Abstract
An investigation was made into the effects of tannery sludge on soil chemical properties and microbial communities in a typical soil profile with long-term tannery sludge contamination, North China. The results showed that trivalent chromium (Cr(III)), ammonium, organic nitrogen, salinity and sulfide were the predominant contaminants in tannery sludge. Although the tannery sludge contained high chromium (Cr, 3,0970 mg/kg), the proportion of mobile Cr forms (exchangeable plus carbonate-bound fraction) only accounted for 1.32%. The X-ray diffraction and X-ray photoelectron spectroscopy results further demonstrated that the Cr existed in a stable state of oxides and iron oxides. The alkaline loam soil had a significant retardation effect on the migration of salinity, ammonium, Cr(III) and sulfide, and the accumulation of these contaminants occurred in soils (0–40 cm). A good correlation (R2 = 0.959) was observed between total organic carbon (TOC) and Cr(III) in the soil profile, indicating that the dissolved organic matter from sludge leachate promoted the vertical mobility of Cr(III) via forming Cr(III)-organic complexes. The halotolerant bacteria (Halomonas and Tepidimicrobium) and organic degrading bacteria (Flavobacteriaceae, Tepidimicrobium and Balneola) became the dominant microflora in the soil profile. High contents of salinity, Cr and nitrogen were the main environmental factors affecting the abundance of indigenous microorganisms in soils.
Highlights
As a dominant traditional manufacture, tannery industry occupies an important part in China’s economy [1]
Clustering of soil samples was based on the nonmetric multidimensional scaling (NMDS) analysis and the unweighted pair group with arithmetic mean (UPGMA) cluster analysis methods
As the important bacteria having the capacity of breaking down complex organic matter in active sludges, Flavobacteriaceae and Ulvibacter were positively correlated with the organic-N [33], which played important roles in the degradation of carbohydrates and organic-N [34]
Summary
As a dominant traditional manufacture, tannery industry occupies an important part in China’s economy [1]. 2019, 16, x FOR PEER REVIEW highly toxic Cr (containing about 1.0-4.0% of trivalent chromium (Cr(III))) [7], the tannery sludge (containing about 1.0–4.0% of trivalent chromium (Cr(III))) [7], the tannery sludge contains high contains high contents of salinity, ammonium and organic-nitrogen (organic-N), which have a higher contents of salinity, ammonium and organic-nitrogen (organic-N), which have a higher solubility and solubility and mobility and further increase the pollution risk to unsaturated zone. Cr stability; (2) determine the vertical distribution and migration characteristics of the contaminants from tannery sludge leaching soil profile; evaluate the effects the contaminantsononsoil from thethe tannery sludge leaching in in thethe soil profile;. Evaluate the effects ofof the contaminants soil microbial properties in the vertical profile.
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