Effects of biochar anodes in rice plant microbial fuel cells on the production of bioelectricity, biomass, and methane

Efficient anode material derived from nutshells for bio-energy production in microbial fuel cell

Biochar is a carbonaceous solid that is prepared through thermo-chemical decomposition of biomass under an inert atmosphere. The present study compares the performance of biochar prepared from Peanut shell, coconut shell and walnut shell in dual chamber microbial fuel cell. The physicochemical and electrochemical analysis of biochar reveals that prepared biochar is macroporous, amorphous, biocompatible, and electrochemically conductive. Polarization studies show that Peanut shell biochar (PSB) exhibited a maximum power density of 165 mW/m2 followed by Coconut shell biochar (CSB) Activated Charcoal (AC) and Walnut shell biochar (WSB). Enhanced power density of PSB was attributed to its surface area and suitable pore size distribution which proved conducive for biofilm formation. Furthermore, the high electrical capacitance of PSB improved the electron transfer between microbes and anode.

Advances in amelioration of air pollution using plants and associated microbes: An outlook on phytoremediation and other plant-based technologies

Globally, air pollution is an unfortunate aftermath of rapid industrialization and urbanization. Although the best strategy is to prevent air pollution, it is not always feasible. This makes it imperative to devise and implement techniques that can clean the air continuously. Plants and microbes have a natural potential to transform or degrade pollutants. Hence, strategies that use this potential of living biomass to remediate air pollution seem to be promising. The simplest future trend can be planting suitable plant-microbe species capable of removing air pollutants like SO2, CO2, CO, NOX and particulate matter (PM) along roadsides and inside the buildings. Established wastewater treatment strategies such as microbial fuel cells (MFC) and constructed wetlands (CW) can be suitably modified to ameliorate air pollution. Green architecture involving green walls and green roofs is facile and aesthetic, providing urban ecosystem services. Certain microbe-based bioreactors such as bioscrubbers and biofilters may be useful in small confined spaces. Several generative models have been developed to assist with planning and managing green spaces in urban locales. The physiological limitations of using living organisms can be circumvent by applying biotechnology and transgenics to improve their potential. This review provides a comprehensive update on not just the plants and associated microbes for the mitigation of air pollution, but also lists the technologies that are available and/or can be modified and used for air pollution control. The article also gives a detailed analysis of this topic in the form of strengths-weaknesses-opportunities-challenges (SWOC). The strategies mentioned in this review would help to attain corporate Environmental Social and Governance (ESG) and Sustainable Development Goals (SDGs), while reducing carbon footprint in the urban scenario. The review aims to emphasise that urbanization is possible while tackling air pollution using facile, green techniques involving plants and associated microbes.

Effective and Economical 3D Carbon Sponge with Carbon Nanoparticles as Floating Air Cathode for Sustainable Electricity Production in Microbial Fuel Cells

The effective and economical 3D floating air cathodes were fabricated by a simple dipping-drying method with carbon black (CB), ethanol, and PTFE solution. Pristine Type I polyurethane sponge (5 pores/mm) and Pristine Type II polyurethane sponge (3 pores/mm) were used as the support. The deposition of CB on the Pristine Type I and Pristine Type II materials was detected by scanning electron microscopy and Fourier transform infrared spectroscopy. The carbon loss rate test exhibited good CB adhesive stability on both floating air cathodes. Besides, Type I/CB floating air cathode displayed 3.7 times higher tensile strength, 10.58 times higher elongation at break, and 3.3 times lower cost than carbon felt. The electricity production ability of carbon cloth (CC) anode with carbon felt, Type I/CB, and Type II/CB cathode MFCs (CC-CF-MFC, CC-I-MFC, and CC-II-MFC) was evaluated. After 130 days, the CC-I-MFC showed a maximum power density (PD) of 92.58 mW/m3, which was 4.6 times higher than the CC-CF-MFC. Compared with Type II/CB, Type I/CB cathode improved the maximum power density by 160% due to the smaller pores, rougher surface, and higher surface wettability. Further, CC-I-MFC exhibited the best overall oxidation-reduction performance and chemical oxygen demand removal efficiency. Consequently, Type I/CB floating air cathode opens a new opportunity for scaling up simple, inexpensive, and high-performance MFCs for energy production.

