Mechanism And Application Studies On Simultaneous Reduction Of Nitrate And Hexavalent Chromium By Pseudomonas Sp.LZ-4

Nitrate and chromium are two of the most popular industrial materials and co-exist in industrial and domestic wastewater.They are toxic to human and other organism,and caused mass destructions of environment.Microbial degradation is one of the most promising and efficient technologies by reducing nitrate to gaseous nitrogen and reducing hexavalent chromium?Cr????to trivalent chromium?Cr?III??.This thesis have analyzed the denitrification ability of Pseudomonas sp.LZ-4 that was selected previously by laboratory,and have done the researches on mechanism and application of strain LZ-4 in simultaneous reduction of nitrate and Cr???.The main conclusions as follows:?1?Strain LZ-4 has efficient denitrification when acetate,glucose,citrate,or succinate is used as sole carbon source.The optimal C/N is 10 and available pH is 6.0-8.0.It can reduce1000mg/L NO₃^--N at most.Strain LZ-4 can simultaneously reduce 10mg/L Cr???and500mg/L NO₃^--N or 20mg/L Cr???and 200mg/L NO₃^--N,the co-remove rates are above80%.?2?The genome sequences showed that strain LZ-4 included these genes that involved in denitrification and Cr???reduction.RT-PCR experiment indicated that Cr???promoted denitrifying genes expression,especially gene nirK?67-fold?,norB?152-fold?and nosZ?207.5-fold?.Nitrate and Cr???mutually promoted Cr???and nitrate reductase activities,which help decrease the Cr???inhibition on denitrification.Speculated electronic mechanism based on genomes suggested that directly electronic completion and inhibition is existed between anaerobic denitrification and Cr???reduction.However,under aerobic condition,Cr???reduction not competed electronic donor directly with denitrification.Therefore,this electronic transfer mechanism have given a reasonable explanation for strain LZ-4 reducing nitrate and Cr???simultaneously under aerobic condition that is different from anaerobic bacteria.?3?Strain LZ-4 immobilized by polyvinyl alcohol-sodium alga acid could continuously remove 95% of 500 mg/L NO₃^--N,80% of 10 mg/L Cr???and 96% of 5000 mg/L COD in batch membrane bioreactor for 46 days.The experiment that activated sludge combined with immobilized LZ-4 treat wastewater with nitrate and Cr???have found that immobilized LZ-4 significantly improved the sludge for removeing 200mg/L nitrate and 30mg/L Cr???with 100% removal efficiency,and increased the removing concentrations of Cr???from10mg/L to 30mg/L.But the ability of sludge is not improved by free-cell.At the same time,immobilized strain LZ-4 increased biomass concentration of sludge for 50% and increasedsettling velocity?SV?for 1-2 folds compared with control,but directly addition of free strain LZ-4 decrease SV and flocculability of sludge.?4?The colonization of strain LZ-4 on sludge was not achieved by directly addition of free cells,but it can be achieved by immobilization.High-throughput sequencing results of microorganisms based on 16 SrRNA indicated that culture substrate is the most importantly influencing factor in microorganisms construct transformation.After being cultivated in wastewater with nitrate and Cr???for 35 days,the sludge have a less microorganisms diversity.In the process of bioaugmentation,free cells have no any influence on construction of microorganism.However,immobilized strain LZ-4 increased the microorganism diversity of sludge.At class level,it declined abundance of Betaproteobacteria and Saprospirae with26.497% and 7.249%,but increased the abundance of Gammaproteobacteria and Alphaproteobacteria with 14.264% and 12.271% when compared with control group.