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Optimizing initial biomass to enhance microplastic sequestration via density-driven bio-flocculation in microalgal systems
Summary
Scientists found that certain algae (like Chlorella and Spirulina) can help clean up microplastic pollution in water by clumping the tiny plastic particles together and settling them out—and that starting with the right amount of algae (around 1000 mg per liter) works best for both growing the algae and removing plastic. This matters because microplastics are increasingly showing up in our water supplies and food, and this research points toward a natural, low-cost way to filter them out before they reach us.
Initial biomass is a key regulator of microalgal resilience to polystyrene microplastics (PS-MPs). This study investigated the responses of four microalgae-Chlorella sp., Scenedesmus sp., Cyclotella sp., and Spirulina sp.-exposed to 5 mg L PS-MPs across biomass gradients of 500 - 1500 mg L. PS-MPs induced species- and density-dependent responses rather than uniform toxicity. Higher initial biomass increased final population yield and extracellular polymeric substance (EPS) production, but reduced specific growth rates due to intensified self-shading and resource competition. Chlorella sp. and Spirulina sp. exhibited stronger resilience, supported by pigment accumulation, coordinated antioxidant regulation, and EPS-mediated PS sequestration. Multivariate analysis further confirmed that biomass level, EPS secretion, photosynthetic performance, and oxidative status collectively structured microalgae-PS interactions. Notably, an initial biomass of 1000 mg L provided the optimal balance between growth performance and remediation efficiency. These findings provide a quantitative framework for optimizing microalgae-based systems for microplastic contaminated wastewater treatment.