Effects of characteristic pollutants in leather sludge leachate on soil ammonia nitrogen transformation and microbial community structures

This paper is the result of soil environmental survey engineering.ObjectiveThis study is aimed to study the effects of characteristic pollutants (Cr(III), salinity, organic matter) in tannery sludge leachate on NH₄⁺-N transformation and microbial community structure in soil. MethodsThe transformation of NH₄⁺-N to NO₃^--N in soil was studied through soil cultivation experiments under different pollution conditions, and the high-throughput sequencing is used to analyze the composition and structure characteristics of microbial community in soil. Results and ConclusionsThe results show that the characteristic pollution components in the tannery sludge leachate inhibit the nitrification process of NH₄⁺-N in the soil, and the influence factors are sorted as follows:Cr(III)>saltness>organic matter. The exogenous Cr(III) pollution has a significant inhibitory effect on the transformation rate and amount of NH₄⁺-N, whereas the saltness and organic matter only delay the start time of nitrification and reduce the nitrification rate in soil. With the increase of Cr(III) content from 100 mg/kg to 250 mg/kg, the transformation amount of NH₄⁺-N decreased from 94.23% to 19.38% after 90 days of culture. The high Cr(III) and salinity in the leachate have a significant impact on the microbial community structure and distribution in the soil at the initial stage of pollution. With the decrease of the bioavailability of Cr(III) and the enhancement of microbial adaptation in soil aging process, the microbial community structure and composition in Cr(III), salinity, and organic matter contaminated soils become similar, and the abundances of nitrifying bacteria (Nitrosospira, Nitrosomonas and Nitrosospira) also have an obvious increase. Conclusions The results of RDA analysis show that the main characteristic factors affecting the evolution of microbial community structure in tanning contaminated soil are:Cr(III) (R²=0.53, P<0.01), NH₄⁺-N (R²=0.59, P<0.005) and NO₃^--N (R²=0.53, P<0.01).