Groundwater pollution and human health risks caused by leachate leakage have become a worldwide environmental problem, and the harm and influence of bacteria in leachate have received increased attention. Setting the isolation distance between landfill sites and groundwater isolation targets is particularly important. Firstly, the intensity model of pollutant leakage source and solute transport model were established for the isolation of pathogenic Escherichia coli. Then, the migration, removal and reduction of bacteria in the aerated zone and ground were simulated. Finally, the isolation distance was calculated based on the acceptable water quality limits, and the influence of hydrogeological arameters was analyzed based on the parameter uncertainty. The results of this study suggest that the isolation distances vary widely ranging from 106 m–5.46 km in sand aquifers, 292 m–13.5 km in gravel aquifers and 2.4–58.7 km in coarse gravel aquifers. The gradient change of groundwater from 0.001 to 0.05 resulted in the isolation distance at the highest gradient position being 2–30 times greater than that at the lowest gradient position. There was a difference in the influence of the thickness of the vadose zone. For example, under the same conditions, with the increase of the thickness of the aeration zone, the isolation distance will be reduced by 1.5–5 times, or under the same thickness of the aeration zone, the isolation distance will be significantly shortened. Accordingly, this needs to be determined based on specific safety isolation requirements. In conclusion, this research has important guiding significance for the environmental safety assessment technology of municipal solid waste landfill.

Porous graphitic carbon nitride (g-C₃N₄) was prepared by dicyandiamide and urea via the pyrolysis method, which possessed enhanced visible-light-driven photocatalytic performance. Its surface area was increased from 17.12 to 48.00 m²/g. The porous structure not only enhanced the light capture capacity, but also accelerated the mass transfer ability. The Di (Dicyandiamide)/Ur (Urea) composite possessed better photocatalytic activity for Rhodamine B in visible light than that of g-C₃N₄. Moreover, the Di/Ur-4:5 composite showed the best photoactivity, which was almost 5.8 times that of g-C₃N₄. The enhanced photocatalytic activity showed that holes and superoxide radical played a key role in the process of photodegradation, which was ascribed to the enhanced separation of photogenerated carriers. The efficient separation of photogenerated electron-hole pairs may be owing to the higher surface area, O dopant, and pore volumes, which can not only improve the trapping opportunities of charge carriers but also the retarded charge carrier recombination. Therefore, it is expected that the composite would be a promising candidate material for organic pollutant degradation.