Long-term bio-power of ceramic microbial fuel cells in individual and stacked configurations

Microbial applications for sustainable space exploration beyond low Earth orbit

With the construction of the International Space Station, humans have been continuously living and working in space for 22 years. Microbial studies in space and other extreme environments on Earth have shown the ability for bacteria and fungi to adapt and change compared to "normal" conditions. Some of these changes, like biofilm formation, can impact astronaut health and spacecraft integrity in a negative way, while others, such as a propensity for plastic degradation, can promote self-sufficiency and sustainability in space. With the next era of space exploration upon us, which will see crewed missions to the Moon and Mars in the next 10 years, incorporating microbiology research into planning, decision-making, and mission design will be paramount to ensuring success of these long-duration missions. These can include astronaut microbiome studies to protect against infections, immune system dysfunction and bone deterioration, or biological in situ resource utilization (bISRU) studies that incorporate microbes to act as radiation shields, create electricity and establish robust plant habitats for fresh food and recycling of waste. In this review, information will be presented on the beneficial use of microbes in bioregenerative life support systems, their applicability to bISRU, and their capability to be genetically engineered for biotechnological space applications. In addition, we discuss the negative effect microbes and microbial communities may have on long-duration space travel and provide mitigation strategies to reduce their impact. Utilizing the benefits of microbes, while understanding their limitations, will help us explore deeper into space and develop sustainable human habitats on the Moon, Mars and beyond.

Characterization and application of novel fly ash blended ceramic membrane in MFC for low-cost and sustainable wastewater treatment and power generation

Field-scale application of the microbial fuel cell (MFC) technology faces a major constraint due to the widely used high-cost proton exchange membrane Nafion, prompting lately, the development of ceramic membranes using different clay minerals. In the present study, the characteristics and applicability of a novel ceramic membrane fabricated using potter's clay (C) blended with varying proportions (0, 5, 10, and 20 wt%) of fly ash (FA), designated as CFA₀, CFA₅, CFA₁₀, and CFA₂₀, were assessed for cost-effective and sustainable use in MFC. On assessing the properties of the membrane, CFA₁₀ was found to exhibit superior quality with fine pore size distribution (average 0.49 μm) favoring higher water uptake and less oxygen diffusion. The CFA₁₀ membrane showed a maximum proton mass transfer coefficient (4.32 ± 0.04 × 10^-5 cm/s) that was about three times that of the control CFA₀. The oxygen mass transfer coefficient of CFA₁₀ was 5.13 ± 0.12 × 10^-5 cm/s, which was about 40% less than in the control. X-ray diffraction (XRD) analysis of CFA membrane revealed the richness of quartz, which facilitates proton conductance and water retention. The CFA₁₀ membrane fitted MFC demonstrated a peak power output of 4.57 W/m³ (twice that in CFA₀) with an average of 80.02 ± 0.86% COD removal and 68.03 ± 0.13% coulombic efficiency in a long-term study indicating its improved applicability and durability. Electrochemical kinetics involving cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) also affirmed the efficacy of CFA₁₀ membrane in MFC showing peak current output of 13.95 mA and low ohmic resistance (74.2 Ω). The novel (CFA₁₀) ceramic membrane amalgamated with the coal fly ash, a waste of concern, shows promise for high MFC performance at a much reduced (98% less) cost that can be used for sustainable scale-up of the technology.

Microbial electro deionization for waste water treatment - A critical review on methods, applications and mechanism

