Microcalorimetric Analysis And Isolation Of Denitrifying Electroactive Bacteria

Currently,solving the environmental pollution and exploring new energy sources are two fundamental issues concerned worldwide.Microbial fuel cells?MFC?provide an emerging wastewater treatment method,which can remove various pollutants such as sulfurous and nitrogenous pollutants from wastewater coupled with power recovery.The microorganism play a crucial role in removal of pollutants from wastewater.The activity of denitrifying electroactive bacteria not only affect the performance of nitrate removal but also become a limiting factor for the performance of denitrifying sulfide removal MFC.In this study,the growth characteristics and metabolic activities of denitrifying electroactive bacteria under different cathodic potentials were analyzed by microcalorimetry.Denitrifying electroactive bacteria were isolated from a denitrifying sulfide removal MFC by potentiostatic gradient dilution method.In addition,the effects of pH in cathodic influent on pollutant removal and power generation of MFC were investigated,which indirectly reflected the effect of denitrifying electroactive bacteria activity on MFC performance.Main conclusions are listed as follows:?1?Microcalorimetric parameters can characterize the growth and metabolic activities of denitrifying electroactive bacteria.The optimal metabolic activity of the denitrifying electroactive bacteria was obtained at a cathode potential of-150 mV,achieving the maximum specific metabolic rate of?3.30±0.22?×10^-10 mgNO₃^--N/min/per.The corresponding growth rate constant of the denitrifying electroactive bacteria was?4.20±0.51?×10^-3 min^-1.?2?When the cathodic potential was 250 mV,nitrite reduction to gaseous nitrogen became the rate-limiting step of denitrification process.The denitrification process mediated by denitrifying electroactive bacteria included two distinct steps:nitrate reduction to nitrite and nitrite reduction to gaseous nitrogen.The growth rate constant of dominant bacteria corresponding to the first step(?5.53±1.15?×10^-3 min^-1)was higher than that to the second step(?5.53±1.15?×10^-3 min^-1).?3?The dominant denitrifying electroactive bacteria were affiliated to the genus Pseudomonas.Its relative abundance was 65.77% after the culture was isolated twice through the direct isolation method.Its relative abundance reached 77.02% after the culture was isolated twice through the enrichment-isolation method.?4?The denitrifier species were affected by the applied cathode potential in potentiostatic environment.After isolation through the direct isolation method and the enrichment-isolation method,same species of denitrifying electroactive bacteria affiliated to the genus Pseudomonas dominated in the isolates,with high similarity to the species of NR114751.1 and NR103934.2.?5?When the external resistance was poised at a level where the limiting current density being obtained,the optimal performance of pollutants removal was obtained at pH 6.The total nitrogen removal loading was 11.9±0.3 gN/?m³·d?and the production efficiency of gaseous nitrogen was 40.7±0.6%.The sulfide removal loading and production efficiency of sulfate also reached the maximum levels of 0.145±0.002kgS/?m³·d?and 71.5±1.4%.The maximum cycle charge of 424.4±0.2 C was achieved at pH 8 when the external resistance was poised at a level equal to the internal resistance.