Microbial desalination cells for improved performance in wastewater treatment, electricity production, and desalination

Microbial electrochemical enhanced composting of sludge and kitchen waste: Electricity generation, composting efficiency and health risk assessment for land use

To realize the energy and resource utilization from organic solid waste, a two-phase microbial desalination cell (TPMDC) was constructed using dewatered sludge and kitchen waste as the anode substrate. The performance of electricity generation and composting efficacy was investigated, along with a comprehensive assessment of the potential health risks associated with the land use of the resulting mixed compost products. Experimental outcomes revealed a maximum open-circuit voltage of 0.893 ± 0.005 V and a maximum volumetric power density of 0.797 ± 0.009 W/m³. After 90 days of composting enhanced by microbial electrochemistry, a significant organic matter removal rate of 31.13 ± 0.44 % was obtained, and the anode substrate electric conductivity was reduced by 30.02 ± 0.04 % based on the anode desalination. Simultaneously, there was an increase in the content of available nitrogen, phosphorus, and potassium, as well as an improvement in the seed germination index. The forms of heavy metals shifted from bioavailable to stable residual states. The non-carcinogenic hazard index (HI) values for heavy metals and polycyclic aromatic hydrocarbons (PAHs) during the land use of compost products were less than 1, and the total carcinogenic risk (TCR) values for heavy metals and PAHs were below the acceptable threshold of 10-4. The occupational population risk of infection from five pathogens was higher than that of the general public, with all risk values ranging from 8.67 × 10-8 to 1, where the highest risk was attributed to occupational exposure to Legionella. These outcomes demonstrated that the mixture of dewatered sludge and kitchen waste was an appropriate anode substrate to enhance TPMDC stability for electricity generation, and its compost products have promising land use suitability and acceptable land use risk, which will provide important guidance for the safe treatment and disposal of organic solid waste.

Impact of different electrodes, mediators, and microbial cultures on wastewater treatment and power generation in the microbial desalination cell (MDC)

Microbial desalination cell (MDC) can treat wastewater and saline water simultaneously and generate power. The aim of the present research work was to identify the critical factors influencing COD reduction and power generation from the MDC reactor and to optimize the control parameters. The experimental study was conducted by using medium to high-strength wastewater from distillery and brewery industry in batch-wise operation. The maximum voltage of 702 mV and current of 2.16 mA were observed for the carbon brush electrode. The mediated aeration process with the presence of potassium ferricyanide was reported in 87% COD reduction and 992 mV voltage generation. The presence of the microbial culture provided 82% COD reduction and 51% TDS reduction. The maximum current density (CD) of 0.04 mA/cm2 was observed for carbon brush, and a maximum power density (PD) of 15.56 mW/cm2 was found with aeration and potassium ferricyanide mediator. This study provided insight towards the impact of the electrode materials and the effects of mediator, aeration, and microbial culture on MDC performance.

A hypothetical model of multi-layered cost-effective wastewater treatment plant integrating microbial fuel cell and nanofiltration technology: A comprehensive review on wastewater treatment and sustainable remediation

Wastewater management has emerged as an uprising concern that demands immediate attention from environmentalists worldwide. Indiscriminate and irrational release of industrial and poultry wastes, sewage, pharmaceuticals, mining, pesticides, fertilizers, dyes and radioactive wastes, contribute immensely to water pollution. This has led to the aggravation of critical health concerns as evident from the uprising trends of antimicrobial resistance, and the presence of xenobiotics and pollutant traces in humans and animals due to the process of biomagnification. Therefore, the development of reliable, affordable and sustainable technologies for the supply of fresh water is the need of the hour. Conventional wastewater treatment often involves physical, chemical, and biological processes to remove solids from the effluent, including colloids, organic matter, nutrients, and soluble pollutants (metals, organics). Synthetic biology has been explored in recent years, incorporating both biological and engineering concepts to refine existing wastewater treatment technologies. In addition to outlining the benefits and drawbacks of the current technologies, this review addresses novel wastewater treatment techniques, especially those using dedicated rational design and engineering of organisms and their constituent parts. Furthermore, the review hypothesizes designing a multi-bedded wastewater treatment plant that is highly cost-efficient, sustainable and requires easy installation and handling. The novel setup envisages removing all the major wastewater pollutants, providing water fit for household, irrigation and storage purposes.

Putting the electro-bugs to work: A systematic review of 22 years of advances in bio-electrochemical systems and the parameters governing their performance

Wastewater treatment using bioelectrochemical systems (BESs) can be considered as a technology finding application in versatile areas such as for renewable energy production and simultaneous reducing environmental problems, biosensors, and bioelectrosynthesis. This review paper reports and critically discusses the challenges, and advances in bio-electrochemical studies in the 21st century. To sum and critically analyze the strides of the last 20+ years on the topic, this study first provides a comprehensive analysis on the structure, performance, and application of BESs, which include Microbial Fuel Cells (MFCs), Microbial Electrolysis Cells (MECs) and Microbial Desalination Cells (MDCs). We focus on the effect of various parameters, such as electroactive microbial community structure, electrode material, configuration of bioreactors, anode unit volume, membrane type, initial COD, co-substrates and the nature of the input wastewater in treatment process and the amount of energy and fuel production, with the purpose of showcasing the modes of operation as a guide for future studies. The results of this review show that the BES have great potential in reducing environmental pollution, purifying saltwater, and producing energy and fuel. At a larger scale, it aspires to facilitate the path of achieving sustainable development and practical application of BES in real-world scenarios.

