Effect of polystyrene microplastics on the volatile fatty acids production from waste activated sludge fermentation

Anaerobic fermentation is crucial to resource utilization of waste activated sludge (WAS). However, accumulated microplastics (MPs) in sludge could not be ignored. Here, a typical MP, polystyrene (PS), was selected to study the effects of different concentrations of PS on anaerobic fermentation under the optimal volatile fatty acids (VFAs) production. Compared to the control, low PS concentrations (30 particles/g total solid) significantly (p = 0.002) increased the production of VFAs to 112.8 ± 2.4% due to solubilization enhancement and enzymatic activity. High concentrations of PS (90 particles/g total solid) significantly (p = 0.000) decreased VFAs production to 83.01 ± 0.76% because of the inactive related microbial activities, although organic matter release was enhanced in the initial stage. Mechanism studies showed that the toxicity of high PS concentration could be attributed to reactive oxygen species (ROS) production, excess sodium dodecyl sulfate (SDS), and synergistic toxicity of aged MPs with external pollutants. [Display omitted] •Low microplastics dosage enhanced acid production by improving solubilization.•High microplastics concentration inhibited microbial activity via the toxic effect.•The adsorption capacity of the aging microplastics in the anaerobic system improved.•Reactive oxygen species and excess sodium dodecyl sulfate increased the toxicity.