Showing papers by "Korneel Rabaey published in 2010"

Microbial electrosynthesis — revisiting the electrical route for microbial production

Abstract: Microbial electrocatalysis relies on microorganisms as catalysts for reactions occurring at electrodes. Microbial fuel cells and microbial electrolysis cells are well known in this context; both use microorganisms to oxidize organic or inorganic matter at an anode to generate electrical power or H(2), respectively. The discovery that electrical current can also drive microbial metabolism has recently lead to a plethora of other applications in bioremediation and in the production of fuels and chemicals. Notably, the microbial production of chemicals, called microbial electrosynthesis, provides a highly attractive, novel route for the generation of valuable products from electricity or even wastewater. This Review addresses the principles, challenges and opportunities of microbial electrosynthesis, an exciting new discipline at the nexus of microbiology and electrochemistry.

Life cycle assessment of high-rate anaerobic treatment, microbial fuel cells, and microbial electrolysis cells.

Abstract: Existing wastewater treatment options are generally perceived as energy intensive and environmentally unfriendly. Much attention has been focused on two new approaches in the past years, (i) microbial fuel cells and (ii) microbial electrolysis cells, which directly generate electrical current or chemical products, respectively, during wastewater treatment. These systems are commonly denominated as bioelectrochemical systems, and a multitude of claims have been made in the past regarding the environmental impact of these treatment options. However, an in-depth study backing these claims has not been performed. Here, we have conducted a life cycle assessment (LCA) to compare the environmental impact of three industrial wastewater treatment options, (i) anaerobic treatment with biogas generation, (ii) a microbial fuel cell treatment, with direct electricity generation, and (iii) a microbial electrolysis cell, with hydrogen peroxide production. Our analysis showed that a microbial fuel cell does not provide a significant environmental benefit relative to the "conventional" anaerobic treatment option. However, a microbial electrolysis cell provides significant environmental benefits through the displacement of chemical production by conventional means. Provided that the target conversion level of 1000 A.m(-3) can be met, the decrease in greenhouse gas emissions and other environmentally harmful emissions (e.g., aromatic hydrocarbons) of the microbial electrolysis cell will be a key driver for the development of an industrial standard for this technology. Evidently, this assessment is highly dependent on the underlying assumptions, such as the used reactor materials and target performance. This provides a challenge and an opportunity for researchers in the field to select and develop appropriate and environmentally benign materials of construction, as well as demonstrate the required 1000 A.m(-3) performance at pilot and full scale.

Initial development and structure of biofilms on microbial fuel cell anodes

Abstract: Microbial fuel cells (MFCs) rely on electrochemically active bacteria to capture the chemical energy contained in organics and convert it to electrical energy. Bacteria develop biofilms on the MFC electrodes, allowing considerable conversion capacity and opportunities for extracellular electron transfer (EET). The present knowledge on EET is centred around two Gram-negative models, i.e. Shewanella and Geobacter species, as it is believed that Gram-positives cannot perform EET by themselves as the Gram-negatives can. To understand how bacteria form biofilms within MFCs and how their development, structure and viability affects electron transfer, we performed pure and co-culture experiments. Biofilm viability was maintained highest nearer the anode during closed circuit operation (current flowing), in contrast to when the anode was in open circuit (soluble electron acceptor) where viability was highest on top of the biofilm, furthest from the anode. Closed circuit anode Pseudomonas aeruginosa biofilms were considerably thinner compared to the open circuit anode (30 ± 3 μm and 42 ± 3 μm respectively), which is likely due to the higher energetic gain of soluble electron acceptors used. The two Gram-positive bacteria used only provided a fraction of current produced by the Gram-negative organisms. Power output of co-cultures Gram-positive Enterococcus faecium and either Gram-negative organisms, increased by 30-70% relative to the single cultures. Over time the co-culture biofilms segregated, in particular, Pseudomonas aeruginosa creating towers piercing through a thin, uniform layer of Enterococcus faecium. P. aeruginosa and E. faecium together generated a current of 1.8 ± 0.4 mA while alone they produced 0.9 ± 0.01 and 0.2 ± 0.05 mA respectively. We postulate that this segregation may be an essential difference in strategy for electron transfer and substrate capture between the Gram-negative and the Gram-positive bacteria used here.

High current generation coupled to caustic production using a lamellar bioelectrochemical system

Abstract: Recently, bioelectrochemical systems (BESs) have emerged as a promising technology for energy and product recovery from wastewaters. To become economically viable, BESs need to (i) reach sufficient turnover rates at scale and (ii) generate a product that offsets the investment costs within a reasonable time frame. Here we used a liter scale, lamellar BES to produce a caustic solution at the cathode. The reactor was operated as a three-electrode system, in which the anode potential was fixed and power was supplied over the reactor to allow spontaneous anodic current generation. In laboratory conditions, with acetate as electron donor in the anode, the system generated up to 1.05 A (at 1.77 V applied cell voltage, 1015 A m−3 anode volume), and allowed for the production of caustic to 3.4 wt %, at an acetate to caustic efficiency of 61%. The reactor was subsequently operated on a brewery site, directly using effluent from the brewing process. Currents of up to 0.38 A were achieved within a six-week time fram...