Enhanced power generation, organics removal and water desalination in a microbial desalination cell (MDC) with flow electrodes

This study introduced a flow electrode microbial desalination cell (FE-MDC), which used activated carbon (AC) particles and carbon nanotubes (CNTs) as the electrode to promote electron harvesting. The recovered electricity energy (0.371 KWh/m³) and columbic efficiency (66.7 %) of the FE-MDC were over 2 times higher than those of the conventional MDC without the flow electrode. Consequently, the salt and COD removal efficiencies were enhanced to 77.8 % and 91.2 %, respectively. Electrochemical analysis implied that the charge transfer resistance of the system was reduced by the flow electrode. Electron accumulation and charging-discharging experiments proved that the flow electrode could accumulate electrons and transfer the electrons to the fixed anode. Bacterial community analysis indicated that the bacterial activity was improved by the flow electrode. The content of the exoelectrogen Pseudomonas increased from 5.0 % to 14.7 %, and Hydrogenophaga improved from 1.4 % to 5.9 %. Finally, a continuous operation mode of the FE-MDC was established, and the flow electrode slurry was returned to the anodic chamber for recirculated utilization. The voltage output, COD removal, and salt removal during the operation mode reached 610 mV, 78.8 %, and 76.1 %, respectively. This study proved that the flow electrode is a promising way to promote the practical application of MDC technology.

Prospective review on bioelectrochemical systems for wastewater treatment: Achievements, hindrances and role in sustainable environment

Bioelectrochemical systems (BESs) are a relatively new arena for producing bioelectricity, desalinating sea water, and treating industrial effluents by removing organic matter. Microbial electrochemical technologies (METs) are promising for obtaining value-added products during simultaneous remediation of pollutants from wastewater. The search for more affordable desalination technology has led to the development of microbial desalination cells (MDCs). MDC combines the operation of microbial fuel cells (MFC) with electrodialysis for water desalination and energy generation. It has received notable interest of researchers in desalination and wastewater treatment because of low energy requirement and eco-friendly nature. Firstly, this article provides a brief overview of MDC technology. Secondly, factors affecting functioning of MDC and its applications have been accentuated. Additionally, challenges and future outlook on the development of this technology have been delineated. State-of-the-art information provided in this review would expand the scope of interdisciplinary and translational research.

Nanomaterials photocatalytic activities for waste water treatment: a review

Water is necessary for the survival of life on Earth. A wide range of pollutants has contaminated water resources in the last few decades. The presence of contaminants incredibly different dyes in waste, potable, and surface water is hazardous to environmental and human health. Different types of dyes are the principal contaminants in water that need sudden attention because of their widespread domestic and industrial use. The toxic effects of these dyes and their ability to resist traditional water treatment procedures have inspired the researcher to develop an eco-friendly method that could effectively and efficiently degrade these toxic contaminants. Here, in this review, we explored the effective and economical methods of metal-based nanomaterials photocatalytic degradation for successfully removing dyes from wastewater. This study provides a tool for protecting the environment and human health. In addition, the insights into the transformation of solar energy for photocatalytic reduction of toxic metal ions and photocatalytic degradation of dyes contaminated wastewater will open a gate for water treatment research. The mechanism of photocatalytic degradation and the parameters that affect the photocatalytic activities of various photocatalysts have also been reported.

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 state-of-the-art review on microbial desalination cells

The rapid growth in population has increased the demand for potable water. Available technologies for its generation are the desalination of sea water through reverse osmosis, electrodialysis etc., which are energy and cost intensive. In this context, microbial desalination cell (MDC) presents a low-cost and sustainable option which can simultaneously treat wastewater, desalinate saline water, produce electrical energy and recover nutrients from wastewater. This review paper is focussed on presenting a detailed analysis of MDCs starting from the principle of operation, microbial community analysis, basic architecture, evolution in design, operational challenges, effect of process parameters, scale-up studies, application in multiple arenas and future prospects. After thorough review, it can be inferred that MDCs can be used as a stand-alone option or pre-treatment step for conventional desalination techniques without the application of external energy. MDCs have been used in multiple applications ranging from desalination, remediation of contaminated water, recovery of energy and nutrients from wastewater, softening of hardwater, biohydrogen production to degradation of waste engine oil. Although, MDCs have been used for multiple applications, still a number of operational challenges have been reported viz., interference of co-existing ions during desalination, membrane fouling, pH imbalance and limited potential of exoelectrogens. However, the re-circulation of anolytes with electrodialysis chamber has led to the maintenance of optimal pH for favourable microbial growth leading to improvement in the overall performance of MDCs. In future, genetic engineering may be used for improving the electrogenic activity of microbial community, next generation materials may be used as anode and cathode, varied sources of wastewater may be explored as anolytes, life cycle analysis and exergy analysis may be carried out to study the impact on environment and detailed pilot scale studies have to be carried out for assessing the feasibility of operation at large scale.

Energy production from treatment of industrial wastewater and boron removal in aqueous solutions using microbial desalination cell

As a result of a much needed paradigm shift worldwide, treated saline water is being considered as a viable option for replacing freshwater resources in agricultural irrigation. Vastly produced geothermal brine in Turkey may pose a significant environmental risk due to its high ionic strength, specifically due to boron. Boron species, which are generally found uncharged in natural waters, are costly to remove using high-throughput membrane technologies such as reverse osmosis. Recent advances in bioelectrochemical systems (BES) has facilitated development of energetically self-sufficient wastewater treatment and desalination. In this study, removal of boron from synthetic solutions and real geothermal waters, along with simultaneous energy production, using the microbial desalination cell (MDC) were investigated. Optimization studies were conducted by varying boron concentrations (5, 10, and 20 mg L^-1), air flow rates (0, 1, and 2 L min^-1), electrode areas (18, 24, 36, and 72 cm²), catholyte solutions, and operating modes. Even though the highest concentration decrease was observed for 20 mg-B L^-1, 5 mg-B L^-1 concentration experiment gave the closest result to the 2.4 mg-B L^-1 limit value asserted by WHO. Effect of electrode surface area was proven to be significant on boron removal efficiency. Employing the optimum conditions acquired with synthetic solutions, boron and COD removal efficiencies from real geothermal brine were 44.3% and 90.6%, respectively. MDC, being in its early levels of technology readiness, produced promising desalination and energy production results in removal of boron from geothermal brine.

