Screening Of Acid-producing Microorganisms In Mining Area And Study On Bioleaching Of Heavy Metals From Microorganisms Fermentation Broth

The rapid development of mining industry brings economic leap,but also brings serious soil heavy metal pollution problem,resulting in soil quality decline and groundwater pollution,endangering the health and safety of animals and plants and human beings.Studies have shown that some soil microorganisms have produce small organic molecules ability,these small molecule organic acid can remove heavy metals in soil environment,especially in alkaline soil,if can separation to produce organic acids of microbes,leaching in alkaline soil heavy metals,it is a great application significance in the field of soil heavy metal pollution in large-scale mining areas.In this study,high-throughput sequencing technology was used to analyze the microbial diversity of mining areas,and then microbial separation technology was used to screen the soil acid microorganism strains in mining areas.We have obtained seven strains of acid-producing microbial.To determine the optimum conditions for acid production,at the same time,to test the resistance of the strain to heavy metals and to analyze the acid production under heavy metal stress.The types and contents of organic acids produced by the strain were qualitatively and quantitatively analyzed by high performance liquid chromatography(HPLC),and the removal effect of heavy metals under the maximum acid production was investigated.Finally,the removal effect of heavy metals and the effects on soil nutrients and enzyme activity of fermentation broth were studied by oscillating leaching and soil column leaching.The main research results are as follows:Firstly,through the high-throughput sequencing to analyze the microbial diversity of different levels pollution soil.The results showed that the fungal community mainly included Ascomycota,Basdiomycota,Mortierellomycota et al.The bacterial community mainly included: Actinobacteriota,Proteobacteria,Acidobacteriota et al.The microbial diversity of the heavy metal polluted samples was lower than that of the control,and the more serious the heavy metal pollution was,the lower the microbial diversity was;Secondly,seven acid-producing strains were isolated from the soil of mining area by using indicator method.By morphological analysis,16 S r RNA,and 18 S r RNA gene sequence analysis,the results were as follows: They are respectively Aspergillus niger ZJ-I,Aspergillus fumigatus ZJ-II,Penicillium chrysogenum ZJ-V,Penicillium glandicola ZJ-VI,Cunninghamella sp.ZJ-VII,Pseudomonas sp.YZB-4,Pseudomonas plecoglossicida YZB-6.Through the comparison of acid production capacity among strains,four strains ZJ-I,ZJ-V,YZB-4 and YZB-6 were determined to optimize the conditions for acid production by acid production capacity determination.Thirdly,It was discovered by oscillation experiments,under heavy metal stress,the tolerance and acid production capacity of four strains decreased with the increase of heavy metal concentration.The removal rates of Pb,Cd and Zn were 60% ? 95%,60% ? 70% and30% ? 60%,respectively,when the content of organic acids reached the maximum in pure culture for 60 h;Fourthly,based on the optimization of fermentation broth type,solid-liquid ratio,leaching time and other parameters,the results of oscillating leaching showed that when the inoculation ratio of ZJ-I ZJ-V YZB-4 and YZB-6 was 4:4:1:1(complex bacteria(4:1)),the removal rate of Zn,Cd and Pb were 42.4%,46.3%,60.2% respectively.When the solid-liquid ratio was 1:20(g/m L)and the oscillating leaching time was 270 min or later,the removal effect of heavy metals was the best and reached equilibrium.Finally,On the basis of optimized oscillation leaching,soil column leaching test was carried out in the mining area.The results showed that the removal rates of Cd,Zn and Pb were 10.02%,52.83%,34.14%,respectively,and the soil enzyme activity and nutrients were recovered after leaching.In this experiment,a number of acid-producing microorganisms were screened from the soil of alkaline mining areas.Some microorganisms have the ability to strongly produce organic acids and leach heavy metals from the soil with their own organic acids,which is of great significance to control soil heavy metal pollution.