Biodegradability of di-(2-ethylhexyl) phthalate by a newly isolated bacterium Achromobacter sp. RX

Di-(2-ethylhexyl) phthalate (DEHP) is a chemical plasticizer that has been commonly used in the manufacture of polyvinyl chloride. DEHP is one of the environmental pollution sources. In this study, a gram-negative strain RX bacterium utilizing DEHP as sole carbon source was isolated from activated sludge through screening test. This strain RX was identified as Achromobacter sp. RX based on its morphology, physiological properties and 16S rRNA gene sequence analysis. The results showed that the optimal conditions for the DEHP degradation were 30.0 °C and pH 7.0. The DEHP degradation induced by strain RX demonstrated nitrogen source dependent, while followed a decreasing degradation rate under the source of: NO₃^- > NH₄⁺ > NO₂^-. The biodegradability of Achromobacter sp. RX was enhanced with Masson pine seed powder as a co-metabolic substrate and Tween-80 as a solubilizing agent. Meanwhile, the degrading kinetics analysis was performed in the condition of DEHP as sole carbon source. The DEHP degradation curves fitted well with the first-order kinetic model at 50-300 mg/L of DEHP, with the half-life ranging from 13.0 to 16.4 h. During the biodegradation of DEHP, mono-(2-ehtylhexyl) phthalate (MEHP) was firstly generated through de-esterification, followed by the formation of phthalic acid and benzoic acid after further de-esterification of MEHP. Benzoic acid was finally mineralized to CO₂ and H₂O. The decontamination of DEHP-contaminated soil by Achromobacter sp. RX was investigated using a rotating-drum bioreactor. Evolution of total organic carbon from the contaminated soil showed that 86.4%-91.7% of DEHP was mineralized at pH 7.0 and 30.0 °C within 96 h. Reusability of Achromobacter sp. RX and its lifetime were observed over six consecutive cycles. Thus, Achromobacter sp. RX possessed high DEHP biodegradability, which provided a good potential in dealing with DEHP-contaminated soil.