Long-term stability of bioelectricity generation coupled with tetrathionate disproportionation

Mechanism and application of modified bioelectrochemical system anodes made of carbon nanomaterial for the removal of heavy metals from soil

Bioelectrochemical techniques are quick, efficient, and sustainable alternatives for treating heavy metal soils. The use of carbon nanomaterials in combination with electroactive microorganisms can create a conductive network that mediates long-distance electron transfer in an electrode system, thereby resolving the issue of low electron transfer efficiency in soil remediation. As a multifunctional soil heavy metal remediation technology, its application in organic remediation has matured, and numerous studies have demonstrated its potential for soil heavy metal remediation. This is a ground-breaking method for remediating soils polluted with high concentrations of heavy metals using soil microbial electrochemistry. This review summarizes the use of bioelectrochemical systems with modified anode materials for the remediation of soils with high heavy metal concentrations by discussing the mass-transfer mechanism of electrochemically active microorganisms in bioelectrochemical systems, focusing on the suitability of carbon nanomaterials and acidophilic bacteria. Finally, we discuss the emerging limitations of bioelectrochemical systems, and future research efforts to improve their performance and facilitate practical applications. The mass-transfer mechanism of electrochemically active microorganisms in bioelectrochemical systems emphasizes the suitability of carbon nanomaterials and acidophilic bacteria for remediating soils polluted with high concentrations of heavy metals. We conclude by discussing present and future research initiatives for bioelectrochemical systems to enhance their performance and facilitate practical applications. As a result, this study can close any gaps in the development of bioelectrochemical systems and guide their practical application in remediating heavy-metal-contaminated soils.

The fate of tetrathionate during the development of a biofilm in biogenic sulfuric acid attack on different cementitious materials

The biodeterioration of cement-based materials in sewer environments occurs because of the production of sulfuric acid from the biochemical oxidation of H₂S by sulfur-oxidizing bacteria (SOB). In the perspective of determining the possible reaction pathways for the sulfur cycle in such conditions, hydrated cementitious binders were exposed to an accelerated laboratory test (BAC test) to reproduce a biochemical attack similar to the one occurring in the sewer networks. Tetrathionate was used as a reduced sulfur source to naturally develop sulfur-oxidizing activities on the surfaces of materials. The transformation of tetrathionate was investigated on materials made from different binders: Portland cement, calcium aluminate cement, calcium sulfoaluminate cement and alkali-activated slag. The pH and the concentration of the different sulfur species were monitored in the leached solutions during 3 months of exposure. The results showed that the formation of different polythionates was independent of the nature of the material. The main parameter controlling the phenomena was the evolution of the pH of the leached solutions. Moreover, tetrathionate disproportionation was detected with the formation of more reduced forms of sulfur compounds (pentathionate, hexathionate and elemental sulfur) along with thiosulfate and sulfate. The experimental findings allowed numerical models to be developed to estimate the amount of sulfur compounds as a function of the pH evolution. In addition, biomass samples were collected from the exposed surface and from the deteriorated layers to identify the microbial populations. No clear influence of the cementitious materials on the selected populations was detected, confirming the previous results concerning the impact of the materials on the selected reaction pathways for tetrathionate transformation.

Mitigating membrane biofouling in biofuel cell system – A review

A biofuel cell (BFC) system can transform chemical energy to electrical energy through electrochemical reactions and biochemical pathways. However, BFC faced several obstacles delaying it from commercialization, such as biofouling. Theoretically, the biofouling phenomenon occurs when microorganisms, algae, fungi, plants, or small animals accumulate on wet surfaces. In most BFC, biofouling occurs by the accumulation of microorganisms forming a biofilm. Amassed biofilm on the anode is desired for power production, however, not on the membrane separator. This phenomenon causes severities toward BFCs when it increases the electrode’s ohmic and charge transfer resistance and impedes the proton transfer, leading to a rapid decline in the system’s power performance. Apart from BFC, other activities impacted by biofouling range from the uranium industry to drug sensors in the medical field. These fields are continuously finding ways to mitigate the biofouling impact in their industries while putting forward the importance of the environment. Thus, this study aims to identify the severity of biofouling occurring on the separator materials for implementation toward the performance of the BFC system. While highlighting successful measures taken by other industries, the effectiveness of methods performed to reduce or mitigate the biofouling effect in BFC was also discussed in this study.

Biofouling of membranes in microbial electrochemical technologies: Causes, characterization methods and mitigation strategies

The scope of the review is to discuss the current state of knowledge and lessons learned on biofouling of membrane separators being used for microbial electrochemical technologies (MET). It is illustrated what crucial membrane features have to be considered and how these affect the MET performance, paying particular attention to membrane biofouling. The complexity of the phenomena was demonstrated and thereby, it is shown that membrane qualities related to its surface and inherent material features significantly influence (and can be influenced by) the biofouling process. Applicable methods for assessment of membrane biofouling are highlighted, followed by the detailed literature evaluation. Finally, an outlook on e.g. possible mitigation strategies for membrane biofouling in MET is provided.

