Phthalate and alkylphenol removal within wastewater treatment plants using physicochemical lamellar clarification and biofiltration

Abstract

Endocrine disrupting compounds (EDCs) have been found in surface waters worldwide. They are known for exerting adverse effects on animals of many species, including humans. EDCs comprise compounds of anthropogenic origin. They can enter waterways via either discharges from wastewater treatment plant (WWTPs), combined sewer overflows (CSO) or atmospheric deposition. In this work, the fate and removal of four phthalates and two alkylphenols: Diethyl phthalate (DEP), Di-n-Butyl phthalate (DnBP), Butyl Benzyl phthalate (BBP), Di-(2-ethylhexyl) phthalate (DEHP), nonylphenol (NP) and octylphenol (OP) were investigated within a wastewater treatment plant (WWTP) using lamellar clarification and biofiltration. This plant receives about 240,000 m 3 d -1 of wastewater. The whole treatment process comprises: screening, grit removal, primary sedimentation using coagulant and flocculant, followed by biofiltration units. Phthalates and alkylphenols were monitored at three locations, including raw sewage, before primary treatment, decanted effluents, before biological treatment, and final effluents, just before discharge to receiving waters. Nine campaigns were performed in 2011 during different seasons. In raw wastewater, DEHP was the major compound (32.42 to 71.88, median 42.95 μg.l -1), followed by DEP (7.00 to 36.03, median 21.00 μg.l -1) and NP (4.08 to 10.63, median 5.95 μg.l -1). Other compounds averaged few μg.l -1. During the WWTP treatment, DEP becomes major contaminant (0.46 to 6.77, median 2.95 μg.l -1), followed by DEHP (0.95 to 6.43, median 2.30 μg.l -1) and NP (0.31 to 1.36, median 0.63 μg.l -1). Contaminant removal depends on the physicochemical characteristics of the compounds. For example, for lamellar clarification, removal efficiency was found to be strongly dependent to log Kow and, hence, to be highly correlated with their sorption coefficient (Kd). As a consequence, compounds with high log Kow (>3) were removed to a significant extent. DEHP was highly removed by lamellar clarification (68.8%), followed by BBP (61.5%) and NP (51.0%). Besides, DEP (log Kow < 3) was slightly removed (13.8%). During biofiltration, both hydrophilic and hydrophobic compounds were equally eliminated. Therefore, DEP (87.3%), OP (88.0%) and DEHP (81.9%) were mostly removed during biological treatment. © 201 WIT Press.