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Nitrobenzene occurs as a pollutant in wastewaters originating from numerous industrial and agricultural activities. It needs to be removed prior to discharge to sewage treatment works because of its high toxicity and persistence. In this study. we investigated the use of a bioelectrochemical system (BES) to remove nitrobenzene at a cathode coupled to microbial oxidation of acetate at an anode. Effective removal of nitrobenzene at rates up to 1.29 ± 0.04 mol m-3 TCC d-1 (total cathodic compartment TCC) was achieved with concomitant energy recovery. Correspondingly, the formation rate for the reduction product aniline was 1.14 ± 0.03 mol m-3 ICC d-1. Nitrobenzene removal and aniline formation rates were significantly enhanced when the BES was supplied with power, reaching 8.57 ± 0.03 and 6.68 ± 0.03 mol m-3 ICC d-1, respectively, at an energy consumption of 17.06 ± 0.16 W m-3 TCC (current density at 59.5 A m-3 TCC). Compared to those of conventional anaerobic biological methods for nitrobenzene removal, the required dosage of organic cosubstrate was significantly reduced in this system. Although aniline was always identified as the major product of nitrobenzene reduction at the cathode of BES in this study, the Coulombic efficiencies of nitrobenzene removal and aniline formation were dependent on the current density of the BES. [ABSTRACT FROM AUTHOR]

This paper, for the first time; describes the development of a microbial biocathode for hydrogen production that is based on a naturally selected mixed culture of electrochemically active micro-organisms. This is achieved through a three- phase biocathode startup procedure that effectively turned an acetate- and hydrogen-oxidizing bioanode into a hydrogen- producing biocathode by reversing the polarity of the electrode. The microbial biocathode that was obtained in this way had a current density of about -1.2 A/m² at a potential of -0.7 V. This was 3.6 times higher than that of a control electrode (-0.3 A/m²). Furthermore, the microbial biocathode produced about 0.63 m³ H2/m³ cathode liquid volume/day at a cathodic hydrogen efficiency of 49% during hydrogen yield tests, whereas the control electrode produced 0.08 m³ H2/m³ cathode liquid volume/day at a cathodic hydrogen efficiency of 25%. The effluent of the biocathode chamber could be used to inoculate another electrochemical cell that subsequently also developed an identical hydrogen-producing biocathode (-1.1 A/m² at a potential of -0.7 V). Scanning electron micrographs of both microbial biocathodes showed a well-developed biofilm on the electrode surface. [ABSTRACT FROM AUTHOR]

Abstract: During membrane treatment of secondary effluent from wastewater treatment plants, a reverse osmosis concentrate (ROC) containing trace organic contaminants is generated. As the latter are of concern, effective and economic treatment methods are required. Here, we investigated electrochemical oxidation of ROC using Ti/Ru0.7Ir0.3O2 electrodes, focussing on the removal of dissolved organic carbon (DOC), specific ultra-violet absorbance at 254 nm (SUVA254), and 28 pharmaceuticals and pesticides frequently encountered in secondary treated effluents. The experiments were conducted in a continuously fed reactor at current densities (J) ranging from 1 to 250 A m−2 anode, and a batch reactor at J = 250 A m−2. Higher mineralization efficiency was observed during batch oxidation (e.g. 25.1 ± 2.7% DOC removal vs 0% removal in the continuous reactor after applying specific electrical charge, Q = 437.0 A h m−3 ROC), indicating that DOC removal is depending on indirect oxidation by electrogenerated oxidants that accumulate in the bulk liquid. An initial increase and subsequent slow decrease in SUVA254 during batch mode suggests the introduction of auxochrome substituents (e.g. –Cl, NH2Cl, -Br, and -OH) into the aromatic compounds. Contrarily, in the continuous reactor ring-cleaving oxidation products were generated, and SUVA254 removal correlated with applied charge. Furthermore, 20 of the target pharmaceuticals and pesticides completely disappeared in both the continuous and batch experiments when applying J ≥ 150 A m−2 (i.e. Q ≥ 461.5 A h m−3) and 437.0 A h m−3 (J = 250 A m−2), respectively. Compounds that were more persistent during continuous oxidation were characterized by the presence of electrophilic groups on the aromatic ring (e.g. triclopyr) or by the absence of stronger nucleophilic substituents (e.g. ibuprofen). These pollutants were oxidized when applying higher specific electrical charge in batch mode (i.e. 1.45 kA h m−3 ROC). However, baseline toxicity as determined by Vibrio fischeri bioluminescence inhibition tests (Microtox) was increasing with higher applied charge during batch and continuous oxidation, indicating the formation of toxic oxidation products, possibly chlorinated and brominated organic compounds. [Copyright &y& Elsevier]

Iodinated X-ray contrast media (ICM) are only to a limited extent removed from conventional wastewater treatment plants, due to their high recalcitrance. This work reports on the cathodic dehalogenation of the ICM iopromide in a bioelectrochemical system (BES), fed with acetate at the anode and iopromide at the cathode. When the granular graphite cathode potential was decreased from -500 to -850 mV vs standard hydrogen electrode (SHE), the iopromide removal and the iodide release rates increased from 0 to 4.62 ± 0.01 mmol m(-3) TCC d(-1) and 0 to 13.4 ± 0.16 mmol m(-3) TCC d(-1) (Total Cathodic Compartment, TCC) respectively. Correspondingly, the power consumption increased from 0.4 ± 1 to 20.5 ± 3.3 W m(-3) TCC. The Coulombic efficiency of the iopromide dehalogenation at the cathode was less than 1%, while the Coulombic efficiency of the acetate oxidation at the anode was lower than 50% at various granular graphite cathode potentials. The results suggest that iopromide could be completely dehalogenated in BESs when the granular graphite cathode potential was controlled at -800 mV vs SHE or lower. This finding was further confirmed using mass spectrometry to identify the dehalogenated intermediates and products of iopromide in BESs. Kinetic analysis indicates that iopromide dehalogenation in batch experiments can be described by a first-order model at various cathode potentials. This work demonstrates that the BESs have a potential for efficient dehalogenation of ICM from wastewater or environmental streams.