Fate of estrogens during the biological treatment of synthetic wastewater in a nitrite-accumulating sequencing batch reactor

The fate of estrone (El), 17beta-estradiol (E2), and 17alpha-ethynylestradiol (EE2) was investigated in two nitrite-accumulating sequencing batch reactors operating under strictly aerobic (SBR1) conditions at different sludge ages (SRT, 1.7 to 17.1 d) and anoxic/anaerobic/aerobic (SBR2) conditions with different phases and durations of redox conditions, using a modified GC-MS analytical method for estrogen detection to ng/L concentrations. In SBR1, > or =98% of E2 was removed (specific E2 removal rate ranged from 0.375 (at SRT 17.1 d) to 2.625 (at SRT 1.7 d) microg E2 x g MLVSS(-1) x d(-1)) regardless of SRT or DO (<1.0 to >5.0 mg/L). Removal of E1 and, to a greater extent, EE2 was adversely affected when this reactor was operated at SRT shorterthan 5.7 d. However, whereas E1 was removed efficiently as long as SRT was long enough for AOB to bring about nitritation, EE2 removal efficiency was significantly lower when SBR1 was operated at SRT longer than 7.5 d. This reduced removal of EE2 may have been caused by the inhibition and toxicity of nitrite, both to the ammonium monooxygenase (AMO) and to the microbial population generally. In SBR2, less removal of E2 was found at the lower MLVSS concentrations, and E1 was not removed by sludge with poor settling qualities. The removal of EE2 observed in SBR2 was considered to be mainly a result of sorption. However, the binding of estrogens to the sludge in this reactor was apparently not as strong as the binding observed in the sludge of the strictly aerobic SBR1, since desorption was observed during the aeration phase in SBR2.