Effects of adding steel slag on humification and characteristics of bacterial community during phosphate-amended composting of municipal sludge.

This study aimed to investigate the effects of different proportions (0%, 5%, 7.5%, and 10%) of steel slag (SS) on humification and bacterial community characteristics during phosphate-amended composting of municipal sludge. Compared with adding KH2PO4 alone, co-adding SS significantly promoted the temperature, pH, nitrification, and critical enzyme activities (polyphenol oxidase, cellulase, laccase); especially organic matter (OM) degradation rate (25.5%) and humification degree (1.8) were highest in the 5%-SS treatment. Excitation-emission matrix-parallel factor confirmed that co-adding SS could promote the conversion of protein-like substances or microbial by-products into humic-like substances. Furthermore, adding 5%-SS significantly improved the relative abundances of Actinobacteria, Firmicutes and the genes related to carbohydrate and amino acid metabolism, and enhanced the interactions of bacterial community in stability and complexity. The partial least squares path model indicated that OM was the primary factor affecting humification. These results provided a promising strategy to optimize composting of municipal sludge via SS.

Green credit guideline and enterprise export green-sophistication.

Green credit is a major policy innovation to guide enterprises to participate in environmental governance actively. This study uses the data of Chinese A-share listed companies from 2007 to 2016, takes the green credit guideline (GCG) issued in 2012 as a quasi-natural experiment, and uses a difference in difference (DID) model to test the effect of GCG on the enterprises' export green-sophistication (EGS) and its internal and external mechanisms. The study finds that GCG improves enterprises' EGS and research and development (R&D) investment is the intermediation channel for GCG to affect EGS. Results of heterogeneity analysis show that the role of GCG in promoting EGS is significantly reflected in enterprises that the government does not subsidize, enterprises in areas with a low degree of financial marketization development, state-owned enterprises, and enterprises with a high degree of equity incentive.