Current advances in microbial fuel cell technology toward removal of organic contaminants - A review

The complete degradation of 1,2-dichloroethane in Escherichia coli by metabolic engineering

1,2-Dichloroethane (1,2-DCA), a widely utilized chemical intermediate and organic solvent in industry, frequently enters the environment due to accidental leaks and mishandling during application processes. Thus, the in-situ remediation of contaminated sites has become increasingly urgent. However, traditional remediation methods are inefficient and costly, while bioremediation presents a green, efficient, and non-secondary polluting alternative. In this study, an engineered strain capable of completely degrading 1,2-DCA was constructed. We introduced six exogenous genes of the 1,2-DCA degradation pathway into E. coli and confirmed their normal transcription and efficient expression in this engineered strain through qRT-PCR and proteomics. The degradation experiments showed that the strain completely degraded 2 mM 1,2-DCA within 12 h. Furthermore, the results of isotope tracing verified that the final degradation product, malic acid, entered the tricarboxylic acid cycle (TCA) of E. coli and was ultimately fully metabolized. Also, morphological changes in the engineered strain and control strain exposed to 1,2-DCA were observed under SEM, and the results revealed that the engineered strain is more tolerant to 1,2-DCA than the control strain. In conclusion, this study paved a new way for humanity to deal with the increasingly complex environmental challenges.

From single-chamber to multi-anodic microbial fuel cells: A review

Microbial fuel cells (MFCs) present a promising solution for wastewater treatment with the added benefits of energy generation, less sludge production and less energy consumption. MFCs have demonstrated high efficiency in the degradation of diverse types of wastewater. Nevertheless, the relatively low power density exhibited by MFCs has imposed certain restrictions on their widespread implementation. Consequently, the need for modification of MFC technology led to the development of stack and multi-chambered MFCs. The modified variations exhibit enhanced scalability and demonstrate greater reliability in terms of power output compared to traditional MFCs. In the present review article, different components of MFCs such as anode, cathode, microbial community and membrane have been reviewed and the advancement in design for better scalability of MFCs has been addressed, emphasizing the benefits associated with stacked and multi-anodic MFCs for enhanced performance. Finally, an update of previous large-scale MFC system applications is presented.

Biotechnology to reduce logistics burden and promote environmental stewardship for Air Force civil engineering requirements

This review provides discussion of advances in biotechnology with specific application to civil engineering requirements for airfield and airbase operations. The broad objectives are soil stabilization, waste management, and environmental protection. The biotechnology focal areas address (1) treatment of soil and sand by biomineralization and biopolymer addition, (2) reduction of solid organic waste by anaerobic digestion, (3) application of microbes and higher plants for biological processing of contaminated wastewater, and (4) use of indigenous materials for airbase construction and repair. The consideration of these methods in military operating scenarios, including austere environments, involves comparison with conventional techniques. All four focal areas potentially reduce logistics burden, increase environmental sustainability, and may provide energy source, or energy-neutral practices that benefit military operations.

Research progress of MOF-based membrane reactor coupled with AOP technology for organic wastewater treatment

MOF-based catalytic membrane reactor (MCMR), which can simultaneously achieve membrane separation and chemical catalytic degradation in an integrated system, is a cutting-edge technology for effective treatment of organic pollutants in water. The coupling of MCMR and advanced oxidation process (AOP) not only significantly improves the pollutant removal efficiency but also inhibits the membrane pollution through self-cleaning effect, thus improving the stability of MCMR. This paper reviews different MCMR systems combined with photocatalysis, Fenton oxidation, and persulfate activation, elucidates the reaction mechanism, discusses key issues to improve system effectiveness, and suggests future challenges and research directions.

Nano-biochar: recent progress, challenges, and opportunities for sustainable environmental remediation

Biochar is a carbonaceous by-product of lignocellulosic biomass developed by various thermochemical processes. Biochar can be transformed into "nano-biochar" by size reduction to nano-meters level. Nano-biochar presents remarkable physico-chemical behavior in comparison to macro-biochar including; higher stability, unique nanostructure, higher catalytic ability, larger specific surface area, higher porosity, improved surface functionality, and surface active sites. Nano-biochar efficiently regulates the transport and absorption of vital micro-and macro-nutrients, in addition to toxic contaminants (heavy metals, pesticides, antibiotics). However an extensive understanding of the recent nano-biochar studies is essential for large scale implementations, including development, physico-chemical properties and targeted use. Nano-biochar toxicity on different organisms and its in-direct effect on humans is an important issue of concern and needs to be extensively evaluated for large scale applications. This review provides a detailed insight on nanobiochar research for (1) development methodologies, (2) compositions and properties, (3) characterization methods, (4) potentiality as emerging sorbent, photocatalyst, enzyme carrier for environmental application, and (5) environmental concerns.

