Cd(Ⅱ) Tolerance Level And Hydrogen Production Of EAB Under Different Sodium Acetate Concentrations

Bioelectrochemical Systems（BESs）has been widely applied in the field of heavy metals removal research,but in the study the treatment of wastewater containing heavy metal Cd（II）is limited by the boundaries of low concentration in the decade,generally less than 50mg/L;but up to 800 mg/L with traditional biotechnology.It suggests that the microbes have great potential on the tolerance of Cd（II）in the treatment of wastewater.This experiment treat four strains of Cd（II）tolerant electrochemical activity bacteria as pure biological cathode catalysts,based on several concentration of sodium acetate to explore Cd（II）tolerance level and hydrogen production.Experimental results show that higher substrate concentration of sodium acetate can increase the resistance of metal Cd（II）concentration.Cd（II）tolerance concentration increased from 60 mg/L to 150 mg/L,when the highest Cd（II）removal rate increased from 1.48±0.05mg/L/h to 5.28±0.07 mg/L/h and the biggest hydrogen production rate increased from0.0029±0.0001 m³/m³/d to 0.0257±0.001 m³/m³/d.That result in higher sodium acetate concentration,higher Cd（II）tolerance level and hydrogen production.With the improvement of sodium acetate substrate concentration,the Cd（II）concentration of the most prolific hydrogen changed,X1,X3 changed from 20 mg/L to 40 mg/L,X5,X7 changed from 40mg/L to 60 mg/L;X7 has the highest hydrogen production rate is 0.0257±0.001 m³H₂/m³/d;There are two kinds of stress reaction of the EAB for the existence of high concentrations of metal Cd（II）.First kind is cellular detoxification mechanism of reaction,catalyticoxidase（CAT）,superoxidedismutase（SOD）,glutathione（GSH）activity increased,produced by the gene expression in cells relieving the effect of biological toxicity.In addition,the EAB secrete a amounts of extracellular polymers,including polysaccharide,protein,nucleic acids,lipids and humus composition will take a detoxification role by the form of combination with Cd（II）.Through the three dimensional fluorescence spectrum analyze extracellular polymeric substances,compared there proportion of five areas.it can be found in X1,the proportion of V region mainly soluble microbial products increased,for X5,mainlyIII ultraviolet area fulvic acid increased.It means that X1 and X5 combined with metal Cd（II）to ease toxicity and remove the metal by V region and III region,as II and IV region to X3 and X7.This study take a new way to improve EAB’s tolerance of heavy metal,as to increase metal removal rate and hydrogen production in BESs.