Pristine and modified biochar applications as multifunctional component towards sustainable future: Recent advances and new insights

Employing biomass for environmental conservation is regarded as a successful and environmentally friendly technique since they are cost-effective, renewable, and abundant. Biochar (BC), a thermochemically converted biomass, has a considerably lower production cost than the other conventional activated carbons. This material's distinctive properties, including a high carbon content, good electrical conductivity (EC), high stability, and a large surface area, can be utilized in various research fields. BC is feasible as a renewable source for potential applications that may achieve a comprehensive economic niche. Despite being an inexpensive and environmentally sustainable product, research has indicated that pristine BC possesses restricted properties that prevent it from fulfilling the intended remediation objectives. Consequently, modifications must be made to BC to strengthen its physicochemical properties and, thereby, its efficacy in decontaminating the environment. Modified BC, an enhanced iteration of BC, has garnered considerable interest within academia. Many modification techniques have been suggested to augment BC's functionality, including its adsorption and immobilization reliability. Modified BC is overviewed in its production, functionality, applications, and regeneration. This work provides a holistic review of the recent advances in synthesizing modified BC through physical, chemical, or biological methods to achieve enhanced performance in a specific application, which has generated considerable research interest. Surface chemistry modifications require the initiation of surface functional groups, which can be accomplished through various techniques. Therefore, the fundamental objective of these modification techniques is to improve the efficacy of BC contaminant removal, typically through adjustments in its physical or chemical characteristics, including surface area or functionality. In addition, this article summarized and discussed the applications and related mechanisms of modified BC in environmental decontamination, focusing on applying it as an ideal adsorbent, soil amendment, catalyst, electrochemical device, and anaerobic digestion (AD) promoter. Current research trends, future directions, and academic demands were available in this study.

Harnessing fungal bio-electricity: a promising path to a cleaner environment

Integrating fungi into fuel cell systems presents a promising opportunity to address environmental pollution while simultaneously generating energy. This review explores the innovative concept of constructing wetlands as fuel cells for pollutant degradation, offering a practical and eco-friendly solution to pollution challenges. Fungi possess unique capabilities in producing power, fuel, and electricity through metabolic processes, drawing significant interest for applications in remediation and degradation. Limited data exist on fungi's ability to generate electricity during catalytic reactions involving various enzymes, especially while remediating pollutants. Certain species, such as Trametes versicolor, Ganoderma lucidum, Galactomyces reessii, Aspergillus spp., Kluyveromyce smarxianus, and Hansenula anomala, have been reported to generate electricity at 1200 mW/m3, 207 mW/m2, 1,163 mW/m3, 438 mW/m3, 850,000 mW/m3, and 2,900 mW/m3, respectively. Despite the eco-friendly potential compared to conventional methods, fungi's role remains largely unexplored. This review delves into fungi's exceptional potential as fuel cell catalysts, serving as anodic or cathodic agents to mitigate land, air, and water pollutants while simultaneously producing fuel and power. Applications cover a wide range of tasks, and the innovative concept of wetlands designed as fuel cells for pollutant degradation is discussed. Cost-effectiveness may vary depending on specific contexts and applications. Fungal fuel cells (FFCs) offer a versatile and innovative solution to global challenges, addressing the increasing demand for alternative bioenergy production amid population growth and expanding industrial activities. The mechanistic approach of fungal enzymes via microbial combinations and electrochemical fungal systems facilitates the oxidation of organic substrates, oxygen reduction, and ion exchange membrane orchestration of essential reactions. Fungal laccase plays a crucial role in pollutant removal and monitoring environmental contaminants. Fungal consortiums show remarkable potential in fine-tuning FFC performance, impacting both power generation and pollutant degradation. Beyond energy generation, fungal cells effectively remove pollutants. Overall, FFCs present a promising avenue to address energy needs and mitigate pollutants simultaneously.

Utilization of rice production residues as a reinforcing agent in bioadhesives based on polyphenols extracted from the bark of trees from the Brazilian Cerrado biome

The scarcity of nonrenewable resources and the increase in environmental pollution have intensified the search for materials that exhibit specific characteristics and are nontoxic, renewable, and sustainable. Thus, the objective of this work was to produce natural polyphenol adhesives reinforced with rice husk and its ash to increase the mechanical resistance and moisture resistance of the glue line in wood bonded joints. Polyphenols were extracted from the bark of Stryphnodendron adstringens (Mart.) Coville (barbatimão). Adhesives were produced with a 50 % solid and 50 % liquid composition. Rice husk and husk ash underwent X-ray fluorescence analysis (XRF). Adhesives and reinforcement material were characterized by Fourier transform infrared (FTIR) and thermogravimetric analyses (TGA). The adhesives were glued in a mechanical press in specimens made of Pinus elliottii, which were subjected to shear testing of the wet and dry glue line. As a result, the chemical components present in rice husk and its ash positively influenced the properties of the adhesives. The mechanical glue line shear test showed that the adhesive reinforced with rice husk ash did not show a statistically significant difference. However, natural adhesives based on polyphenols from barbatimão strengthened with rice husk and ash showed improved properties, demonstrating how much it pays to use the residue of rice production to reinforce the matrix of tannin adhesives. Thus, it can be determined that reinforcement with rice husk and ash is efficient in improving some properties of natural adhesives based on polyphenols.

