Synergistic Effects Of Cadmium-resistant EAB And Cathode Electrons On Hydrogen Production

Biocathode bioelectrochemical systems(BESs)has shown promising for heavy metalremoval with simultaneous hydrogen production.However,roles of electrochemically active bacteria(EAB),in particular relationships between EAB and cathodic electrons in heavy metal removal and hydrogen production are still unclear.In this study,four EAB were successfully isolated from well-developed Cd-removed biocathode BESs and tentatively identified as Ochrobactrum sp.ST1,Pseudomonas sp.ST3,Pseudomonas delhiensis ST5 and Ochrobactrum anthropi ST7.Synergistic effects of Cd-resistant EAB and cathodic electrons on hydrogen production were observed for all four EAB,achieving up to 0.0124 ± 0.0001 m3/m3/d(ST7),appreciably higher than 0.0017 ± 0.0002 m3/m3/d(ST1),0.0018 ± 0.0000 m3/m3/d(ST3)and 0.0028 ±0.0001 m3/m3/d(ST5).While the presence of Cd(?)improved the synergistic effects for EAB ST3 and ST7,resulting in enhanced hydrogen production of 34%(ST3)and 69%(ST7).Hydrogen production in EAB ST1 was negligibly affected by Cd(?),compared to the adverse effect on ST5.For ST1,ST3 and ST5,hydrogen production was dependent on extracellular polymer substance(EPS),accounting for 25%(ST5)of the total.Although EPS of ST7 under20 mg/L Cd(?)performed best,it only made a little contribution(3%).By measurement of intracellular enzyme superoxyde dismutase(SOD),catalytic oxidase(CAT),glutathione(GSH)and dehydrogenase(DH),electrons can relieve the toxic effects of metal on EAB,but the strengthening or weakening hydrogen production of the synergism is mainly caused by the change of biomass and DH.Cyclic voltammetry(CV)results were consistent with the conclusions mentioned above.In the open circuit controls,EAB can facilitate Cd(?)removal compared to abiotic cathode with a max increase of 37%(ST5)under 20 mg/L Cd(?).Cd(?)removal in the closed circuit controls was superior to that in the open circuit controls,and the max increased percentage 21%(ST1)of EAB was lower to 51% chemical growth due to Cd(?)reducing slower or harder.CV and XPS analysis demonstrated the presence of EAB ST3 and ST5 adversely affected Cd(?)removal whereas EAB ST1 and ST7 had negligible effects on Cd(?)removal.The four EAB in concert exhibited increased Cd(?)removal with the increase ininitial Cd(?)concentration,during which cathodic electrons played an increased role in Cd(?)removal.