Evaluating removal of steroid estrogens by a model alga as a possible sustainability benefit of hypothetical integrated algae cultivation and wastewater treatment systems

The wastewater treatment field is increasing its emphasis on energy and resource recovery, while still prioritizing environmental protection. In this vein, there is growing interest in integration of algae cultivation and wastewater as a means to produce bioenergy while also removing dissolved nutrients. This paper assesses algae-mediated removal of estrogenic steroid hormones, which is an important but previously undocumented water quality benefit for municipal and livestock waste treatment facilities, because these entities discharge significant amounts of estrogens and nutrients. Bench-scale experiments were used to investigate apparent removal of four steroid hormones by a model alga, Scenedesmus dimorphus. Removal efficiencies were roughly 85% for 17α-estradiol and estrone and 95% for 17β-estradiol and estriol over eight days. Sorption, direct-photolysis, and algae-mediated biotransformation were evaluated as possible removal mechanisms. Removal was mainly achieved by algae-mediated biotransformation, and a partial mechanism has been proposed based on observed products. A bioassay indicates that removal of the parent estrogens does not always remove estrogenic activity, although estrogenicity associated with 17β-estradiol did decrease slightly. Overall, this study highlights a novel synergy between water and energy sustainability in integrated algae farming and wastewater treatment systems. These systems should be studied further to see if energy production could motivate voluntary removal of currently unregulated emerging contaminants.