Anaerobic Electrochemical Membrane Bioreactors Strengthen Steroid Estrogen Removal: The Pivotal Role of Planktonic Sludge

Conventional anaerobic biological technologies face severe challenges in removing steroid estrogens (SEs) because of the absence of electron acceptors under anaerobic conditions. In this study, an electrochemical anaerobic membrane bioreactor (AneMBR) was developed to efficiently remove 17α-ethinylestradiol (EE2) in wastewater while recovering chemical energy as methane. The average EE2 removal efficiency reached 83.1% in AneMBR, attributed primarily to significantly enhanced biodegradation, which demonstrates the advantages of this technology. The degradation kinetics results showed an 83.6% increase in the EE2 biodegradation rate by planktonic sludge under a 0.8 V electric field, along with enhanced sorption capacity, microbial activity, and c-type cytochrome secretion. The electric field provides supplemental energy for microbial metabolism, strengthens the conversion of EE2 into estradiol and estrone, and further converts them to low-endocrine-disrupting small-molecule organic compounds. These results were further confirmed by the upregulation of the functional genes involved in EE2 metabolism. This study develops a promising technology for improving SE removal in anaerobic methane fermentation systems and elaborates on the significance and metabolic mechanisms of planktonic sludge in electrically strengthened biotreatment systems for SE removal.