Search Results (6)

Bioelectrochemical systems (BESs), rather than physicochemical processes, are used for wastewater remediation, electricity production, and zero carbon dioxide emission. Textile effluents contain organic and inorganic compounds that can fuel BESs. The main goal of this study was to understand the interplay between the anode material, its surface area, the potential applied to the working electrode (WE), and the concentration of the co-substrate, and how these factors lead to the formation of highly efficient thermohalophilic bioanodes (THB) retrieved from Chott El Djerid (SCD) hypersaline sediment for the treatment of synthetic textile wastewater. To this end, twenty-seven bioanode formation experiments were designed using a Box-Behnken matrix and response surface methodology to understand concomitant interactions. All experiments were conducted in electrochemical reactors of final volume 750 mL inoculated with 80% of enrichment medium containing three azo dyes at a concentration of 300 ppm and 20% of biocatalyst microbial SCD source, at 45 °C. The optimal levels were predicted using NemrodW software as carbon felt (CF) anode material, 6 cm² anode surface, 7 g/L glucose concentration, and −0.1 V applied potential. These theoretical results were experimentally validated, using maximum current output of 5.23 ± 0.30 A/m², decolorization rate of 100%, and a chemical oxygen demand (COD) removal rate of 96 ± 1%. Illumina Miseq results revealed that bacterial community harbored the bioanode was dominated at phylum level by Firmicutes (67.1%). At the species level, the biofilm was mainly colonized by Orenia metallireducens species (59.5%). Obtained findings show a promising application of THB in the degradation of recalcitrant molecules as well as for the energy recovery. Full article

The treatment of textile wastewater (TWW) loaded with recalcitrant azo dyes in bioelectrochemical systems (BES) rather than in physicochemical processes is a low-cost and environmentally friendly process. The main objective of this study is to investigate the potential of different saline sediments collected from extreme Tunisian environments for the formation of bioanodes capable ofsimultaneous azo dyes degradation and electric current generation in synthetic (STWW) and real textile wastewaters (RTWW) characterized by a varied composition of azo dyes and a high salinity. The obtained bioanodes and anolytes were studied comparatively by electrochemical, microscopic, analytical, and molecular tools.Based on the UV–visible spectra analysis, the breakdown of the azo bond was confirmed. With RTWW, the BES achieved a chemical oxygen demand (COD) abatement rate of 85%with a current density of 2.5 A/m². Microbial community analysis indicated that a diverse community of bacteria was active for effluent treatment coupled with energy production. At the phylum level, the electrodes were primarily colonized by proteobacteria and firmicutes, which are the two phyla most involved in bioremediation. The analysis of the microbial community also showed the abundance of Marinobacter hydrocarbonoclasticus and Marinobacter sp. species characterized by their high metabolic capacity, tolerance to extremophilic conditions, and role in hydrocarbon degradation. Full article

It is the ambition of many researchers to finally be able to close in on the fundamental, coupled phenomena that occur during the formation and expression of electrocatalytic activity in electroactive biofilms. It is because of this desire to understand that bioelectrochemical systems (BESs) have been miniaturized into microBES by taking advantage of the worldwide development of microfluidics. Microfluidics tools applied to bioelectrochemistry permit even more fundamental studies of interactions and coupled phenomena occurring at the microscale, thanks, in particular, to the concomitant combination of electroanalysis, spectroscopic analytical techniques and real-time microscopy that is now possible. The analytical microsystem is therefore much better suited to the monitoring, not only of electroactive biofilm formation but also of the expression and disentangling of extracellular electron transfer (EET) catalytic mechanisms. This article reviews the details of the configurations of microfluidic BESs designed for selected objectives and their microfabrication techniques. Because the aim is to manipulate microvolumes and due to the high modularity of the experimental systems, the interfacial conditions between electrodes and electrolytes are perfectly controlled in terms of physicochemistry (pH, nutrients, chemical effectors, etc.) and hydrodynamics (shear, material transport, etc.). Most of the theoretical advances have been obtained thanks to work carried out using models of electroactive bacteria monocultures, mainly to simplify biological investigation systems. However, a huge virgin field of investigation still remains to be explored by taking advantage of the capacities of microfluidic BESs regarding the complexity and interactions of mixed electroactive biofilms. Full article

