Bioelectrochemical treatment and recovery of copper from distillery waste effluents using power and voltage control strategies.

Copper recovery from distillery effluent was studied in a scalable bioelectro-chemical system with approx. 6.8 L total volume. Two control strategies based on the control of power with maximum power point tracking (MPPT) and the application of 0.5 V using an external power supply were used to investigate the resultant modified electroplating characteristics. The reactor system was constructed from two electrically separated, but hydraulically connected cells, to which the MPPT and 0.5 V control strategies were applied. Three experiments were carried out using a relatively high copper concentration i.e. 1000 mg/L followed by a lower concentration i.e. 50 mg/L, with operational run times defined to meet the treatment requirements for distillery effluents considered. Real distillery waste was introduced into the cathode to reduce ionic copper concentrations. This waste was then recirculated to the anode as a feed stock after the copper depletion step, in order to test the bioenergy self-sustainability of the system. Approx. 60-95% copper was recovered in the form of deposits depending on starting concentration. However, the recovery was low when the anode was supplied with copper depleted distillery waste. Through process control (MPPT or 0.5 V applied voltage) the amount and form of the copper recovered could be manipulated.

A new sequential injection analysis-capillary electrophoresis system with amperometric detection.

A novel and fully automated sequential injection analysis manifold coupled to a capillary electrophoresis apparatus with amperometric detection, is described. The sequential injection manifold was isolated from the high voltage by inserting an air plug into the circuit. Small buffer reservoirs were used to avoid the need to pump fresh buffer to the interface during the electrophoretic separation. No decoupling device was used to mitigate the interference from the high voltage electric field, instead the potential shift induced by the separation voltage, was accounted for. The new hydrodynamic injection method presented is based on the overpressure created in the circuit when a pinch valve is closed for a predetermined time. The injection method yields RSD values of peak height and area below 2.55 and 1.82%, respectively, at different durations of valve closure (n = 5). The capillary and working electrode alignment was achieved by adapting a commercial available capillary union. When the electrode was replaced, the alignment method proved to be very reliable, yielding RSD values of peak height and area lower than 2.64 and 2.08%, respectively (n = 8). Using this system with a gold microelectrode, dopamine, and epinephrine could be quantified within the concentration range of 1-500 µM and detected at a concentration of 0.3 µM. The methods here presented could be applied for the development of new capillary electrophoresis systems with amperometric detection and/or to the design of fully automated systems for online process monitoring purposes.

Anodic electro-fermentation of 3-hydroxypropionic acid from glycerol by recombinant Klebsiella pneumoniae L17 in a bioelectrochemical system.

BACKGROUND: 3-Hydroxypropionic acid (3-HP) is an important platform chemical which can be produced biologically from glycerol. Klebsiella pneumoniae is an ideal biocatalyst for 3-HP because it can grow well on glycerol and naturally synthesize the essential coenzyme B12. On the other hand, if higher yields and titers of 3-HP are to be achieved, the sustained regeneration of NAD+ under anaerobic conditions, where coenzyme B12 is synthesized sustainably, is required. RESULTS: In this study, recombinant K. pneumoniae L17 overexpressing aldehyde dehydrogenase (AldH) was developed and cultured in a bioelectrochemical system (BES) with the application of an electrical potential to the anode using a chronoamperometric method (+0.5 V vs. Ag/AgCl). The BES operation resulted in 1.7-fold enhancement of 3-HP production compared to the control without the applied potential. The intracellular NADH/NAD+ ratio was significantly lower when the L17 cells were grown under an electric potential. The interaction between the electrode and overexpressed AldH was enhanced by electron shuttling mediated by HNQ (2-hydroxy-1,4-naphthoquinone). CONCLUSIONS: Enhanced 3-HP production by the BES was achieved using recombinant K. pneumoniae L17. The quinone-based electron transference between the electrode and L17 was investigated by respiratory uncoupler experiments. This study provides a novel strategy to control the intracellular redox states to enhance the yield and titer of 3-HP production as well as other bioconversion processes.

Increased biohydrogen yields, volatile fatty acid production and substrate utilisation rates via the electrodialysis of a continually fed sucrose fermenter.