Natural hematite as low-cost auxiliary material for improving soil remediation by in-situ microbial community

Microbial-mineral interaction has a broad application prospect in the field of environmental remediation of organic pollutants. However, the disadvantages of long repair cycle and low repair rate limit its industrial application. In this study, natural hematite was used as an auxiliary material for soil remediation in a bio-electrochemical system. It was found that the power density of soil microbial fuel cell (SMFC) system composed of 2.0 mm hematite was 2.889 mW/m2, which is 2.7 times compared with the blank group (1.068 mW/m2) in the particle size optimization experiment. A similarly increased power density (1.068 to 2.467 mW/m2) was observed when the hematite content changed from 0 to 20% in the concentration optimization experiment. Under 20% and 2.0-mm hematite condition, the phenol removal rate was closed to 99% after 7 days, which is 1.9-folds compared with blank control (53%). These results suggest that addition of hematite enhances soil porosity and conductivity, and increases the number of electron acceptors in soil. These findings inspire that this economic and abundant natural mineral is expected to be a potential auxiliary material in the field of soil organic pollutant purification, and expand the understanding of interactions between hematite and microorganisms in nature.

The race between classical microbial fuel cells, sediment-microbial fuel cells, plant-microbial fuel cells, and constructed wetlands-microbial fuel cells: Applications and technology readiness level

Microbial fuel cell (MFC) is an interesting technology capable of converting the chemical energy stored in organics to electricity. It has raised high hopes among researchers and end users as the world continues to face climate change, water, energy, and land crisis. This review aims to discuss the journey of continuously progressing MFC technology from the lab to the field so far. It evaluates the historical development of MFC, and the emergence of different variants of MFC or MFC-associated other technologies such as sediment-microbial fuel cell (S-MFC), plant-microbial fuel cell (P-MFC), and integrated constructed wetlands-microbial fuel cell (CW-MFC). This review has assessed primary applications and challenges to overcome existing limitations for commercialization of these technologies. In addition, it further illustrates the design and potential applications of S-MFC, P-MFC, and CW-MFC. Lastly, the maturity and readiness of MFC, S-MFC, P-MFC, and CW-MFC for real-world implementation were assessed by multicriteria-based assessment. Wastewater treatment efficiency, bioelectricity generation efficiency, energy demand, cost investment, and scale-up potential were mainly considered as key criteria. Other sustainability criteria, such as life cycle and environmental impact assessments were also evaluated.

Roles of microalgae-based biofertilizer in sustainability of green agriculture and food-water-energy security nexus

For years, agrochemical fertilizers have been used in agriculture for crop production. However, intensive utilization of chemical fertilizers is not an ecological and environmental choice since they are destroying soil health and causing an emerging threat to agricultural production on a global scale. Under the circumstances of the increasing utilization of chemical fertilizers, cultivating microalgae to produce biofertilizers would be a wise solution since desired environmental targets will be obtained including (1) replacing chemical fertilizer while improving crop yields and soil health; (2) reducing the harvest of non-renewable elements from limited natural resources for chemical fertilizers production, and (3) mitigating negative influences of climate change through CO₂ capture through microalgae cultivation. Recent improvements in microalgae-derived-biofertilizer-applied agriculture will be summarized in this review article. At last, the recent challenges of applying biofertilizers will be discussed as well as the perspective regarding the concept of circular bio-economy and sustainable development goals (SDGs).

Pros and Cons of Biochar to Soil Potentially Toxic Element Mobilization and Phytoavailability: Environmental Implications

While the potential of biochar (BC) to immobilize potentially toxic elements (PTEs) in contaminated soils has been studied and reviewed, no review has focused on the potential use of BC for enhancing the phytoremediation efficacy of PTE-contaminated soils. Consequently, the overarching purpose in this study is to critically review the effects of BC on the mobilization, phytoextraction, phytostabilization, and bioremediation of PTEs in contaminated soils. Potential mechanisms of the interactions between BC and PTEs in soils are also reviewed in detail. We discuss the promises and challenges of various approaches, including potential environmental implications, of BC application to PTE-contaminated soils. The properties of BC (e.g., surface functional groups, mineral content, ionic content, and π-electrons) govern its impact on the (im)mobilization of PTEs, which is complex and highly element-specific. This review demonstrates the contrary effects of BC on PTE mobilization and highlights possible opportunities for using BC as a mobilizing agent for enhancing phytoremediation of PTEs-contaminated soils.

