Removal of environmental estrogens by bacterial cell immobilization technique

Contamination of steroidal estrogens in the environment has raised a great public concern, and therefore, developing an effective method for removal of trace amount of environmental estrogens is necessary. In this study, two estrogen-degrading bacteria were isolated from activated sludge and were identified as strain Sphingomonas sp. AHC-F and strain Sphingobium sp. AX-B. They were capable of utilizing estrone (E1) and 17ß-estradiol (E2) as sole carbon and energy source. Cell immobilization technique was applied to these two estrogen-degrading bacteria. Confocal laser-scanning microscopy images with live and dead staining of entrapped bacterial cells showed that most bacteria were present inside the porous structure and were mostly viable after immobilization procedures. Batch estrogen degradation study showed that immobilized strains AHC-F and AX-B could effectively degrade 2 mg/L of E2 and its metabolite E1. Immobilized bacteria column reactors using pure culture of strain AHC-F were set up for continuous-flow removal of 850 ng/L of E2 in the influent. The removal efficiency of E2 and equivalent estrogenic quantity of E2 (EEQ) could achieve 94 and 87% under 12 h hydraulic retention time (HRT), respectively. Increasing HRT could further improve the removal efficiency of EEQ. When the HRT increased to 72 h, the effluent concentrations of E2 and E1 were not detectable by gas chromatography-mass spectrometry. Our results also proved that most of the estrogen removal was due to biodegradation. This study has demonstrated the potential use of immobilized bacteria technique for the removal of environmental estrogens.