Green approach and strategies for wastewater treatment using bioelectrochemical systems: A critical review of fundamental concepts, applications, mechanism, and future trends

Millions of litters of multifarious wastewater are directly disposed into the environment annually to reduce the processing costs leading to eutrophication and destroying the clean water sources. The bioelectrochemical systems (BESs) have recently received significant attention from researchers due to their ability to convert waste into energy and their high efficiency of wastewater treatment. However, most of the performed researches of the BESs have focused on energy generation, which created a literature gap on the utilization of BESs for wastewater treatment. The review highlights this gap from various aspects, including the BESs trends, fundamentals, applications, and mechanisms. A different review approach has followed in the present work using a bibliometric review (BR) which defined the literature gap of BESs publications in the degradation process section and linked the systematic review (SR) with it to prove and review the finding systematically. The degradation mechanisms of the BESs have been illustrated comprehensively in the current work, and various suggestions have been provided for supporting future studies and cooperation.

Algae-Assisted Microbial Desalination Cell: Analysis of Cathode Performance and Desalination Efficiency Assessment

Algae-assisted microbial desalination cells represent a sustainable technology for low-energy fresh water production in which microalgae culture is integrated into the system to enhance oxygen reduction reaction in the cathode chamber. However, the water production (desalination rate) is low compared to conventional technologies (i.e., reverse osmosis and/or electrodialysis), as biocathodes provide low current generation to sustain the desalination process. In this sense, more research efforts on this topic are necessary to address this bottleneck. Thus, this study provides analysis, from the electrochemical point of view, on the cathode performance of an algae-assisted microbial desalination cell (MDC) using Chlorella vulgaris. Firstly, the system was run with a pure culture of Chlorella vulgaris suspension in the cathode under conditions of an abiotic anode to assess the cathodic behavior (i.e., cathode polarization curves in light-dark conditions and oxygen depletion). Secondly, Geobacter sulfurreducens was inoculated in the anode compartment of the MDC, and the desalination cycle was carried out. The results showed that microalgae could generate an average of 9–11.5 mg/L of dissolved oxygen during the light phase, providing enough dissolved oxygen to drive the migration of ions (i.e., desalination) in the MDC system. Moreover, during the dark phase, a residual concentration of oxygen (ca. 5.5–8 mg/L) was measured, indicating that oxygen was not wholly depleted under our experimental conditions. Interestingly, the oxygen concentration was restored (after complete depletion of dissolved oxygen by flushing with N2) as soon as microalgae were exposed to the light phase again. After a 31 h desalination cycle, the cell generated a current density of 0.12 mA/cm2 at an efficiency of 60.15%, 77.37% salt was removed at a nominal desalination rate of 0.63 L/m2/h, coulombic efficiency was 9%, and 0.11 kWh/m3 of electric power was generated. The microalgae-assisted biocathode has an advantage over the air diffusion and bubbling as it can self-sustain a steady and higher concentration of oxygen, cost-effectively regenerate or recover from loss and sustainably retain the system’s performance under naturally occurring conditions. Thus, our study provides insights into implementing the algae-assisted cathode for sustainable desalination using MDC technology and subsequent optimization.

Advancements in spontaneous microbial desalination technology for sustainable water purification and simultaneous power generation: A review

Population growth and rapid urbanization have put a lot of pressure on the already scarce freshwater around the globe. The availability of freshwater is not only limited but it is non-uniform also. Available desalination technologies help mitigate water shortage; however, these techniques are energy-intensive and unsustainable. Desalination technologies utilizing renewable energy and bio-electrochemical systems have been developed to achieve limited sustainability. With technological advancements, microbial desalination cell (MDC) has been developed which is capable of desalination, wastewater treatment, and power generation simultaneously. This review critically examined the performance of various MDC techniques concerning their stimulus parameters including COD removal, total desalination rate, total dissolved solids reduction rate, Coulombic efficiency, and power density. Limitations of MDCs have also been incorporated in the review. Work on MDC coupled with other robust desalination techniques offering advantages such as better desalination and more water recovery e.g. osmotic-MDC etc. has been included. Researchers have tremendously worked on MDCs with different electro-catalysts. Few of these are not sustainable and costly. Authors have reviewed critically with belief that it will pave a way for the commercialization of this eco-friendly technology.

Pushing microbial desalination cells towards field application: Prevailing challenges, potential mitigation strategies, and future prospects

Microbial desalination cells (MDCs) have been experimentally proven as a versatile bioelectrochemical system (BES). They have the potential to alleviate environmental pollution, reduce water scarcity and save energy and operational costs. However, MDCs alone are inadequate to realise a complete wastewater and desalination treatment at a high-efficiency performance. The assembly of identical MDC units that hydraulically and electrically connected can improve the performance better than standalone MDCs. In the same manner, the coupling of MDCs with other BES or conventional water reclamation technology has also exhibits a promising performance. However, the scaling-up effort has been slowly progressing, leading to a lack of knowledge for guiding MDC technology into practicality. Many challenges remain unsolved and should be mitigated before MDCs can be fully implemented in real applications. Here, we aim to provide a comprehensive chronological-based review that covers technological limitations and mitigation strategies, which have been developed for standalone MDCs. We extend our discussion on how assembled, coupled and scaled-up MDCs have improved in comparison with standalone and lab-scale MDC systems. This review also outlines the prevailing challenges and potential mitigation strategies for scaling-up based on large-scale specifications and evaluates the prospects of selected MDC systems to be integrated with conventional anaerobic digestion (AD) and reverse osmosis (RO). This review offers several recommendations to promote up-scaling studies guided by the pilot scale BES and existing water reclamation technologies.