Applications of Nanomaterials in Microbial Fuel Cells: A Review

Microbial fuel cells (MFCs) are an environmentally friendly technology and a source of renewable energy. It is used to generate electrical energy from organic waste using bacteria, which is an effective technology in wastewater treatment. The anode and the cathode electrodes and proton exchange membranes (PEM) are important components affecting the performance and operation of MFC. Conventional materials used in the manufacture of electrodes and membranes are insufficient to improve the efficiency of MFC. The use of nanomaterials in the manufacture of the anode had a prominent effect in improving the performance in terms of increasing the surface area, increasing the transfer of electrons from the anode to the cathode, biocompatibility, and biofilm formation and improving the oxidation reactions of organic waste using bacteria. The use of nanomaterials in the manufacture of the cathode also showed the improvement of cathode reactions or oxygen reduction reactions (ORR). The PEM has a prominent role in separating the anode and the cathode in the MFC, transferring protons from the anode chamber to the cathode chamber while preventing the transfer of oxygen. Nanomaterials have been used in the manufacture of membrane components, which led to improving the chemical and physical properties of the membranes and increasing the transfer rates of protons, thus improving the performance and efficiency of MFC in generating electrical energy and improving wastewater treatment.

Effects of bioelectricity generation processes on methane emission and bacterial community in wetland and carbon fate analysis

Wetlands are an important carbon sink for greenhouse gases (GHGs), and embedding microbial fuel cell (MFC) into constructed wetland (CW) has become a new technology to control methane (CH4) emission. Rhizosphere anode CW-MFC was constructed by selecting rhizome-type wetland plants with strong hypoxia tolerance, which could provide photosynthetic organics as alternative fuel. Compared with non-planted system, CH4 emission flux and power output from the planted CW-MFC increased by approximately 0.48 ± 0.02 mg/(m2·h) and 1.07 W/m3, respectively. The CH4 emission flux of the CW-MFC operated under open-circuit condition was approximately 0.46 ± 0.02 mg/(m2·h) higher than that under closed-circuit condition. The results indicated that plants contributed to the CH4 emission from the CW-MFC, especially under open-circuit mode conditions. The CH4 emission from the CW-MFC was proportional to external resistance, and it increased by 0.67 ± 0.01 mg/(m2·h) when the external resistance was adjusted from 100 to 1000 Ω. High throughput sequencing further showed that there was a competitive relationship between electrogenic bacteria and methanogens. The flora abundance of electrogenic bacteria was high, while methanogens mainly consisted of Methanothrix, Methanobacterium and Methanolinea. The form and content of element C were analysed from solid phase, liquid phase and gas phase. It was found that a large amount of carbon source (TC = 254.70 mg/L) was consumed mostly through microbial migration and conversion, and carbon storage and GHGs emission accounted for 60.38% and 35.80%, respectively. In conclusion, carbon transformation in the CW-MFC can be properly regulated via competition of microorganisms driven by environmental factors, which provides a new direction and idea for the control of CH4 emission from wetlands.

A novel three-chamber modular PMFC with bentonite/flyash based clay membrane and oxygen reducing biocathode for long term sustainable bioelectricity generation

In this work, a novel three-chamber modular plant microbial fuel cell (PMFC) was designed and tested for long term sustainable generation of bioelecricity. The modular setup makes operation easy and hassle-free as placing every components, i.e., membranes, electrodes, and even changing the plants, becomes very convenient. The novel membrane assembly design combined with pre-activated electrodes with increased surface area helped promote biofilm growth and electrocatalytic activity on anode and cathode surface. The new design resulted in improved performance and stability of the PMFC system for long term usage with minimal maintenance. The use of composite membrane consisting of clay, bentonite, and fly ash mixture was used for the first time in PMFC research and proved to be an excellent alternative to existing expensive Nafion membranes. The power density and current density has increased up to 24.56 mW m-2 and 52 mA m-2 respectively, which is 63% increase in power production and is amongst the highest in PMFC research.

Impact of light on microalgal photosynthetic microbial fuel cells and removal of pollutants by nanoadsorbent biopolymers: Updates, challenges and innovations

Photosynthetic microbial fuel cells (PMFCs) with microalgae have huge potential for treating wastewater while simultaneously converting light energy into electrical energy. The efficiency of such cells directly depends on algal growth, which depends on light intensity. Higher light intensity results in increased potential as well as enhancement in generation of biomass rich in biopolymers. Such biopolymers are produced either by microbes at anode and algae at cathode or vice versa. The biopolymers recovered from these biological sources can be added in wastewater alone or in combination with nanomaterials to act as nanoadsorbents. These nanoadsorbents further increase the efficiency of PMFC by removing the pollutants like metals and dyes. In this review firstly the effect of different light intensities on the growth of microalgae, importance of diatoms in a PMFC and their impact on PMFCs efficiencies have been narrated. Secondly recovery of biopolymers from different biological sources and their role in removal of metals, dyes along with their impact on circular bioeconomy have been discussed. Thereafter bottlenecks and future perspectives in this field of research have been narrated.

