Mechanism of microplastics effects on the purification of heavy metals in piggery effluents by microalgae

Microalgae is an effective bioremediation technique employed for treating piggery effluent. There is insufficient study on how the presence of microplastics (MPs) in wastewater affects the ability of microalgae to remove heavy metals from piggery effluent. This study aims to investigate the influence of Cu2+ (2 mg/L) and Zn2+ (2 mg/L), two prevalent heavy metals found in piggery wastewater, on their removal by microalgae (Desmodesmus sp. CHX1) in the presence of four types of MPs: polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene terephthalate (PET). The results revealed that smaller particle size MPs promoted chlorophyll accumulation, while larger particle size inhibits it. Additionally, higher concentrations of MPs promoted chlorophyll accumulation, while lower concentrations inhibited it. As for heavy metals, the presence of microplastics reduced the removal of Cu2+ and Zn2+ by Desmodesmus sp. CHX1. The highest inhibition of Cu2+ was 30%, 10%, 19%, and 16% of the control (CK), and the inhibition of Zn2+ was 7%, 4%, 4%, and 13%, respectively, under PE, PVC, PP and PET MPs treatments. Furthermore, Desmodesmus sp. CHX1 can secrete more extracellular polymeric substances (EPS) and form heterogeneous aggregates with MPs to resist their pressure. The findings elucidate the impact of MPs on microalgae in bioremediation settings and offer useful insights into the complex relationships between microalgae, MPs, and heavy metals in the environment.