Bacterial community structure corresponds to performance during cathodic nitrate reduction

Abstract: Microbial fuel cells (MFCs) have applications other than electricity production, including the capacity to power desirable reactions in the cathode chamber. However, current knowledge of the microbial ecology and physiology of biocathodes is minimal, and as a result more research dedicated to understanding the microbial communities active in cathode biofilms is required. Here we characterize the microbiology of denitrifying bacterial communities stimulated by reducing equivalents generated from the anodic oxidation of acetate. We analyzed biofilms isolated from two types of cathodic denitrification systems: (1) a loop format where the effluent from the carbon oxidation step in the anode is subjected to a nitrifying reactor which is fed to the cathode chamber and (2) an alternative non-loop format where anodic and cathodic feed streams are separated. The results of our study indicate the superior performance of the loop reactor in terms of enhanced current production and nitrate removal rates. We hypothesized that phylogenetic or structural features of the microbial communities could explain the increased performance of the loop reactor. We used PhyloChip with 16S rRNA (cDNA) and fluorescent in situ hybridization to characterize the active bacterial communities. Our study results reveal a greater richness, as well as an increased phylogenetic diversity, active in denitrifying biofilms than was previously identified in cathodic systems. Specifically, we identified Proteobacteria, Firmicutes and Chloroflexi members that were dominant in denitrifying cathodes. In addition, our study results indicate that it is the structural component, in terms of bacterial richness and evenness, rather than the phylogenetic affiliation of dominant bacteria, that best corresponds to cathode performance.

Treatment of sulfide containing material

Abstract: A method for treating a sulfide containing solution comprises providing an electrochemical system comprising a first electrode compartment having a first electrode and a second electrode compartment having a second electrode, supplying the first electrode compartment with the sulfide containing solution and operating the first electrode as an anode to oxidise sulfide to form elemental sulfur or other sulfur forms more oxidized than sulfide, subsequently operating the first electrode compartment as a cathode and operating the second electrode compartment as an anode such that elemental sulfur or other sulfur forms more oxidised than sulfide in the first electrode compartment is reduced to sulfide or polysulfide (or both) and feeding the sulfide containing solution to the second electrode compartment to oxidise sulfide to form elemental sulfur or other sulfur forms more oxidized than sulfide and subsequently operating the second electrode compartment as a cathode and operating the first electrode compartment as an anode such that sulfur or other sulfur forms more oxidised than sulfide in the second electrode compartment is reduced to sulfide or polysulfide (or both) and feeding the sulfide containing solution to the first electrode compartment to oxidise sulfide to form sulfur or other sulfur forms more oxidised than sulfide, wherein a cathode solution containing sulfide or polysulfide of enhanced concentration when compared to the solution fed to the anode is obtained.

Bioelectrochemical hydrogen peroxide production – an opportunity for sustainable mitigation of membrane bioreactor fouling

Abstract: Membranes in membrane bioreactors (MBR) are typically cleaned with sodium hypochlorite. The latter is a strong oxidant and of concern due to the possible formation of chlorinated hydrocarbons. Here, we propose a new concept for chemical membrane cleaning with hydrogen peroxide (H2O2), generated onsite in a bioelectrochemical system. The energy present in the wastewater organics can be used to power the production process. We investigated bioelectrochemical H2O2 production from a synthetic wastewater in an inclinedbed reactor and discuss the possibility of using H2O2 to replace sodium hypochlorite for membrane cleaning. Low current, the use of carbon fiber as opposed to graphite, and low pH in the cathode all benefited H2O2 production. It was also possible to generate H2O2 with a net energy output, i.e. by operating the reactor as a microbial fuel cell. The highest H2O2 concentration produced in this study was 176.3 mg/l, which was obtained at a production rate of 1.26 mg/h and an energy input of 0.32 kWh/kgH2O2. A concentration of 91.6 mg/l, a production rate of 0.54 mg/h and an energy output of 0.18 kWh/kgH2O2 was obtained when the reactor was operated as a microbial fuel cell. For application in a MBR, a relatively small portion (>3.8 mg/l BOD) of the influent organic compounds would have to be converted to current by the electroactive bacteria living on the anode to produce sufficient amount of H2O2 for membrane cleaning. However, the produced H2O2 concentration must likely reach a concentration of 0.2-0.5%.

Microbial electrosynthesis: From electricity to biofuels and biochemicals

Abstract: Electricity is one of the most widely available forms of energy and can be produced abundantly and sustainably. Microbial electrosynthesis is a new research field, in which renewable electricity can be used to drive microbial production processes. This allows commodity chemicals to be produced by electrically tapping into the plethora of useful biofuels and biochemicals that microorganisms can make.

High rate electrochemical sulfide removal from synthetic feed and real domestic wastewater

Abstract: The microbial reduction of sulfate to hydrogen sulfide causes sewer pipe corrosion, one of the major issues in the water infrastructure [1]. Oxygen injection is presently considered as an attractive option for sulfide abatement in sewer systems. Oxygen can both inhibit the activity of sulfate reducing bacteria (SRB) and oxidize the sulfide that has been produced [2]. It is less expensive than most other chemicals and can target rising mains where the SRB activity is the highest [3]. Unfortunately, oxygen injection in sewer systems has some disadvantages, such as inefficiencies during dosing (i.e., coarse bubbles, which results in a significant loss of undissolved gas to the air in gas release valves downstream). In addition, the transport and storage of pure oxygen carries serious safety issues and precise control of dosing is not straightforward [4]. Here we propose an electrochemical system that can generate the oxygen in-situ. Compared to traditional methods for oxygen supply, the advantages of this in-situ oxygen generation are the high transfer efficiency, fine dispersion, high controllability (i.e. oxygen addition is directly related to current input) and no requirement for transport and storage. IrOx coated titanium anodes were used to perform the electrochemical oxidation from synthetic feed and real domestic wastewater [5].