Bio-electrochemical frameworks governing microbial fuel cell performance: technical bottlenecks and proposed solutions

Microbial fuel cells (MFCs) are recognized as a future technology with a unique ability to exploit metabolic activities of living microorganisms for simultaneous conversion of chemical energy into electrical energy. This technology holds the promise to offer sustained innovations and continuous development towards many different applications and value-added production that extends beyond electricity generation, such as water desalination, wastewater treatment, heavy metal removal, bio-hydrogen production, volatile fatty acid production and biosensors. Despite these advantages, MFCs still face technical challenges in terms of low power and current density, limiting their use to powering only small-scale devices. Description of some of these challenges and their proposed solutions is demanded if MFCs are applied on a large or commercial scale. On the other hand, the slow oxygen reduction process (ORR) in the cathodic compartment is a major roadblock in the commercialization of fuel cells for energy conversion. Thus, the scope of this review article addresses the main technical challenges of MFC operation and provides different practical approaches based on different attempts reported over the years.

Sustainable operation requires addressing key MFC-bottleneck issues. Enhancing extracellular electron transfer is the key to elevated MFC performance.

A review of recent advances in electrode materials for emerging bioelectrochemical systems: From biofilm-bearing anodes to specialized cathodes

Bioelectrochemical systems (BES), mainly microbial fuel cells (MEC) and microbial electrolysis cells (MFC), are unique biosystems that use electroactive bacteria (EAB) to produce electrons in the form of electric energy for different applications. BES have attracted increasing attention as a sustainable, low-cost, and neutral-carbon option for energy production, wastewater treatment, and biosynthesis. Complex interactions between EAB and the electrode materials play a crucial role in system performance and scalability. The electron transfer processes from the EAB to the anode surface or from the cathode surface to the EAB have been the object of numerous investigations in BES, and the development of new materials to maximize energy production and overall performance has been a hot topic in the last years. The present review paper discusses the advances on innovative electrode materials for emerging BES, which include MEC coupled to anaerobic digestion (MEC-AD), Microbial Desalination Cells (MDC), plant-MFC (P-MFC), constructed wetlands-MFC (CW-MFC), and microbial electro-Fenton (BEF). Detailed insights on innovative electrode modification strategies to improve the electrode transfer kinetics on each emerging BES are provided. The effect of materials on microbial population is also discussed in this review. Furthermore, the challenges and opportunities for materials scientists and engineers working in BES are presented at the end of this work aiming at scaling up and industrialization of such versatile systems.

Recent advances in soil microbial fuel cells for soil contaminants remediation

The cost-effective and eco-friendly approaches are needed for decontamination of polluted soils. The bio-electrochemical system, especially microbial fuel cells (MFCs) offer great promise as a technology for remediation of soil, sediment, sludge and wastewater. Recently, soil MFCs (SMFCs) have been attracting increasing amounts of interest in environmental remediation, since they are capable of providing a clean and inexhaustible source of electron donors or acceptors and can be easily controlled by adjusting the electrochemical parameters. In this review, we comprehensively covered the principle of SMFCs including the mechanisms of electron releasing and electron transportation, summarized the applications for soil contaminants remediation by SMFCs with highlights on organic contaminants degradation and heavy metal ions removal. In addition, the main factors that affected the performance of SMFCs were discussed in details which would be helpful for performance optimization of SMFCs as well as the efficiency improvement for soil remediation. Moreover, the key issues need to be addressed and future perspectives are presented.

Modification on biochars for applications: A research update

Biochars are the solid product of biomass under pyrolysis or gasification treatment, whose wholesale prices are lower than commercial activated carbons and other fine materials now in use. The employment of biochars as a renewable resource for field applications, if feasible, would gain apparent economic niche. Modification using physical or chemical protocol to revise the surface properties of biochar for reaching enhanced performances of target application has attracted great research interests. This article provided an overview of biochar application, particularly with the respect to the use of modified biochar as preferred soil amendment, adsorbent, electrochemical material, anaerobic digestion promotor, and catalyst. Based on literature works the current research trends and the prospects and research needs were outlined.