Electrodialysis (ED) removed volatile fatty acids (VFAs) from a continually-fed, hydrogen-producing fermenter. Simultaneously, electrochemical removal and adsorption removed gaseous H2 and CO2, respectively. Removing VFAs via ED in this novel process increased H2 yields by a factor of 3.75 from 0.24molH2mol-1hexose to 0.90molH2mol-1hexose. VFA production and substrate utilisation rates were consistent with the hypothesis that end product inhibition arrests H2 production. The methodology facilitated the recovery of 37g of VFAs, and 30L H2 that was more than 99% pure, both of which are valuable, energy dense chemicals. Typically, short hydraulic and solid retention times, and depressed pH levels are used to suppress methanogenesis, but this limits H2 production. To produce H2 from real world, low grade biomass containing complex carbohydrates, longer hydraulic retention times (HRTs) are required. The proposed system increased H2 yields via increased substrate utilisation over longer HRTs.

Maximising biohydrogen yields via continuous electrochemical hydrogen removal and carbon dioxide scrubbing.

The use of electrochemical hydrogen removal (EHR) together with carbon dioxide removal (CDR) was demonstrated for the first time using a continuous hydrogen producing fermenter. CDR alone was found to increase hydrogen yields from 0.07molH2molhexose to 0.72molH2molhexose. When CDR was combined with EHR, hydrogen yields increased further to 1.79molH2molhexose. The pattern of carbohydrate utilisation and volatile fatty acid (VFA) production are consistent with the hypothesis that increased yields are the result of relieving end product inhibition and inhibition of microbial hydrogen consumption. In situ removal of hydrogen and carbon dioxide as demonstrated here not only increase hydrogen yield but also produces a relatively pure product gas and unlike other approaches can be used to enhance conventional, mesophilic, CSTR type fermentation of low grade/high solids biomass.

Removal and recovery of inhibitory volatile fatty acids from mixed acid fermentations by conventional electrodialysis.

Hydrogen production during dark fermentation is inhibited by the co-production of volatile fatty acids (VFAs) such as acetic and n-butyric acid. In this study, the effectiveness of conventional electrodialysis (CED) in reducing VFA concentrations in model solutions and hydrogen fermentation broths is evaluated. This is the first time CED has been reported to remove VFAs from hydrogen fermentation broths. During 60 min of operation CED removed up to 99% of VFAs from model solutions, sucrose-fed and grass-fed hydrogen fermentation broths, containing up to 1200 mg l(-1) each of acetic acid, propionic acid, i-butyric acid, n-butyric acid, i-valeric acid, and n-valeric acid. CED's ability to remove VFAs from hydrogen fermentation broths suggests that this technology is capable of improving hydrogen yields from dark fermentation.

Inhibition of methane production in microbial fuel cells: operating strategies which select electrogens over methanogens.

Methanogenesis may diminish coulombic efficiency of microbial fuel cells (MFCs), although its importance is application dependent; e.g., suppression of methanogenesis may improve MFC sensing accuracy, but may be tolerable in COD removal from wastewaters. Suppression of methanogenesis was investigated in three H-type MFCs, enriched and acclimated with acetate, propionate and butyrate substrates and subsequently operated under open and closed circuit (OC/CC) regimes. Altering the polarisation state of the electrode displaces microorganisms from the anodic biofilm and leads to observable methane inhibition. The planktonic archeal community was compared to the electrode biofilm whilst under the OC/CC regimes. Semi-quantitative DNA analyses indicate a shift in some dominant species, from the electrode to the solution, during OC operation. The effect of prolonged starvation on anodic species was also studied. The results indicate progressive inhibition of methanogenesis from OC/CC operations; and virtual cessation of methanogenesis when an MFC was starved for a significant period.

The influence of anodic helical design on fluid flow and bioelectrochemical performance.

In this study three different tubular helical anode designs are compared, for each helical design the pitch and nominal sectional area/liquid flow channel between the helicoids was varied and this produced maximum power densities of 11.63, 9.2 and 6.73Wm(-3) (small, medium and large helical flow channel cross-sections). It is found that the level of mixing and the associated shear rates present in the anodes affects both the power development and biofilm formation. The small helical flow channel carbon anode produced 40% more biofilm and this result was related to modelling data which determined a system shear rate of 237s(-1), compared to 52s(-1) and 47s(-1) for the other reactor configurations. The results from computational fluid dynamic modelling further distinguishes between convective flow conditions and supports the influence of helical structure on system performance, so establishing the importance of anodic design on the overall electrogenic biofilm activity.

