Different sizes of polystyrene microplastics induced distinct microbial responses of anaerobic granular sludge

Recent investigations confirmed the inhibitory effect of microplastics with single sizes on the anaerobic granular sludge (AGS) wastewater treatment system. However, the differences of toxicity from different sizes of microplastics toward AGS and their underlying mechanism are still unclear. In this work, the responds of AGS exposed to different particle sizes of polystyrene microplastics (PS-MPs) were reported. The results showed that the increasing particle sizes (from 0.5 mu m to 150 mu m) of PS-MPs induced a gradually increasing and distinct inhibitory (from 6.7% to 16.2%) effect on the cumulative methane production by AGS, accompanied by the similar decreasing organic carbon degradation trends. Correspondingly, the integrity and the cell viability of the AGS granules were damaged and the populations of the key acidogens and methanogens were reduced when exposed to PS-MPs, which was particularly evident in the reactors affected by the larger micron-sized PS-MPs. The zeta potential and contact angle indicated that the larger-sized PS-MPs had the stronger dispersive properties and affinity for AGS, causing the higher oxidative stress and leachates toxicity. Further investigation revealed that the tolerance of AGS to PS-MPs toxicity also exhibited size-dependent trend. Larger particles (e.g., 150 mu m) of PS-MPs inhibited extracellular polymeric substance (EPS) secretion, while smaller particles (e.g., 0.5 mu m) promoted EPS generation with the release of more humic acid, alleviating their toxicity.

Automated summary

The inhibitory effect of different sizes of polystyrene microplastics (PS-MPs) on an anaerobic granular sludge (AGS) wastewater treatment system was investigated. The results showed that larger PS-MPs had a stronger inhibitory effect on methane production and organic carbon degradation by AGS, as well as causing damage to AGS granules and reduction in acidogens and methanogens populations.