Combined Treatment Of Anaerobic Sludge,Kitchen Waste And Ferrous Sulfate To Chromium Contaminated Soil

China is a large country of chromate production.Chromium pollution is an environmental problem left behind by the rapid development of China's industry.Due to the limitation of economic and technological conditions,most of the chromium residue is simply stacked without effective harmless treatment.Chromium residue has a high concentration of water-soluble Cr(?),which can spread to the surrounding water,soil and atmospheric environment under the action of natural environment and produces serious ecological pollution problems.Therefore,the treatment of chromium contaminated soil has attracted public attention.The detoxification of chromium contaminated soil with anaerobic sludge and kitchen waste was studied in this paper.The synergistic effects of anaerobic sludge combined with kitchen waste and ferrous sulfate detoxified chromium contaminated soil were investigated.The optimum combination of mixed remediation agents was determined by orthogonal design experiments and the initial Cr(?)concentration,soil pH,water content and mixed remediation agents(weight)were studied,and the factors such as chromium contaminated soil were treated by factors such as chromium contaminated soil.The reaction mechanism of Cr(?)reduction by mixed reagents was also analyzed.The main results of the experiment are as follows:(1)In the synergistic effect experiments of anaerobic sludge combined with kitchen waste and ferrous sulfate detoxifying chromium contaminated soil,the water-soluble Cr(?)concentration in the control group was the least,and the number 8 experiments group was the largest.Among them,after 8 days of anaerobic fermentation,the concentration of Cr(?)decreased by 1425.99 mg/kg,and the reduction rate was 32.79%.The reduction rate is 18.24%higher than that of the blank control group,and the reduction rate is 1%?8%higher than that of the other experimental group.It can be seen that the combination of anaerobic sludge,kitchen waste and ferrous sulfate has synergistic effect,and the reduction effect of Cr(?)is better than that of single or 22 combinations of three kinds of raw materials.(2)The 9 optimal experimental schemes determined by orthogonal design,the 1 experimental combination performed the best effect,in which the water-soluble Cr(?)concentration of the twenty-seventh day mixture is the lowest.Through the analysis of variance and the significant level test,it was found that the reaction time of the mixed reagents had a significant effect on the reduced water-soluble Cr(?),and the ferrous sulfate had a significant effect,while the anaerobic sludge:food waste had no significant effect on the reduced water-soluble Cr(?).According to the consideration of various factors,the optimum combination of mixed reagents should be selected as 10000 mg/kg,5 days of reaction time and anaerobic sludge:three parameters of kitchen waste =5:1.(3)The reduction of Cr(?)by mixed reagents was influenced by the concentration of soil initial Cr(?),the ratio of mixed remediation agents(weight)and chromium contaminated soil,pH and water content;? In the initial Cr(?)concentration of soil,with the increase of initial Cr(?)concentration,the reduction of Cr(?)reduced gradually.The trend of reduction of Cr(?)by mixed restorants was more obvious,which the longer the time needed for reduction,of which the soil decreased fastest with the initial Cr(?)concentration of 580 mg/kg.At fifth days of fermentation.it is completely reduced to Cr(?);? A mixed repair agent(weight ratio):the smaller the ratio of chromium soil,the more the organic matter and the microbial biomass provided,the more beneficial to the reduction of soil Cr(?),and the mixed remediation agent:the chromium soil = 1:1 experimental group has the fastest reduction rate of Cr(?)and in the reaction.Cr(?)is all reduced;? The lower the soil pH,the lower the pH,the increase of the redox potential and the stronger the oxidation capacity of the soil,which is beneficial to the reduction of Cr(?)to the rate of Cr(?).Under the condition of pH= 5,the reduction effect of Cr(?)is the best;? in the process of fermentation,high water content can dilute Cr(?)concentration and improve the mass transfer rate of the reaction process,which is beneficial to the reduction of Cr(?).When the water content is 75%,the reduction of Cr(?)reaches the maximum,the concentration of Cr(?)decreases from 935.25 mg/kg to 30.76 mg/kg,and the reduction rate is 96.71%.(4)The Cr(?)in the soil exists different forms in the soil,among which water-soluble chromium,iron manganese oxide bound chromium,organic compound chromium and residue chromium were accounted for more than 80%of the total chromium.After 18 days treatment,most of the combined state chromium in water soluble and iron manganese is converted into organic combined chromium,and a small amount of chromium is converted into residual chromium,and the migration ability of chromium in the environment is obviously reduced.(5)Through the dynamic test,it is found that the process of reducing Cr(?)by the mixed repair agent is mainly composed of two first order reactions,1-8 day is a rapid reaction stage,8-20 day is a slow reaction stage,and the reaction rate constant is 0.129 and 0.022,respectively.