Bacterial respiration of nitrate is a natural process of nitrate reduction, which has been industrialized to treat anthropic nitrate pollution. This process, also known as “microbial denitrification”, is widely documented from the fundamental and engineering points of view for the enhancement of the removal of nitrate in wastewater. For this purpose, experiments are generally conducted with heterotrophic microbial metabolism, neutral pH and moderate nitrate concentrations (<50 mM). The present review focuses on a different approach as it aims to understand the effects of hydrogenotrophy, alkaline pH and high nitrate concentration on microbial denitrification. Hydrogen has a high energy content but its low solubility, 0.74 mM (1 atm, 30 °C), in aqueous medium limits its bioavailability, putting it at a kinetic disadvantage compared to more soluble organic compounds. For most bacteria, the optimal pH varies between 7.5 and 9.5. Outside this range, denitrification is slowed down and nitrite (NO₂⁻) accumulates. Some alkaliphilic bacteria are able to express denitrifying activity at pH levels close to 12 thanks to specific adaptation and resistance mechanisms detailed in this manuscript, and some bacterial populations support nitrate concentrations in the range of several hundred mM to 1 M. A high concentration of nitrate generally leads to an accumulation of nitrite. Nitrite accumulation can inhibit bacterial activity and may be a cause of cell death. Full article

Effective and eco-friendly technologies are required for the treatment of tannery wastewater as its biological toxicity and large volume leads toground water pollution. Hydrophobic (unmodified carbon felt) and hydrophilic modified carbon felt with Linde Type A zeolite (LTA zeolite) and bentonite were examined for their effects on bacterial attachment, current generation, and tannery wastewater treatment efficiency. Chronoamperometry and cyclic voltammetry confirmed the higher electron transfer obtained with modified anodes. Maximum current densities of 24.5 and 27.9 A/m² were provided with LTA zeolite and bentonite-modified anodes, respectively, while the unmodified carbon felt gave a maximum current density of 16.9 A/m². Compared with hydrophobic unmodified carbon felt, hydrophilic modified electrodes increased the exploitation of the internal surface area of the 3D structure of the carbon felt by the electroactive biofilm. The study revealed 93.8 ± 1.7% and 96.3 ± 2.1% of chemical oxygen demand (COD) reduction for LTA zeolite and bentonite, respectively. Simultaneous chromium removal was achieved with values of 94.6 ± 3.6 and 97.5 ± 2.2 for LTA zeolite and bentonite, respectively. This study shows the potential approach of carbon felt clay modification for the efficient tannery wastewater treatment using bioelectrochemicals systems (BESs) accompanied with high current recovery. Full article

Use of photocatalytic paint-like coatings may be a way to protect building materials from microbial colonization. Numerous studies have shown the antimicrobial efficiency of TiO ${}_2$ photocatalysis on various microorganisms. However, few have focused on easy-to-apply solutions and on photocatalysis under low irradiance. This paper focuses on (a) the antibacterial properties of a semi-transparent coating formulated using TiO ${}_2$ particles and (b) the microscopic investigations of bacterial biofilm development on TiO ${}_2$ -coated building materials under accelerated growth conditions. Results showed significant antibacterial activity after few hours of testing. The efficiency seemed limited by the confinement of the TiO ${}_2$ particles inside the coating binder. However, a pre-irradiation with UV light can improve efficiency. In addition, a significant effect against the formation of a bacterial biofilm was also observed. The epifluorescence approach, in which fluorescence is produced by reflect rather than transmitted light, could be applied in further studies of microbial growth on coatings and building materials. Full article