| With the continuous development of China's industrialization,various industrial industries produced a large amount of industrial solid waste,and most of the industrial solid waste would be disposed of in a stacked manner.A large amount of industrial solid waste contained various heavy metals and organic pollutants stored under natural conditions(rain,snow,etc.),which would polluted water and soil and other ecological environments in the form of leachate and eventually endangered human,animal and plant life activities.In this study,cobalt industry industrial waste residue,electroplating sludge and waste incineration bottom ash accumulated in the industrial industry in Zhejiang Province was selected.Firstly,an urease-producing strain(Lysinibacillus fusiformis)with good heavy metal resistance was selected from the industrial waste residue of cobalt industry.After the urease activity test of the strain,the industrial solid waste leachate was repaired and the cobalt industry industrial waste residue was solidified.Finally,the leachate after the repair was subjected to ecotoxicological research.The main conclusions of this study were as follows:(1)The urease-producing strain(Lysinibacillus fusiformis)used in this study was screened from the industrial waste of cobalt industry.Lysinibacillus fusiformis had a good ability to hydrolyze urea;The carbonate ion obtained by hydrolyzing urea could be rapidly combined to form a calcium carbonate precipitate under the condition of calcium chloride,and the crystal form of the calcium carbonate precipitated by the infrared spectroscopy and XRD characterization was determined to be calcite.(2)During the repair process,due to the hydrolysis of urea,the pH value increased rapidly,and the conductivity also grew in the experimental group.Thecalcium ion coupled with the carbonate ion obtained by urea hydrolysis produced calcium carbonate precipitation,so the concentration of calcium ions decreased rapidly.The biomineralization in the experimental group significantly increased the remediation effect of heavy metal in the leachate.The removal rate of cobalt in the leachate of cobalt industry industrial sludge reached 74.7%,the removal rate of copper reached 56.8%;the removal rate of cadmium in electroplating sludge leachate was as high as 98.9%,the removal rate of nickel was 47.1%,and the removal rate of copper was 81.8%,the removal rate of zinc was 97.9%;the removal rate of arsenic in waste incineration bottom leachate was 20.4%,the removal rate of cadmium was75.8%,and the removal rate of lead was 96.0%.(3)SEM-EDXA results showed that the surface of the bacteria in the precipitate after the biomineralization repair was rough,and there was a cementation phenomenon,there were crystal structures with different shapes,and the target heavy metal component was contained in the precipitate.XRD analysis showed that the precipitates after repairing the three kinds of leachate were all calcium carbonate precipitates and reached the role of fixing heavy metal.(4)According to Tessier's five-step extraction analysis,the heavy metal in the precipitate after biomineralization was mainly in the form of carbonate-bound state.The precipitates produced in the control group were mainly exchangeable,and heavy metals in exchangeable state might cause secondary pollution due to desorption and other phenomena.(5)The concentration of cobalt in the leachate of industrial waste in the cobalt industry after the precipitation of the calcium carbonate precipitated by microorganisms was significantly reduced.After 12 days of solidification,the concentration of cobalt in the leachate was 77.15±16.64 mg/L;In the control group using no urease-producing bacteria solidification,the cobalt in the leachate also decreased to some extent,and the final cobalt concentration was 445.78±20.17 mg/L.(6)The main form of cobalt in the industrial waste residue of cobalt industry after biomineralization and solidification was carbonate-bound state,and the cobalt concentration in the carbonate-bound state was as high as 454.13±64.51 mg/kg,accounting for 78.62%;The main form of cobalt in the control group was the exchangeable state,and the concentration was 444.72±68.29 mg/kg,accounting for77.78%.(7)The leachate was produced by the solidification of cobalt industrial waste residue gradually decreases with the increase of the dilution factor,and the toxiceffect on chlorella was gradually reduced.When the dilution factor was 50 times,the chlorophyll fluorescence parameter Fv/Fm of Chlorella was 0.34±0.01 at 8h.It could be seen that the toxic effect of the cobalt industrial waste leachate on the Chlorella after the biomineralization and solidification was significantly reduced,which could be used as a new solid waste pretreatment technology to improve environmental risks.(8)With the increasing dilution factor,the effect of industrial waste leachate on the chlorophyll fluorescence parameters and the photosynthetic oxygen evolution rate of Chlorella gradually decreased.When the dilution factor was 50 times,the leachate of the experimental group repaired by biomineralization had little effect on the chlorophyll fluorescence parameters of Chlorella,while the chlorophyll fluorescence parameters of Chlorella in the control group and the blank group were significantly reduced.So the toxicity of leachate after microbial-induced calcium carbonate precipitation was significantly reduced,which reduced the harm to the ecological environment. |
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