• Energy Research

In recent years novel applications of bioelectrochemical systems are exemplified by phototrophic biocathodes, biocompatible enzymatic fuel cells and biodegradable microbial fuel cells (MFCs). Herein, transparent silk fibroin membranes (SFM) with various fibroin content (2%, 4% and 8%) were synthesised and employed as separators in MFCs and compared with standard cation exchange membranes (CEM) as a control. The highest real-time power performance of thin-film SFM was reached by 2%-SFM separators: 25.7 ± 7.4 μW, which corresponds to 68% of the performance of the CEM separators (37.7 ± 3.1 μW). Similarly, 2%-SFM revealed the highest coulombic efficiency of 6.65 ± 1.90%, 74% of the CEM efficiency. Current for 2%-SFM reached 0.25 ± 0.03 mA (86% of CEM control). Decrease of power output was observed after 23 days for 8% and 4% and was a consequence of deterioration of SFMs, determined by physical, chemical and biological studies. This is the first time that economical and transparent silk fibroin polymers were successfully employed in MFCs.

Microbial Fuel Cells (MFCs) are emerging as an effective means of treating different types of waste including urine and wastewater. However, the fate of pathogens in an MFC-based system remains unknown, and in this study we investigated the effect of introducing the enteric pathogen Salmonella enterica serovar enteritidis in an MFC cascade system. The MFCs continuously fed with urine showed high disinfecting potential. As part of two independent trials, during which the bioluminescent S. enteritidis strain was introduced into the MFC cascade, the number of viable counts and the level of bioluminescence were reduced by up to 4.43±0.04 and 4.21±0.01 log-fold, respectively. The killing efficacy observed for the MFCs operating under closed-circuit conditions, were higher by 1.69 and 1.72 log-fold reduction than for the open circuit MFCs, in both independent trials. The results indicated that the bactericidal properties of a well performing anode were dependent on power performance and the oxidation-reduction potential recorded for the MFCs. This is the first time that the fate of pathogenic bacteria has been investigated in continuously operating MFC systems.

AbstractMicrobial fuel cells (MFCs) made with different types of ceramic membranes were investigated to find a low‐cost alternative to commercially available proton exchange membranes. The MFCs operated with fresh human urine as the fuel. Pyrophyllite and earthenware produced the best performance to reach power densities of 6.93 and 6.85 W m−3, respectively, whereas mullite and alumina achieved power densities of 4.98 and 2.60 W m−3, respectively. The results indicate the dependence of bio‐film growth and activity on the type of ceramic membrane applied. The most favourable conditions were created in earthenware MFCs. The performance of the ceramic membranes was related to their physical and chemical properties determined by environmental scanning electron microscopy and energy dispersive X‐ray spectroscopy. The cost of mullite, earthenware, pyrophyllite and alumina was estimated to be 13.61, 4.14, 387.96 and 177.03 GBP m−2, respectively. The results indicate that earthenware and mullite are good substitutes for commercially available proton exchange membranes, which makes the MFC technology accessible in developing countries.

Anodophilic bacteria have the ability to generate electricity in microbial fuel cells (MFCs) by extracellular electron transfer to the anode. We investigated the anode‐specific responses of Shewanella oneidensis MR‐1, an exoelectroactive Gammaproteobacterium, using for the first time iTRAQ and 2D‐LC MS/MS driven membrane proteomics to compare protein abundances in S. oneidensis when generating power in MFCs, and growing in a continuous culture. The regulated dataset produced was enriched in membrane proteins. Proteins shown to be more abundant in anaerobic electroactive anodic cells included efflux pump TolC and an uncharacterised tetratricopeptide repeat (TPR) protein, whilst the TonB2 system and associated uncharacterised proteins such as TtpC2 and DUF3450 were more abundant in microaerobic planktonic cells. In order to validate the iTRAQ data, the functional role for TolC was examined using a δTolC knockout mutant of S. oneidensis. Possible roles for the uncharacterised proteins were identified using comparative bioinformatics. We demonstrate that employing an insoluble extracellular electron acceptor requires multiple proteins involved in cell surface properties. All MS and processed data are available via ProteomeXchange with identifier PXD004090.

Air cathode microbial fuel cells (MFCs) were used in a cascade-system, to treat neat human urine as the fuel. Their long-term operation caused biodeterioration and biofouling of the cathodes. The cathodes were made from two graphite-painted layers, separated by a current collector. The initial performance of the MFCs was reaching average values of 105.5 ± 32.2 μW and current of 1164.5 ± 120.2 μA. After 3 months of operation the power performance decreased to 9.8 ± 3.5 μW, whilst current decreased to 461.2 ± 137.5 μA. Polarisation studies revealed significant transport losses accompanied by a biofilm formation on the cathodes. The alkaline lysis procedure was established to remove the biomass and chemical compounds adsorbed on the cathode's surface. As a result, the current increased from 378.6 ± 108.3 μA to 503.8 ± 95.6 μA. The additional step of replacing the outer layer of the cathode resulted in a further increase of current to 698.1 ± 130 μA. Similarly, the power performance of the MFCs was recovered to the original level reaching 105.3 ± 16.3 μW, which corresponds to 100% recovery. Monitoring bacterial cell number on the cathode's surface showed that biofilm formed during operation was successfully removed and composed mainly of dead bacterial cells after treatment. To the best of the authors' knowledge, this is the first time that the performance of deteriorating cathodes, has been successfully recovered for MFCs in-situ. Through this easy, fast and inexpensive procedure, designing multilayer cathodes may help enhance the range of operating conditions, if a biofilm forms on their surface.

AbstractMicrobial electrochemical technology is emerging as an alternative way of treating waste and converting this directly to electricity. Intensive research on these systems is ongoing but it currently lacks the evaluation of possible environmental transmission of enteric viruses originating from the waste stream. In this study, for the first time we investigated this aspect by assessing the removal efficiency of hepatitis B core and surface antigens in cascades of continuous flow microbial fuel cells. The log-reduction (LR) of surface antigen (HBsAg) reached a maximum value of 1.86 ± 0.20 (98.6% reduction), which was similar to the open circuit control and degraded regardless of the recorded current. Core antigen (HBcAg) was much more resistant to treatment and the maximal LR was equal to 0.229 ± 0.028 (41.0% reduction). The highest LR rate observed for HBsAg was 4.66 ± 0.19 h−1 and for HBcAg 0.10 ± 0.01 h−1. Regression analysis revealed correlation between hydraulic retention time, power and redox potential on inactivation efficiency, also indicating electroactive behaviour of biofilm in open circuit control through the snorkel-effect. The results indicate that microbial electrochemical technologies may be successfully applied to reduce the risk of environmental transmission of hepatitis B virus but also open up the possibility of testing other viruses for wider implementation.