General Fate Model for Microconstituents in an Activated Sludge System

Nine laboratory-scale continuous flow porous-pot bioreactors, operating at various solids retention times (SRT) and hydraulic retention times, were used to simulate activated sludge systems, and to evaluate biodegradation kinetic models for the fate of 17α-ethinylestradiol (EE2), bisphenol-A (BPA), and triclosan (TCS) at the μg/L range. Mathematical models were applied to describe the degradation mechanism of selected microconstituents and the pseudo-second-order model was found to best fit the results when active microconstituent degraders (XC) were used (r2 = 0.99). The result of XC estimation showed that SRT plays an important role in formation of the biomass capable of degrading selected microconstituents. It is also observed that microconstituent degraders are naturally present in an activated sludge system, even at low SRTs; however, the concentration of XC is dependent on SRT. It seems that biodegradation studies should incorporate XC, and not mixed liquor suspended solids concentration, in their kinetic formulations.