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International audience; Single-chamber microbial fuel cells (MFCs) with air-cathodes and new anodes made of stainless steel entangled wires are developed. Increasing the cathode surface area significantly increases performances (doubling the cathode surface area increases the maximum power by +23,3 % and tripling it by +59,8 %). By contrast, increasing the anode surface area rapidly leads to performance saturation (doubling the anode surface area increases the maximum power by +37.8 % but tripling it by only +39.3 %). In addition, decreasing the electrode spacing from 6 cm to 4 cm improves the maximum power by +21.3 % and from 4 cm to 2 cm by +27.9 %. This results permit to optimally dimension the architecture of the MFC in order to maximize energy production while minimizing the amount of materials used to minimize costs. This in turn is likely to enable the development of effective solutions for energy harvesting.

Background The flame-oxidized stainless steel anode (FO-SSA) is a newly developed electrode that enhances microbial fuel cell (MFC) power generation; however, substrate preference and community structure of the biofilm developed on FO-SSA have not been well characterized. Herein, we investigated the community on FO-SSA using high-throughput sequencing of the 16S rRNA gene fragment in acetate-, starch-, glucose-, and livestock wastewater-fed MFCs. Furthermore, to analyze the effect of the anode material, the acetate-fed community formed on a common carbon-based electrode—carbon-cloth anode (CCA)—was examined for comparison. Results Substrate type influenced the power output of MFCs using FO-SSA; the highest electricity was generated using acetate as a substrate, followed by peptone, starch and glucose, and wastewater. Intensity of power generation using FO-SSA was related to the abundance of exoelectrogenic genera, namely Geobacter and Desulfuromonas, of the phylum Proteobacteria, which were detected at a higher frequency in acetate-fed communities than in communities fed with other substrates. Lactic acid bacteria (LAB)—Enterococcus and Carnobacterium—were predominant in starch- and glucose-fed communities, respectively. In the wastewater-fed community, members of phylum Planctomycetes were frequently detected (36.2%). Exoelectrogenic genera Geobacter and Desulfuromonas were also detected in glucose-, starch-, and wastewater-fed communities on FO-SSA, but with low frequency (0–3.2%); the lactate produced by Carnobacterium and Enterococcus in glucose- and starch-fed communities might affect exoelectrogenic bacterial growth, resulting in low power output by MFCs fed with these substrates. Furthermore, in the acetate-fed community on FO-SSA, Desulfuromonas was abundant (15.4%) and Geobacter had a minor proportion (0.7%), while in that on CCA, both Geobacter and Desulfuromonas were observed at similar frequencies (6.0–9.8%), indicating that anode material affects exoelectrogenic genus enrichment in anodic biofilm. Conclusions Anodic community structure was dependent on both substrate and anode material. Although Desulfuromonas spp. are marine microorganisms, they were abundant in the acetate-fed community on FO-SSA, implying the presence of novel non-halophilic and exoelectrogenic species in this genus. Power generation using FO-SSA was positively related to the frequency of exoelectrogenic genera in the anodic community. Predominant LAB in saccharide-fed anodic biofilm caused low abundance of exoelectrogenic genera and consequent low power generation.

This paper provides the information on the optimum conditions of the treatment process of the boat pressure washing wastewater (BPWW) by the combination of the ozonation and electrochemical (EC) methods developed on the laboratory and pilot plant scale. The initial effluent was highly enriched in heavy metals and elevated levels of organic contaminants. The concentrations of V, Cr, Fe, Cu, Zn, TOC, and COD exceeded the upper permissible limits of 22, 20, 6, 112, 17, 4, and 2 times, respectively. The main mechanisms of the organic matter destruction were the ozone oxidation and the indirect oxidation with chlorine/hypochlorite formed by the anodic oxidation of chloride already present in the wastewater. The heavy metal removal was forced by the coagulation/flocculation using Fe(2+), Fe(3+), and Al(3+) ions released into the treated solution by electrochemical corrosion of the sacrificial stainless steel and aluminum electrodes. At the optimum conditions obtained with the pilot plant, the removal efficiencies of the parameters V, Cr, Fe, Ni, Cu, Zn, Pb, TOC, and COD were 100.00 %, 99.35 %, 99.51 %, 87.31 %, 99.83 %, 99.65 %, 100.00 %, 88.46 %, and 76.28 %, respectively. All the parameters in the final effluent were in agreement with regulated values. The advantages of this system compared to its physico-chemical counterparts are as follows: (1) no need for the external addition of flocculating agents since they are electrochemically generated inside the treatment tank; (2) minimal pH changes during the treatment process not requiring pH adjustment by acids/basis; (3) a significantly lower amount of sludge since only Fe and Al ions were released in the solution; (4) flocs formed by the electrocoagulation can be easily separated by the filtration due to their higher stability, lower content of the bound water and larger surface compared to chemical flocs; (5) the final EC effluent is clear, colourless and odourless, containing the less total dissolved solids and organics, thence more suitable for the reuse compared to the one obtained by the standard chemical treatment.