Influence of electric potential on structure and function of biofilm in wastewater treatment reactor: Bacterial oxidation of organic carbons coupled to bacterial denitrification

Abstract

Carbon electrode was applied to a wastewater treatment system as biofilm media. The spatial distribution of heterotrophic bacteria in aerobic wastewater biofilm grown on carbon electrode was investigated by scanning electron microscopy, atomic force microscopy, and biomass measurement. Five volts of electric oxidation and reduction potential were chai charged to the carbon anode and cathode of the bioelectrochemical system, respectively, but were not charged to electrodes of a conventional system. To correlate the biofilm architecture of bacterial populations with their activity, the bacterial treatment efficiency of organic carbons was Measured in the bioelectrochemical system and compared with that in the conventional system. In the SEM image, the biofilm on the anodic medium of the bioelectrochemical system looked intact and active; however, that on the carbon medium of the conventional system appeared to be shrinking or damaging. In the AFM image, the thickness of biofilm formed oil the carbon medium was about two times of those on the anodic medium. The bacterial treatment efficiency of organic Carbons in the bloelectrochem ical system was about 1.5 times higher than that in the conventional system. Some denitrifying bacteria can metabolically oxidize H, Coupled to reduction of NO3- to N-2. H-2 was produced from the cathode in the bioelectrochemical system by electrolysis of water but was not so in the conventional system. The denitrification efficiency was less than 22% in the conventional system and more than 77% in the bioelectrochemical system. From these results, we found that the electrochemical coupling reactions between aerobic and anaerobic reactors may be a useful tool for unprovement of wastewater treatment and denitrification efficiency, without special manipulations such as bacterial growth condition control. C/N ratio (the ratio of carbon to nitrogen) control, MLSS returning, or biofilm refreshing.