Augmenting Microbial Fuel Cell power by coupling with Supported Liquid Membrane permeation for zinc recovery.

Simultaneous removal of organic and zinc contamination in parallel effluent streams using a Microbial Fuel Cell (MFC) would deliver a means of reducing environmental pollution whilst also recovering energy. A Microbial Fuel Cell system has been integrated with Supported Liquid Membrane (SLM) technology to simultaneously treat organic- and heavy metal containing wastewaters. The MFC anode was fed with synthetic wastewater containing 10 mM acetate, the MFC cathode chambers were fed with 400 mg L(-1) Zn(2+) and this then acted as a feed phase for SLM extraction. The MFC/SLM combination produces a synergistic effect which enhances the power performance of the MFC significantly; 0.233 mW compared to 0.094 mW in the control. It is shown that the 165 ± 7 mV difference between the MFC/SLM system and the MFC control is attributable to the lower cathode pH in the integrated system experiment, the consequent lower activation overpotential and higher oxygen reduction potential. The change in the substrate removal efficiency and Coulombic Efficiency (CE) compared to controls is small. Apart from the electrolyte conductivity, the conductivities of the bipolar and liquid membrane were also found to increase during operation. The diffusion coefficient of Zn(2+) through the liquid membrane in the MFC/SLM (4.26*10(-10) m(2) s(-1)) is comparable to the SLM control (5.41*10(-10) m(2) s(-1)). The system demonstrates that within 72 h, 93  ±  4% of the zinc ions are removed from the feed phase, hence the Zn(2+) removal rate is not significantly affected and is comparable to the SLM control (96  ±  1%), while MFC power output is significantly increased.

Control of power sourced from a microbial fuel cell reduces its start-up time and increases bioelectrochemical activity.

Microbial fuel cell (MFC) performance depends on the selective development of an electrogenic biofilm at an electrode. Controlled biofilm enrichment may reduce start-up time and improve subsequent power performance. The anode potential is known to affect start-up and subsequent performance in electrogenic bio-catalytic consortia. Control strategies varying electrical load through gradient based maximum power point tracking (MPPT) and transient poised anode potential followed by MPPT are compared to static ohmic loading. Three replicate H-type MFCs were used to investigate start-up strategies: (1) application of an MPPT algorithm preceded by poised-potential at the anode (+0.645 V vs Ag/AgCl); (2) MFC connected to MPPT-only; (3) static external load of 1 kΩ and 500 Ω. Active control showed a significant reduction in start-up time from 42 to 22 days, along with 3.5-fold increase in biocatalytic activity after start-up. Such active control may improve applicability by accelerating start-up and enhancing MFC power and bio-catalytic performance.

Microbial fuel cell type biosensor for specific volatile fatty acids using acclimated bacterial communities.

Volatile fatty acid (VFA) concentration is one of the most important parameters for monitoring bio-processes such as anaerobic digestion and microbial fuel cells. In this study the correlation between VFA concentration and current/voltage responses and electrochemical properties by using the MFC technology was evaluated. The discrimination between different species of VFA by using two methods i.e., coulombic efficiency and cyclic voltammetry was investigated. Columbic efficiency gave a slow response of greater than 20h, particularly at concentration levels of 20mgl(-1). By using cyclic voltammetry to measure the oxidation peak at a consistent scan rate showed linear correlation to VFA concentration and peak current produced, up to <40mgl(-1)) in a rapid response time of 1-2min. The results presented showed good correlations between the individual VFA species concentration and charge, and also current generated. A MFC based biosensor array was produced capable of measuring individual acetate, propionate and butyrate concentrations with sensitivity down to 5mgl(-1) and up to 40mgl(-1).

Enhanced power production of a membrane electrode assembly microbial fuel cell (MFC) using a cost effective poly [2,5-benzimidazole] (ABPBI) impregnated non-woven fabric filter.

A membrane electrode assembly (MEA) microbial fuel cell (MFC) with a non-woven paper fabric filter (NWF) was investigated as an alternative to a proton exchange membrane (PEM) separator. The MFC with a NWF generated a cell voltage of 545 mV and a maximum power density of 1027 mW/m(3), which was comparable to that obtained from MFCs with a PEM (551 mV, 609 mW/m(3)). The MFC with a NWF showed stable cell performance (550 mV) over 300 days, whereas, the MFC with PEM performance decreased significantly from 551 mV to 415 mV due to biofilm formation and chemical precipitation on the membrane surface. Poly [2,5-benzimidazole] (ABPBI) was evaluated with respect to its capacity to increased proton conductivity and contact between separator and electrodes. The overall performance of the MFC with ABPBI was improved by enhancing the ion conductivity and steric contact, producing 766 mW/m(3) at optimum loading of 50 mg ABPBI/cm(2).

