Denitrifying Bacterial Communities Affect Current Production and Nitrous Oxide Accumulation in a Microbial Fuel Cell

Abstract

The biocathodic reduction of nitrate in Microbial Fuel Cells (MFCs) is an alternative to remove nitrogen in low carbon to nitrogen wastewater and relies entirely on microbial activity. In this paper the community composition of denitrifiers in the cathode of a MFC is analysed in relation to added electron acceptors (nitrate and nitrite) and organic matter in the cathode. Nitrate reducers and nitrite reducers were highly affected by the operational conditions and displayed high diversity. The number of retrieved species-level Operational Taxonomic Units (OTUs) for narG, napA, nirS and nirK genes was 11, 10, 31 and 22, respectively. In contrast, nitrous oxide reducers remained virtually unchanged at all conditions. About 90% of the retrieved nosZ sequences grouped in a single OTU with a high similarity with Oligotropha carboxidovorans nosZ gene. nirS-containing denitrifiers were dominant at all conditions and accounted for a significant amount of the total bacterial density. Current production decreased from 15.0 A·m−3 NCC (Net Cathodic Compartment), when nitrate was used as an electron acceptor, to 14.1 A·m−3 NCC in the case of nitrite. Contrarily, nitrous oxide (N2O) accumulation in the MFC was higher when nitrite was used as the main electron acceptor and accounted for 70% of gaseous nitrogen. Relative abundance of nitrite to nitrous oxide reducers, calculated as (qnirS+qnirK)/qnosZ, correlated positively with N2O emissions. Collectively, data indicate that bacteria catalysing the initial denitrification steps in a MFC are highly influenced by main electron acceptors and have a major influence on current production and N2O accumulation.

Microbial electrochemical systems for nitrate removal from diluted streams

“…Although a few genera of the families Rhodobacteraceae (Alphaproteobacteria) [74,154] and Rhodocyclaceae (Betaproteobacteria) [71,74,87,93] have been previously identified in cathodic biofilms of bioelectrochemical systems, the community structure observed in our cathodic denitrifying biofilm differs considerably from that of other studies, which is attributed mainly to the different inoculum source and the high salinity of media used in the experiments herein.…”

“…Nitrate reductases were previously found in smaller amounts when an effluent from an air cathode was used as feed for cathodic denitrification [74], confirming a possible shift from the use of NO3 -to O2 as electron acceptor. However, in that specific study, it was likely that the presence of both approximately 31 mg L -1 COD (corresponding to 39 mg L -1 sodium acetate) and Oxygen (concentration not informed) could be responsible for a reduction in Coulombic Efficiency observed during that specific feeding regime.…”

“…Many studies have shown bio-anodic organic matter oxidation coupled to bio-cathodic nitrogen removal and power generation in Microbial Fuel Cells [53,54,[70][71][72][73][74][75]. In the study done by Virdis and collaborators [53], the setup was organised as a "loop configuration", where an acetate-and ammonium-containing stream was inserted in the anodic chamber for acetate reduction, carried to an external aerated compartment for nitrification, and then finally passed through the cathodic compartment for denitrification.…”

Extracellular Electron Transfer of <i>Pseudomonas stutzeri</i> Driven by Lithotrophic and Mixotrophic Denitrification

“…7 These studies have encouraged us to hypothesize that the microbial denitrification activity can be regulated by optimizing environmental redox states. 8,9 As a first step toward controlling bacterial denitrification, the present study investigated the EET ability of Pseudomonas stutzeri, a model organism for the study of bacterial denitrification. P. stutzeri is characterized as its diverse and versatile bioenergetics for denitrification.…”

Bioelectrochemical Treatment of Contaminated Groundwater

“…Autotrophic denitrification is a more sustainable solution because carbon is not necessary, and thus, no carbon dioxide is released, leading to better bio stability. The cathode of BES can perform autotrophic nitrogen oxidised compounds (nitrate, nitrite and even nitrous oxide) removals [8][9][10]. BES are capable to treat nitrates at a maximum removal of 226 gNO 3 -·m -3 ·d -1, without no nitrous oxide emission (a greenhouse gas), neither affecting other parameters of quality [11].…”