Electro deionization using microbial communities has been proven as a competent method for desalination and abatement of water pollution by removing ionic chemicals from the target waters. Microbial Desalination Cell (MDC) facilitates microbial deionization which can either support or be a substitute for the conventional desalination methods. Generation of electricity is accomplished by the bio electrochemical oxidation of organic compounds present as contaminants in wastewater which in turn attribute to the migration of ions in MDC system. The present review aims to elucidate the theory, principles and the application of microbial desalination cell and microbial fuel cell (MFC) in treatment of saline and wastewaters. Air cathode MDC and stacked MDC for purification of saline water are found to give promising results. Air pump assisted microbial desalination cell reported 150.39 ppm h^-1 of salt removal with an operational time period of 80 h and showed consistent results. Hence the air cathode assisted MDC showed dominant capacity of salt removal compared to stacked MDC. Also, three major types of microbial fuel cell, namely photosynthetic biofilm MFC, constructive wetland MFC and ceramic membrane supported MFC are reviewed for their potentials in wastewater treatment by deionization method and electricity generation. Complete (100%) removal of chemical oxygen demand was reported by photosynthetic microbial fuel cell operated for 16 days having 435.8 Ω of external resistance. When constructive wetland microbial fuel cell was operated for 10 days with 1000 ohms of external resistance, it exhibited complete (100%) removal of chemical oxygen demand from the wastewater. About 92% of chemical oxygen demand removal was demonstrated by ceramic membrane supported microbial fuel. Compared to ceramic membrane microbial fuel cell, photosynthetic and constructive wetland microbial fuel cell displayed better performance in terms of pollutant removal capacity and economical factor. Ability of the electrogenic species, namely Geobacter, Shewanella, Clostridium and Bacillus and the photosynthetic species, namely Chorella Vulgaris Rhodopsuedomonas, and Scenedesmus abundans in microbial deionization methods and their performance levels reported by several researchers are presented.

Use of activated carbon and camphor carbon as cathode and clay cup as proton exchange membrane in a microbial fuel cell for the bioenergy production from crude glycerol biodegradation

This work characterizes two alternative materials to substitute the most expensive microbial fuel cells (MFCs) components: proton exchange membrane (PEM) and cathode. Crude glycerol biodegradation was studied in MFCs using a clay cup as a PEM and activated carbon and camphor carbon mixture (CAC) as a cathode. The cathode performance was compared with Platinum on carbon cloth. Two clay cup single-chamber MFCs were operated with each cathode and fed with 2000 mg/L of crude glycerol. Electrochemical properties were characterized by linear sweep voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. Biodegradation efficiencies were estimated with the chemical oxygen demand (COD) removal percentage. MFCs with CAC showed a maximum power density of 100 mW/m². This result was a 43.47% power response regarding MFCs with Platinum. COD removal efficiencies of 94% were achieved in 37 days for both cells. The Columbic efficiencies were 24.04% and 22.78% for the MFCs with Platinum and CAC. The economic analysis showed a cost of USD 9.97 for MFCs with CAC. This cost is five times lower than when using Platinum. MFCs utilizing clay cups and CAC showed an acceptable performance for the bioenergy production from crude glycerol biodegradation above all economic advantage in the cell cost.

Ceramic-microbial fuel cell (C-MFC) for waste water treatment: A mini review

Microbial fuel cell (MFC) is a bio-electrochemical system that utilizes the activity of electrogenic bacteria to generate electricity. When wastewater is used as feed in MFC, its organic constituents are hydrolyzed and oxidized by the bacteria. Hence, this technology is a source of clean electricity while simultaneously treating wastewater. Over the years much research has been done to improve its efficiency as well as to reduce the cost of implementation and functioning. However, scalability and commercialization of this technology still faces several challenges. This mini review discusses the use of ceramics in MFCs using wastewater feed as a method of overcoming the current technological challenges. Ceramics can be used as separators, chassis or electrode, conferring facile chemical and structural stability. The material is low-cost, environment-friendly and easily available. Studies reporting stacked configurations have been mentioned, and those that have reported field studies and technology oriented practical applications. Critical analysis of the scalability of the use of ceramics for the dual purpose of electricity generation as well as wastewater treatment has been done in this review. Future research directives towards potential sustainable commercialization have also been mentioned. C-MFC is a promising technology and the primary aim of this review is to help enhance the knowledge base for the optimization of use of ceramics in MFC to achieve large-scale clean electricity generation and sewage treatment.

Advancements in Bioelectricity Generation Through Nanomaterial-Modified Anode Electrodes in Microbial Fuel Cells

The use of nanotechnology in bioelectrochemical systems to recover bioelectricity and metals from waste appears to be a potentially appealing alternative to existing established procedures. This trend exactly characterizes the current renewable energy production technology. Hence, this review focuses on the improvement of the anode electrode by using different functional metal oxide-conducting polymer nanocomposites to enhance microbial fuel cell (MFC) performance. Enhancement of interfacial bioelectrocatalysis between electroactive microorganisms and hierarchical porous nanocomposite materials could enhance cost-effective bioanode materials with superior bioelectrocatalytic activity for MFCs. In this review, improvement in efficiency of MFCs by using iron oxide- and manganese oxide-based polypyrrole hybrid composites as model anode modifiers was discussed. The review also extended to discussing and covering the principles, components, power density, current density, and removal efficiencies of biofuel cell systems. In addition, this research review demonstrates the application of MFCs for renewable energy generation, wastewater treatment, and metal recovery. This is due to having their own unique working principle under mild conditions and using renewable biodegradable organic matter as a direct fuel source.

