Single-chamber microbial fuel cells as on-line shock-sensors for volatile fatty acids in anaerobic digesters

Mechanistic and data-driven modeling of carbon respiration with bio-electrochemical sensors

Bioelectrochemical sensor (BES) technologies have been developed to measure soluble carbon concentrations in wastewater. However, architectures and analytical methods developed in controlled laboratory environments fail to predict BES behavior during field deployments at water resource recovery facilities (WRRFs). Here, we examine the possibilities and obstacles associated with integrating BESs into environmental sensing networks and machine learning algorithms to monitor the biodegradable carbon dynamics and microbial metabolism at WRRFs. This approach highlights the potential of BESs to provide real-time insights into full-scale biodegradable carbon consumption across WRRFs.

Biodegradation of human faecal sludge for photosynthetic bioelectricity generation and seawater desalination in a microbial desalination cell

ABSTRACTInaccessibility and expensiveness of vital infrastructures are the main problems in some urban and rural areas to supply fresh water, sustainable energy, and wastewater treatment. An effective solution is the integration of several systems in an environmentally friendly technology of the photosynthetic microbial desalination cell (PMDC). The aim of this study is to assess the process characterisation of an algae-based PMDC, which was loaded with a high-strength mixture of human feces and urine (HFS). The PMDC was also able to efficiently remove COD and total nitrogen of HFS by 50% and 94%, respectively. The maximum power density, voltage, and desalination efficiency of 362.5 mW/m², 175.2 mV, and 60% were accomplished. Adequate parameter adjustment led to a remarkable maximum of 2.25 g/L.d in the ion removal rate. In addition, an energy balance was governed showing that zero or positive net energy in PMDC is feasible by replacing the main energy consumers. Based on the results, this type of MDC had a high efficiency for simultaneous saline water desalination and HFS treatment, which makes it attractive for further studies of upscaling and its application in remote areas.

Structure evolution of air cathodes and their application in electrochemical sensor development and wastewater treatment

Cathode structure and material are the most important factors to determine the performance and cost of single chamber air-cathode microbial fuel cell (MFC), which is the most promising type of MFC technology. Since the first air cathode was invented in 2004, five major structures (1-layer, 2-layer, 3-layer, 4-layer and separator-support) have been invented and modified to fit new material, improve power performance and lower MFC cost. This paper reviewed the structure evolution of air cathodes in past 18 years. The benefits and drawbacks of these structures, in terms of power generation, material cost, fabrication procedure and modification process are analyzed. The practical application cases (e.g., sensor development and wastewater treatment) employed with different cathode structures were also summarized and analyzed. Based on practical performance and long-term cost analysis, the 2-layer cathode demonstrated much greater potential over other structures. Compared with traditional activated-sludge technology, the cost of an MFC-based system is becoming competitive when employing with 2-layer structure. This review not only provides a detailed development history of air cathode but also reveals the advantages/disadvantages of air cathode with different structures, which will promote the research and application of air-cathode MFC technology.

Recent Implementations of Hydrogel-Based Microbial Electrochemical Technologies (METs) in Sensing Applications

Hydrogel materials have been used extensively in microbial electrochemical technology (MET) and sensor development due to their high biocompatibility and low toxicity. With an increasing demand for sensors across different sectors, it is crucial to understand the current state within the sectors of hydrogel METs and sensors. Surprisingly, a systematic review examining the application of hydrogel-based METs to sensor technologies has not yet been conducted. This review aimed to identify the current research progress surrounding the incorporation of hydrogels within METs and sensors development, with a specific focus on microbial fuel cells (MFCs) and microbial electrolysis cells (MECs). The manufacturing process/cost, operational performance, analysis accuracy and stability of typical hydrogel materials in METs and sensors were summarised and analysed. The current challenges facing the technology as well as potential direction for future research were also discussed. This review will substantially promote the understanding of hydrogel materials used in METs and benefit the development of electrochemical biosensors using hydrogel-based METs.