Recent progress in environmentally friendly bio-electrochemical devices for simultaneous water desalination and wastewater treatment

Bio-electrochemical systems (BESs) use electroactive micro-organisms for degrading organic materials in wastes for energy and/or chemical production. Microbial based desalination system is a cost-effective and environmentally friendly technique that can be used for water desalination with simultaneous wastewater treatment and energy harvesting. These systems can be used as a standalone technology for water desalination such as microbial desalination cell, microbial electrolysis desalination cell, or a hybrid with other desalination technology. This review summarized the recent progress in using BESs for water desalination, including microbial fuel cell-based desalination (MDC) and microbial electrolysis cell-based desalination (MEDC). The different scaling up trials to commercialize this technology, including the controlling parameters, are discussed. Moreover, the different hybrid desalination systems based on BES are summarized. Finally, the challenges facing the commercialization of the MDC systems were summarized.

Biohybrid Conjugated Polymer Materials for Augmenting Energy Conversion of Bioelectrochemical Systems

Bioelectrochemical systems (BESs) provide favorable opportunities for the sustainable conversion of energy from biological metabolism. Biological photovoltaics (BPVs) and microbial fuel cells (MFCs) respectively realize the conversion of renewable solar energy and bioenergy into electrical energy by utilizing electroactive biological extracellular electron transfer, however, along with this energy conversion progress, relatively poor durability and low output performance are challenges as well as opportunities. Advances in improving bio-electrode interface compatibility will help to solve the problem of insufficient performance and further have a far-reaching impact on the development of bioelectronics. Conjugated polymers (CPs) with specific optical and electrical properties (absorption and emission spectra, energy band structure and electrical conductivity) afforded by π-conjugated backbones are conducive to enhancing the electron generation and output capacity of electroactive organisms. Furthermore, the water solubility, functionality, biocompatibility and mechanical properties optimized through appropriate modification of side chain provide a more adaptive contact interface between biomaterials and electrodes. In this minireview, we summarize the prominent contributions of CPs in the aspect of augmenting the photovoltaic response of BPVs and power supply of MFCs, and specifically discussed the role of CPs with expectation to provide inspirations for the design of bioelectronic devices in the future.

Feasibility study on applying the iron-activated persulfate system as a pre-treatment process for clofibric acid selective degradation in municipal wastewater

Clofibric acid (CFA) was selected as an example of the widespread micropollutants in municipal wastewater to investigate the feasibility of the application of an iron-activated persulfate (Fe-PS) system for selective micropollutants removal prior to biological wastewater treatment. In pure CFA solution, the CFA degradation rate was accelerated with an increase in oxidant dosage and 2.15 mg·L^-1 (0.01 mM) CFA could be completed removed within 30 min with 270 mg·L^-1 (1 mM) potassium persulfate (PS) activated by 56 mg·L^-1 iron powder (Fe). Although both sulfate radicals (SO₄^∙-) and hydroxyl radicals (HO^∙) were generated in the Fe-PS system, SO₄^∙- was identified as the dominant oxidant for CFA degradation. To investigate the interference from model compounds in the municipal wastewater, CFA degradation in different concentrations of ammonia or/and glucose solutions, the synthetic municipal wastewater, and real municipal wastewater systems were investigated. A complete removal of CFA was achieved with ammonia or/and glucose interferences. Less than 3% ammonia was removed due to the formation of aminopropyl radicals. About 15% degradation of dissolved organic carbon (DOC) was mainly attributed to the oxidation of glucose by HO^∙, Indicating the excellent selective oxidation ability of the Fe-PS system targeting at CFA over glucose. Even though the alkalinity significantly hindered the oxidation of CFA in both synthetic and real municipal wastewater system, the removal efficiency of CFA was significantly higher than that of DOC. The decrease of CFA removal efficiency in municipal wastewater system comparing to the other tests was due to the slow degradation of PS in the system and further hindered the SO₄^∙- generation. Therefore, the impacts of other impurities in municipal wastewater on the oxidation activities of Fe-PS system should be further investigated. In general, this study confirmed the feasibility of using the Fe-PS system for selective degrading resistant CFA in municipal wastewater.

Investigating the potential of locally sourced wastewater as a feedstock of microbial desalination cell (MDC) for bioenergy production

Freshwater sources are limited and access to clean water is an acute challenge in recent decades. The sustainable water treatments methods are need of time and water desalination is one of the most interesting technology. Most desalination technologies are required high energy input while Microbial Desalination Cells (MDCs) represent a sustainable option that has added benefit of solving the ever-increasing wastewater treatment and management problem. MDCs are a customized type of Microbial Fuel Cells (MFCs) that depend on the electric potential generated by organic media to decrease salt concentration by electro-dialysis and give an unconventional way of clean water production. In this research, various experiments were conducted to examine the desalination ability of an indigenously designed experimental setup using domestic wastewater inoculated with sewage sludge under identical conditions. The electrochemical properties of the system, comprising the polarization curve and Electrochemical Impedance Spectroscopy (EIS), were examined along with the scope of chemical oxygen demand (COD) exclusion, to distinguish the cell behaviour. Furthermore, acidic water and Phosphate Buffer Solution (PBS) were tested as potential catholytes compared to the performance of the wastewater was gauged at various salt concentrations. The maximum salt removal efficiency was 31%, power density and current density were 32 mW-m^-2 and 246 mA-m^-2 respectively at a salt concentration of 35 g-L^-1 that decreases with a decline in salt concentration. The maximum achieved power density and current density were 32 mW-m^-2 and 246 mA-m^-2 respectively. The applied method has huge potential to scaleup for large scale application in coastal regions.