Microbial fuel cell scale-up options: Performance evaluation of membrane (c-MFC) and membrane-less (s-MFC) systems under different feeding regimes

In recent years, bioelectrochemical systems have advanced towards upscaling applications and tested during field trials, primarily for wastewater treatment. Amongst reported trials, two designs of urine-fed microbial fuel cells (MFCs) were tested successfully on a pilot scale as autonomous sanitation systems for decentralised area. These designs, known as ceramic MFCs ( c -MFCs) and self-stratifying MFCs ( s -MFC), have never been calibrated under similar conditions. Here, the most advanced versions of both designs were assembled and tested under similar feeding conditions. The performance and efficiency were evaluated under different hydraulic retention times (HRT), through chemical oxygen demand measures and polarisation experiments. Results show that c -MFCs displayed constant performance independently from the HRT (32.2 ± 3.9 W m-3) whilst displaying high energy conversion efficiency at longer HRT (NER COD  = 2.092 ± 0.119 KWh.Kg COD -1, at 24h HRT). The s -MFC showed a correlation between performance and HRT. The highest performance was reached under short HRT (69.7 ± 0.4 W m-3 at 3h HRT), but the energy conversion efficiency was constant independently from the HRT (0.338 ± 0.029 KWh.Kg COD -1). The c -MFCs and s -MFCs similarly showed the highest volumetric efficiency under long HRT (65h) with NER V of 0.747 ± 0.010 KWh.m-3 and 0.825 ± 0.086 KWh.m-3, respectively. Overall, c -MFCs seems more appropriate for longer HRT and s -MFCs for shorter HRT.

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.

Microbial fuel cell coupled Fenton oxidation for the cathodic degradation of emerging contaminants from wastewater: Applications and challenges

Urbanization and industrialization have resulted in the escalation of the occurrence of emerging contaminants (EC) in the wastewater and ultimately to the receiving water bodies due to their bio-refractory nature. The presence of ECs in the water bodies adversely affects all three domains of life, viz. bacteria, archaea and eukaryotes, and eventually the ecosystem. Fenton oxidation is one of the most suitable method that is capable of degrading a variety of ECs by employing a strong oxidizing agent in the form of •OH. The coupling of Fenton oxidation with microbial fuel cell (MFC) offers benefits, such as low-cost, minimal requirement of external energy, and in-situ generation of oxidizing agents. The resulting system, termed as bio-electro-Fenton MFC (BEF-MFC), is capable of degrading the ECs in the cathodic chamber, while harvesting bioelectricity and simultaneously removing oxidizable organic matter from wastewater in the anodic chamber. This review discusses the applications of BEF-MFC for the treatment of dyes, pharmaceuticals, pesticides, and real complex wastewaters. Additionally, the effect of operating conditions on the performance of BEF-MFC are elaborated and emphasis is also given on possible future direction of research that can be adopted in BEF-MFC in the purview of up-scaling.

Electrosynthesis, modulation, and self-driven electroseparation in microbial fuel cells

Microbial electrosynthesis (MES) represents a sustainable platform that converts waste into resources, using microorganisms within an electrochemical cell. Traditionally, MES refers to the oxidation/reduction of a reactant at the electrode surface with externally applied potential bias. However, microbial fuel cells (MFCs) generate electrons that can drive electrochemical reactions at otherwise unbiased electrodes. Electrosynthesis in MFCs is driven by microbial oxidation of organic matter releasing electrons that force the migration of cationic species to the cathode. Here, we explore how electrosynthesis can coexist within electricity-producing MFCs thanks to electro-separation of cations, electroosmotic drag, and oxygen reduction within appropriately designed systems. More importantly, we report on a novel method of in situ modulation for electrosynthesis, through additional “pin” electrodes. Several MFC electrosynthesis modulating methods that adjust the electrode potential of each half-cell through the pin electrodes are presented. The innovative concept of electrosynthesis within the electricity producing MFCs provides a multidisciplinary platform converting waste-to-resources in a self-sustainable way.

