Interactions and Synergistic Co-Conversion of Microplastics and Microalgae: A Review

Escalating global plastic pollution has resulted in the pervasive accumulation of microplastics (MPs) in aquatic environments. Due to their strong pollutant adsorption capacity and difficulties in recovery, MPs pose severe challenges to conventional water treatment technologies. Microalgae, characterized by high environmental adaptability and robust metabolic capabilities, exhibit significant potential for MP bioremediation. This review systematically elucidates the interaction mechanisms between microalgae and MPs, bioremediation strategies, and downstream co-conversion pathways. Specifically, extracellular polymeric substances (EPS) secreted by microalgae act as key drivers for hetero-aggregation, facilitating interfacial adhesion via charge neutralization and hydrogen bonding. The size ratio of MPs to algal cells regulates aggregation behavior: comparable sizes promote co-sedimentation, whereas significantly larger MPs obstruct light, and nanoscale particles induce cytotoxicity. MP toxicity is further modulated by particle concentration and the degree of aging. Conversely, microalgae accelerate MP degradation through physical abrasion and enzymatic hydrolysis. Effective bioremediation requires matching the surface properties of algal strains with MPs, regulating biofilm formation, and balancing hydrodynamic shear forces. Regarding resource recovery, the co-pyrolysis or liquefaction of algal biomass and MPs reduces nitrogen- and oxygen-containing impurities in bio-oil via the hydrogen-donor effect of MPs. This process can also yield porous carbon with a high specific surface area or fluorescent carbon quantum dots. However, current research faces notable limitations. Most studies on toxicity and degradation rely on static, single-species systems that fail to simulate realistic hydrodynamic parameters (e.g., flow velocity and turbulence intensity) and the synergistic effects of co-existing pollutants (e.g., heavy metals and pharmaceutical compounds). Furthermore, co-conversion technologies are limited by discontinuous operation and a lack of robust models correlating feedstock ratios with product quality. Future research should prioritize the development of multi-algal synergistic remediation systems and the introduction of dynamic flow simulations to replicate real aquatic environments. Remediation efficacy must be evaluated under multi-pollutant conditions. Additionally, developing multi-stage continuous-flow reactors with optimized catalysis is crucial. Ultimately, these efforts will bridge the gap between remediation and resource utilization, promoting the transition of bioremediation technology from laboratory research to industrial application.