Study On The Isolation Of Chromium Resistant Strains And Disposal Of Tannery Sludge In Tannery Industry

Tannery sludge contains various toxic and hazardous chemicals,such as organic compounds,heavy metals（especially chromium）,sulfides,salts,proteins,polyphenols,surfactants,dyes and syntans,making them very difficult to deal with solid waste.At present,most of chromium-bearing tanning sludges have been studied for the removal of chromium from chromium-bearing tanning sludges.Few researches have been done on the reduction of chrome-containing tanning sludges.Traditional physicochemical treatment methods are expensive and prone to produce secondary pollution.Therefore,there is a need to find an economical and effective method for treating this portion of solid waste.In this experiment,18chromate-resistant strains were isolated,acclimated and enriched by microorganisms in high-chromium sludge.High-chromium sludge was reduced by adding chromium-tolerant bacteria.The experiment also studied the characteristics of chromium-resistant strains（Cr（VI）tolerance,reduction,temperature,pH,etc.）and chromium resistance mechanism.The main research results are as follows:1.Research on reduction of chromium containing tannery sludge by chromium resistant strain.The results showed that 18 chromate-resistant strains isolated from high-chromium-containing sludge could effectively reduce the amount of sludge.Within the first 15 days after adding mixed chromate-resistant strains,the amount of sludge decreased continuously and the amount of sludge Decrement conforms to the first-order reaction kinetics.When the inoculation amount is 2%and 20%,the sludge is reduced by 6%and26%respectively.As the amount of tannery sludge decreases,the TOC is also decreasing.When the inoculum size is 20%,the maximum removal rate of TOC can reach 30%.Different conditions of temperature,pH,carbon source of sludge reduction has a certain impact.Temperature and pH are too high and too low is not conducive to sludge reduction.2.Study on the properties of chromium resistant Strains.The results showed that 5 out of 18 chromate-resistant strains isolated from high chromium-containing sludge showed strong tolerance and reducibility,which were respectively Stenotrophomonas pavanii WY601,Bacillus cereus BPC543,Bacillus subtilis strain BTS741,Microbacterium sp.MMCC609,Proteus mirabilis PCL312.The Cr（Ⅵ）removal rates of WY601,MMCC609,BPC543,BTS741 and PCL312 strains were 90%,79%,83.8%,84.12%and90.12%when Cr（Ⅵ）concentration was 300 mg/L.Under the optimal conditions（37℃,180 rpm,pH6）,the reducibility of Cr（Ⅵ）（600 mg/L）was over 80%in 70 h in WY601,BPC543,BTS741,MMCC609 and PCL312 strains,The five dominant mixed bacteria in 40h,the Cr（Ⅵ）（600 mg/L）reduction rate of up to 100%.The strains WY601,BPC543,BTS741,MMCC609 and PCL312 also have strong ability to remove other heavy metals such as Pb,Fe,Mn,Zn,Ni,Cd,Cu and Co.3.Study on chromium resistance mechanism of WY601 Strain.The results showed that the reduction of chromium in WY601 strain mainly occurred on the extracellular and cellular membranes,and extracellular secretion played a major role in the detoxification of chromium.When the pH was 7 and the temperature was 37℃,the reductase activity and relative stability highest;different heavy metal ions and electron donors have different effects on the reductase activity of WY601 strain,Cu²⁺significantly increased the activity of chromium reductase,increased by 20%,while Hg²⁺have strong inhibition for enzyme make its relative activity reduced to 35%.Reductase activity could be increased in all electron donors tested.