Biodegradation Kinetics of 17α-Ethinylestradiol in Activated Sludge Treatment Processes

Biodegradation is the primary removal mechanism of the potent endocrine-disrupting estrogen 17-ethinylestradiol (EE2) during activated sludge (AS) wastewater treatment. Analysis of AS treatment process designs to optimize EE2 removal requires knowledge of EE2 biodegradation kinetics. However, there is little information on EE2 biodegradation kinetics for different types of systems and under long-term studies. EE2 biodegradation kinetics were investigated at 20 degrees C using laboratory-scale sequencing batch reactors simulating aerobic, anaerobic/aerobic enhanced biological phosphorus removal, and anoxic/aerobic biological nitrogen removal processes fed synthetic wastewater. Three sets of reactor experiments were conducted using different municipal AS plant seed sources and with solid retention times (SRTs) ranging from 8 to 13 days. EE2 biodegradation was described by a pseudo first-order biodegradation rate model with a rate coefficient (k(b)) normalized to the reactor volatile suspended solids (VSS). EE2 k(b) values were determined from batch degradation tests and from calibration of the model to the reactor process. Significant EE2 biodegradation occurred only under aerobic conditions. Observed EE2 k(b) values for aerobic, anaerobic/aerobic, and anoxic/aerobic operations ranged from 4 to 22 L/g VSS-day, 4 to 19 L/g VSS-day, and 3 to 20 L/g VSS-day, respectively. Model simulations showed that the EE2 removal efficiency could range from 72% to over 99% for these coefficients at a 10-day SRT. Predicted EE2 removal efficiency at a given k(b) value can be improved by operating at a higher SRT upto a limit, by having a greater number of aerobic reactor stages, and by having a higher influent biodegradable chemical oxygen demand concentration.