Dual role of macrophytes in constructed wetland-microbial fuel cells using pyrrhotite as cathode material: A comparative assessment

In the recent years many studies have shown that wetland plants play beneficial roles in bioelectricity enhancement in constructed wetland-microbial fuel cell (CW-MFC) because of the exudation of root oxygen and root exudates. In this study, the long-term roles of plants on the bioelectricity generation and contaminant removal were investigated in multi-anode (Anode1 and Anode2) and single cathode CW-MFCs. The electrode distances were 20 cm between Anode1-cathode and 10 cm between Anode2-cathode, respectively. Additionally, the employment of natural conductive pyrrhotite mineral as cathode material was firstly investigated in CW-MFC system. A cathode potential of -98 ± 52 mV to -175 ± 60 mV was achieved in the unplanted (CW-MFC 1), and planted CW-MFCs with Iris pseudacorus (CW-MFC 2), Lythrum salicaria (CW-MFC 3), and Phragmites australis (CW-MFC 4). The maximum power densities of Anode1-cathode and Anode2-cathode were 8.23 and 15.29 mW/m² in CW-MFC 1, 8.51 and 1.67 mW/m² in CW-MFC 2, 5.67 and 3.15 mW/m² in CW-MFC 3, and 7.59 and 14.71 mW/m² in CW-MFC 4, respectively. Interestingly, smaller power density was observed at Anode2-cathode, which has shorter electrode distance than Anode1-cathode in both CW-MFC 2 and CW-MFC 3, which indicates the negative role of oxygen released from the flourished plant roots at Anode2 micro-environment in power production. Therefore, recovering power from commercial CW-MFCs with flourished plants will be a challenge. The contradiction between keeping short electrode distance and avoiding the interference from plant roots to maintain anaerobic anode may be solved by the proposed modular CW-MFCs.

Operation mechanism of constructed wetland-microbial fuel cells for wastewater treatment and electricity generation: A review

Constructed wetland-microbial fuel cells (CWL-MFCs) are eco-friendly and sustainable technology, simultaneously implementing contaminant removal and electricity production. According to intensive research over the last five years, this review on the operation mechanism was conducted for in-depth understanding and application guidance of CWL-MFCs. The electrochemical mechanism based on anodic oxidation and cathodic reduction is the core for improved treatment in CWL-MFCs compared to CWLs. As the dominant bacterial community, the abundance and gene-expression patterns of electro-active bacteria responds to electrode potentials and contaminant loadings, further affecting operational efficiency of CWL-MFCs. Plants benefit COD and N removal by supplying oxygen for aerobic degradation and rhizosphere secretions for microorganisms. Multi-electrode configuration, carbon-based electrodes and rich porous substrates affect transfer resistance and bacterial communities. The possibilities of CWL-MFCs targeting at recalcitrant contaminants like flame retardants and interchain interactions among effect components need systematic research.

Improved bio-electricity production in bio-electrochemical reactor for wastewater treatment using biomass carbon derived from sludge supported carbon felt anode

Microbial fuel cell (MFC), a promising bio-electrochemical reactor could decompose organics in wastewater by redox processes of electro-active microorganism in anode and produce bio-energy, and the total MFC performance could mainly rely on electrochemical performance anode. Here, biomass carbon derived from municipal sludge was employed as low-cost and high-performance bio-anode for enhancing bioelectricity generation and wastewater treatment in MFC simultaneously. The electrochemical tests demonstrated that the large electrochemical active surface area, strong conductivity, and good biocompatibility in sludge carbon (SC) electrode resulted in higher power density (615.2 mW m^-2) and lower power loss (5.4%) than those of none carbon (NC) electrode in long term operation. After 30-cycle of continuous running, the low loss of chemical oxygen demand (COD) removal was achieved up to 5.2%, which was smaller than that of NC electrode (14.1%), indicating that the MFC with SC anode could effectively treat wastewater and keep stable redox processes in anode electrode. After the formation of biofilm, the charge transfer resistance of SC electrode (16.38 Ω) was 72.4% lower than that of NC electrode (59.35 Ω). High-throughput analysis of biofilm exhibit Proteobacteria was the dominant electro-active bacteria, and the modification of SC could slightly change the bacterial community. Therefore, resource utilization of natural wastes provided the novel concept of anode catalyst fabrication for MFC in enhancing electron transfer, power output and wastewater decomposition.

Three-dimensional electrodes enhance electricity generation and nitrogen removal of microbial fuel cells

