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BACKGROUND: This work studies the in situ electrobioremediation (EBR) of clay soil polluted with 2,4‐dichlorophenoxyacetic acid (2,4‐D) in a two‐stage method. First, a fixed‐bed biofilm reactor able to biodegrade 2,4‐D in wastewater was developed; second, a portion of the biofilm‐covered bed was included in the polluted soil and used as a biological permeable reactive barrier (BioPRB), whereas electrokinetics were used to promote the contact between pollutant and microorganisms into the soil. RESULTS: The fixed‐bed biofilm reactor successfully treated wastewater polluted with 2,4‐D concentrations up to 1200 mg L−1 and under non‐oxygenated conditions because of the culture ability to use nitrate as electron acceptor. A portion of the stationary biofilm was later used as a BioPRB in the polluted soil to perform in situ EBR study. The study was performed in a bench scale set‐up using potentiostatic conditions (1.0 V cm−1), room temperature and periodic polarity reversal (2 d−1) in a 10 day batch experiment. The feasibility of the proposed technology was checked by the comparison with a conventional in situ bioremediation test without electrokinetics. The EBR treatment, coupling electrokinetics with the previously developed BioPRB, offered 85% removal efficiency of 2,4‐D after 10 days. According to the low removal efficiency observed in the reference test, it was proved that the electrokinetic transport phenomena improved contact between pollutant and microorganisms and clearly increased 2,4‐D removal rate. CONCLUSIONS: According to these results it is considered that the combination of electrokinetics and biobarriers could be a promising technology to achieve remediation of low permeable soils polluted with pesticides. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract Oxyfluorfen is a non-polar herbicide that may cause severe soil pollution. The present work studies the possible improvement due to surfactant addition in the efficiency of electro-bioremediation of a clay soil polluted which such a non-polar, low-mobility pollutant. Two-week-long batch electro-bioremediation experiments were performed in a bench-scale device. Oxyfluorfen-polluted soil (20 mg kg−1) was inoculated with an acclimated microbial culture, and several experiments were performed using different surfactant concentrations in the electrode wells (0.0, 2.5, 5.0, 10.0 and 20.0 g L−1 of SDS, sodium dodecyl sulphate). Experiments were performed under 1.0 V cm−1 and electrode polarity reversal. It was observed that the electro-osmotic flow (EOF) increased with SDS concentration and that SDS was successfully distributed across the soil, probably improving the oxyfluorfen mobility. Additionally, microbiological activity was fully maintained during the experiments. Electro-bioremediation without SDS removed 14% of the oxyfluorfen, while under 2.5 g L−1 SDS, the efficiency increased to 22% because of an expected improvement in the contact between the different species in the soil. However, higher SDS concentrations (between 10.0 and 20.0 g L−1) caused a decrease in the oxyfluorfen removal efficiency, as SDS is an easily biodegradable compound and was preferably used as substrate by the microbial culture instead of oxyfluorfen. Additionally, the use of high concentrations of SDS was clearly inefficient, as high amounts of the surfactant were lost through the EOF, and even low amounts of oxyfluorfen were removed to the electrode wells, which means that ex situ treatment of the polluted water would be needed. Graphical abstract Unlabelled Image Highlights • Oxyfluorfen polluted clay soil was treated through electro-bioremediation. • Surfactant (SDS) addition improved electro-osmotic flow and oxyfluorfen mobility. • Low SDS dosage increased oxyfluorfen removal efficiencies up to 22% in 2 weeks. • High SDS dosage washed out surfactant and pollutant and biodegradation rate decreased. [ABSTRACT FROM AUTHOR]

This work studies the feasibility of the periodic polarity reversal strategy (PRS) in a combined electrokinetic-biological process for the remediation of clayey soil polluted with a herbicide. Five two-weeks duration electrobioremediation batch experiments were performed in a bench scale set-up using spiked clay soil polluted with oxyfluorfen (20 mg kg −1 ) under potentiostatic conditions applying an electric field between the electrodes of 1.0 V cm −1 (20.0 V) and using PRS with five frequencies ( f ) ranging from 0 to 6 d −1 . Additionally, two complementary reference tests were done: single bioremediation and single electrokinetic. The microbial consortium used was obtained from an oil refinery wastewater treatment plant and acclimated to oxyfluorfen degradation. Main soil conditions (temperature, pH, moisture and conductivity) were correctly controlled using PRS. On the contrary, the electroosmotic flow clearly decreased as f increased. The uniform soil microbial distribution at the end of the experiments indicated that the microbial activity remained in every parts of the soil after two weeks when applying PRS. Despite the adapted microbial culture was capable of degrade 100% of oxyfluorfen in water, the remediation efficiency in soil in a reference test, without the application of electric current, was negligible. However, under the low voltage gradients and polarity reversal, removal efficiencies between 5% and 15% were obtained, and it suggested that oxyfluorfen had difficulties to interact with the microbial culture or nutrients and that PRS promoted transport of species, which caused a positive influence on remediation. An optimal f value was observed between 2 and 3 d −1 . [ABSTRACT FROM AUTHOR]

Bioelectrochemical systems are a promising technology capable of reducing CO2 emissions, a renewable carbon source, using electroactive microorganisms for this purpose. Purple Phototrophic Bacteria (PPB) use their versatile metabolism to uptake external electrons from an electrode to fix CO2. In this work, the effect of the voltage (from −0.2 to −0.8 V vs. Ag/AgCl) on the metabolic CO2 fixation of a mixed culture of PPB under photoheterotrophic conditions during the oxidation of a biodegradable carbon source is demonstrated. The minimum voltage to fix CO2 was between −0.2 and −0.4 V. The Calvin–Benson–Bassham (CBB) cycle is the main electron sink at these voltages. However, lower voltages caused the decrease in the current intensity, reaching a minimum at −0.8 V (−4.75 mA). There was also a significant relationship between the soluble carbon uptake in terms of chemical oxygen demand and the electron consumption for the experiments performed at −0.6 and −0.8 V. These results indicate that the CBB cycle is not the only electron sink and some photoheterotrophic metabolic pathways are also being affected under electrochemical conditions. This behavior has not been tested before in photoheterotrophic conditions and paves the way for the future development of photobioelectrochemical systems under heterotrophic conditions. [ABSTRACT FROM AUTHOR]

Bioelectrochemical systems are a promising technology capable of reducing CO 2 emissions, a renewable carbon source, using electroactive microorganisms for this purpose. Purple Phototrophic Bacteria (PPB) use their versatile metabolism to uptake external electrons from an electrode to fix CO 2 . In this work, the effect of the voltage (from -0.2 to -0.8 V vs. Ag/AgCl) on the metabolic CO 2 fixation of a mixed culture of PPB under photoheterotrophic conditions during the oxidation of a biodegradable carbon source is demonstrated. The minimum voltage to fix CO 2 was between -0.2 and -0.4 V. The Calvin-Benson-Bassham (CBB) cycle is the main electron sink at these voltages. However, lower voltages caused the decrease in the current intensity, reaching a minimum at -0.8 V (-4.75 mA). There was also a significant relationship between the soluble carbon uptake in terms of chemical oxygen demand and the electron consumption for the experiments performed at -0.6 and -0.8 V. These results indicate that the CBB cycle is not the only electron sink and some photoheterotrophic metabolic pathways are also being affected under electrochemical conditions. This behavior has not been tested before in photoheterotrophic conditions and paves the way for the future development of photobioelectrochemical systems under heterotrophic conditions.