Microalgae-based technology for wastewater treatment: exploring organic micropollutants removal

Abstract

Organic micropollutants (OMPs) need to be removed from wastewater as they can negatively affect aquatic organisms. It has been demonstrated that microalgae-based technologies are efficient in removing OMPs from wastewater. In this study, the removal processes and kinetics of six persistent OMPs (diclofenac, clarithromycin, benzotriazole, metoprolol, carbamazepine and mecoprop) were studied during cultivation of Scenedesmus obliquus in batch mode. These OMPs were added as individual compounds and in a mixture. The short experiments (8 days) were designed to avoid masking of OMPs removal processes by light and nutrient limitation. The results show that diclofenac, clarithromycin, and benzotriazole were mainly removed by photodegradation (diclofenac), biodegradation (benzotriazole), or a combination of the two processes (clarithromycin). Peroxidase was involved in intracellular and extracellular biodegradation when benzotriazole was present as individual compound. Carbamazepine, metoprolol and mecoprop showed no significant biodegradation or photodegradation, and neglectable removal (<5%) by bioadsorption and bioaccumulation. The mixture of OMPs had an adverse effect on the photodegradation of clarithromycin and diclofenac, with reduced first-order kinetic constants compared to the individual compounds. Benzotriazole biodegradation was inhibited by the presence of the mixture of OMPs. This indicates that the presence of the OMPs inhibits the photodegradation and biodegradation of some individual OMPs. These results will improve our understanding on the removal processes of individual and mixtures of OMPs by microalgae-based technologies for wastewater treatment.