Thionine increases electricity generation from microbial fuel cell using Saccharomyces cerevisiae and exoelectrogenic mixed culture.

Microbial fuel cells (MFCs) have been shown to be capable of clean energy production through the oxidation of biodegradable organic waste using various bacterial species as biocatalysts. In this study we found Saccharomyces cerevisiae, previously known electrochemcially inactive or less active species, can be acclimated with an electron mediator thionine for electrogenic biofilm formation in MFC, and electricity production is improved with facilitation of electron transfer. Power generation of MFC was also significantly increased by thionine with both aerated and non-aerated cathode. With electrochemically active biofilm enriched with swine wastewater, MFC power increased more significantly by addition of thionine. The optimum mediator concentration was 500 mM of thionine with S. cerevisae in MFC with the maximum voltage and current generation in the microbial fuel cell were 420 mV and 700 mA/m(2), respectively. Cyclic voltametry shows that thionine improves oxidizing and reducing capability in both pure culture and acclimated biofilm as compared to non-mediated cell. The results obtained indicated that thionine has great potential to enhance power generation from unmediated yeast or electrochemically active biofilm in MFC.

Operational temperature regulates anodic biofilm growth and the development of electrogenic activity.

The operational temperature of microbial fuel cell reactors influences biofilm development, and this has an impact on anodic biocatalytic activity. In this study, we compared three microbial fuel cell (MFC) reactors acclimated at 10°C, 20°C and 35°C to investigate the effect on biomass development, methanogenesis and electrogenic activity over time. The start-up time was inversely influenced by temperature, but the amount of biomass accumulation increased with increased temperatures, the 10°C, 20°C and 35°C acclimated biofilms resulted in 0.57, 0.82 and 5.43 g biomass (volatile suspended solids) per litre respectively at 56 weeks of operation. Biofilm build-up on the 35°C anode was further demonstrated by scanning electron microscopy, which showed large aggregations of biomass accumulating on the anode when compared to 10°C and 20°C biofilms. Biomass accumulation had a direct impact on biocatalytic performance, with the maximum power at 35°C after 60 weeks of operation being 2.14 W m(-3) and power densities for the 10°C and 20°C reactors being and 4.29 W m(-3). Methanogenic activity was also shown to be higher at 35°C, with a rate of 10.1 mmol CH(4) biofilm per gram of volatile suspended solid (VSS) per day, compared to 0.28 mmol CH(4) per gram of VSS per day produced at 20°C. These results demonstrate that higher MFC operating temperatures could be detrimental to the biocatalytic performance of electrochemically active bacteria in anodic biofilms due to biomass accumulation with enhanced development of non-electrogenic communities (e.g. methanogens and fermenters), meaning that, over time, psychro- or mesophilic operation can have beneficial effects for the development of electrogenically active populations in the reactor.

Spatiotemporal development of the bacterial community in a tubular longitudinal microbial fuel cell.

The spatiotemporal development of a bacterial community in an exoelectrogenic biofilm was investigated in sucrose-fed longitudinal tubular microbial fuel cell reactors, consisting of two serially connected modules. The proportional changes in the microbial community composition were assessed by polymerase chain reaction-denaturing gradient gel electrophoresis (DGGE) and DNA sequencing in order to relate them to the performance and stability of the bioelectrochemical system. The reproducibility of duplicated reactors, evaluated by cluster analysis and Jaccard's coefficient, shows 80-90% similarity in species composition. Biofilm development through fed-batch start-up and subsequent stable continuous operation results in a population shift from γ-Proteobacteria- and Bacteroidetes- to Firmicutes-dominated communities, with other diverse species present at much lower relative proportions. DGGE patterns were analysed by range-weighted richness (Rr) and Pareto-Lorenz evenness distribution curves to investigate the evolution of the bacterial community. The first modules shifted from dominance by species closely related to Bacteroides graminisolvens, Raoultella ornithinolytica and Klebsiella sp. BM21 at the start of continuous-mode operation to a community dominated by Paludibacter propionicigenes-, Lactococcus sp.-, Pantoea agglomerans- and Klebsiella oxytoca-related species with stable power generation (6.0 W/m(3)) at day 97. Operational strategies that consider the dynamics of the population will provide useful parameters for evaluating system performance in the practical application of microbial fuel cells.

