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Microbial electrochemical systems that integrate the advantages of inorganic electrocatalysis and microbial catalysis are expected to provide sustainable solutions to the increasing energy shortages, resource depletion, and climate degradation. However, sluggish extracellular electron transfer (EET) at the interface between electroactive microorganisms and inorganic electrode materials is a critical bottleneck that limits the performance of systems. Electrocatalytic nanomaterials are highly competitive in overcoming this obstacle due to their effective association with microbial catalysis. Therefore, this review focuses on the cutting-edge applications and enhancement mechanisms of nanomaterials with electrocatalytic activity in promoting microbial EET. First, the EET mechanism of microbial electrocatalysis in both microbial anodes and cathodes is briefly introduced, and then recent applications of various electrocatalytic nanomaterials in diverse microbial electrochemical systems are summarized, including heteroatom-doped carbons and precious metal, as well as transition metal oxides, sulfides, carbides, and nitrides. The synergistic effects of nanomaterial electrocatalysis and microbial catalysis on enhancing interfacial EET are analyzed. Finally, the challenges and perspectives of realizing high-performance microbial electrochemical systems are also discussed in order to offer some reference for further research. [ABSTRACT FROM AUTHOR]

Abstract Soil contamination poses a serious threat to ecosystem and human well-being. Compared to conventional physical and chemical treatment, the microbial electrochemical system (MES) offers a sustainable and environment-friendly solution for soil bioremediation. In principle, soil microbe degrades organic substrate and releases electron in anode region. The electron flows through electric circuit to the cathode and finally is accepted by oxygen or oxidized metals. With various inherent advantages, MES has been applied in petroleum hydrocarbon, chlorinated organics and heavy metals bioremediation in soils. This paper aims to review the recent advances of MES in soil bioremediation, including main mechanisms of contaminant removal with MES, configurations of soil MES and current development in bioremediation of soil contaminated by organic and inorganic pollutants. Moreover, challenges and future prospects of soil MES are discussed. Graphical abstract Image 1 Highlights • The different principles and configurations of MES in soil bioremediation are systematically introduced. • Recent advances in contaminant removal especially for hydrocarbon and heavy metal are extensively reviewed. • Current challenges and future prospects of soil MES are discussed. [ABSTRACT FROM AUTHOR]

A sediment microbial fuel cell (SMFC) is a system in which MFC is applied to a sediment layer of an aqueous system for water purification. SMFCs can remove contaminants from sediments and decompose organic matter while simultaneously producing electrical energy. SMFC is installed in the form of installing an anode in the sediment at the bottom of the water system and a cathode in the water layer above the sediment, and connecting the two electrodes through an external circuit. Early SMFCs were developed to be used as power sources in hard-to-reach deep water areas or remote areas. However, recently, it has attracted a lot of attention as a technology for biologically purifying pollutants through its own power supply. Furthermore, it is being developed as a means of monitoring the environmental condition of the installed area. Despite the importance of SMFC, no comprehensive review has yet been published to the Korean readers on the trends and prospects of SMFC research. Therefore, in this review paper, the mechanism of SMFC, their mechanism of removal of organic, inorganic, and heavy metals, and the current state of SMFC technology are discussed, and future prospects are presented.

A milk-processing plant was drafted as a distinctive staple industry amid the diverse field of industries. Dairy products such as yogurt, cheese, milk powder, etc., consume a huge amount of water not only for product processing, but also for sanitary purposes and for washing dairy-based industrial gear. Henceforth, the wastewater released after the above-mentioned operations comprises a greater concentration of nutrients, chemical oxygen demand, biochemical oxygen demand, total suspended solids, and organic and inorganic contents that can pose severe ecological issues if not managed effectively. The well-known processes such as coagulation–flocculation, membrane technologies, electrocoagulation, and other biological processes such as use of a sequencing batch reactor, upflow sludge anaerobic blanket reactor, etc., that are exploited for the treatment of dairy effluent are extremely energy-exhaustive and acquire huge costs in terms of fabrication and maintenance. In addition, these processes are not competent in totally removing various contaminants that exist in dairy effluent. Accordingly, to decrease the energy need, microbial electrochemical technologies (METs) can be effectively employed, thereby also compensating the purification charges by converting the chemical energy present in impurities into bioelectricity and value-added products. Based on this, the current review article illuminates the application of diverse METs as a suitable substitute for traditional technology for treating dairy wastewater. Additionally, several hindrances on the way to real-world application and techno-economic assessment of revolutionary METs are also deliberated. [ABSTRACT FROM AUTHOR]

Microbial electrochemical system (MES) technology has been widely investigated for organic degradation. However, the removal of recalcitrant organic contaminants containing halogen-, nitro-, or azo-groups remains a great challenge. Integrating the cathodic and anodic processes in an MES is able to improve or complete the mineralization of the target halogen-, nitro- and azo-organics via a sequential reductive and oxidative process. In this way, a cathode is used to reduce the toxic target organics, while an anode is to oxidize the residual organics from the reduction process and at the same time generate electrons to support the reduction process. This paper has provided a concise review about the sequential cathode-anode contaminant degradation in an MES and its specific mechanisms. Potential strategies to improve the MES degradation performance were discussed, mainly including the application and development of the biocatalyzed cathode as well as the optimization of the anodic operating condition and the improvement of anodic bacteria and electrode material. Perspectives on future directions were proposed and the key challenges were identified as the competitive or inhibitive influence of other compounds that could coexist in real wastewater on the target contaminants.

The study of electromicrobiology has grown into its own field over the last decades and involves microbially driven redox reactions at electrodes as part of a microbial electrochemical system (MES). The microorganisms known to use electrodes as either electron acceptors; electricigens, or electron donors; electrotrophs, drive the redox reactions within these systems through extracellular electron transfer (EET) processes. These exoelectrogenic microorganisms form biofilms, referred to as electroactive biofilms (EAB), in order to maximize adherence and contact with electrode surfaces and with one another. In this review, we will discuss the key differences between biofilms that utilize the electrode as an electron acceptor or donor, including their mechanisms for electron transfer, structural and functional compositions as well as which species are enriched for in each microenvironment. Lastly, we will discuss the intricacies of interspecies and intraspecies biofilm formation in electrode biofilms and considerations required for future bioengineering efforts. [ABSTRACT FROM AUTHOR]

Anode properties are critical for the performance of microbial electrolysis cells (MECs). In the present study, Fe nanoparticle-modified graphite disks were used as anodes to investigate the effects of nanoparticles on the performance of Shewanella oneidensis MR-1 in MECs. Results demonstrated that the average current densities produced with Fe nanoparticle-decorated anodes up to 5.89-fold higher than plain graphite anodes. Whole genome microarray analysis of the gene expression showed that genes encoding biofilm formation were significantly up-regulated as a response to nanoparticle-decorated anodes. Increased expression of genes related to nanowires, flavins, and c-type cytochromes indicates that enhanced mechanisms of electron transfer to the anode may also have contributed to the observed increases in current density. The majority of the remaining differentially expressed genes associated with electron transport and anaerobic metabolism demonstrate a systemic response to increased power loads. [ABSTRACT FROM AUTHOR]