Nutrient conversion and recovery from wastewater using electroactive bacteria

Wastewater is widely recognized as a sink of active nitrogen and phosphorus, and the recovery of both nutrients as fertilizers is widely studied in recent years. Electroactive bacteria increasingly attract attentions in this area because they are able to produce an electric field in microbial electrochemical systems to concentrate ammonium and phosphate for recovery. Importantly, these unique bacteria are able to convert nitrate and nitrite directly to ammonium, maximizing the active nitrogen species capable of recovery. Ferric ions produced by electroactive bacteria can be precipitated with phosphate to recover as vivianite in neutral wastewaters. All these processes employed electroactive bacteria as both nitrate and iron reducer and bioelectric field generator. The mechanism as well as technologies are summarized, and the challenges to further improve their performance are discussed.

Performance of Exoelectrogenic Bacteria Used in Microbial Desalination Cell Technology

The tri-functional purpose of Microbial Desalination Cell (MDC) has shown a great promise in our current scarcity of water, an increase in water pollution and the high cost of electricity production. As a biological system, the baseline force that drives its performance is the presence of exoelectrogens in the anode chamber. Their presence in the anodic chamber of MDC systems enables the treatment of water, desalination of seawater, and the production of electrical energy. This study reviews the characteristics of exoelectrogens, as a driving force in MDC and examines factors which influence their growth and the performance efficiency of MDC systems. It also addresses the efficiency of mixed cultures with certain predominant species as compared to pure cultures used in MDC systems. Furthermore, the study suggests the need to genetically modify certain predominant strains in mixed cultures to enhance their performance in COD removal, desalination and power output and the integration of MDC with other technologies for cost-effective processes.

Enhancing the water desalination and electricity generation of a microbial desalination cell with a three-dimensional macroporous carbon nanotube-chitosan sponge anode

Microbial desalination cells (MDCs) are promising bioelectrochemical systems that are being investigated for simultaneous seawater desalination, electricity generation, and wastewater treatment. Anode materials play an important role in determining the performance of MDCs. In this study, a three-dimensional (3D) macroporous sponge was coated with compatible and conductive carbon nanotube-chitosan (CNT-CS) as a composite electrode for MDCs. Experimental results showed that the flexible CNT-CS sponge exhibited a high capacitance (159.4F/g at 20mVs^-1), good cycling stability (96% specific capacitance retention after 1000 cyclic voltammetry cycles) and low resistance. Moreover, the MDC with a CNT-CS sponge anode generated a high power density of 1776.6mW/m² (per electrode area) and desalination rate of 16.5mgh^-1, which are significantly higher than those of commercial carbon felt electrodes under the same conditions. The improved MDC performance can be attributed to the continuous 3D macroporous structure of the sponge anode promoting the bacterial loading capacity on the electrode surface. Moreover, the presence of CNTs also further enhances extracellular electron transfer. Our results demonstrate that an MDC operating with a 3D CNT-CS sponge anode offers an effective means for manufacturing high-performance MDCs with wide applicability to bioelectrochemical systems.

Oral exposure to cadmium and mercury alone and in combination causes damage to the lung tissue of Sprague-Dawley rats

Environmental presence and human exposure to heavy metals in air and cigarette smoke has led to a worldwide increase in respiratory disease. The effects of oral exposure to heavy metals in liver and kidney structure and function have been widely investigated and the respiratory system as a target is often overlooked. The aim of the study was to investigate the possible structural changes in the lung tissue of Sprague-Dawley rats after oral exposure for 28 days to cadmium (Cd) and mercury (Hg), alone and in combination at 1000 times the World Health Organization's limit for each metal in drinking water. Following exposure, the general morphology of the bronchiole and lungs as well as collagen and elastin distribution was evaluated using histological techniques and transmission electron microscopy. In the lungs, structural changes to the alveoli included collapsed alveolar spaces, presence of inflammatory cells and thickening of the alveolar walls. In addition, exposure to Cd and Hg caused degeneration of the alveolar structures resulting in confluent alveoli. Changes in bronchiole morphology included an increase in smooth muscle mass with luminal epithelium degeneration, detachment and aggregation. Prominent bronchiole-associated lymphoid tissue was present in the group exposed to Cd and Hg. Ultrastructural examination confirmed the presence of fibrosis where in the Cd exposed group, collagen fibrils arrangement was dense, while in the Hg exposed group, additional prominent elastin was present. This study identified the lungs as target of heavy metals toxicity following oral exposure resulting in cellular damage, inflammation and fibrosis and increased risk of respiratory disease where Hg showed the greatest fibrotic effect, which was further, aggravated in combination with Cd.

Multi-agent simulation regulated by microbe-oriented thermodynamics and kinetics equations for exploiting interspecies dynamics and evolution between methanogenesis, sulfidogenesis, hydrogenesis and exoelectrogenesis

Multi-agent simulation (MAS) regulated by microbe-oriented thermodynamics and kinetics equations were performed for exploiting the interspecies dynamics and evolution in anaerobic respiration and bioelectrochemical systems. A newly-defined kinetically thermodynamic parameter is recognized microbes as agents in various conditions, including electron donors and acceptors, temperature, pH, etc. For verification of the MAS, the treatment of synthetic wastewater containing glucose and acetate was evaluated in four 25°C laboratory-scale reactors with different electron acceptors and cathode materials that had potential for methanogenesis, hydrogenesis, sulfidogenesis and exoelectrogenesis. Within 1000 h operation, the reactors performance and microbial structures using 16S rRNA sequencing matched with the MAS, suggesting acetoclastic exoelectrogenesis predominance (Geobacter). After 2400 h, MAS observed the co-existence of acetoclastic methanogenesis and acetoclastic and propionate exoelectrogenesis, as was reported previously. Such microbial evolution from the short-term to long-term operation likely resulted from the glucose-driven propionate. The MAS developed is applicable in a wide range of complex engineering and natural ecosystems.

