Polycarbonate microplastics induce oxidative stress in anaerobic digestion of waste activated sludge by leaching bisphenol A

Polycarbonate (PC) microplastics are frequently detected in waste activated sludge. However, understanding the potential impact of PC microplastics on biological sludge treatment remains challenging. By tracking the changes in methane production under different concentrations of PC microplastics, a dose-dependent effect of PC microplastics on anaerobic digestion of sludge was observed. PC microplastics at 10-60 particles/g total solids (TS) improved methane production by up to 24.7 ± 0.1 % (at 30 particles/g TS), while 200 particles/g TS PC microplastics reduced methane production by 8.09 ± 0.1 %. Bisphenol A (BPA) leached from 30 particles/g TS PC microplastics (1.26 ± 0.18 mg/L) down-regulated intracellular reactive oxygen species (ROS) production, thereby enhancing enzyme activity, biomass viability, and abundance of methanogenic (Methanobacterium sp. and Methanosarcina sp.), ultimately boosting methane production. Conversely, BPA leached from 200 particles/g TS PC microplastics (4.02 ± 0.15 mg/L) stimulated ROS production, resulting in decreased biomass viability and even apoptosis. Modulation of oxidative stress by leaching monomeric BPA is an underappreciated transformative mechanism for improving the mastery of the potential behavior of microplastics in biological sludge treatment.