A comprehensive review on emerging constructed wetland coupled microbial fuel cell technology: Potential applications and challenges

Constructed wetlands (CWs) integrated with bioelectrochemical systems (BESs) are being intensively researched with the names like constructed wetland-microbial fuel cell (CW-MFC), electro-wetlands, electroactive wetlands, and microbial electrochemical technologies-based constructed wetland since the last decade. The implantation of BES in CW facilitates the tuning of redox activities and electron flow balance in aerobic and anaerobic zones in the CW bed matrix, thereby alleviating the limitation associated with electron acceptor availability and increasing its operational controllability. The benefits of CW-MFC include high treatment efficiency, electricity generation, and recalcitrant pollutant abatement. This article presents CW-MFC technology's journey since its emergence to date, encompassing the research done so far, including the basic principle and functioning, bio-electrocatalysts as its machinery, influential factors for microbial interactions, and operational parameters controlling different processes. A few key challenges and potential applications are also discussed for the CW-MFC systems.

Estimation of total energy requirement for sewage treatment by a microbial fuel cell with a one-meter air-cathode assuming Michaelis–Menten COD degradation

Calculations of chemical oxygen demand (COD) degradation in sewage by a microbial fuel cell (MFC) were used to estimate the total energy required for treatment of the sewage. Mono-exponential regression (MER) and the Michaelis–Menten equation (MME) were used to describe the MFC's COD removal rate (CRR). The tubular MFC used in this study (ϕ 5.0 × 100 cm) consisted of an air core surrounding a carbon-based cathode, an anion exchange membrane, and graphite non-woven fabric immersed in sewage. The MFC generated 0.26 A m⁻² of the electrode area and 0.32 W m⁻³ of the sewage water, and 3.9 W h m⁻³ in a chemostat reactor supplemented continuously with sewage containing 180 mg L⁻¹ of COD with a hydraulic retention time (HRT) of 12 h. The COD removal and coulombic efficiency (CE) were 46% and 19%, respectively, and the energy generation efficiency (EGE) was 0.054 kW h kg⁻¹-COD. The CRR and current in the MFC were strongly dependent on the COD, which could be controlled by varying the HRT. The MER model predicted first-order rate constants of 0.054 and 0.034 for reactors with and without MFC, respectively. The difference in these values indicated that using MFC significantly increased the COD removal. The results of fitting the experimental data to the MME suggested that the total COD can be separated into nondegradable CODs (C_n) and degradable CODs (C_d) via MFC. The values of CRR for C_d and CE suggest that MFC pretreatment for 12 hours prior to aeration results in a 75% decrease in net energy consumption while reducing sewage COD from 180 to 20 mg L⁻¹.

Calculations of chemical oxygen demand (COD) degradation in sewage by a microbial fuel cell (MFC) were used to estimate the total energy required for treatment of the sewage.

Evaluation of artificial neural network algorithms for predicting the effect of the urine flow rate on the power performance of microbial fuel cells

Microbial fuel cell (MFC) power performance strongly depends on the biofilm growth, which in turn is affected by the feed flow rate. In this work, an artificial neural network (ANN) approach has been used to simulate the effect of the flow rate on the power output by ceramic MFCs fed with neat human urine. To this aim, three different second-order algorithms were used to train our network and then compared in terms of prediction accuracy and convergence time: Quasi-Newton, Levenberg-Marquardt, and Conjugate Gradient. The results showed that the three training algorithms were able to accurately simulate power production. Amongst all of them, the Levenberg-Marquardt was the one that presented the highest accuracy (R = 95%) and the fastest convergence (7.8 s). These results show that ANNs are useful and reliable tools for predicting energy harvesting from ceramic-MFCs under changeable flow rate conditions, which will facilitate the practical deployment of this technology.

