Combination of a Highly Efficient Biological System and Visible-Light Photocatalysis Pretreatment System for the Removal of Phthalate Esters from Wastewater

Abstract

To save energy and increase treatment efficiency, a visible-light photocatalysis system was coupled with a biological treatment system for the continuous removal of phthalate esters (PAEs) from synthetic wastewater. Di-(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), and dimethyl phthalate (DMP) were treated using an iodine-doped TiO2 photocatalyst, and the reactions followed first-order kinetics (similar to ultraviolet TiO2 photocatalysis) to produce phthalic acid as an intermediate product. The effects of various operating factors, such as PAE concentrations, pH, light intensity, retention time (RT), and the coexistence of PAEs, on individual PAE removal were investigated. DEHP-degrading bacteria were isolated from DEHP-contaminated soil, purified through serial dilution, and then identified through DNA sequencing. The results indicated that the optimal operating conditions for PAE removal with a visible-light photoreactor were a pH of 5, a temperature of 30 °C, a light intensity of 300 W, and an RT of 5.5 min. DEHP, which contains long and branched chains, was more difficult to degrade than DMP, which contains short alkyl side chains. Pseudomonas sp. was the most dominant bacteria in the DEHP-contaminated soil and was inoculated in a packed bed reactor (PBR) for complete PAE degradation. The effluent containing PAEs was pretreated using the visible-light photoreactor under a short RT. This treatment resulted in the effluent becoming biodegradable, and PAEs could be completely removed from the treated effluent by using the PBR. The coupled photobiological system achieved removal efficiencies of 99.6%, 99.9%, and 100% for DEHP, DBP, and DMP, respectively, during the continuous treatment. The results of this study indicate that the developed coupled system is an effective, energy-saving, and cost-efficient tool for treating wastewater containing PAEs.