The chromium migration risk from tannery sludge into shallow soil and groundwater: Influence factors, modeling, and microbial response

Combined pollution in tannery sludge landfill has become increasingly serious. Accurate identification of the contribution of coexisting substances to Cr migration in tannery sludge sites was essential for the selection of remediation methods for tannery contaminated sites. However, the effect of the coexisting substances on their contribution to Cr migration remained unclear. In this study, the analytical method of panel data and soil column experiments were combined for the first time to quantify the extent to which different contaminants contribute to Cr migration, and further identify the dominant microbial species. Results showed that NH3-N inhibited the migration of Cr(VI), while NO3--N and fatliquor agent promoted the migration of Cr(VI). The panel data analysis showed that the order of the contribution rate of the factors affecting the Cr(VI) migration was Cr(VI) concentration, coexisting substances, and environment factors. In addition, Veronii was the dominant popular in fatliquors-contaminated soils. The relative abundance of Veronii increased from 6.31% to 30.48% in the fatliquors treatment group, while it decreased to 21.65% in the fatliquors and Cr treatment group. This study provided a quantitative method to the contribution rate of various factors to Cr migration under rainfall, taken into account the response of the microbial community in each experimental group, and provided theoretical support for the selection of remediation methods in soil and groundwater for tannery sites.