Microplastics (MPs), as frequent pollutants, persist in aquatic environments and have an impact on the growth and biomass production of microalgae. This study employed MPs of polyethylene (PE), polystyrene (PS), and polypropylene (PP) at concentrations of 250 mg/L with MP sizes of 50, 100, 300, and 500 µm to investigate their influences on the growth and bio-production of Scenedesmus quadricauda. The results revealed that MPs suppressed the growth of S. quadricauda and increased algal lipid production. The order of the MPs in terms of their inhibitory and lipid production effect was the following: PP > PS > PE. The order of their size sensitivity was 50 > 100 > 300 > 500 µm. In the 50 µm PP culture, the inhibition of microalgal growth (inhibition rate: 49.26%) and accumulation of lipids (total lipid content: 65.40%) were most significant, especially with neutral lipid content. Additionally, scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) analyses proved that the rough MP surface led to high aggregation of microalgae, reduced the intensities of the protein-, lipid-, and carbohydrate-related bands and affected the structure of the algal cells.
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