Highly effective removal of microplastics by microalgae Scenedesmus abundans

The highly effective removal of multiple kinds of microplastics (MPs) by microalgae Scenedesmus abundans was accomplished and the main mechanism of the MPs removal was identified as hetero-aggregation. The accurate quantification of removal efficiency was achieved by quantifying free suspended microparticles before and after the microalgae treatment. Scenedesmus abundans was tested against three kinds of plastics, including polystyrene (PS), poly(methyl methacrylate) (PMMA), and polylactide (PLA), and a total removal efficiency (η) higher than 84% was achieved for all MPs. Among these MPs, S. abundans were highly effective for removing PMMA microparticles (η = 98%). For the other two kinds of MPs, pre-exposure was required to achieve a total removal efficiency higher than 70%. As validated by SEM, a long-term exposure to MPs (greater than 2 days) promoted the formation of bound extracellular polymeric substances (EPS) and hetero-aggregation, leading to a much higher fraction of MPs removed by aggregations (ηa greater than 70%). On the contrary, if MPs exposure is short, enhanced adsorption onto solid surfaces can play an important role in the MPs removal, especially in the case of PLA. In this aspect, the abundance of soluble EPS was proportional to the amount of MPs adsorbed onto the container wall. These results suggest that the removal efficiency of microplastics, as well as the underlying mechanism, was affected by both plastic kind and exposure duration. Pre-exposure to MPs greatly increased the removal efficiency and can be a promising strategy for real-life practices.