Comparison of estrogen compounds removal efficiency in sample and alternating anoxic/aerobic activated sludge process

Abstract

The occurrence and the removal efficiency of natural estrogens, estrone (E1), 17β-estradiol (E2) and estriol (E3), as well as a synthetic estrogen, 17α-ethinylestradiol (EE2), were investigated in two sewage treatment plants (STPs) employing different activated sludge processes in Tunisia, by monitoring their concentrations in dissolved wastewater. The analytes were extracted by solid-phase extraction and then analyzed by gas chromatography coupled with mass spectrometry (GC-MS). Results indicate that natural and synthetic estrogens were detected in the STP influent samples. The concentrations of natural and synthetic estrogens (except E1) detected in the effluents of alternating activated sludge process were generally lower than the limit of detection. On the other hand, all estrogens were not totally removed through the simple activated sludge process; as a result, they were detected in effluent samples. E3 showed the highest concentration in the influent samples at 98 ng L -1 in the alternating anoxic/aerobic activated sludge process, and at 102 ng L -1 in the simple activated sludge. Two different types of diurnal variation of estrogens discharge were identified. The two STPs had approximately similar daily loads of estrogens in influents at 112.7 µg d -1 and 109.58 µg d -1 , respectively. The distribution of estrogens in the STPs is affected by their metabolisms in human body and their transition through biological treatment processes. Removal efficiency varied among STPs; high removal of estrogens (84-97%) with the exception of E1 (80%), were generally achieved in alternating anoxic/aerobic activated sludge process with a high hydraulic retention time (40 h) and treatment stages for removal of nitrogen. E1 showed the lowest removal of all estrogens in the two STPs. This could be caused by conversion of E2 to E1 in the treatment process, or by cleavage of estrogen conjugates. On the other hand, E3 showed the highest removal of all estrogens both in alternating anoxic/aerobic and simple activated sludge processes at 97.5% and 85.5%, respectively). EE2, which is particularly sensitive to human consumption as the oral contraceptive, were removed by approximately 77.5%) in the simple activated sludge process. Filamentous bacteria were less effective in removal estrogens than protozoa.