Ammonia/ammonium removal/recovery from wastewaters using bioelectrochemical systems (BES): A review

This review updates the current research efforts on using BES to recover NH₃/NH₄⁺, highlighting the novel configurations and introducing the working principles and the applications of microbial fuel cell (MFC), microbial electrolysis cell (MEC), microbial desalination cell (MDC), and microbial electrosynthesis cell (MESC) for NH₃/NH₄⁺ removal/recovery. However, commonly studied BES processes for NH₃/NH₄⁺ removal/recovery are energy intensive with external aeration needed for NH₃ stripping being the largest energy input. In such a process bipolar membranes used for yielding a local alkaline pool recovering NH₃ is not cost-effective. This gives a chance to microbial electrosynthesis which turned out to be a potential alternative option to approach circular bioeconomy. Furtherly, the reactor volume and NH₃/NH₄⁺ removal/recovery efficiency has a weakly positive correlation, indicating that there might be other factors controlling the reactor performance that are yet to be investigated.

Increase in Electrical Parameters Using Sucrose in Tomato Waste

The use of organic waste as fuel for energy generation will reduce the great environmental problems currently caused by the consumption of fossil sources, giving agribusiness companies a profitable way to use their waste. In this research, tomato waste with different percentages of sucrose (0-target, 5, 10, and 20%) was used in microbial fuel cells manufactured on a laboratory scale with zinc and copper electrodes, managing to generate maximum peaks of voltage and a current of 1.08 V and 6.67 mA in the cell with 20% sucrose, in which it was observed that the optimum operating pH was 5.29, while the MFC with 0% (target) sucrose generated 0.91 V and 3.12 A on day 13 with a similar pH, even though all the cells worked in an acidic pH. Likewise, the cell with 20% sucrose had the lowest internal resistance (0.148541 ± 0.012361 KΩ) and the highest power density (224.77 mW/cm2) at a current density of 4.43 mA/cm2, while the MFC with 0% sucrose generated 160.52 mW/cm2 and 4.38 mA/cm2 of power density and current density, respectively, with an internal resistance of 0.34116 ± 0.2914 KΩ. In this sense, the FTIR (Fourier-transform infrared spectroscopy) of all the substrates used showed a high content of phenolic compounds and carboxylate acids. Finally, the MFCs were connected in a series and managed to generate a voltage of 3.43 V, enough to light an LED (green). These results give great hope to companies and society that, in the near future, this technology can be taken to a larger scale.

Review on microbial fuel cells applications, developments and costs

The microbial fuel cell (MFC) technology has attracted significant attention in the last years due to its potential to recover energy in a wastewater treatment. The idea of using an MFC in industry is very attractive as the organic wastes can be converted into energy, reducing the waste disposal costs and the energy needs while increasing the company profit. However, taking aside these promising prospects, the attempts to apply MFCs in large-scale have not been succeeded so far since their lower performance and high costs remains challenging. This review intends to present the main applications of the MFC systems and its developments, particularly the advances on configuration and operating conditions. The diagnostic techniques used to evaluate the MFC performance as well as the different modeling approaches are described. Towards the introduction of the MFC in the market, a cost analysis is also included. The development of low-cost materials and more efficient systems, with high higher power outputs and durability, are crucial towards the application of MFCs in industrial/large scale. This work is a helpful tool for discovering new operation and design regimes.

A critical review on early-warning electrochemical system on microbial fuel cell-based biosensor for on-site water quality monitoring

The microbial fuel cell (MFC) sensor is a very promising self-powered self-sustainable system for early warning water quality detection. These sensors are cost-effective, biodegradable, compact in design, and portable in nature are favorable for real-time in situ water quality monitoring. This review represents the mechanism action behind the toxicity detection, optimization strategies, process parameters, role of biofilm, the role of external resistance, hydrodynamic study, and mathematical modeling for improving the performance of the sensor. Additionally, the techno-economic prospect of this MFC-based sensor and its challenges, limitations are addressed to make it economically more favorable for commercial use. The future direction is also explored based on the sensor's disadvantages and limitations. Comprehensively, this review covered all the possible directions of MFC sensor fabrication, their application, recent advancement, prospects challenges, and their possible solutions.