Electrochemical monitoring of Acidithiobacillus thiooxidans biofilm formation on graphite surface with elemental sulfur

Inorganic wastewaters and sediments from the mining industry and mineral bioleaching processes have not been fully explored in bioelectrochemical systems (BES). Knowledge of interfacial changes due to biofilm evolution under acidic conditions may improve applications in electrochemical processes, specifically those related to sulfur compounds. Biofilm evolution of Acidithiobacillus thiooxidans on a graphite plate was monitored by electrochemical techniques, using the graphite plate as biofilm support and elemental sulfur as the only energy source. Even though the elemental sulfur was in suspension, S⁰ particles adhered to the graphite surface favoring biofilm development. The biofilms grown at different incubation times (without electric perturbation) were characterized in a classical three electrode electrochemical cell (sulfur and bacteria free culture medium) by non-invasive electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The biofilm structure was confirmed by Environmental Scanning Electrode Microscopy, while the relative fractions of exopolysaccharides and extracellular hydrophobic compounds at different incubation times were evaluated by Confocal Laser Scanning Microscopy. The experimental conditions chosen in this work allowed the EIS monitoring of the biofilm growth as well as the modification of Extracellular Polymeric Substances (EPS) composition (hydrophobic/ exopolysaccharides EPS ratio). This strategy could be useful to control biofilms for BES operation under acidic conditions.

Biological sulfur oxidation in wastewater treatment: A review of emerging opportunities

Sulfide prevails in both industrial and municipal waste streams and is one of the most troublesome issues with waste handling. Various technologies and strategies have been developed and used to deal with sulfide for decades, among which biological means make up a considerable portion due to their low operation requirements and flexibility. Sulfur bacteria play a vital role in these biotechnologies. In this article, conventional biological approaches dealing with sulfide and functional microorganisms are systematically reviewed. Linking the sulfur cycle with other nutrient cycles such as nitrogen or phosphorous, and with continued focus of waste remediation by sulfur bacteria, has led to emerging biotechnologies. Furthermore, opportunities for energy harvest and resource recovery based on sulfur bacteria are also discussed. The electroactivity of sulfur bacteria indicates a broad perspective of sulfur-based bioelectrochemical systems in terms of bioelectricity production and bioelectrochemical synthesis. The considerable PHA accumulation, high yield and anoxygenic growth conditions in certain phototrophic sulfur bacteria could provide an interesting alternative for bioplastic production. In this review, new merits of biological sulfide oxidation from a traditional environmental management perspective as well as a waste to resource perspective are presented along with their potential applications.

Biosensors based on lithotrophic microbial fuel cells in relation to heterotrophic counterparts: research progress, challenges, and opportunities

Biosensors based on the microbial fuel cell (MFC) platform have been receiving increasing attention from researchers owing to their unique properties. The lithotrophic MFC, operated with a neutrophilic iron-oxidizing bacterial community, has recently been developed and proposed to be used as a biosensor to detect iron, and likely metals in general, in water samples. Therefore, in this review, important aspects of the lithotrophic MFC-based biosensor, including its configuration, fabrication, microbiology, electron transfer mechanism, sensing performance, etc. were carefully discussed in comparison with those of heterotrophic (organotrophic) counterparts. Particularly, the challenges for the realization of the practical application of the device were determined. Furthermore, the application potentials of the device were also considered and positioned in the context of technologies for metal monitoring and bioremediation.

Weak electricigens: A new avenue for bioelectrochemical research

Electroactivity appears to be a phylogenetically diverse trait independent of cell wall classification, with both Gram-negative and Gram-positive electricigens reported. While numerous electricigens have been observed, the majority of research focuses on a select group of highly electroactive species. Under favorable conditions, many microorganisms can be considered electroactive, either through their own mechanisms or exogenously-added mediators, producing a weak current. Such microbes should not be dismissed based on their modest electroactivity. Rather, they may be key to understanding what drives extracellular electron transfer in response to transient limitations of electron acceptor or donor, with implications for the study of pathogens and industrial bioprocesses. Due to their low electroactivity, such populations are difficult to grow in bioelectrochemical systems and characterise with electrochemistry. Here, a critical review of recent research on weak electricigens is provided, with a focus on the methodology and the overall relevance to microbial ecology and bioelectrochemical systems.

The effect of anode potential on bioelectrochemical and electrochemical tetrathionate degradation

The effect of poised anode potential on electricity production and tetrathionate degradation was studied in two-chamber flow-through electrochemical (ES) and bioelectrochemical systems (BES). The minimum anode potential (vs. Ag/AgCl) for positive current generation was 0.3V in BES and 0.5V in the abiotic ES. The anode potential required to obtain average current density above 70mAm^-2 was 0.4V in BES and above 0.7V in ES. ES provided higher coulombic efficiency, but the average tetrathionate degradation rate remained significantly higher in BES (above 110mgL^-1d^-1) than in the abiotic ES (below 35mgL^-1d^-1). This study shows that at anode potentials below 0.7V, the electrochemical tetrathionate degradation is only efficient with microbial catalyst and that significantly higher tetrathionate degradation rates can be obtained with bioelectrochemical systems than with electrochemical systems at the tested anode potentials.