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Impact of Nano–Sized Polyethylene Terephthalate on Microalgal–Bacterial Granular Sludge in Non–Aerated Wastewater Treatment
Summary
This study found that nano-sized PET microplastics at concentrations up to 30 mg/L had little impact on a microalgal-bacterial wastewater treatment system, but at 50 mg/L began degrading performance after two weeks by suppressing algal growth and disrupting energy metabolism in the microbial community. The granular sludge responded by producing extracellular polymers that adsorbed the nanoplastics, acting as a partial defense mechanism. These findings suggest that current nanoplastic contamination levels in municipal wastewater are unlikely to severely compromise this emerging treatment technology, but higher concentrations could be problematic.
The widely used plastics in our daily lives have resulted in ubiquitous microplastics and nanoplastics in wastewater, such as polyethylene terephthalate (PET). As an emerging green process for wastewater treatment and resource recovery, microalgal–bacterial granular sludge (MBGS) aligns with the concept of the circular economy. However, it is unclear whether the tiny PET can affect the MBGS process. Thus, this study investigated the impact of nano–sized PET (nPET) on the MBGS process. The results showed that 10 to 30 mg/L nPET had no obvious impact on pollutant removal as compared with the control group. However, the performance of the MBGS with the addition of 50 mg/L nPET became worse after 15 days. Scanning electron microscopy revealed that the MBGS adsorbed nPET by generating extracellular polymeric substances. Further microbial analyses showed that the algal abundance in prokaryotes slowly declined with increasing concentrations of nPET, while the reduced energy storage and electron transfer in eukaryotes might lead to an inferior performance at 50 mg/L nPET. Overall, the MBGS was demonstrated to exhibit good adaptability to nPET–containing wastewater, which showed the potential to be applied for the treatment of municipal wastewater containing nanoplastics.