Integrating anaerobic digestion with bioelectrochemical system for performance enhancement: A mini review

Strategies for enhancing performance of anaerobic digestion (AD) process has been widely studied. The bioelectrochemical system (BES), including microbial fuel cell, microbial electrolysis cell (MEC), microbial desalination cell, and microbial electrosynthesis, had been proposed to integrate with AD for performance enhancement. This mini-review summarizes the current researches that integrated AD with BES to enhance the performance of the former. The working principles of BES were introduced. The integrated configurations of AD-BES as well as the associated applications were summarized. The statistics analysis for AD-MEC performances reported in literature were then performed to confirm the effects of reactor size and applied voltage on the methane productivity and enhancement. The challenges and prospects of the integrated AD-BES were delineated, and the potential scenarios of applying integrated AD-BES in field were discussed.

One-Compartment InGaN Nanowire Fuel Cell in the Light and Dark Operating Modes

A one-compartment H₂O₂ photofuel cell (PFC) with a photoanode based on InGaN nanowires (NWs) is introduced for the first time. The electrocatalytic and photoelectrocatalytic properties of the InGaN NWs are studied in detail by cyclic voltammetry, current versus time measurements, photovoltage measurements, and electrochemical impedance spectroscopy. In parallel, IrO _x (OH) _y as the co-catalyst on the InGaN NWs is evaluated to boost the catalytic activity in the dark and light. For the PFC, Ag is the best as the cathode among Ag, Pt, and glassy carbon. The PFC operates in the dark as a conventional fuel cell (FC) and under illumination with 25% increased electrical power generation at room temperature. Such dual operation is unique, combining FC and PFC technologies for the most flexible use.

Recent developments in monitoring technology for anaerobic digesters: A focus on bio-electrochemical systems

With the increasing popularity of waste to energy conversion, demand for large-scale operation of anaerobic digestors has emerged in the market. However, the process instabilities in anaerobic digestors limit the expansion of facilities to high loading rates. The irregularities in the process can be addressed directly by altering the feedstock characteristics provided an on-hand, robust, and sensitive monitoring device is available. In this context, the bioelectrochemical system has emerged as an excellent tool for monitoring and optimizing the anaerobic process within the reactor. This article reviews the gradual evolution in techniques and approaches for monitoring of anaerobic digestion (AD) process. An analysis of the recently popular biosensing techniques has been done with a focus on the bioelectrochemical monitoring system and its operation mode. A brief attempt to highlight the current challenges in the field of bioelectrochemical process monitoring for AD has also been made, which can be supportive of future research.

Emerging trends in microbial fuel cell diversification-Critical analysis

Global need for transformation from fossil-based to bio-based economy is constantly emerging for the production of low-carbon/renewable energy/products. Microbial fuel cell (MFC) catalysed by bio-electrochemical process gained significant attention initially for its unique potential to generate energy. Diversification of MFC is an emerging trend in the context of prioritising/enhancing product output while exploring the mechanism specificity of individual processes. Bioelectrochemical treatment system (BET), microbial electrosynthesis system (MES), bioelectrochemical system (BES), electro-fermentation (EF), microbial desalination cell (MDC), microbial electrolysis cell (MEC) and electro-methanogenesis (EM) are the diversified MFC systems that are being researched actively. Owing to its broad diversification, MFC domain is increasing its potential credibility as a platform technology. Microbial catalyzed electrochemical reactions are the key which directly/indirectly are proportionally linked to electrometabolic activity of microorganisms towards final anticipated output. This review intends to holistically document the mechanisms, applications and current trends of MFC diversifications towards multi-faced applications.