Electro-Microbiology as a Promising Approach Towards Renewable Energy and Environmental Sustainability

Microbial electrochemical technologies provide sustainable wastewater treatment and energy production. Despite significant improvements in the power output of microbial fuel cells (MFCs), this technology is still far from practical applications. Extracting electrical energy and harvesting valuable products by electroactive bacteria (EAB) in bioelectrochemical systems (BESs) has emerged as an innovative approach to address energy and environmental challenges. Thus, maximizing power output and resource recovery is highly desirable for sustainable systems. Insights into the electrode-microbe interactions may help to optimize the performance of BESs for envisioned applications, and further validation by bioelectrochemical techniques is a prerequisite to completely understand the electro-microbiology. This review summarizes various extracellular electron transfer mechanisms involved in BESs. The significant role of characterization techniques in the advancement of the electro-microbiology field is discussed. Finally, diverse applications of BESs, such as resource recovery, and contributions to the pursuit of a more sustainable society are also highlighted.

Improving bioelectricity generation and COD removal of sewage sludge in microbial desalination cell

Improving wastewater treatment process and water desalination are two important solutions for increasing the available supply of fresh water. Microbial desalination cells (MDCs) with common electrolytes display relatively low organic matter removal and high cost. In this study, sewage sludge was used as the substrate in the Microbial desalination cell (MDC) under three different initial salt concentrations (5, 20 and 35 g.L^-1) and the maximum salt removal rates of 50.6%, 64% and 69.6% were obtained under batch condition, respectively. The MDC also produced the maximum power density of 47.1 W m^-3 and the averaged chemical oxygen demand (COD) removal of 58.2 ± 0.89% when the initial COD was 6610 ± 83 mg L^-1. Employing treated sludge as catholyte enhanced COD removal and power density to 87.3% and 54.4 W m^-3, respectively, with counterbalancing pH variation in treated effluent. These promising results showed, for the first time, that the excess sewage sludge obtained from biological wastewater treatment plants could be successfully used as anolyte and catholyte in MDC, achieving organic matter biodegradation along with salt removal and energy production. In addition, using treated sludge as catholyte will improve the performance of MDC and introduce a more effective method for both sludge treatment and desalination.

Enhancing forward osmosis water recovery from landfill leachate by desalinating brine and recovering ammonia in a microbial desalination cell

In this work, a microbial desalination cell (MDC) was employed to desalinate the FO treated leachate for reduction of both salinity and chemical oxygen demand (COD). The FO recovered 51.5% water from a raw leachate and the recovery increased to 83.5% from the concentrated leachate after desalination in the MDC fed with either acetate or another leachate as an electron source and at a different hydraulic retention time (HRT). Easily-degraded substrate like acetate and a long HRT resulted in a low conductivity desalinated effluent. Ammonia was also recovered in the MDC cathode with a recovery efficiency varying from 11 to 64%, affected by current generation and HRT. Significant COD reduction, as high as 65.4%, was observed in the desalination chamber and attributed to the decrease of both organic and inorganic compounds via diffusion and electricity-driven movement.

Bioremediation of steel plant wastewater and enhanced electricity generation in microbial desalination cell

Microbial desalination cell (MDC) is a propitious technology towards water desalination by utilizing wastewater as an energy source. In this study, a multi-chambered MDC was used to bioremediate steel plant wastewater using the same wastewater as a fuel for anodic bacteria. A pure culture of Pseudomonas putida MTCC 1194 was isolated and inoculated to remove toxic phenol. Three different inoculum conditions, namely P. putida (INC-A), a mixture of P. putida and activated sludge (INC-B), and activated sludge alone (INC-C) were employed in an anodic chamber to mainly compare the electricity generation and phenol degradation in MDCs. The study revealed the maximum phenol removal of 82 ± 2.4%, total dissolved solids (TDS) removal of 68 ± 1.5%, and power generation of 10.2 mW/m² using INC-B. The synergistic interactions between microorganisms, can enhance the toxic phenol degradation and also electricity generation in MDC for onsite wastewater application.

Microbial desalination cell with sulfonated sodium poly(ether ether ketone) as cation exchange membranes for enhancing power generation and salt reduction

Microbial desalination cell (MDC) is a bioelectrochemical system capable of oxidizing organics, generating electricity, while reducing the salinity content of brine streams. As it is designed, anion and cation exchange membranes play an important role on the selective removal of ions from the desalination chamber. In this work, sulfonated sodium (Na⁺) poly(ether ether ketone) (SPEEK) cation exchange membranes (CEM) were tested in combination with quaternary ammonium chloride poly(2,6-dimethyl 1,4-phenylene oxide) (QAPPO) anion exchange membrane (AEM). Non-patterned and patterned (varying topographical features) CEMs were investigated and assessed in this work. The results were contrasted against a commercially available CEM. This work used real seawater from the Pacific Ocean in the desalination chamber. The results displayed a high desalination rate and power generation for all the membranes, with a maximum of 78.6 ± 2.0% in salinity reduction and 235 ± 7 mW m⁻² in power generation for the MDCs with the SPEEK CEM. Desalination rate and power generation achieved are higher with synthesized SPEEK membranes when compared with an available commercial CEM. An optimized combination of these types of membranes substantially improves the performances of MDC, making the system more suitable for real applications.

