Removal and degradation pathway analysis of 17β-estradiol from raw domestic wastewater using immobilised functional microalgae under repeated loading

The natural hormone, 17 beta-estradiol (E2), is a frequently detected endocrine disrupter, and its transformation into oestrone and carcinogenic catechol oestrogen quinones via degradation is a problem that must be considered when choosing wastewater bioremediation agents. In this study, the performance of immobilised functional microalgae with respect to E2 removal and degradation was investigated under repeated loadings of domestic wastewater. The wastewater treatment using the immobilised microalgae resulted in a significant enhancement of nitrogen, phosphorus, and E2 removal efficiencies, which were in the ranges 40-86 %,26-72 %, and 85-99 %, respectively. The E2 removal pathway was inferred, and metabolisation via hydroxylation, O-methylation, glycosylation, dehydrogenation, and dicarboxylation owing to the immobilised algae cells, was theorised. Additionally, no other forms of natural oestrogens, including estrone or quinone metabolites, were detected in the metabolites. Therefore, immobilised functional microalgae at concentrations above 200 beads/mL are recommended as an effective and safe approach to restoring E2-contaminated wastewater.