Effects of different improvement methods synergizing ryegrass on ecological restoration of coal gangue substrate

In order to investigate the feasibility of substrate improvement and vegetation restoration in the ecological restoration of coal gangue dumps, this paper uses sodium formate as a bactericide to sterilize coal gangue. Edible fungus residue, phosphogypsum, and distillery sludge were added in different proportions to create diverse planting substrates for ryegrass. The experiment monitored the physicochemical characteristics of the leachate, growth of ryegrass, and the microbial community structure of the substrate. The results are as follows: 1) All substrates significantly elevated the pH of the coal gangue leachate and decreased the concentration of heavy metals such as Fe, Mn, and Cu. The addition of 5% edible fungus residue and 20% distillery sludge (S₄) showed the best combined effect. 2) The addition of edible fungus residue, phosphogypsum, and distillery sludge can significantly promote the growth of ryegrass. The largest biomass of ryegrass was observed in the coal gangue substrate supplemented with 5% edible fungus residue, 10% phosphogypsum, and 20% distillery sludge. All the heavy metals in ryegrass plants meet the limits of feed raw materials in the Hygienical Standard for Feeds (GB 13078－2017). 3) Substrate improvement significantly increased the diversity and relative abundance of the bacterial community. Sodium formate sterilization obviously changed the bacterial community structure. Among the other improved methods, Proteobacteria, Actinobacteriota, Firmicutes, Chloroflexi, and Bacteroidota were the dominant bacterial phyla. Overall, the addition of 5% edible fungus residue and 20% distillery sludge has the best control effect on the dissolution of pollutants in the coal gangue and can quickly restore the vegetation of coal gangue, providing better environmental and economic benefits.