Microbial fuel cell soft sensor for real-time toxicity detection and monitoring

Real-time toxicity detection and monitoring using a microbial fuel cell (MFC) is often based on observing current or voltage changes. Other methods of obtaining more information on the internal state of the MFC, such as electrochemical impedance spectroscopy (EIS), are invasive, disruptive, time consuming, and may affect long-term MFC performance. This study proposes a soft sensor approach as a non-invasive real-time method for evaluating the internal state of an MFC biosensor during toxicity monitoring. The proposed soft sensor approach is based on estimating the equivalent circuit model (ECM) parameters in real time. A flow-through MFC biosensor was operated at several combinations of carbon source (acetate) and toxicant (copper) concentrations. The ECM parameters, such as internal resistance, capacitance, and open-circuit voltage, were estimated in real time using a numerical parameter estimation procedure. The soft sensor approach proved to be an adequate replacement for EIS measurements in quantifying changes in the biosensor internal parameters. The approach also provided additional information, which could lead to earlier detection of the toxicity onset.

Using an anaerobic digestion tank as the anodic chamber of an algae-assisted microbial fuel cell to improve energy production from food waste

Anaerobic digestion is sensitive to a wide variety of inhibitory substances that are the primary cause of anaerobic digester failure. Herein, an anaerobic digestion (AD) tank, which also functioned as the anodic chamber of an algae-assisted microbial fuel cell (AMFC), was established to treat food waste (FW) under an inhibition-relieved condition. About 2.9 L of CH₄ was yielded by the AD-AMFC system, which was more than double the CH₄ produced by the AD system, and 34% higher than that from the AD-MFC system. The result suggests that the bioelectrochemical system and algae successfully improved the AD performance and energy production. The AD-AMFC system had the highest volatile fatty acid (VFA) concentration in the initial 20 days, but it maintained the lowest VFA concentration in the following days. Those results indicate that the AMFC shortened the acclimatisation phase of the AD process and then alleviated the adverse impact of VFAs by consuming VFAs as a substrate for electricity generation. Alkalinity generated by algal growth and cathode reactions buffered the H⁺ that migrated from the anolyte, which facilitated the pH recovery of the AD process. Ammonia inhibition of the AD was also relieved by the AMFC through reduction of the ammonia concentration to less than 500 mg/L in the anolyte. Additionally, the COD removal rate was improved to 89%, since the AMFC facilitated the decomposition of large molecules. The present study developed a practical structure for an AD tank and also explained the reason as to why the AMFC improved the AD performance.

Biosensing capabilities of bioelectrochemical systems towards sustainable water streams: Technological implications and future prospects

Bioelectrochemical systems (BESs) have been intensively investigated over the last decade owing to its wide-scale environmentally friendly applications, among which wastewater treatment, power generation and environmental monitoring for pollutants are prominent. Different variants of BES such as microbial fuel cell, microbial electrolysis cell, microbial desalination cell, enzymatic fuel cell, microbial solar cell, have been studied. These microbial bioelectrocatalytic systems have clear advantages over the existing analytical techniques for sustainable on-site application in wide environmental conditions with minimum human intervention, making the technology irrevocable and economically feasible. The key challenges to establish this technology are to achieve stable and efficient interaction between the electrode surface and microorganisms, reduction of time for start-up and toxic-shock recovery, sensitivity improvement in real-time conditions, device miniaturization and its long-term economically feasible commercial application. This review article summarizes the recent technical progress regarding bio-electrocatalytic processes and the implementation of BESs as a biosensor for determining various compositional characteristics of water and wastewater.

Bioelectricity production from fermentable household waste in a dual-chamber microbial fuel cell

In this study, the use of a dual-chamber microbial fuel cell for the production of bioelectricity from a food residue biomass (FORBI) product was investigated. Food residue biomass was produced by drying and shredding the pre-sorted fermentable fraction of household food waste collected door-to-door in the Municipality of Halandri, Athens, Greece. Different organic loads of food residue biomass expressed as chemical oxygen demand (COD) were examined (0.7, 0.9, 1.4, 2.8, 6 and 14 g COD L^-1, respectively). It was observed that an increase of the initial concentration of the final extract resulted in a corresponding increase in the operating time. The microbial fuel cell potential increased from 33.3 mV to 46 mV as the concentration was increased from 0.7 to 14 g COD L^-1. The best performance in terms of maximum power density (29.6 mW m^-2) corresponding to a current density of 88 mA m^-2 was observed for 6 g COD L^-1. Setting the external resistance at its optimal value (R_ext = 2 kΩ) as determined by polarisation experiments, P_yield drastically increased to 13.7 and 17.3 Joule (g FORBI)^-1 in two consecutive cycles. The results demonstrate that readily biodegradable substrates, such as food residue biomass, can be effectively used for enhanced bioelectricity harvesting in a microbial fuel cell.