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Thin and more conductive cation exchange membranes were employed in MDCs.

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CEMs with different topographical patterns were investigated.

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Maximum power achievement in MDC was 235 ± 7 mW m⁻².

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Maximum desalination achieved was 78.6 ± 2% over 3 days operations.

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SPEEK CEM membranes outperformed commercial membranes.

Investigation of patterned and non-patterned poly(2,6-dimethyl 1,4-phenylene) oxide based anion exchange membranes for enhanced desalination and power generation in a microbial desalination cell

Quaternary ammonium poly(2,6-dimethyl 1,4-phenylene oxide) (QAPPO) anion exchange membranes (AEMs) with topographically patterned surfaces were assessed in a microbial desalination cell (MDC) system. The MDC results with these QAPPO AEMs were benchmarked against a commercially available AEM. The MDC with the non-patterned QAPPO AEM (Q1) displayed the best desalination rate (a reduction of salinity by 53 ± 2.7%) and power generation (189 ± 5 mW m^- 2) when compared against the commercially available AEM and the patterned AEMs. The enhanced performance with the Q1 AEM was attributed to its higher ionic conductivity and smaller thickness leading to a reduced area specific resistance. It is important to note that Real Pacific Ocean seawater and activated sludge were used into the desalination chamber and anode chamber respectively for the MDC - which mimicked realistic conditions. Although the non-patterned QAPPO AEM displayed better performance over the patterned QAPPO AEMs, it was observed that the anodic overpotential was smaller when the MDCs featured QAPPO AEMs with larger lateral feature sizes. The results from this study have important implications for the continuous improvements necessary for developing cheaper and better performing membranes in order to optimize the MDC.

Impact of dissolved carbon dioxide concentration on the process parameters during its conversion to acetate through microbial electrosynthesis

The reduction of carbon dioxide (CO₂) released from industry can help to reduce the emissions of greenhouse gases (GHGs) to the atmosphere while at the same time producing value-added chemicals and contributing to carbon fixation.

Supercapacitive microbial desalination cells: New class of power generating devices for reduction of salinity content

In this work, the electrodes of a microbial desalination cell (MDC) are investigated as the positive and negative electrodes of an internal supercapacitor. The resulting system has been named a supercapacitive microbial desalination cell (SC-MDC). The electrodes are self-polarized by the red-ox reactions and therefore the anode acts as a negative electrode and the cathode as a positive electrode of the internal supercapacitor. In order to overcome cathodic losses, an additional capacitive electrode (AdE) was added and short-circuited with the SC-MDC cathode (SC-MDC-AdE). A total of 7600 discharge/self-recharge cycles (equivalent to 44 h of operation) of SC-MDC-AdE with a desalination chamber filled with an aqueous solution of 30 g L^-1 NaCl are reported. The same reactor system was operated with real seawater collected from Pacific Ocean for 88 h (15,100 cycles). Maximum power generated was 1.63 ± 0.04 W m^-2 for SC-MDC and 3.01 ± 0.01 W m^-2 for SC-MDC-AdE. Solution conductivity in the desalination reactor decreased by ∼50% after 23 h and by more than 60% after 44 h. There was no observable change in the pH during cell operation. Power/current pulses were generated without an external power supply.

Ozone-cathode microbial desalination cell; An innovative option to bioelectricity generation and water desalination

Microbial desalination cell (MDC) is a new approach of water desalination methods, which is based on ionic species removal from water in proportion to the electric current generated by bacteria. However, the low current generation and insufficient deionization in this technology have created challenges to improve the process. Here, the performance of MDC using ozone as a new electron acceptor (O₃-MDC) was evaluated versus another operated independently with oxygen (O₂-MDC). Results showed the maximum open-circuit voltages of 628 and 1331 mV for 20 g L^-1 NaCl desalination in O₂-MDC and O₃-MDC, respectively. The O₃-MDC produced a maximum power density of 4.06 W m^-2 (about 11 times higher than O₂-MDC) while at the same time was able to remove about 74% of salt (55.58% in the O₂-MDC). Each cycle of O₂-MDC and O₃-MDC operation lasted about 66 and 94 h, respectively, indicating a more stable current profile in the O₃-MDC. Moreover, sequencing test based on 16S rRNA gene showed that the anode biofilm had more diverse microbial community than anolyte sample. Proteobacteria, Firmicutes and Acidobacteria were from dominant microbial communities in anode biofilm sample. Accordingly, the results revealed that ozone can enhance MDC performance either as a desalination process or as a pre-treatment reactor for downstream desalination processes.

Unravelling and Reconstructing the Nexus of Salinity, Electricity, and Microbial Ecology for Bioelectrochemical Desalination

Microbial desalination cells (MDCs) are an emerging concept for simultaneous water/wastewater treatment and energy recovery. The key to developing MDCs is to understand fundamental problems, such as the effects of salinity on system performance and the role of microbial community and functional dynamics. Herein, a tubular MDC was operated under a wide range of salt concentrations (0.05-4 M), and the salinity effects were comprehensively examined. The MDC generated higher current with higher salt concentrations in the desalination chamber. When fed with 4 M NaCl, the MDC achieve a current density of 300 A m^-3 (anode volume), which was one of the highest among bioelectrochemical system studies. Community analysis and electrochemical measurements suggested that electrochemically active bacteria Pseudomonas and Acinetobacter transferred electrons extracellularly via electron shuttles, and the consequent ion migration led to high anode salinities and conductivity that favored their dominance. Predictive functional dynamics and Bayesian networks implied that the taxa putatively not capable of extracellular electron transfer (e.g., Bacteroidales and Clostridiales) might indirectly contribute to bioelectrochemical desalination. By integrating the Bayesian network with logistic regression, current production was successfully predicted from taxonomic data. This study has demonstrated uncompromised system performance under high salinity and thus has highlighted the potential of MDCs as an energy-efficient technology to address water-energy challenges. The statistical modeling approach developed in this study represents a significant step toward understating microbial communities and predicting system performance in engineered biological systems.

