Polyethylene microplastics increase extracellular polymeric substances production in aerobic granular sludge

Wastewater treatment plants act as microplastic (MPs) sinks and secondary MP pollution sources. Little is known about the effect of MPs on biomass and the efficiency of biological wastewater treatment. This study assessed the impact of polyethylene (PE) MPs concentrations (1, 10, 50 mg/L) in wastewater on biological conversions and extracellular poly-meric substances (EPS) production (including alginate) in aerobic granular sludge (AGS). PE MPs did not worsen the efficiency of biological treatment but stimulated the production of EPS and alginate in AGS. The alginate content in-creased from 238.7 +/- 4.4 mg/g MLSS in control to 441.6 +/- 13.8 mg/g MLSS at the highest PE load in wastewater. The presence of MP changed AGS morphology and worsened the settling properties of biomass, causing biomass wash-out from the reactors. At the highest PE load in wastewater, the biomass concentration in the reactor effluent was over 2.8 times higher than in the control.

Automated summary

This study assessed the impact of polyethylene microplastics on aerobic granular sludge and found that the microplastics did not decrease the efficiency of biological treatment, but instead stimulated the production of extracellular polymeric substances and alginate. However, the presence of microplastics changed the morphology of the granular sludge and worsened the settling properties of the biomass.