Toward a Hybrid Biosensor System for Analysis of Organic and Volatile Fatty Acids in Fermentation Processes

Monitoring of organic acids (OA) and volatile fatty acids (VFA) is crucial for the control of anaerobic digestion. In case of unstable process conditions, an accumulation of these intermediates occurs. In the present work, two different enzyme-based biosensor arrays are combined and presented for facile electrochemical determination of several process-relevant analytes. Each biosensor utilizes a platinum sensor chip (14 × 14 mm2) with five individual working electrodes. The OA biosensor enables simultaneous measurement of ethanol, formate, d- and l-lactate, based on a bi-enzymatic detection principle. The second VFA biosensor provides an amperometric platform for quantification of acetate and propionate, mediated by oxidation of hydrogen peroxide. The cross-sensitivity of both biosensors toward potential interferents, typically present in fermentation samples, was investigated. The potential for practical application in complex media was successfully demonstrated in spiked sludge samples collected from three different biogas plants. Thereby, the results obtained by both of the biosensors were in good agreement to the applied reference measurements by photometry and gas chromatography, respectively. The proposed hybrid biosensor system was also used for long-term monitoring of a lab-scale biogas reactor (0.01 m3) for a period of 2 months. In combination with typically monitored parameters, such as gas quality, pH and FOS/TAC (volatile organic acids/total anorganic carbonate), the amperometric measurements of OA and VFA concentration could enhance the understanding of ongoing fermentation processes.

Self-Powered Biosensors

Self-powered electrochemical biosensors utilize biofuel cells as a simultaneous power source and biosensor, which simplifies the biosensor system, because it no longer requires a potentiostat, power for the potentiostat, and/or power for the signaling device. This review article is focused on detailing the advances in the field of self-powered biosensors and discussing their advantages and limitations compared to other types of electrochemical biosensors. The review will discuss self-powered biosensors formed from enzymatic biofuel cells, organelle-based biofuel cells, and microbial fuel cells. It also discusses the different mechanisms of sensing, including utilizing the analyte being the substrate/fuel for the biocatalyst, the analyte binding the biocatalyst to the electrode surface, the analyte being an inhibitor of the biocatalyst, the analyte resulting in the blocking of the bioelectrocatalytic response, the analyte reactivating the biocatalyst, Boolean logic gates, and combining affinity-based biorecognition elements with bioelectrocatalytic power generation. The final section of this review details areas of future investigation that are needed in the field, as well as problems that still need to be addressed by the field.

Microbial Fuels Cell-Based Biosensor for Toxicity Detection: A Review

With the unprecedented deterioration of environmental quality, rapid recognition of toxic compounds is paramount for performing in situ real-time monitoring. Although several analytical techniques based on electrochemistry or biosensors have been developed for the detection of toxic compounds, most of them are time-consuming, inaccurate, or cumbersome for practical applications. More recently, microbial fuel cell (MFC)-based biosensors have drawn increasing interest due to their sustainability and cost-effectiveness, with applications ranging from the monitoring of anaerobic digestion process parameters (VFA) to water quality detection (e.g., COD, BOD). When a MFC runs under correct conditions, the voltage generated is correlated with the amount of a given substrate. Based on this linear relationship, several studies have demonstrated that MFC-based biosensors could detect heavy metals such as copper, chromium, or zinc, as well as organic compounds, including p-nitrophenol (PNP), formaldehyde and levofloxacin. Both bacterial consortia and single strains can be used to develop MFC-based biosensors. Biosensors with single strains show several advantages over systems integrating bacterial consortia, such as selectivity and stability. One of the limitations of such sensors is that the detection range usually exceeds the actual pollution level. Therefore, improving their sensitivity is the most important for widespread application. Nonetheless, MFC-based biosensors represent a promising approach towards single pollutant detection.