Temporal Microbial Community Dynamics in Microbial Electrolysis Cells – Influence of Acetate and Propionate Concentration

Abstract

Microbial electrolysis cells (MECs) are widely considered as a next generation wastewater treatment system. However, fundamental insight on the temporal dynamics of microbial communities associated with MEC performance under different organic types with varied loading concentrations is still unknown, nevertheless this knowledge is essential for optimizing this technology for real-scale applications. Here, the temporal dynamics of anodic microbial communities associated with MEC performance was examined at low (0.5 g COD/L) and high (4 g COD/L) concentrations of acetate or propionate, which are important intermediates of fermentation of municipal wastewaters and sludge. The results showed that acetate-fed reactors exhibited higher performance in terms of maximum current density (I: 4.25 ± 0.23 A/m2), coulombic efficiency (CE: 95 ± 8%), and substrate degradation rate (98.8 ± 1.2%) than propionate-fed reactors (I: 2.7 ± 0.28 A/m2; CE: 68 ± 9.5%; substrate degradation rate: 84 ± 13%) irrespective of the concentrations tested. Despite of the repeated sampling of the anodic biofilm over time, the high-concentration reactors demonstrated lower and stable performance in terms of current density (I: 1.1 ± 0.14 to 4.2 ± 0.21 A/m2), coulombic efficiency (CE: 44 ± 4.1 to 103 ± 7.2%) and substrate degradation rate (64.9 ± 6.3 to 99.7 ± 0.5%), while the low-concentration reactors produced higher and dynamic performance (I: 1.1 ± 0.12 to 4.6 ± 0.1 A/m2; CE: 52 ± 2.5 to 105 ± 2.7%; substrate degradation rate: 87.2 ± 0.2 to 99.9 ± 0.06%) with the different substrates tested. Correlating reactor’s performance with temporal dynamics of microbial communities showed that relatively similar anodic microbial community composition but with varying relative abundances was observed in all the reactors despite differences in the substrate and concentrations tested. Particularly, Geobacter was the predominant bacteria on the anode biofilm of all MECs over time suggesting its possible role in maintaining functional stability of MECs fed with low and high concentrations of acetate and propionate. Taken together, these results provide new insights on the microbial community dynamics and its correlation to performance in MECs fed with different concentrations of acetate and propionate, which are important volatile fatty acids in wastewater.

Enhanced CO2 Conversion to Acetate through Microbial Electrosynthesis (MES) by Continuous Headspace Gas Recirculation

“…This result was in agreement with another study [33], where Desulfovibrio was present in a high relative abundance as a planktonic member, although the same authors also identified this genus on their enriched electrodes in previous work [34]. Desulfovibrio has been mainly described as a biological hydrogen producer [32], and its presence along with Pseudomonas, both belonging to the Proteobacteria phylum, has been described in other MES systems [35]. Regarding Pseudomonas, there is physiological evidence that it can develop hydrogenase activity [36] and produce shuttles in BES, thus potentially playing an important role in the extracellular electron transfer [23,37].…”

Competition of two highly specialized and efficient acetoclastic electroactive bacteria for acetate in biofilm anode of microbial electrolysis cell

“…From the perspective of wastewater treatment with resource recovery, EAB that are highly specialized seem to be more efficient in terms of CE and current density. For instance, Geobacter sulfurreducens , a model EAB, is highly specialized and is currently considered the most important current-producing bacterium, and it is the most commonly identified anodic EAB derived from municipal wastewater in microbial fuels cells (MFCs) or microbial electrolysis cells (MECs), using acetate containing growth medium 6 , 7 , 15 , 16 . G. sulfurreducens interact with the anode by direct electron transfer using outer membrane cytochromes 17 and nanowires 18 to externalize the electrons from cell to the anode.…”

Shear Stress Affects Biofilm Structure and Consequently Current Generation of Bioanode in Microbial Electrochemical Systems (MESs)

“…The anode biofilm is a complex aggregation of microbial communities and substances developed from planktonic microorganisms attached to the anode surface. It has been found that several factors can affect the formation, structure, and performance of anode biofilms, including the substrate concentration ( Hari et al, 2017 ), electron acceptor ( Ucar et al, 2017 ), anode solution ( Liu et al, 2017 ), electrode potential ( Bosire and Rosenbaum, 2017 ), and electric field intensity ( Du et al, 2018 ).…”