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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 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.

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Summary This study focuses on a semi‐single‐chamber microbial electrolysis cell (MEC) based on an anode made of carbon cloth (CCp) combined with stainless‐steel (SS) and encapsulated in a dialysis bag with different molecular weight cut‐offs of 2, 14, and 50 kDa (D2‐, D14‐, and D50‐COMBp, respectively). The encapsulated anode was inoculated with Geobacter sulfurreducens in a small volume directly into the dialysis bag. While the MEC with the non‐encapsulated anode was inoculated into the main chamber volume. The hydrogen evolution rates obtained in the MECs based on D2‐COMBp, D14‐COMBp, and D50‐COMBp anodes were 0.134 ± 0.005, 0.144 ± 0.014, and 0.160 ± 0.009 m3m−2d−1, respectively; while the COMBp led to only 0.122 ± 0.004 m3m−2d−1. When the MEC utilizing D50‐COMBp was fed with wastewater, the current density was only 12.4 ± 0.21 A m−2, compared to feeding with acetate (15.7 ± 0.63 A m−2). The encapsulated anode in the presence of wastewater included 70% of G. sulfurreducens, while the non‐encapsulated included only 58%.

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