UV and solar-based photocatalytic degradation of organic pollutants from ceramics industrial wastewater by Fe-doped ZnS nanoparticles

UV and solar-based photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) as an organic contaminant in ceramics industry wastewater by ZnS and Fe-doped ZnS NPs was the focus of this research. Nanoparticles were prepared using a chemical precipitation process. The cubic, closed-packed structure of undoped ZnS and Fe-doped ZnS NPs was formed in spherical clusters, according to XRD and SEM investigations. According to optical studies, the optical band gaps of pure ZnS and Fe-doped ZnS nanoparticles are 3.35 and 2.51 eV, respectively, and Fe doping increased the number of carriers with high mobility, improved carrier separation and injection efficiency, and increased photocatalytic activity under UV or visible light. Doping of Fe increased the separation of photogenerated electrons and holes and facilitated charge transfer, according to electrochemical impedance spectroscopy investigations. Photocatalytic degradation studies revealed that in the present pure ZnS and Fe-doped ZnS nanoparticles, 100% treatment of 120 mL of 15 mg/L phenolic compound was obtained after 55- and 45-min UV-irradiation, respectively, and complete treatment was attained after 45 and 35-min solar light irradiation, respectively. Because of the synergistic effects of effective surface area, more effective photo-generated electron and hole separation efficiency, and enhanced electron transfer, Fe-doped ZnS demonstrated high photocatalytic degradation performance. The study of Fe-doped ZnS's practical photocatalytic treatment capability for removing 120 mL of 10 mg/L 2,4-DCP solution made from genuine ceramic industrial wastewater revealed Fe-doped ZnS's excellent photocatalytic destruction of 2,4-DCP from real industrial wastewater.

Simple sonochemical synthesis, characterization of TmVO4 nanostructure in the presence of Schiff-base ligands and investigation of its potential in the removal of toxic dyes

Thulium vanadate (TmVO4) nanorods were successfully prepared by a simple sonochemical approach using Schiff-base ligands. Additionally, TmVO4 nanorods were employed as a photocatalyst. The most optimal crystal structure and morphology of TmVO4 have been determined and optimized by varying Schiff-base ligands, the molar ratio of H2Salen, the sonication time and power, and the calcination time. A Eriochrome Black T (EBT) analysis revealed that the specific surface area was 24.91 m2/g. A bandgap of 2.3 eV was determined by diffuse reflectance spectroscopy (DRS) spectroscopy, which makes this compound suitable for visible photocatalytic applications. In order to assess the photocatalytic performance under visible light, two anionic dyes (EBT) and cationic dyes (Methyl Violet (MV)) were used as models. A variety of factors have been studied in order to improve the efficiency of the photocatalytic reaction, including dye type, pH, dye concentration, and catalyst loading. Under visible light, the highest efficiency was achieved (97.7%) when 45 mg TmVO4 nanocatalysts were present in 10 ppm Eriochorome Black T at pH = 10.

Food Waste Utilization for Reducing Carbon Footprints towards Sustainable and Cleaner Environment: A Review

There is world-wide generation of food waste daily in significant amounts, leading to depletion of natural resources and deteriorating air quality. One-third of global food produced is wasted laterally with the food value chain. Carbon footprint is an efficient way of communicating the issues related to climate change and the necessity of changing behavior. Valorization or utilization of food wastes helps in resolving issues related to environment pollution. Reduction in the carbon footprint throughout the chain of food supply makes the whole process eco-friendly. Prevailing food waste disposal systems focus on their economic and environmental viability and are putting efforts into using food waste as a resource input to agriculture. Effective and advanced waste management systems are adopted to deal with massive waste production so as to fill the gap between the production and management of waste disposal. Food waste biorefineries are a sustainable, eco-friendly, and cost-effective approach for the production of platform chemicals, biofuels, and other bio-based materials. These materials not only provide sustainable resources for producing various chemicals and materials but have the potential to reduce this huge environmental burden significantly. In this regard, technological advancement has occurred in past few years that has proven suitable for tackling this problem.

Biochar-microorganism interactions for organic pollutant remediation: Challenges and perspectives

Numerous harmful chemicals are introduced every year in the environment through anthropogenic and geological activities raising global concerns of their ecotoxicological effects and decontamination strategies. Biochar technology has been recognized as an important pillar for recycling of biomass, contributing to the carbon capture and bioenergy industries, and remediation of contaminated soil, sediments and water. This paper aims to critically review the application potential of biochar with a special focus on the synergistic and antagonistic effects on contaminant-degrading microorganisms in single and mixed-contaminated systems. Owing to the high specific surface area, porous structure, and compatible surface chemistry, biochar can support the proliferation and activity of contaminant-degrading microorganisms. A combination of biochar and microorganisms to remove a variety of contaminants has gained popularity in recent years alongside traditional chemical and physical remediation technologies. The microbial compatibility of biochar can be improved by optimizing the surface parameters so that toxic pollutant release is minimized, biofilm formation is encouraged, and microbial populations are enhanced. Biocompatible biochar thus shows potential in the bioremediation of organic contaminants by harboring microbial populations, releasing contaminant-degrading enzymes, and protecting beneficial microorganisms from immediate toxicity of surrounding contaminants. This review recommends that biochar-microorganism co-deployment holds a great potential for the removal of contaminants thereby reducing the risk of organic contaminants to human and environmental health.

