The Effects of Microplastics on Floc Formation, Nutrient Removal and Settleability in Wastewater Treatment

Microplastics (MPs) are ubiquitous anthropogenic pollutants and contaminants of concern that are being manufactured as plastic materials are relied upon in daily life, including packaging, cosmetics and other production sectors. One of the ways that MPs enter the environment is via wastewater treatment plants (WWTPs). This study attempts to shed light on the potential interactions of these pollutants with microorganisms and some of the processes they facilitate in WWTPs by finding the effects of polyethylene (PE) MPs on the growth of wastewater (WW) microorganisms, nutrient removal (with a focus on nitrogen compounds), settleability of total suspended solids (TSS), and on the immediate and short-term floc formation. The two highest concentrations of PE MPs enhanced growth over an approximately 3-day period. Then, the absorbance values decreased, possible due to the formation of biofilms causing a decrease in planktonic cells. The high concentrations of PE MPs are seen to slow growth compared to the lower concentrations of MPs. PE MPs had a positive effect on nitrite oxidation but little to no effect on nitrification as a whole. Over the short term (1 to 7 days), MPs had little to no effect on floc size. Beyond 7 days, PE MPs had a positive effect on floc size. TSS was higher in reactors amended with MPs (528.9 mg/L) in comparison to the TSS values in the control reactors (212.2 mg/L) without MPs. The results indicate that MPs serve as nuclei for floc formation.