Appraising co-composting efficiency of biodegradable plastic bags and food wastes: Assessment microplastics morphology, greenhouse gas emissions, and changes in microbial community

Abstract

Biodegradable plastic bags (BPBs) to collect food waste and microplastics (MPs) produced from their biodegradation have received considerable scientific attention recently. Therefore, the current study was carried out to assess the co-composting efficiency of biodegradable plastic bags (polylactic acid (PLA) + polybutylene terephthalate (PBAT) + ST20 and PLA + PBAT+MD25) and food waste. The variations in greenhouse gas (GHG) emissions, microbial community and compost fertility were likewise assessed. Compared with the control, PLA + PBAT+ST20 and PLA + PBAT+MD25 both accelerated organic matter degradation and increased temperature. Moreover, PLA + PBAT+ST20 aggravated CH4 and CO2 emissions by 12.10 % and 11.01 %, respectively. PLA + PBAT+MD25 decreased CH4 and CO2 emissions by 5.50 % and 9.12 %, respectively. Meanwhile, compared with PLA + PBAT+ST20, the combined effect of plasticizer and inorganic additive in PLA + PBAT+MD25, reduced the NO3−-N contents, seed germination index (GI) and compost maturity. Furthermore, adding BPBs changed the richness and diversity of the bacterial community (Firmicutes, Proteobacteria and Bacteroidetes). Likewise, redundancy analysis (RDA) showed that the co-compost system of BPBs and food waste accelerated significantly bacterial community succession from Firmicutes and Bacteroidetes at the initial stage to Proteobacteria and Actinobacteria at the mature stage, increased co-compost temperature to over 64 °C and extended thermophilic composting phase, and promoted the degradation of MPs. Additionally, according to structural equation model quantification results, the inorganic additive of PLA + PBAT+MD25 had more serious toxicity to microorganisms and had significantly adverse effects on GI through CO2-C (λ = −0.415, p < 0.05) and NO3−-N (λ = −0.558, p < 0.001), thus reduced compost fertility and quality. The results also indicated that the BPBs with ST20 as an additive could be more suitable for industrial composting than the BPBs with MD25 as an additive. This study provided a vital basis for understanding the potential environmental and human health risks of the MPs' generated by the degradation of BPBs in compost.