Photocatalytic Microbial Fuel Cells and Performance Applications: A Review

In recent years, photocatalytic microbial fuel cells have gradually become a hot research topic in pollutant treatment, using either in situ or indirectly the oxidation of organic pollutants by catalytic materials under light and the biodegradation and mineralization of various components in wastewater by microorganisms, or through the generation of electricity by the microbial fuel cell (MFC) system to promote the photogeneration and separation of electrons and holes by the catalytic materials of the photocatalytic cell (PC) system. This study aims to provide new ideas for the development of environmentally friendly wastewater treatment technologies by investigating the use of photocatalytic cells for the efficient degradation and resource utilization of target pollutants. This study aims to raise awareness of the use of photocatalytic microbial fuel cells for pollutant degradation by providing an overview of the practical status of photocatalytic microbial fuel cells. This is achieved by reviewing the key cathode development, production capacity, and progress in the degradation of pollutants in photocatalytic microbial fuel cells. The issues facing future developments are also discussed in terms of how photocatalytic microbial fuel cells work and how they degrade pollutants. This study shows that photocatalytic microbial fuel cells are beneficial for achieving renewable energy (bioenergy, photovoltaic, etc.) capacity and dealing with environmental pollution and that this is a novel technology that deserves to be promoted to achieve the current dual carbon targets.

Microbial fuel cells for mineralization and decolorization of azo dyes: Recent advances in design and materials

Microbial fuel cells (MFCs) exhibit tremendous potential in the sustainable management of dye wastewater via degrading azo dyes while generating electricity. The past decade has witnessed advances in MFC configurations and materials; however, comprehensive analyses of design and material and its association with dye degradation and electricity generation are required for their industrial application. MFC models with high efficiency of dye decolorization (96-100%) and a wide variation in power generation (29.4-940 mW/m²) have been reported. However, only 28 out of 104 studies analyzed dye mineralization - a prerequisite to obviate dye toxicity. Consequently, the current review aims to provide an in-depth analysis of MFCs potential in dye degradation and mineralization and evaluates materials and designs as crucial factors. Also, structural and operation parameters critical to large-scale applicability and complete mineralization of azo dye were evaluated. Choice of materials, i.e., bacteria, anode, cathode, cathode catalyst, membrane, and substrate and their effects on power density and dye decolorization efficiency presented in review will help in economic feasibility and MFCs scalability to develop a self-sustainable solution for treating azo dye wastewater.

Improvement of zero waste sustainable recovery using microbial energy generation systems: A comprehensive review

Microbial energy generation systems, i.e., bioelectrochemical systems (BESs) are promising sustainable technologies that have been used in different fields of application such as biofuel production, biosensor, nutrient recovery, wastewater treatment, and heavy metals removal. However, BESs face great challenges such as large-scale application in real time, low power performance, and suitable materials for their configuration. This review paper aimed to discuss the use of BES systems such as conventional microbial fuel cells (MFCs), as well as plant microbial fuel cell (P-MFC), sediment microbial fuel cell (S-MFC), constructed wetland microbial fuel cell (CW-MFC), osmotic microbial fuel cell (OsMFC), photo-bioelectrochemical fuel cell (PBFC), and MFC-Fenton systems in the zero waste sustainable recovery process. Firstly, the configuration and electrode materials used in BESs as the main sources to improve the performance of these technologies are discussed. Additionally, zero waste recovery process from solid and wastewater feedstock, i.e., energy recovery: electricity generation (from 12 to 26,680 mW m^-2) and fuel generation, i.e., H₂ (170 ± 2.7 L^-1 L^-1 d^-1) and CH₄ (107.6 ± 3.2 mL^-1 g^-1), nutrient recovery of 100% (PO₄³-P), and 13-99% (NH₄⁺-N), heavy metal removal/recovery: water recovery, nitrate (100%), sulfate (53-99%), and sulfide recovery/removal (99%), antibiotic, dye removal, and other product recovery are critically analyzed in this review paper. Finally, the perspective and challenges, and future outlook are highlighted. There is no doubt that BES technologies are an economical option for the simultaneous zero waste elimination and energy recovery. However, more research is required to carry out the large-scale application of BES, as well as their commercialization.

Heterogeneous Advanced Oxidation Processes: Current Approaches for Wastewater Treatment

Nowadays, water pollution is one of the most dangerous environmental problems in the world. The presence of the so-called emerging pollutants in the different water bodies, impossible to eliminate through conventional biological and physical treatments used in wastewater treatment plants due to their persistent and recalcitrant nature, means that pollution continues growing throughout the world. The presence of these emerging pollutants involves serious risks to human and animal health for aquatic and terrestrial organisms. Therefore, in recent years, advanced oxidation processes (AOPs) have been postulated as a viable, innovative and efficient technology for the elimination of these types of compounds from water bodies. The oxidation/reduction reactions triggered in most of these processes require a suitable catalyst. The most recent research focuses on the use and development of different types of heterogeneous catalysts, which are capable of overcoming some of the operational limitations of homogeneous processes such as the generation of metallic sludge, difficult separation of treated water and narrow working pH. This review details the current advances in the field of heterogeneous AOPs, Fenton processes and photocatalysts for the removal of different types of emerging pollutants.