Study On Microbial Elution Of Heavy Metal Pollution In Livestock And Poultry Manure

Livestock and poultry manure is used as traditional organic fertilizer in China,which is widely used in agricultural production after composting.However,with the gradual increase in the annual output of livestock manure,the heavy metal content in livestock manure exceeds the standard,and the untreated livestock and poultry manure will pollute the ecological environment after being applied to the farmland,thereby affecting the animals humans and animals health.Harmless treatment of livestock manure.Bioleaching technology is widely used in the removal of heavy metals in the environment due to its mild effect,high removal rate for most heavy metals,low purchase,and environmentally friendly.However,livestock manure contains a large amount of soluble organic matter,which inhibits the growth of autotrophic bacteria and affects the biological leaching effect.Studies have shown that some heterotrophic bacteria,such as acidophilus,can degrade soluble organic matter in livestock and poultry manure and provide suitable growth conditions for autotrophic bacteria.Because autotrophic bacteria usually use 1:1 sulfuric acid for pre-acidification before bioleaching heavy metals,but the amount of sulfuric acid used increases as the scale of bioleaching continues to expand,which not only increases the cost of bioleaching,but also pollute the environment.The heterotrophic bacteria Aspergillus niger can produce organic acids in the process of growth and metabolism to reduce the p H of the leaching environment and provide a suitable growth environment for the autotrophic bacteria Thiobacillus ferrooxidans.In this paper,the synergistic bioleaching technology of Thiobacillus ferrooxidans and yeast was constructed and used for the removal of heavy metals in chicken manure.The effects of yeast addition,initial substrate concentration and initial p H on the removal of heavy metals from chicken manure by bioleaching were investigated by shaking flask experiments.Secondly,using Thiobacillus ferrooxidans and Aspergillus niger synergistically applied to the bioleaching of livestock and poultry manure,the removal effect of heavy metals was investigated and the changes of heavy metal forms were also explored.In addition,the changes of chicken manure on the occurrence of heavy metals in soil,soil physicochemical properties,soil biological properties,etc.after bioleaching were also investigated,as well as subsequent research on soil agricultural utilization.The research in this paper shows the following:（1）The results of the shake flask test showed that the addition of yeast effectively degraded the soluble organic matter in chicken manure,thereby reducing its toxicity to Thiobacillus ferrooxidans and improving the bioleaching efficiency.The optimal system for bioleaching is:according to the solid-liquid ratio（w/v）,the addition of dry chicken manure is 2%,p H=3,and the addition of substrate is Fe²⁺(30g·L^-1)accounting for 10%,Bacteria liquid inoculation amount is 10%,yeast addition amount is 5 g·L^-1,and basic salt is 80%.Under this system,after 12d leaching,the leaching rates of Zn and Cu were 75%and 90%,respectively.At this time,the leaching effect was the best,which was in line with the agricultural land soil pollution risk control standards for subsequent agricultural applications（GB15618-2018）.（2）The synergistic results of Thiobacillus ferrooxidans and Aspergillus niger showed that the leaching rate of heavy metals Cu and Zn was lower than that of single Aspergillus or the synergistic application of Thiobacillus ferrooxidans and yeast.In addition,the distribution of heavy metals in chicken manure after bioleaching has a significant change,which reduces the harm to the environment to a certain extent.（3）The results of agricultural application studies show that,in agricultural application,the unneutralized group tends to change moderately compared with the control group（raw chicken manure）and the neutralized group（the chicken manure after bioleaching is neutralized with slaked lime）soil properties.In addition,the unneutralized group had little effect on soil enzyme activity,and the germination and growth of pakchoi seeds also reached the standard.Therefore,a combination of various factors indicates the necessity of bioleaching heavy metals from chicken manure as an organic fertilizer.