Bidirectional electron transfer biofilm assisted complete bioelectrochemical denitrification process

Abstract

The biocathode of microbial electrochemical system (MES) accomplished bioelectrochemical denitrification in low C/N wastewater with low demand of exogenous electron donor. However, nitrite accumulation limited the overall nitrogen removal and challenged the further application of bioelectrochemical denitrification process. In this study, a bidirectional electron transfer cathodic biofilm dominated by Geobacter sp. was obtained by polarity reversion from anode to achieve complete nitrogen removal of 98 ± 1.2% (R1), where the Geobacter sp. was sustained by adding 0.1 g L–1 sodium acetate. However, in autotrophic circumstance after electrode reversal, the Geobacter sp. in cathodic biofilm (R2) rapidly lost along with a remarkable drop of nitrogen removal from 76 ± 8.7% (R2-S) to 47 ± 6.6% (R2-1M). Directly domesticated denitrifying biocathode (R3) obtained the lowest total nitrogen removal of 7 ± 3.8%. From principal co-ordinates analysis (PCoA), the function and bio-community of R1 and R2-S demonstrated high similarity with those of anode, while that of R2-1M were much similar with that of R3. The non-turnover CV and DPV indicated that electrochemical active bacteria, such as Geobacter sp., lasted from anode sustained functioning in biofilm of R1, which acted as “electron bridge” to provide extra access for denitrifiers to get electrons from cathode. The mediated electron transfer (MET) was considered as the main mechanism in this “electrode–to–cell–to–cell” pathway by CV analyses with different scan rates.