Partition of six phthalic acid esters in soluble and solid residual fractions of wastewater sludges

Distributions of six priority controlled Phthalic acid esters (PAEs), including di-methyl phthalate (DMP), di-ethyl phthalate (DEP), di-butyl phthalate (DBP), benzyl butyl phthalate (BBP), di-(2-ethylhexyl) phthalate (DEHP), di-octyl phthalate (DOP) were studied based on soluble and insoluble fractions of sludge samples collected at four wastewater treatment plants in Shanghai, China. Three sludge samples comprised hydrophilic colloidal particles of high protein contents and low aromaticity. Meanwhile, these sludges contained DBP of 4.2-5.7 mg kg-1 dried solids (ds) and DEHP of 21.1-55.6 mg kg-1 ds, respectively. Another sludge sample comprised mainly hydrophobic colloidal particles of humic substances and high aromaticity. It contained DBP of 1.18 mg kg-1 ds and DEHP of 2.89 mg kg-1 ds, respectively. The most abundant components noted amongst the six studied PAEs were DBP and DEHP, which mostly associated with the insoluble fraction of sludge. Specifically, the DBP and DEHP in insoluble fraction (the solid residual phase) accounted for 89.8-98.2% and 88.6-99.6% of those in the whole sludge. The partition coefficients of DBP and DEHP for the soluble and insoluble fractions of sludge correlated with the suspension SUVA254, suggesting that interaction between π-electrons of DBP or DEHP and those of organic particulates in suspension contributes most of the sorption processes. © Taylor & Francis, 2008.