Extractive biodegradation of diphenyl ethers in a cloud point system: Pollutant bioavailability enhancement and surfactant recycling

The biodegradation of diphenyl ethers (DEs) in the environment is limited by their high hydrophobicity. The enhancement of DE bioavailability by a cloud point system (CPS) was investigated in this study. Three CPSs (i.e., Triton X-114, Triton X-114 + Triton X-45, and Brij30 + TMN-3) were tested to promote DE biodegradation. Biocompatibility tests showed that the biodegradation of DE and 4-bromodiphenyl ether (4-BDE) was inhibited by TX-114, unaffected by TX-114 + TX-45, and promoted by Brij30 + TMN-3 over 48 h of cultivation with Cupriavidus basilensis and 4% (w/v) nonionic surfactants. Further optimization with 2% (w/v) Brij30 + TMN-3 yielded residual DE and 4-BDE quantities of 143 and 154 mg/L, respectively, lower than quantities in the control. During degradation, DE content did not decrease in the dilute phase, but sharply decreased in the coacervate phase, indicating that the DEs gradually diffused and transferred from the coacervate phase to the dilute phase for degradation by microbial cells. This behavior also enhanced the bioavailability of DEs in the CPS. By removing the cell-rich dilute phase and adding fresh degradation medium and DE to the coacervate phase, surfactants were successfully recovered and reused twice without affecting DE biodegradation. Results demonstrated that a CPS with 2% (w/v) Brij30 + TMN-3 not only enhanced the bioavailability of DEs, but also decreased the treatment cost through surfactant recycling, which is beneficial for large-scale applications.