Biodegradation of di-(2-ethylhexyl) phthalate in sewage sludge

Di-(2-ethylhexyl) phthalate (DEHP) is widely used as a plasticizer in the production of polyvinyl chloride to impart flexibility to the product. Because of its mutagenicity and carcinogenicity, the presence of DEHP in sludge limits the application of sludge as a soil fertilizer. In this study, sludges were collected from three sewage treatment plants and thirteen wastewater treatment plants of different industries in Taiwan. A supercritical fluid extraction (SFE) was first established as an effective method for determining the concentration of DEHP in sludge. Laboratory-scale land-simulated experiments were performed to investigate the biodegradation of DEHP in sludge under various conditions (moisture, temperature, sunlight and ventilation). DEHP was found in aerobically and anaerobically digested sludges and their values significantly exceeded the restricted concentration of DEHP for sludge land application. DEHP was found to degrade in sludge under the conditions of good ventilation, sufficient sunlight and proper moisture. The indigenous microorganisms in the sludge appeared to dominate the biodegradation of DEHP in sludge. However about 70% of DEHP remained in sludge after 189 d indicating that DEHP is persistent in the environment.