Study On Synergistic Degradation Of Dye Wastewater By Mixed Microbial Culture Of Electroactive Bacteria And Fungus Using Starch As Carbon Source

The massive production and use of dyes not only cause serious environmental pollution problems,but also seriously threaten human health.Therefore,it is urgent to treat dye wastewater.Because of environmental friendliness,biological method is considered as the most promising method.Especially electroactive microbe,due to non-specific degradation effect,it has been widely applied in studies of environmental pollution remediation.However,lactate was widely used as carbon source in those studies,which resulted in high cost of carbon source,because most of electroactive bacteria lack the ability to use relatively cheap macromolecular organic carbon source,such as starch.Thus,to solve this problem,the model electroactive bacteria,Shewanella oneidensis MR-1,was selected in our study,and the mixed microbial culture system of S.oneidensis MR-1 and brown rot fungus(Gloeophyllum trabeum)was constructed to realize the pollution remediation by electroactive bacteria using starch as carbon source.Firstly,dye pollutants with different structure types were used to evaluate the anaerobic degradation effect of this mixed microbial system.Then,methyl orange(MO),a model azo dye,was utilized to optimize degradation parameters in this mixed microbial system to achieve the maximum degradation efficiency,and the toxicity of MO metabolites was evaluated.Finally,the degradation mechanism of this mixed microbial system was further explored from two aspects of biology and chemistry.The main conclusions are as follows:(1)By innovatively constructing the mixed microbial culture system of S.oneidensis MR-1 and G.trabeum,the reductive degradation of pollutants by S.oneidensis MR-1 was successfully achieved with starch as carbon source,so the cost of carbon source for pollution remediation of electrochemically active microorganisms was decreased.(2)The mixed microbial culture system of S.oneidensis MR-1 and G.trabeum could effectively degrade different structure types of dyes(azo dye MO with high polarity,azo dye Cationic Red with neutral polarity,azo dye Methyl Red with low polarity,triphenylmethane dye Aniline Blue,metal complex dye Naphthol Green B),and the degradation efficiency of dyes all exceeded 92%,so this system had broad and universal degradability.(3)The degradation effect of the mixed microbial culture system of S.oneidensis MR-1 and G.trabeum is influenced by many factors such as initial dye concentration,inoculation ratio of bacteria and fungus,temperature,pH and salinity.But it is less affected by salinity,and has a good tolerance of high salt environment.The optimal degradation conditions obtained are as follows: initial concentration of MO was 100 mg/L,inoculation ratio of S.oneidensis MR-1 and G.trabeum was 2:3(V/V),concentration of starch was 2 g/L,temperature was is 30?,and pH was 7.0.Under optimized conditions,the degradation efficiency of MO after 10 h was 96.1%,and its phytotoxicity after degradation was decreased.(4)The dye degradation in the mixed microbial culture system of S.oneidensis MR-1 and G.trabeum is caused by the synergistic effect of S.oneidensis MR-1 and G.trabeum.Among them,G.trabeum gradually decomposed macromolecular starch into small molecular ethanol to provide small molecular carbon source for S.oneidensis MR-1 degrading pollutants.S.oneidensis MR-1 is the main undertaker of pollutant degradation.The produced small molecule carbon source was used by S.oneidensis MR-1 to release electrons through anaerobic dissimilation respiration for reductive degradation of dye.And compared with pure culture system of S.oneidensis MR-1 system,the electron transport pathway during the degradation of MO has not changed.MO was still extracellularly degraded into N,N-dimethylbenzene-1,4-diamine and 4-amino benzenesulfonic acid due to its azo bond cleavage.