Showing papers by "Korneel Rabaey published in 2012"

Conversion of wastes into bioelectricity and chemicals by using microbial electrochemical technologies.

Abstract: Waste biomass is a cheap and relatively abundant source of electrons for microbes capable of producing electrical current outside the cell. Rapidly developing microbial electrochemical technologies, such as microbial fuel cells, are part of a diverse platform of future sustainable energy and chemical production technologies. We review the key advances that will enable the use of exoelectrogenic microorganisms to generate biofuels, hydrogen gas, methane, and other valuable inorganic and organic chemicals. Moreover, we examine the key challenges for implementing these systems and compare them to similar renewable energy technologies. Although commercial development is already underway in several different applications, ranging from wastewater treatment to industrial chemical production, further research is needed regarding efficiency, scalability, system lifetimes, and reliability.

Electrochemical resource recovery from digestate to prevent ammonia toxicity during anaerobic digestion

Abstract: Ammonia inhibition during anaerobic digestion limits the substrate loading rate and endangers process stability. Furthermore, digestates are interesting feedstocks for nutrient recovery. In this lab-scale study, an electrochemical cell was used to investigate the NH4+ flux from anode to cathode. Under optimal conditions with synthetic wastewater, an NH4+ charge transfer efficiency of 96% and NH4+ flux of 120 g N m–2 d–1 could be obtained at a concomitant electricity input of 5 kWh kg–1 N removed. A more selective NH4+ transfer could be established by maintaining a high concentration of other cations in the cathode compartment. Comparable NH4+ fluxes could be obtained with digestate at an electrical power input of 13 kWh kg–1 N removed and 41% current efficiency. The ammonium level in the digestate could be lowered from 2.1 to 0.8 – 1.2 g N L–1. Interestingly, also potassium fluxes of up to 241 g K+ m–2 d–1 could be obtained at 23% current efficiency. As the cathode can be operated at high pH without the n...

Non-invasive characterization of electrochemically active microbial biofilms using confocal Raman microscopy

Abstract: Electrochemically active biofilms rely on microorganisms capable of extracellular electron transfer. Such biofilms are involved in the dissimilatory reduction of metal oxides in natural environments as well as electricity driving and driven processes at the electrodes of microbial bioelectrochemical systems. In this work we present the application of confocal Raman microscopy (CRM) as a non-invasive, label-free, and in vivo characterization method of acetate oxidizing anodic biofilms, grown from primary wastewater inoculum and dominated by Geobacter species (>85% of sequences analysed using pyrotag sequencing). Using the resonance Raman effect of the heme protein cytochrome c (Cyt c)—an ubiquitous component of extracellular electron transfer reactions—it was possible to collect characteristic spectral information of electrochemically active biofilms at pixel integration times of 0.2 s and an excitation wavelength of 532 nm. This allowed monitoring of biofilm development at different growth stages, without impacting its structural or metabolic activity. Furthermore, we demonstrate the possibility of non-invasive investigation of the spatial redox electrochemistry (up to a compositional level) of electrochemically active biofilms, as we observed significant changes in the vibrational properties of Cyt c resulting from shifts in the anodic potential between different redox conditions. Compared to conventional methods requiring destructive sample manipulation and fixation, the proposed approach based on CRM allows the non-invasive analysis of microbial aggregates with minimal sample preparation or prior knowledge of the sample.

Operational and technical considerations for microbial electrosynthesis.

Abstract: Extracellular electron transfer has, in one decade, emerged from an environmental phenomenon to an industrial process driver. On the one hand, electron transfer towards anodes leads to production of power or chemicals such as hydrogen, caustic soda and hydrogen peroxide. On the other hand, electron transfer from cathodes enables bioremediation and bioproduction. Although the microbiology of extracellular electron transfer is increasingly being understood, bringing the processes to application requires a number of considerations that are both operational and technical. In the present paper, we investigate the key applied aspects related to electricity-driven bioproduction, including biofilm development, reactor and electrode design, substrate fluxes, surface chemistry, hydrodynamics and electrochemistry, and finally end-product removal/toxicity. Each of these aspects will be critical for the full exploitation of the intriguing physiological feat that extracellular electron transfer is today.

The diversity of techniques to study electrochemically active biofilms highlights the need for standardization.