A review on the contribution of electron flow in electroactive wetlands: Electricity generation and enhanced wastewater treatment

In less than a decade, bioelectrochemical systems/microbial fuel cell integrated constructed wetlands (electroactive wetlands) have gained a considerable amount of attention due to enhanced wastewater treatment and electricity generation. The enhancement in treatment has majorly emanated from the electron transfer or flow, particularly in anaerobic regions. However, the chemistry associated with electron transfer is complex to understand in electroactive wetlands. The electroactive wetlands accommodate diverse microbial community in which each microbe set their own potential to further participate in electron transfer. The conductive materials/electrodes in electroactive wetlands also contain some potential, due to which, several conflicts occur between microbes and electrode, and results in inadequate electron transfer or involvement of some other reaction mechanisms. Still, there is a considerable research gap in understanding of electron transfer between electrode-anode and cathode in electroactive wetlands. Additionally, the interaction of microbes with the electrodes and understanding of mass transfer is also essential to further understand the electron recovery. This review mainly deals with the electron transfer mechanism and its role in pollutant removal and electricity generation in electroactive wetlands.

Resilience and limitations of MFC anodic community when exposed to antibacterial agents

•

MFC cascade can withstand and degrade high concentrations of ampicillin.

•

Chloroxylenol caused loss of power and microbial community within MFC cascade.

•

MFC anodic biofilm responds differentially to different inhibitory chemical agents.

•

MFC cascade has the potential for bioremediation of certain chemical agents.

This study evaluates the fate of certain bactericidal agents introduced into microbial fuel cell (MFC) cascades and the response of the microbial community. We tested the response of functioning urine fed MFC cascades using two very different bactericidal agents: a common antibiotic (Ampicillin, 5 g/L) and a disinfectant (Chloroxylenol 4.8 g/L) in concentrations of up to 100 times higher than the usual dose. Results of power generation showed that the established bacteria community was able to withstand high concentrations of ampicillin with good recovery after 24 h of minor decline. However, power generation was adversely affected by the introduction of chloroxylenol, resulting in a 99% loss of power generation. Ampicillin was completely degraded within the MFC cascade (>99.99%), while chloroxylenol remained largely unaffected. Analysis of the microbial community before the addition of the bactericidal agents showed a significant bacterial diversity with at least 35 genera detected within the cascade. Microbial community analysis after ampicillin treatment showed the loss of a small number of bacterial communities and proportional fluctuations of specific strains within the individual MFCs community. On the other hand, there was a significant shift in the bacterial community after chloroxylenol treatment coupled with the loss of at least 13 bacterial genera across the cascade.

Optimisation of the internal structure of ceramic membranes for electricity production in urine-fed microbial fuel cells

The need to find a feasible alternative to commercial membranes for microbial fuel cells (MFCs) poses an important challenge for the practical implementation of this technology. This work aims to analyse the influence of the internal structure of low-cost terracotta clay-based membranes on the behaviour of MFCs. To this purpose, 9 different combinations of temperature and time were used to prepare 27 MFC separators. The results show that the temperature has a significant effect on both porosity and pore size distribution, whereas the ramp time do not show a significant influence on these parameters. It was observed that kilning temperatures higher than 1030 °C dramatically reduce the porosity of the samples, reaching a minimum value of 16.85%, whereas the pore size increases as the temperature also increases. Among the membranes with similar porosities, those with a medium pore size distribution exhibited the lowest bulk resistance allowing MFCs to reach the highest power output (94.67 μW cm^-2). These results demonstrate the importance of not only the porosity but also the pore size distribution of the separator in terms of MFC performance and longevity, which for these experiments was for 90 days.

Optimisation of the internal structure of ceramic membranes for electricity production in urine-fed microbial fuel cells

The need to find a feasible alternative to commercial membranes for microbial fuel cells (MFCs) poses an important challenge for the practical implementation of this technology. This work aims to analyse the influence of the internal structure of low-cost terracotta clay-based membranes on the behaviour of MFCs. To this purpose, 9 different combinations of temperature and time were used to prepare 27 MFC separators. The results show that the temperature has a significant effect on both porosity and pore size distribution, whereas the ramp time do not show a significant influence on these parameters. It was observed that kilning temperatures higher than 1030 °C dramatically reduce the porosity of the samples, reaching a minimum value of 16.85%, whereas the pore size increases as the temperature also increases. Among the membranes with similar porosities, those with a medium pore size distribution exhibited the lowest bulk resistance allowing MFCs to reach the highest power output (94.67 μW cm^-2). These results demonstrate the importance of not only the porosity but also the pore size distribution of the separator in terms of MFC performance and longevity, which for these experiments was for 90 days.