/L. The adsorption removal was calculated through mass balance during laboratory-scale cross-flow NF membrane rig working. The results showed that adsorption of PAEs on membranes was related to membrane pore size, substance characteristics, and coexisting nature organic matter (NOM). No significant effect of the PAEs concentration was observed. The order of adsorption removal in all water matrices was DCHP > DEHP > DBP > DEP. In Milli-Q water, the adsorption of PAEs decreased with increase of pH. The humic acid (HA) added in the simulated water increased the adsorption of PAEs on NF90 but decreased that on NF70, and the ions (K+, Ca2+) added in the simulated water affected the adsorption by influencing membrane structure, HA structure and interaction between membrane and HA, and the same result was obtained in the river water.