Abstract:

This study focused on the effects of polyethylene terephthalate （PET） microplastics with a particle size ranging from 30 to 250 μm on the co?digestion performance of sewage sludges and food wastes under the mesophilic conditions. The total solid levels were set to be 0， 0.45， 1.44 and 2.88 mg/g TS， and the daily methane production， cumulative methane production， soluable chemical oxigen demand， ammonia nitrogen， volatile fatty acids， and microbial communities in the anaerobic co?digestion system were investigated. The results indicated that the PET microplastics inhibited the production of methane， and a higher microplastic concentration generated a more significant inhibition effect. The presence of the PET microplastics increased the risk of ammonia and acid inhibition. The cumulative methane yields decreased by 54.49 % and 49.58 % for the microplastics with particle sizes of 30 and 250 μm， respectively， at a total solid level of 2.88 mg/g TS. The microplastics increased the bacterial diversity but decreased the archaeal diversity. During the co?digestion process， the microplastics not only inhibited the abundances of the Prevotella， Proteiniphilum， and Methanosaeta but also weakened the pathway of acetic acid methanogenesis. A correlation analysis proved that the particle size of microplastics was positively correlated with Euryarchaetota （r=0.945，p<0.01）. When the particle size of microplastics was smaller， the inhibition on the abundance of methanogens was more remarkable. Methanogens were more sensitive to the microplastics than other bacteria.

Key words: microplastics, food waste, sewage sludge, anaerobic co?digestion, microbial community structure