The reduction of oxygen at the cathode is one of the major bottlenecks of microbial fuel cells (MFCs). While research so far has mainly focused on chemical catalysis of this oxygen reduction, here we ...present a continuously wetted cathode with microorganisms that act as biocatalysts for oxygen reduction. We combined the anode of an acetate oxidizing tubular microbial fuel cell with an open air biocathode for electricity production. The maximum power production was 83 ± 11 W m-3 MFC (0.183 L MFC) for batch-fed systems (20−40% Coulombic yield) and 65 ± 5 W m-3 MFC for a continuous system with an acetate loading rate of 1.5 kg COD m-3 day-1 (90 ± 3% Coulombic yield). Electrochemical precipitation of manganese oxides on the cathodic graphite felt decreased the start-up period with approximately 30% versus a non-treated graphite felt. After the start-up period, the cell performance was similar for the pretreated and non-treated cathodic electrodes. Several reactor designs were tested, and it was found that enlargement of the 0.183 L MFC reactor by a factor 2.9−3.8 reduced the volumetric power output by 60−67%. Biocathodes alleviate the need to use noble or non-noble catalysts for the reduction of oxygen, which increases substantially the viability and sustainability of MFCs.
Microbial Fuel Cells for Sulfide Removal Rabaey, Korneel; Van de Sompel, Kirsten; Maignien, Lois ...
Environmental science & technology,
09/2006, Letnik:
40, Številka:
17
Journal Article
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Thus far, microbial fuel cells (MFCs) have been used to convert carbon-based substrates to electricity. However, sulfur compounds are ubiquitously present in organic waste and wastewater. In this ...study, a MFC with a hexacyanoferrate cathodic electrolyte was used to convert dissolved sulfide to elemental sulfur. Two types of MFCs were used, a square type closed to the air and a tubular type in which the cathode compartment was open to the air. The square-type MFCs demonstrated a potential-dependent conversion of sulfide to sulfur. In the tubular system, up to 514 mg sulfide L-1 net anodic compartment (NAC) day-1 (241 mg L-1 day-1 total anodic compartment, TAC) was removed. The sulfide oxidation in the anodic compartment resulted in electricity generation with power outputs up to 101 mW L-1 NAC (47 W m-3 TAC). Microbial fuel cells were coupled to an anaerobic upflow anaerobic sludge blanket reactor, providing total removals of up to 98% and 46% of the sulfide and acetate, respectively. The MFCs were capable of simultaneously removing sulfate via sulfide. This demonstrates that digester effluents can be polished by a MFC for both residual carbon and sulfur compounds. The recovery of electrons from sulfides implies a recovery of energy otherwise lost in the methane digester.
The residue of a fatty acid distillation was used as a diesel fuel in a medium speed diesel engine. This bio-oil was heated to 110 °C to decrease the viscosity to 8 mPa s. The injectors working with ...the bio-oil failed prematurely with operation times ranging from 50 to 1500 h. The injectors and the fuel were investigated in order to know the reasons of the failure and to improve the operation of the engine. The investigation revealed different causes, including plastic deformation and clogging of the injector’s passages, as well as micro cracks, erosion and cavitation damage. The failed injectors were compared with non affected ones from the same engine and injectors from fossil diesel fuelled engines. It was found that the chemical and physical composition of the fuel enforced the failure of the injectors.
► Injector failing occurred by a fatty acid distillation residue as diesel fuel. ► SEM analysis show details of the failures. ► Main damage was caused by the alkalis, water and contamination content of the fuel. ► Surface treatment can improve erosion & oxidation resistance.
