Effects of common microplastics on aerobic composting of cow manure: Physiochemical characteristics, humification and microbial community

With the detection of microplastics in organic/biomass wastes, the risks of utilizing aerobic composting technology to treat wastes were increasingly recognized, but the impacts of microplastics on composting remain largely unidentified. The objective of this study was to investigate the effect of common microplastics (polypropylene (PP) and polyethylene (PE)) during 55 days composting. In this study, 0.5% PP and 0.5% PE were separately added to the mixture of cow manure, corn straw and bean dregs. The treatment without microplastics was regarded as control (CK). Microplastics significantly reduced the seed germination index values and the NO3−-N contents by 32.40%− 42.78% and 30.37%− 37.04%, respectively. Moreover, the degree of polymerization and humification index of CK were maximum at the end of composting (3.64% and 27.75%) compared to the microplastics added treatments. The alpha and beta diversity analyses showed that the exposure of microplastics reduced the abundance and diversity of bacterial communities. On day 3, the differences in bacterial community composition were mainly caused by time, while the effect of microplastics was more pronounced in the long-term composting. The relative abundance of potential bacterial pathogens at the end of composting in the CK was 2.14%− 2.96% lower than that in the microplastics added treatments. In summary, the results indicated that microplastics reduced compost quality while increased the potential pathogenic risk of composted products.