Sustainable wastewater treatment: how might microbial fuel cells contribute.

The need for cost-effective low-energy wastewater treatment has never been greater. Clean water for our expanding and predominantly urban global population will be expensive to deliver, eats into our diminishing carbon-based energy reserves and consequently contributes to green house gases in the atmosphere and climate change. Thus every potential cost and energy cutting measure for wastewater treatment should be explored. Microbial fuel cells (MFCs) could potentially yield such savings but, to achieve this, requires significant advances in our understanding in a few critical areas and in our designs of the overall systems. Here we review the research which might accelerate our progress towards sustainable wastewater treatment using MFCs: system control and modelling and the understanding of the ecology of the microbial communities that catalyse the generation of electricity.

Modular tubular microbial fuel cells for energy recovery during sucrose wastewater treatment at low organic loading rate.

Energy recovery while treating low organic loads has been investigated using longitudinal tubular microbial fuel cell (MFC) reactors. Duplicate reactors, each consisting of two modules, were operated with influent sucrose organic loading rates (OLRs) between 0.04 and 0.42 g COD/l/d. Most soluble COD (sCOD) removal occurred in the first modules with predominantly VFAs reaching the second modules. Coulombic efficiency (CE) in the second modules ranged from 9% to 92% which was 3-4 times higher than the first modules. The maximum energy production was 1.75 W h/g COD in the second modules at OLR 0.24 g/l/d, up to 10 times higher than the first modules, attributable to non-fermentable substrate. A simple plug flow model of the reactors, including a generic non-electrogenic reaction competing for acetate, was developed. This modular tubular design can reproducibly distribute bioprocesses between successive modules and could be scalable, acting as a polishing stage while reducing energy requirements in wastewater treatment.

ADM1 can be applied to continuous bio-hydrogen production using a variable stoichiometry approach.

The IWA Anaerobic Digestion Model No.1 (ADM1) has been extensively used in recent years. However, its application to non-methanogenic systems is limited by the use of constant-stoichiometry to describe product formation from carbohydrate fermentation. This study presents a modification of the ADM1 using a variable stoichiometry approach, derived from experimental information. The biomass and product yields from glucose degradation are assumed to be dynamically depending on the total concentration of undissociated acids in the reactor. Experimental data from an 11 L mesophilic continuous bio-hydrogen reactor fed with 20, 40, 50 and 10 g/L of sucrose, were used to validate the approach. The modified model achieved good predictions of the experimental data, using the standard ADM1 parameter values, without any parameter fitting beyond the implementation of the variable stoichiometry. The modification approach proposed extends the applicability of the ADM1 to non-methanogenic fermentative systems and in particular to continuous bio-hydrogen production.

Fermentative production of hydrogen from a wheat flour industry co-product.

The global flour industry produces 96 million ton/year of wheatfeed, which is mainly used for animal feed. This co-product is high in carbohydrates and potentially a significant substrate for biohydrogen production. A 10 l bioreactor, inoculated with sewage sludge, was operated on wheatfeed (10 g l(-1)) at pH 5.5 and 35 degrees C in batch and semi-continuous mode (15 h hydraulic retention time (HRT)). Wheatfeed hydrolysate was also investigated in continuous mode (15 h HRT). NaOH-H2O2 treatment of 25 g l(-1) wheatfeed resulted in hydrolysate containing on average 8.1 g l(-1) total sugar. Hydrogen yields of 64 and 56 m3 H(2) per ton dry weight were produced from wheatfeed in batch and 56 m3 H2 per ton dry weight of wheatfeed in semi-continuous mode. Hydrogen yields from hydrolysate were only 22 and 31 m3 H2 per ton dry weight, (or 0.9 mol H2 per mol hexose degraded, assuming all sugar is hexose). Fermentation of unhydrolysed wheatfeed is therefore recommended. It is calculated that approximately 264 m3/ton of CH4 can be produced from a subsequent anaerobic digestion stage. The biohydrogen produced (diesel equivalents) from the 1.2 million ton/year of wheatfeed in the UK would be more than twice that required for transportation by the UK flour industry.