Influence of operational parameters (sludge retention time and hydraulic residence time) on the removal of estrogens by membrane bioreactor

This paper deals with the removal of two natural estrogens, estrone (E1) and 17 beta-estradiol (E2) and a synthetic one 17 alpha ethinylestradiol (EE2) from wastewater in a laboratory-scale membrane bioreactor (MBR). The effects of both solid retention time (SRT) and hydraulic residence time (HRT) were studied using synthetic wastewater in the MBR. At 35, 45, 60, 75, and 95 days, SRT was studied. The HRT was varied in the range of 7-12 h. The results showed that the increases in HRT and SRT enhanced the biodegradation process after adaptation to microorganisms. At HRT of 12 h, the estrogen removals were close to 100% in the MBR. The highest estrogen removals were obtained at SRT of 60 days. Continuous tests showed a linear relationship between nitrification and estrogen removal rates. The most biodegradable compound was the E2. The membrane fouling rates increased with the decreased of SRT and HRT. Optimal process conditions in this work was obtained at the SRT and HRT of 60 days and 12 h, respectively, with high efficient of estrogen removal, nitrification efficiencies, as well as a minimum membrane fouling rate.