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Microplastics (MPs) pose significant environmental risks due to their persistence and ubiquity in aquatic systems. Among advanced wastewater treatment technologies, microalgal-bacterial granular sludge (MBGS) offers a phototrophic-aerobic system with excellent nutrient removal and structural resilience. This study investigates the effects of polylactic acid (PLA)-based biodegradable MPs (0–50 mg/L) on MBGS performance. Key findings reveal that low PLA concentrations (≤5 mg/L) had minimal impact on MBGS structure and function. However, at 50 mg/L, mixed liquor suspended solids (MLSS) declined by 26.9 %, sludge volume index (SVI 5 ) more than doubled (from ∼35–75.4 mL/g), and zeta potential dropped sharply to −32.9 mV, indicating granule destabilization. Nutrient removal efficiency was also compromised: total nitrogen removal plummeted from > 96–44.4 %, while phosphate removal decreased from > 95 % to < 30 %. EPS composition shifted significantly, with a 63.17 % reduction in phosphorus uptake rate and altered protein/polysaccharide ratios, reflecting microbial stress. Microbial diversity declined, particularly among polyphosphate-accumulating organisms, although genera such as Paracoccus and Pseudomonas showed resilience. Importantly, system restoration was achieved within 30 days post-exposure, with restoration of structural, functional, and microbial parameters. This study provides the first detailed evaluation of PLA microplastic effects in MBGS systems, emphasizing that even biodegradable polymers can disrupt wastewater treatment processes at elevated concentrations.
Kedves et al. (Tue,) studied this question.
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