The electrochemical oxidation of anionic (sodium dodecylbenzenesulfonate) and cationic (hexadecyltrimethyl ammonium chloride) aqueous dilute surfactant solutions at a BDD (boron-doped diamond) ...electrode has been studied by batch electrolysis experiments and potentiodynamic measurements. In the potential region of water decomposition (
E>2.3 V vs. SHE), surfactants could be deactivated and oxidised with total organic carbon (TOC) removals up to 82% by the action of intermediates of water discharge (e.g. hydroxyl radicals). Of the investigated process parameters, the initial electrolyte pH had the highest impact on surfactant oxidation. An initial pH of 10 significantly enhanced the electrochemical oxidation of both surfactants. The process was not diffusion-controlled and instantaneous current efficiencies (ICE) for TOC removal were in all cases low, varying from 5 to 12% on average. The surfactant deactivation and oxidation potential of the BDD electrode was compared with other carbon-based electrodes. Applying an equal electrode surface, the BDD electrode showed much higher surfactant removals compared to plane graphite. Graphite granules and carbon felt suffered from abrasion, leading to additional carbon loading of the surfactant solutions. Based on the current electrolysis configuration, the specific energy requirement with the BDD electrode for the electrochemical oxidation of surfactants was estimated at 10–20 kW h m
−3 effective wastewater.
BACKGROUND: Supported liquid membranes (SLM) are an alternative technique to remove and recover metals from diluted process solutions and waste-water. In the present work, the removal of Co(II) from ...a synthetic CoSO₄ solution containing initial amounts of cobalt(II) in the range 100-200 ppm (0.1-0.2 g dm⁻³) has been studied on a pilot scale. By performing batch equilibrium experiments, the optimal settings, i.e. the composition of the organic phase, the pH of the feed, the type and concentration of the stripping agent were determined.RESULTS: It is shown that the equilibrium characteristics of a synergistic extractant mixture containing di-2-ethyl-hexylphosphoric acid (D2EHPA) and 5-dodecylsalicylaldoxime (LIX 860-I) are superior to D2EHPA. Both hydrochloric acid and sulfuric acid have been evaluated as stripping solutions in liquid-liquid extraction tests and as the receiving phase in a SLM configuration. Although equilibrium tests showed no difference in stripping characteristics between both chemicals, it was observed that in a SLM configuration the stability of the system when hydrochloric acid is used is poor. With a commercially available SLM module (Liqui-Cel Extra-Flow 4 x 28) having a surface area of 19 m², a steady Co(II) flux of 0.140 gm⁻²h⁻¹ has been obtained at influent concentrations of cobalt between 100 and 200 ppm with 3 mol dm⁻³ sulfuric acid as stripping phase.CONCLUSIONS: The results obtained show that a supported liquid membrane containing a synergistic mixture of LIX 860-I and D2EHPA gives the possibility of recovering cobalt from dilute solutions. Copyright
BACKGROUND: The electrochemical oxidation of 1,4-dioxane at a boron doped diamond (BDD) surface on a niobium substrate anode was studied because (i) 1,4 dioxane is a resistant contaminant in ...waste-waters and ground-waters which needs to be removed/oxidized and (ii) most of the currently applied techniques for removal/oxidation require chemicals.RESULTS: Results show that in the potential region supporting electrolyte stability 1,4-dioxane can be oxidized directly. Adhesive products, which cause electrode fouling, are also formed during oxidation in this potential region. The BDD anode can be restored to its initial activity by simple anodic treatment in the potential region of electrolyte decomposition. In this region, oxidation reactions leading to complete oxidation of 1,4-dioxane, can take place due to electro-generated hydroxyl radicals. Therefore, dioxane can only be effectively oxidized at these potentials. The effect of current density on the oxidation of 1,4-dioxane has been investigated. The experimental results have also been compared with a theoretical chemical oxygen demand (COD)-instantaneous current efficiency (ICE) model. At a current density above 32 mA cm⁻², the oxidation process is completely controlled by mass transfer and no intermediates are formed. 92% of the COD can be removed with a total consumption of 7 Ah L⁻¹.CONCLUSIONS: Results show that dioxane can be effectively and completely oxidized at a BDD anode. Copyright
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