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Microalgal-Bacterial Granular Sludge under Emerging Stressors: Effects of Zinc Oxide Nanoparticles and Degradable Microplastics Derived from Polylactic Acid and Polycaprolactone
Summary
This study is actually about wastewater treatment, not direct human exposure, but it matters because it tests how well a promising eco-friendly treatment system (using algae and bacteria to clean water) holds up when exposed to zinc nanoparticles and "biodegradable" microplastics—the kind increasingly used in packaging and other products. The researchers found that while low levels of these pollutants alone had minor effects, the combination of multiple pollutants together caused much bigger problems, cutting the system's water-cleaning abilities by more than half. This suggests that as our waste streams contain more mixed pollutants, the green technologies we're coun
High Resolution Image Download MS PowerPoint Slide The increasing discharge of emerging contaminants (ECs) such as zinc oxide nanoparticles (ZnO NPs) and degradable microplastics (DMPs) into aquatic environments poses a growing challenge for next-generation wastewater treatment technologies. This study investigates the individual and combined effects of ZnO NPs, polylactic acid (PLA), and polycaprolactone (PCL) microplastics on microalgal-bacterial granular sludge (MBGS), a promising low-energy biotechnological system. Using photosequencing batch reactors, changes in extracellular polymeric substances (EPS), chlorophyll content, and microbial activity were monitored across multiple exposure scenarios. The results revealed significant, concentration-dependent alterations. While low-dose exposures (5 mg/L) to individual contaminants marginally stimulated ammonia oxidation or algal growth, combined exposures, especially ZnO+PCL and ZnO+PLA+PCL, induced synergistic inhibitory effects. EPS protein fractions decreased by up to 82%; chlorophyll content decreased by 52%, and specific ammonia and phosphorus uptake rates were reduced by more than 60% at a concentration of 10 mg/L. Principal coordinate analysis (PCoA) confirmed the pronounced system-level perturbations under mixed contaminant stress. These findings underscore the ecological vulnerability of MBGS to co-occurring ECs and highlight the need for pollutant-specific resilience strategies in the design and operation of sustainable wastewater technologies.