Abstract
Microbial fuel cells (MFCs) can be designed to combine water treatment with concomitant electricity production. Animal manure treatment has been poorly explored using MFCs, and its implementation at full-scale primarily relies on the bacterial distribution and activity within the treatment cell. This study reports the bacterial community changes at four positions within the anode of two almost identically operated MFCs fed swine manure. Changes in the microbiome structure are described according to the MFC fluid dynamics and the application of a maximum power point tracking system (MPPT) compared to a fixed resistance system (Ref-MFC). Both external resistance and cell hydrodynamics are thought to heavily influence MFC performance. The microbiome was characterised both quantitatively (qPCR) and qualitatively (454-pyrosequencing) by targeting bacterial 16S rRNA genes. The diversity of the microbial community in the MFC biofilm was reduced and differed from the influent swine manure. The adopted electric condition (MPPT vs fixed resistance) was more relevant than the fluid dynamics in shaping the MFC microbiome. MPPT control positively affected bacterial abundance and promoted the selection of putatively exoelectrogenic bacteria in the MFC core microbiome (Sedimentibacter sp. and gammaproteobacteria). These differences in the microbiome may be responsible for the two-fold increase in power production achieved by the MPPT-MFC compared to the Ref-MFC.
Highlights
Continuous and unsustainable animal production causes an accumulation of undesirable products such as swine manure, which has a complex organic matter and nitrogen content that contributes to environmental pollution
The two Microbial fuel cells (MFCs) behaved in terms of their organic matter removal rate (ORR) and no significant differences were found at an organic loading rate (OLR) of 10.5 ± 0.7 kg COD m-3 d-1 (ANOVA test, p = 0.61)
The ratio between the CH4 and CO2 flow rates decreased to 2 in the maximum power point tracking system (MPPT)-MFC primarily due to an increase in CO2 production (17 mL d-1). This increment of CO2 emissions in the MPPT-MFC suggested a higher efficiency of the exoelectrogenic process
Summary
Continuous and unsustainable animal production causes an accumulation of undesirable products such as swine manure, which has a complex organic matter and nitrogen (primarily ammonium) content that contributes to environmental pollution. 1.4 billion tonnes of swine manure are generated in the European Union, where the main contributor country is France [1]. Many technologies have been proposed to treat these pollutants, of which the most commonly employed is anaerobic digestion. PLOS ONE | DOI:10.1371/journal.pone.0164044 October 4, 2016
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