Abstract: Microbial bioelectrochemical systems (BESs) employ whole microorganisms to catalyze electrode reactions. BESs allow electricity generation from wastewater, electricity-driven (bio)production, biosensing, and bioremediation. Many of these processes are perceived as highly promising; however, to date the performance of particularly bioproduction processes is not yet at the level required for practical applications. Critical to enabling high catalytic activity are the electrochemically active microorganisms. Whether the biocatalyst comes as a planktonic cell, a surface monolayer of cells, or a fully developed biofilm, effective electron transfer and process performance need to be achieved. However, despite many different approaches and extensive research, many questions regarding the functioning of electroactive microorganisms remain open. This is certainly due to the complexity of bioelectrochemical processes, as they depend on microbial, electrochemical, physical-chemical, and operational considerations. This versatility and complexity calls for a plethora of analytical tools required to study electrochemically active microorganisms, especially biofilms. Here, we present an overview of the parameters defining electroactive microbial biofilms (EABfs) and the analytical toolbox available to study them at different levels of resolution. As we will show, a broad diversity of techniques have been applied to this field; however, these have often led to conflicting information. Consequently, to alleviate this and further mature the field of BES research, a standardized framework appears essential.

A bioelectrochemical system as stabilizing and remediating agent in anaerobic digestion

Abstract: Anaerobic digestion (AD) is a key technology for biorefinery side streams. To ensure stable methane production, a balanced Bacteria - Archaea community is required. Several environmental factors, e.g. abrupt pH changes, organic overloading and high salt concentrations, can distort this delicate balance. Here we evaluated whether a bioelectrochemical system (BES) could improve stability and remediate AD systems which exhibited process failure. To evaluate this, a BES was introduced in three continuously stirred tank reactor (CSTR) systems, at a fixed potential difference of 1V and 0.5V and open circuit conditions respectively. Three other CSTR systems were operated under similar conditions without a BES. The reactors were fed with diluted molasses at an organic loading rate of 2 g COD L-1 d-1. Molasses was selected because of its high concentrations of salts, especially K+, which may inhibit methanogenesis. During the first 35 days of operation, all six reactors maintained a stable methane production of 0.6 L CH4 Lreactor-1 d-1. After that, methane production declined and volatile fatty acids (VFA) accumulated in the three reactors without a BES until 50% system inhibition was achieved after 90 days of operation. Methane production remained stable in the three reactors with BES, i.e. no decline in methane production was detected, which demonstrates the stabilizing effect of the BES. After 90 days the BES were transferred to the reactors with 50% system inhibition in order to evaluate the remediation potential of the BES. Immediately after introduction of the BES, remediation took place in the three reactors, i.e. a rise in CH4 production and VFA removal, although no difference between the treatments, could be detected, thus indicating the strong remediating capacity of the BES in AD. Microbial community analysis by means of DGGE and Q-PCR was carried out to evaluate the effect of the BES on the microbial community in AD. This study demonstrated that, in contrast to several other studies which could only increase methane production by introducing a BES in AD, a BES can remediate anaerobic digestion systems which exhibited severe process failure.

Benefits from the plant-sediment MFC

Abstract: A sediment microbial fuel cell uses the reduced organic matter in the anaerobic subsurface of a waterlogged system to produce a small electrical current. This current is used in the overlying waterlayer to reduce a terminal electron acceptor, usually oxygen. In such a system, the catalyst on the electrodes is usually of a microbial nature. A plant-sediment microbial fuel cell is characterized by a continuous supply of organic matter to the anode electrode by means of rhizodeposition. A Plant Sediment MFC faces several challenges such as 1) placement of the anode electrode/current collector at the site with the highest organic carbon concentration, i.e. the rhizosphere/plane and 2) A high internal resistance due to a relatively large distance between anode and cathode and usually a low conductivity of pore liquid. These two conditions create bottlenecks that need to be improved or circumvented in order increase the comparatively low power output from a plant-sediment MFC. In this work the first bottleneck is targeted while suggestions are done to address the second bottleneck. Moreover, an attempt is made to increase the value-creation of the Plant-Sediment MFC beyond electrical power. Therefore the impact of introducing an anode as alternative electron acceptor in a microbial niche is investigated. As a model CH4 emissions of the rhizosphere of rice plants is used. Here, the PlantSediment MFC can possibly make an impact one of the largest anthropogenic sources of atmospheric CH4 release [1].