The anode activity in a microbial electrolysis cell (MEC) is known to be a limiting factor in hydrogen production. In this study, the MEC was constructed using different anode materials and a platinum-coated carbon-cloth cathode (CC). The anodes were comprised of CC, stainless steel (SS), and a combination of the two (COMB). The CC and SS anodes were also treated with plasma to improve their surface morphology and hydrophilic properties (CCP and SSP, respectively). A combined version of CCP attached to SS was also applied (COMBP). After construction of the MEC using the different anodes, we conducted electrochemical measurements and examination of biofilm viability. Under an applied voltage of 0.6 V (Ag/AgCl), the currents of a MEC based on CCP and COMBP were 11.66 ± 0.1331 and 16.36 ± 0.3172 A m⁻², respectively, which are about three times higher compared to the untreated CC and COMB. A MEC utilizing an untreated SS anode exhibited current of only 0.3712 ± 0.0108 A m⁻². The highest biofilm viability of 0.92 OD₅₄₀ ± 0.07 and hydrogen production rate of 0.0736 ± 0.0022 m³ d⁻¹ m⁻² at 0.8 V were obtained in MECs based on the COMBP anode. To our knowledge, this is the first study that evaluated the effect of plasma-treated anodes and the use of a combined anode composed of SS and CC for hydrogen evolution in a MEC.

Microbial electrolysis cells (MECs) are an emerging technology capable of harvesting part of the potential chemical energy in organic compounds while producing hydrogen. One of the main obstacles in MECs is the bacterial anode, which usually contains mixed cultures. Non-exoelectrogens can act as a physical barrier by settling on the anode surface and displacing the exoelectrogenic microorganisms. Those non-exoelectrogens can also compete with the exoelectrogenic microorganisms for nutrients and reduce hydrogen production. In addition, the bacterial anode needs to withstand the shear and friction forces existing in domestic wastewater plants. In this study, a bacterial anode was encapsulated by a microfiltration membrane. The novel encapsulation technology is based on a small bioreactor platform (SBP) recently developed for achieving successful bioaugmentation in wastewater treatment plants. The 3D capsule (2.5 cm in length, 0.8 cm in diameter) physically separates the exoelectrogenic biofilm on the carbon cloth anode material from the natural microorganisms in the wastewater, while enabling the diffusion of nutrients through the capsule membrane. MECs based on the SBP anode (MEC-SBPs) and the MECs based on a nonencapsulated anode (MEC control) were fed with Geobacter medium supplied with acetate for 32 days, and then with artificial wastewater for another 46 days. The electrochemical activity, chemical oxygen demand (COD), bacterial anode viability and relative distribution on the MEC-SBP anode were compared with the MEC control. When the MECs were fed with artificial wastewater, the MEC-SBP produced (at −0.6 V) 1.70 ± 0.22 A m⁻², twice that of the MEC control. The hydrogen evolution rates were 0.017 and 0.005 m³ m⁻³ day⁻¹, respectively. The COD consumption rate for both was about the same at 650 ± 70 mg L⁻¹. We assume that developing the encapsulated bacterial anode using the SBP technology will help overcome the problem of contamination by non-exoelectrogenic bacteria, as well as the shear and friction forces in wastewater plants.

Bioaugmentation is a bioremediation option based on increasing the natural in-situ microbial population that possesses the ability to degrade the contaminating pollutant. In this study, a diesel-degrading consortium was obtained from an oil-contaminated soil. The diesel-degrading consortium was grown on wood waste that was plasma-pretreated. This plasma treatment led to an increase of bacterial attachment and diesel degradation rates. On the 7th day the biofilm viability on the plasma-treated wood waste reached 0.53 ± 0.02 OD 540 nm, compared to the non-treated wood waste which was only 0.34 ± 0.02. Biofilm attached to plasma-treated and untreated wood waste which was inoculated into artificially diesel-contaminated soil (0.15% g/g) achieved a degradation rate of 9.3 mg day⁻¹ and 7.8 mg day⁻¹, respectively. While, in the soil that was inoculated with planktonic bacteria, degradation was only 5.7 mg day⁻¹. Exposing the soil sample to high temperature (50 °C) or to different soil acidity did not influence the degradation rate of the biofilm attached to the plasma-treated wood waste. The two most abundant bacterial distributions at the family level were Xanthomonadaceae and Sphingomonadaceae. To our knowledge, this is the first study that showed the advantages of biofilm attached to plasma-pretreated wood waste for diesel biodegradation in soil.

The bacterial anode in microbial fuel cells was modified by increasing the biofilm’s adhesion to the anode material using kaolin and graphite nanoparticles. The MFCs were inoculated with G. sulfurreducens, kaolin (12.5 g·L⁻¹), and three different concentrations of graphite (0.25, 1.25, and 2.5 g·L⁻¹). The modified anode with the graphite nanoparticles (1.25 g·L⁻¹) showed the highest electroactivity and biofilm viability. A potential of 0.59, 0.45, and 0.23 V and a power density of 0.54 W·m⁻², 0.3 W·m⁻², and 0.2 W·m⁻² were obtained by the MFCs based on kaolin–graphite nanoparticles, kaolin, and bare anodes, respectively. The kaolin–graphite anode exhibited the highest Coulombic efficiency (21%) compared with the kaolin (17%) and the bare (14%) anodes. Scanning electron microscopy and confocal laser scanning microscopy revealed a large amount of biofilm on the kaolin–graphite anode. We assume that the graphite nanoparticles increased the charge transfer between the bacteria that are in the biofilm and are far from the anode material. The addition of kaolin and graphite nanoparticles increased the attachment of several bacteria. Thus, for MFCs that are fed with wastewater, the modified anode should be prepared with a pure culture of G. sulfurreducens before adding wastewater that includes non-exoelectrogenic bacteria.