One of the critical problems for practical application of microbial fuel cells (MFCs) is the poor electron transfer between microbial cells and anode. Hence, good biocompatibility and high specific surface area of electrodes are indispensable for MFC scale-up. In this study, three-dimensional electrode MFC (3DEMFC) was developed by filling biochar between anode and cathode. Three types of biochar electrodes (biochar, biochar and zeolite mixture, and MgO-modified biochar) were employed, and the performance of 3DEMFCs treating nitrogen in wastewater was investigated. The results showed that the highest power density of MFCs was 4.45 ± 0.21 W m^-3 achieved by 3DEMFC filled with MgO-modified biochar, and the overall power generation of 3DEMFCs (2.40 ± 0.28 ~ 4.45 ± 0.21 W m^-3) was higher than that of MFC without biochar (1.31 ± 0.24 W m^-3). The linear sweep voltammetry (LSV) results also demonstrated biochar addition to MFC was conducive to electron transfer between microbes and anode and MgO-modified biochar presented the highest coulombs transfer ability. Moreover, the highest removal efficiencies of ammonium, total nitrogen, and COD (93.6 ± 3.2%, 84.8 ± 2%, and 91.6 ± 1.3%, respectively) were achieved by 3DEMFC containing MgO-modified biochar, and simultaneous short-cut nitrification and denitrification were observed in MFCs. Furthermore, the SEM images displayed the bacteria adhesion on biochar and the biofilm dry weights of MgO-modified biochar after experiment was the highest of 103 ± 4 mg g^-1 among three kinds of biochar electrodes. Therefore, the power generation and nitrogen removal conspicuously enhanced in 3DEMFCs and biochar exhibited excellent biocompatibility and distinct electrochemical performance for MFC practical applications in wastewater treatment.

Evolution of the functionalities and structures of biochar in pyrolysis of poplar in a wide temperature range

This study studied the change of functionalities in the biochar formed in pyrolysis of poplar wood in a wide range of temperature. The in situ Diffuse Reflectance Infrared Fourier transform spectroscopy characterization indicated that aldehydes and ketones functionalities formation initiated at 100 °C, dominated at 300 to 500 °C. Carboxyl group was less stable than carbonyls. Cellulose crystal in poplar decomposed slightly at 300 °C and significantly at 350 °C. The temperature from 250 to 350 °C significantly affected biochar yields, while the drastic fusion of the ring structures in biochar occurred from 550 to 650 °C, making biochar more aliphatic while less more aromatic. High pyrolysis temperature also created more defective structures in the biochar and favored the absorption of the CO₂ generated during the pyrolysis. The results provide the reference information for understanding the structural configuration and evolution of the functionalities during in pyrolysis of poplar biomass.

CH4 control and associated microbial process from constructed wetland (CW) by microbial fuel cells (MFC)

Global warming is becoming more severe. We here proposed an innovative green technique aimed at reducing the CH₄ emissions from constructed wetlands (CWs) in which CH₄ is controlled by microbial fuel cells (MFCs). The results of our work indicated that CH₄ emissions from CWs could be controlled by operating MFC. The CH₄ fluxes significantly decreased in the MFC-CW (close circuit CC) compared with the control MFC-CW (open circuit OC). The bioelectricity generation and COD removal rates also differed in the two systems. The highest power density (0.27 W m^-3) and the lowest CH₄ emissions (4.7 mg m^-2 h^-1) were observed in the CC system. The plants' effects on the performance of the MFC-CWs were also investigated. The plant species had a profound impact on the CH₄ emissions and electricity production in MFC-CWs. The greatest CH₄ flux (9.5 mg m^-2 h^-1) was observed from the MFC-CW planted with Typha orientalis, while the CH₄ emissions from the MFC-CW planted with Cyperus alternifolius were reduced by 45%. Additional microbial processes were investigated. Quantitative real-time PCR (q-PCR) analysis indicated that the gene abundance of eubacterial 16 S rRNA, particulate methane monooxygenase (pmoA), and methyl coenzyme M reductase (mcrA) significantly differed for the control CW and MFC-CWs planted with different plants. In the CC systems, the mcrA genes in the anode were low, while the pmoA genes in the cathode were high. The operation of MFCs in CWs changed the exoelectrogenic and methanogenic community structures. Sequencing analysis indicated that phylotypes related to Geobacter, Bacteroides, and Desulfovibrio were specifically enriched in the CC systems. The results demonstrated that the operation of MFCs in the CWs resulted in the competition between the electrogenes and methanogenes, which resulted in distinctive microbial populations and biochemical processes that suppressed the CH₄ emissions from the CWs.

Spraying carbon powder derived from mango wood biomass as high-performance anode in bio-electrochemical system

Microbial fuel cell is a green and sustainable bio-electrochemical system that can harvest bioelectricity from organic matter conversion by bacteria in wastewater, but weak electrochemical activity and poor biocompatibility between electro-active bacteria and anode limit its scale-up application. In the present, the biomass carbon derived from mango wood was prepared via one-step carbonization method for anode materials in microbial fuel cell. A desirable anode C/1050 with large electrochemical active surface area (75.3 cm²), low electron transfer resistance (4.36 Ω), and benign biocompatibility were developed, achieving power density up to 589.8 mW·m^-2. This study provides a low-cost and high-performance biomass carbon used as anode material in microbial fuel cell for practical application.

