Acclimatization And Characteristics Of The Total Cyanide-Degrading Strains In The Spent Pot Lining Derived From Electrolytic Aluminum Industry

The solid waste of spent pot lining（SPL）derived from the electrolytic aluminum industry is classified as industrial hazardous waste,and the component of cyanide is a highly toxic substance that is strictly regulated for emission.The harmless treatment of SPL is therefore very important and necessary.The existing methods to remove cyanide mainly by means of high temperature and chemical oxidation reactions,which often leads to high energy consumption and serious pollution.Meanwhile,the complexity and the cost of subsequent treatment processes are accordingly added.Based on the functional properties of biodegradation of cyanide,the acclimazation and degradation characteristic of cyanide-degrading strains in the specific SPLenvironment were researched.The study will lay the foundation for further discussing the SPL biodegradation mechanism of cyanide in theory and developing new processes technologically.The main achievements of the study were summarized as follows.Acclimazation of the total cyanide-degradation strains and the analysis of community.The cyanide contaminated soils around a mining area and an aluminum company in Guangxi were collected and sampled for strains acclimazation using water leaching solution of SPL.ICP-MS analysis showed that ferrocyanide and ferricyanide were the mian existence form of total cyanide in the water leaching solution of SPL.The acclimazation of cyanide-degrading strains were performed using the barren medium by gradually increasing the concentrations of ferrocyanide and ferricyanide up to 1000 mg/L.Finally,two consortium B and P that was capable of tolerating a p H 10.0 alkaline condition and degrading total cyanide were obtained after re-screening.Community and metagenomic analysis of consortium revealed that the consortiums B and P contained 80 and 69 genera respectively,and bacteria were the main species.A heigher proportion of genera was Providencia,Bacillus and Proteus,among which Providencia was the dominant genus.The characteristics of consortium B with good degradation ability of total cyanide were further studied.The effects of C/N ratios,p H,temperature,biomass,medium volumes,ferricyanide concentration and salinity on the biodegradation in the inorganic medium were investigated.Results showed that the biodegradation effeciency was 55.6±1.9%for 50 mg/L ferricyanide at C/N=6:1,p H 10.0,temperature of 30℃,medium volume of 75 m L,inoculation amount of 10%and salinity of 1%.Ferricyanide could be used as the sole of nitrogen source for the growth of consortium B,and the value of OD₆₀₀ was increased from 0.860±0.010 to 1.411±0.009.The degradation product concentrations of iron and ammonium ions were 3.20±0.19 mg/Land 48.20±1.50 mg/L respectively,which was higher than that of the blank group.However,the experimental concentrations were less than the theoretical values.It was considered that the ammonium-nitrogen might be further used as the nitrogen source,and the iron ion might be adsorbed by consortium B.The putative genes of encoding cyanohydrin hydratase,thiocyanate-generating enzyme and cytochrome bo oxidase involved in the degradation of ferricyanide were annotated in the analysis of metagenome.In addition,the putative genes for the tolerance of alkalinity,salinity,both high and low temperature were also found,indicating great potential for practical application.The biological remediation of the actual water leaching solution of SPL,SPL and cyanide-contaminated soil were carried out.For the actual water leaching solution of SPL,the biological remediation efficiency of 50 mg/L total cyanide complexes was 66.5±2.2%.Due to the limitation of mass transfer in the solid phase,the biological remediation efficiency of SPL with total cyanide complexes concentration of 50 mg/kg was only 23.0±2.8%.Adding glucose as a carbon source and increasing the inoculation amount to 20%could improve the remediation efficiency to 38.2±2.1%.However,the addition of ammonium sulfate as a nitrogen source was ineffective.Under the same conditions as SPL,the biological remediation efficiency of cyanide-contaminated soil could reach64.3±2.9%.The enhanced remediation efficiency could be ascribed to the loose structure of soil,benefiting mass transfer,and thus incresaing the proliferation of consortium B.These results are the foundation for further in-depth research on mechanism and engineering application.