Effective removal of toxicity and estrogenic activity from secondary sewage by microalgae-bacteria consortia

Sewage treatment by microalgae-bacteria consortia has been shown to satisfactorily reduce organic matter, nutrients, pathogenic microorganisms and some organic micropollutants. However, to date toxicity and estrogenic activity has only been estimated by removal of parent compounds responsible for this biological activity, without regard to the products of incomplete degradation or the potential interactive effects of the mixture of the degradation products. Therefore, an effects directed approach was undertaken to investigate estrogenic activity and toxicity removals by a microalgae-bacteria consortia in anaerobically treated municipal sewage. Heterotrophic bacteria present in the highly toxic municipal sewage reduced toxicity by half under aerobic conditions, however, only the microalgae-bacteria consortium eliminated toxicity after 48 h, indicating the advantages of combining both aerobic heterotrophy and photoautotrophy for toxicity elimination. Estrogenic activity was eliminated within 48 h in the low (<0.45 μm) and high (>0.7 μm) sewage solids fractions, with less than 6% remaining in the solids between 0.45 and 0.7 μm. The results corroborate the purported capacity of microalgae-bacteria consortia to effectively remove toxicity and estrogenic activity and not only toxic and estrogenic parent compounds from UASB-treated sewage, with both bacterial and algal metabolism involved in this removal.