Microplastics (MPs) are persistent emerging contaminants in wastewater (WW) that conventional treatment systems fail to remove effectively, posing environmental and human health risks. Microalgae-based systems have emerged as sustainable alternatives for WW treatment, offering efficient nutrient removal and biomass production. However, the impact of MPs on microalgal performance under different WW conditions remains poorly explored.
This study evaluated the physiological responses and bioremediation efficiency of Chlorella vulgaris exposed to 100 mg/L of five of the most common MPs, namely polypropylene (PP), polystyrene (PS), polyamide (PA), low-density polyethylene (LDPE), and high-density polyethylene (HDPE). For that, different experimental conditions were studied, including variations in nitrogen (N) and organic carbon levels and photoperiod regimes (12/12 h light/dark vs. continuous light).
Results revealed heterogeneous metabolic responses depending on MP type and environmental conditions. PE derivatives (HDPE and LDPE) consistently reduced esterase activity, while PS under N-limited conditions increased it. LDPE triggered intracellular oxidative stress only under N limitation. Despite these metabolic effects, C. vulgaris maintained its growth and biomass generation in most scenarios, except under nutrient-starved and 12/12 h light/dark conditions, where growth was inhibited by 13–27 %. Heterotrophic metabolism partially compensated for reduced photosynthetic activity during dark periods. Under N-limited conditions, C. vulgaris demonstrated high bioremediation efficiency, with up to 94 % N and >97.5 % glucose removal, even in the presence of MPs. In contrast, limited organic carbon (as glucose) severely impaired nutrient removal due to energy deficits. A 12/12 h photoperiod also reduced N uptake by constraining light-dependent energy production, although glucose consumption remained high (>98 %).
Overall, the study highlights that different WW experimental conditions modulate MP-induced stress. Nutrient limitation and light/dark cycles can intensify metabolic disruption, while N-limited environments promote adaptive responses. C. vulgaris demonstrated high resilience, maintaining its bioremediation capacity and supporting its potential as a robust, eco-friendly tool for MP-contaminated WW polishing.