Microbial fuel cell system: a promising technology for pollutant removal and environmental remediation

The microbial fuel cell (MFC) system is a promising environmental remediation technology due to its simple compact design, low cost, and renewable energy producing. MFCs can convert chemical energy from waste matters to electrical energy, which provides a sustainable and environmentally friendly solution for pollutant degradations. In this review, we attempt to gather research progress of MFC technology in pollutant removal and environmental remediation. The main configurations and pollutant removal mechanism by MFCs are introduced. The research progress of MFC systems in pollutant removal and environmental remediation, including wastewater treatment, soil remediation, natural water and groundwater remediation, sludge and solid waste treatment, and greenhouse gas emission control, as well as the application of MFCs in environmental monitoring have been reviewed. Subsequently, the application of MFCs in environmental monitoring and the combination of MFCs with other technologies are described. Finally, the current limitations and potential future research has been demonstrated in this review.

A Review of Non-Soil Biochar Applications

Biochar is the solid residue that is recovered after the thermal cracking of biomasses in an oxygen-free atmosphere. Biochar has been used for many years as a soil amendment and in general soil applications. Nonetheless, biochar is far more than a mere soil amendment. In this review, we report all the non-soil applications of biochar including environmental remediation, energy storage, composites, and catalyst production. We provide a general overview of the recent uses of biochar in material science, thus presenting this cheap and waste-derived material as a high value-added and carbonaceous source.

Performance and Long Distance Data Acquisition via LoRa Technology of a Tubular Plant Microbial Fuel Cell Located in a Paddy Field in West Kalimantan, Indonesia

A Plant Microbial Fuel Cell (Plant-MFCs) has been studied both in the lab and in a field. So far, field studies were limited to a more conventional Plant-MFC design, which submerges the anode in the soil and places the cathode above the soil surface. However, for a large scale application a tubular Plant-MFC is considered more practical since it needs no topsoil excavation. In this study, 1 m length tubular design Plant-MFC was installed in triplicate in a paddy field located in West Kalimantan, Indonesia. The Plant-MFC reactors were operated for four growing seasons. The rice paddy was grown in a standard cultivation process without any additional treatment due to the reactor instalation. An online data acquisition using LoRa technology was developed to investigate the performance of the tubular Plant-MFC over the final whole rice paddy growing season. Overall, the four crop seasons, the Plant-MFC installation did not show a complete detrimental negative effect on rice paddy growth. Based on continuous data analysis during the fourth crop season, a continuous electricity generation was achieved during a wet period in the crop season. Electricity generation dynamics were observed before, during and after the wet periods that were explained by paddy field management. A maximum daily average density from the triplicate Plant-MFCs reached 9.6 mW/m² plant growth area. In one crop season, 9.5-15 Wh/m² electricity can be continuously generated at an average of 0.4 ± 0.1 mW per meter tube. The Plant-MFC also shows a potential to be used as a bio sensor, e.g., rain event indicator, during a dry period between the crop seasons.

Activated Carbon Mixed with Marine Sediment is Suitable as Bioanode Material for Spartina anglica Sediment/Plant Microbial Fuel Cell: Plant Growth, Electricity Generation, and Spatial Microbial Community Diversity

Wetlands cover a significant part of the world’s land surface area. Wetlands are permanently or temporarily inundated with water and rich in nutrients. Therefore, wetlands equipped with Plant-Microbial Fuel Cells (Plant-MFC) can provide a new source of electricity by converting organic matter with the help of electrochemically active bacteria. In addition, sediments provide a source of electron donors to generate electricity from available (organic) matters. Eight lab-wetlands systems in the shape of flat-plate Plant-MFC were constructed. Here, four wetland compositions with activated carbon and/or marine sediment functioning as anodes were investigated for their suitability as a bioanode in a Plant-MFC system. Results show that Spartina anglica grew in all of the plant-MFCs, although the growth was less fertile in the 100% activated carbon (AC100) Plant-MFC. Based on long-term performance (2 weeks) under 1000 ohm external load, the 33% activated carbon (AC33) Plant-MFC outperformed the other plant-MFCs in terms of current density (16.1 mA/m2 plant growth area) and power density (1.04 mW/m2 plant growth area). Results also show a high diversity of microbial communities dominated by Proteobacteria with 42.5%–69.7% relative abundance. Principal Coordinates Analysis shows clear different bacterial communities between 100% marine sediment (MS100) Plant-MFC and AC33 Plant-MFC. This result indicates that the bacterial communities were affected by the anode composition. In addition, small worms (Annelida phylum) were found to live around the plant roots within the anode of the wetland with MS100. These findings show that the mixture of activated carbon and marine sediment are suitable material for bioanodes and could be useful for the application of Plant-MFC in a real wetland. Moreover, the usage of activated carbon could provide an additional function like wetland remediation or restoration, and even coastal protection.