In situ probing the effect of potentials on the microenvironment of heterotrophic denitrification biofilm with microelectrodes

•Heterotrophic biofilm can use electrode as electron donor for denitrification.•High pH suppressed the activities of reductases involving in denitrification.•Low potential reduced the electron supply for denitrification processes.

Bio-electrochemical reactor provides a promising technology to remove nitrogen contaminants in water. In this study, a heterotrophic biofilm for denitrification process was developed, and stable total nitrogen removal efficiencies (>80%) were achieved. Fluorescence in situ hybridization showed that genes norB mainly transcribed in inner biofilm while genes nosZ showed similar transcription activities in the entire biofilm. The microelectrodes of pH and nitrous oxide (N2O) were applied to profile the microenvironment of denitrification biofilm. In all measurements, the microenvironment pH decreased as a function of biofilm depth. The highest N2O concentration of 90 μM in biofilm was detected when the bulk solution pH was 7.3, and an applied potential of −0.2 V did not decrease the yield of N2O in biofilm at pH 7.3. Nevertheless, pH 9.5 or an applied potential of −0.4 V seemed not to suppress the yield of N2O in biofilm.

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