A New Method for Modulation, Control and Power Boosting in Microbial Fuel Cells

Halobacterium salinarum NRC-1 Sustains Voltage Production in a Dual-Chambered Closed Microbial Fuel Cell

Sustained bioenergy production from organisms that thrive in high salinity, low oxygen, and low nutrition levels is useful in monitoring hypersaline polluted environments. Microbial fuel cell (MFC) studies utilizing single species halophiles under salt concentrations higher than 1 M and as a closed microbial system are limited. The current study aimed to establish baseline voltage, current, and power density from a dual-chambered MFC utilizing the halophile Halobacterium salinarum NRC-1. MFC performance was determined with two different electrode sizes (5 cm² and 10 cm²), under oscillating and nonoscillating conditions, as well as in a stacked series. A closed dual-chamber MFC system of 100 mL capacity was devised with Halobacterium media (4.3 M salt concentration) as both anolyte and catholyte, with H. salinarum NRC-1 being the anodic organism. The MFC measured electrical output over 7, 14, 28, and 42 days. MFC output increased with 5 cm² sized electrodes under nonoscillating (p < 0.0001) relative to oscillating conditions. However, under oscillating conditions, doubling the electrode size increased MFC output significantly (p = 0.01). The stacked series MFC, with an electrode size of 10 cm², produced the highest power density (1.2672 mW/m²) over 14 days under oscillation. Our results highlight the potentiality of H. salinarum as a viable anodic organism to produce sustained voltage in a closed-MFC system.

Microbial fuel cells and their electrified biofilms

Bioelectrochemical systems (BES) represent a wide range of different biofilm-based bioreactors that includes microbial fuel cells (MFCs), microbial electrolysis cells (MECs) and microbial desalination cells (MDCs). The first described bioelectrical bioreactor is the Microbial Fuel Cell and with the exception of MDCs, it is the only type of BES that actually produces harvestable amounts of electricity, rather than requiring an electrical input to function. For these reasons, this review article, with previously unpublished supporting data, focusses primarily on MFCs. Of relevance is the architecture of these bioreactors, the type of membrane they employ (if any) for separating the chambers along with the size, as well as the geometry and material composition of the electrodes which support biofilms. Finally, the structure, properties and growth rate of the microbial biofilms colonising anodic electrodes, are of critical importance for rendering these devices, functional living 'engines' for a wide range of applications.

Microbial fuel cell performance for aromatic hydrocarbon bioremediation and common effluent treatment plant wastewater treatment with bioelectricity generation through series-parallel connection

Microbial fuel cell (MFC) is an emerging technology which has been immensely investigated for wastewater treatment along with electricity generation. In the present study, the treatment efficiency of MFC was investigated for hydrocarbon containing wastewater by optimizing various parameters of MFC. Mediator-less MFC (1·2 l) was constructed, and its performance was compared with mediated MFC with Escherichia coli as a biocatalyst. MFC with electrode having biofilm proved to be better compared with MFC inoculated with suspended cells. Analysis of increasing surface area of electrode by increasing their numbers indicated increase in COD reduction from 55 to 75%. Catholyte volume was optimized to be 750 ml. Sodium benzoate (0·721 g l^-1 ) and actual common effluent treatment plant (CETP) wastewater as anolyte produced 0·8 and 0·6 V voltage and 89 and 50% COD reduction, respectively, when a novel consortium of four bacterial strains were used. Twenty MFC systems with the developed consortium when electrically connected in series-parallel connection were able to generate 2·3 V and 0·5 mA current. This is the first report demonstrating the application of CETP wastewater in the MFC system, which shows potential of the system towards degradation of complex organic components present in industrial wastewater.

Electrosynthesis, modulation, and self-driven electroseparation in microbial fuel cells

Microbial electrosynthesis (MES) represents a sustainable platform that converts waste into resources, using microorganisms within an electrochemical cell. Traditionally, MES refers to the oxidation/reduction of a reactant at the electrode surface with externally applied potential bias. However, microbial fuel cells (MFCs) generate electrons that can drive electrochemical reactions at otherwise unbiased electrodes. Electrosynthesis in MFCs is driven by microbial oxidation of organic matter releasing electrons that force the migration of cationic species to the cathode. Here, we explore how electrosynthesis can coexist within electricity-producing MFCs thanks to electro-separation of cations, electroosmotic drag, and oxygen reduction within appropriately designed systems. More importantly, we report on a novel method of in situ modulation for electrosynthesis, through additional “pin” electrodes. Several MFC electrosynthesis modulating methods that adjust the electrode potential of each half-cell through the pin electrodes are presented. The innovative concept of electrosynthesis within the electricity producing MFCs provides a multidisciplinary platform converting waste-to-resources in a self-sustainable way.

Removal of aspirin from aqueous solution using electroactive bacteria induced by alternating current

This study aims to improve bacterial laccase enzyme activity (LEA) and dehydrogenase activity (DHA) affecting acetylsalicylic acid (ASA) biodegradation using an alternating current (AC). A microbial consortium was inoculated in an electroactive bioreactor supplied with an AC by a function generator under operating conditions of amplitude (AMPL) = 2-10 peak-to-peak voltage (Vpp), optical fiber splice tray (OFST) = 0.1 V, and sine wave frequency = 10 Hz. The obtained results revealed that at an applied voltage of 8 Vpp and an OFST of 0.1 for 12 h, the maximum bacterial LEA and DHA were 30.6 U/mL and 75.5 micro grTF/cm2.gr biomass; respectively. Cell viability and permeability were equal to 95.7% and 0.3%; respectively, at the voltage of 8 Vpp. Moreover, liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) analyses showed that by-products had lower intensity at 8 Vpp compared with that of 2 Vpp voltage. Finally, the results demonstrated an optimum applied voltage of the AC, which could stimulate and promote bacterial LEA and DHA. Therefore, an electroactive bioreactor supplied with an AC can be a novel system for stimulation of enzyme activities in the process of ASA biodegradation.

Selective recovery of lead and zinc through controlling cathodic potential in a bioelectrochemically-assisted electrodeposition system

Proper treatment of mining wastewaters is critically important to minimize contamination by heavy metals contained in those wastewaters. Herein, a bioelectrochemically-assisted electrodeposition (BES-EDP) system was developed and investigated for selective removal and recovery of Pb and Zn from a mimicked smelting wastewater. It was observed that those two metals were reduced at different cathodic potentials and electrodeposition time. At a cathodic potential of -0.75 V vs. Ag/AgCl, 98.5 ± 1.4 % of Pb was recovered after 10 h of reaction while there was little Zn deposition. Increasing the cathodic potential to -1.2 V could achieve 98.7 ± 0.7 % of Zn with the electrodeposition time of 6 h. The composition of the deposits confirmed the results from solution analysis and metal oxides were also formed during metal reduction. The diffusion impedance was much higher than the charge transfer resistance, suggesting that the diffusion process was a rate limiting step for electrodeposition. The diffusion process was verified by chronoamperometry with a good fit in Cottrell equation. The electrodeposition equilibrium constant k₀ was determined as 3.76 cm s^-1. Those results have demonstrated the feasibility of using bioelectricity to assist with selective metal recovery and warrant further investigation of technologies for sustainable management of mining wastewaters.