h i g h l i g h t sThe levels of organophosphate esters (OPEs) in Henan province were lower than those of South China. Chlorinated OPEs were predominant in sewage sludge. Triphenyl phosphate (TPhP) level in sewage sludge depends on wastewater characteristics. The levels of OPEs in sewage sludge were independent of the total organic carbon (TOC) and solid retention time. . Tris(2-chloroethyl) phosphate (TCEP), tris(2-butoxyethyl)phosphate (TBEP), and tris(2-chloroiso-propyl)phosphate (TCPP) were found to be predominant, with concentrations ranging from 2.50 to 203, 1.60 to 383, and 6.70 e161 mg kg À1 , respectively. The potential factors affecting OPE levels in sewage sludge, such as wastewater source, sludge characteristics, operational conditions, treatment techniques, and total organic carbon (TOC) of sludge in WWTPs were investigated. The results indicated that the total concentration of OPEs in sewage sludge has no significant relationship with the individual parameters (p > 0.05). However, significant correlations were found between triphenyl phosphate (TPhP) level and treatment capacity (R ¼ 0.484, p < 0.05), processing volume (R ¼ 0.495, p < 0.05), and serving population (R ¼ 0.591, p < 0.05). Furthermore, the relationship between treatment techniques and the total concentration of OPEs in sewage sludge was also investigated in this study, and the results illustrated that the levels of OPEs in sludge were independent of the solid retention time (SRT).

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