Removal of estrone, 17α-ethinylestradiol, and 17β-estradiol in algae and duckweed-based wastewater treatment systems

摘要

Background, aim, and scope Many pollutants have received significant attention due to their potential estrogenic effect and are classified as endocrine disrupting compounds (EDCs). Because of possible ecological effects and increased attention for water reuse schemes, it is important to increase our understanding of the EDC removal capacities of various wastewater treatment systems. However, there has so far been little research on the fate and behavior of EDCs in stabilization pond systems for wastewater treatment, which represent an important class of wastewater treatment systems in developing countries because of their cost-effectiveness. The aim of this work is to study the fate and behavior of EDCs in algae and duckweed ponds. Because the synthetic hormone 17a-ethinylestradiol (EE2) and the natural hormones estrone (El), as well as 17β-estradiol (E2), have been detected in effluents of sewage treatment plants and been suggested as the major compounds responsible for endocrine disruption in domestic sewage; El, E2, and EE2 were therefore chosen as target chemicals in this current work. Materials and methods Both batch tests and continuous-flow tests were carried out to investigate the sorption and biodegradation of estrogens in algae and duckweed pond systems. The applied duckweed was a Lemna species. The applied algae was a mixture of pure cultures of six different algae genera, i.e., Anabaena cylindrica, Chlorococcus, Spirulina platensis, Chlorella, Scenedesmus quadricauda, and Anaebena var. Synthetic wastewater were used in all tests. The concentrations of estrogens were measured with three different enzyme-linked immunosorbent assay kits specific for El, E2, or EE2. When the concentrations of estrogens in water samples were below the lowest quantitative analysis range (0.05 mu g/1), preconcentration of the water samples were performed by means of solid phase extraction (SPE) with C18 cartridges. Results The 6-day batch tests show that the presence of algae or duckweed accelerated the removal of the three estrogens from the synthetic wastewater. More estrogens were removed in the tests with duckweed than in tests with algae or with wastewater. In the sorption tests, a swift sorption of the three estrogens was observed when the estrogens were contacted with duckweed or algae, while the estrogen concentrations in tap water kept unchanged during the 3-h sorption tests. The mass balances indicated that only about 5% of the estrogens were bound to the algae sediment or duckweed at the end of the 6-day tests. Results of the continuous-flow tests revealed that the algae and duckweed ponds effectively removed El, E2, and EE2 even at nanograms per liter level. Interconversion of El and E2 occurred both in batch and continuous-flow tests. E2 could be readily transformed to El, especially in the tests with algae.