Enhancing biodegradation and energy generation via roughened surface graphite electrode in microbial desalination cell

The microbial desalination cell (MDC) is known as a newly developed technology for water and wastewater treatment. In this study, desalination rate, organic matter removal and energy production in the reactors with and without desalination function were compared. Herein, a new design of plain graphite called roughened surface graphite (RSG) was used as the anode electrode in both microbial fuel cell (MFC) and MDC reactors for the first time. Among the three type of anode electrodes investigated in this study, RSG electrode produced the highest power density and salt removal rate of 10.81 W/m³ and 77.6%, respectively. Such a power density was 2.33 times higher than the MFC reactor due to the junction potential effect. In addition, adding the desalination function to the MFC reactor enhanced columbic efficiency from 21.8 to 31.4%. These results provided a proof-of-concept that the use of MDC instead of MFC would improve wastewater treatment efficiency and power generation, with an added benefit of water desalination. Furthermore, RSG can successfully be employed in an MDC or MFC, enhancing the bio-electricity generation and salt removal.

Integrated membrane and microbial fuel cell technologies for enabling energy-efficient effluent Re-use in power plants

Municipal wastewater is an attractive alternative to freshwater sources to meet the cooling water needs of thermal power plants. Here we offer an energy-efficient integrated microbial fuel cell (MFC)/ultrafiltration (UF) process to purify primary clarifier effluent from a municipal wastewater treatment plant for use as cooling water. The microbial fuel cell was shown to significantly reduce chemical oxygen demand (COD) in the primary settled wastewater effluent upstream of the UF module, while eliminating the energy demand required to deliver dissolved oxygen in conventional aerobic treatment. We investigated surface modification of the UF membranes to control fouling. Two promising hydrophilic monomers were identified in a high-throughput search: zwitterion (2-(Methacryloyloxy)-ethyl-dimethyl-(3-sulfopropyl ammoniumhydroxide, abbreviated BET SO₃^-), and amine (2-(Methacryloyloxy) ethyl trimethylammonium chloride, abbreviated N(CH₃)₃⁺). Monomers were grafted using UV-induced polymerization on commercial poly (ether sulfone) membranes. Filtration of MFC effluent by membranes modified with BET SO₃^- and N(CH₃)₃⁺ exhibited a lower rate of resistance increase and lower energy consumption than the commercially available membrane. The MFC/UF process produced high quality cooling water that meets the Electrical Power Research Institute (EPRI) recommendations for COD, a suite of metals (Fe, Al, Cu, Zn, Si, Mn, S, Ca and Mg), and offered extremely low corrosion rates (<0.05 mm/yr). A series of AC and DC diagnostic tests were used to evaluate the MFC performance.

Microbial electrochemical nutrient recovery in anaerobic osmotic membrane bioreactors

This study demonstrates that by incorporating a microbial electrochemical unit into an anaerobic osmotic membrane bioreactor (AnOMBR), the system addressed several challenges faced by traditional anaerobic membrane bioreactors and recovered biogas, nitrogen, and phosphorus while maintaining high effluent quality with low dissolved methane. The microbial recovery cell (MRC)-AnOMBR system showed excellent organic (>93%) and phosphorus removal (>99%) and maintained effluent COD below 20 mg/L. Furthermore, the reactor effectively recovered up to 65% PO₄^3- and 45% NH₄⁺ from the influent, which can be further improved if membranes with higher selectivity are used. Nutrients removal from bulk solution mitigated NH₄⁺ penetration to the draw solution and reduced scaling potential caused by PO₄^3-. The maximum methane yield was 0.19 L CH₄/g COD, and low methane (<2.5 mL CH₄/L) was detected in the effluent. Further improvement can be made by increasing charge efficiency for better nutrient and energy recovery.

Bioelectricity generation and dewatered sludge degradation in microbial capacitive desalination cell

Microbial desalination cell (MDC) is a new approach for the synergy in bioelectricity generation, desalination and organic waste treatment without additional power input. However, current MDC systems cause salt accumulation in anodic wastewater and sludge. A microbial capacitive desalination cell (MCDC) with dewatered sludge as anodic substrate was developed to address the salt migration problem and improve the sludge recycling value by special designed-membrane assemblies, which consisted of cation exchange membranes (CEMs), layers of activated carbon cloth (ACC), and nickel foam. Experimental results indicated that the maximum power output of 2.06 W/m³ with open circuit voltage (OCV) of 0.942 V was produced in 42 days. When initial NaCl concentration was 2 g/L, the desalinization rate was about 15.5 mg/(L·h) in the first 24 h, indicating that the MCDC reactor was suitable to desalinize the low concentration salt solution rapidly. The conductivity of the anodic substrate decreased during the 42-day operation; the CEM/ACC/Ni assemblies could effectively restrict the salt accumulation in MCDC anode and promote dewatered sludge effective use by optimizing the dewatered sludge properties, such as organic matter, C/N, pH value, and electric conductivity (EC).

Bioelectrochemical systems-driven directional ion transport enables low-energy water desalination, pollutant removal, and resource recovery

Bioelectrochemical systems (BESs) are integrated water treatment technologies that generate electricity using organic matter in wastewater. In situ use of bioelectricity can direct the migration of ionic substances in a BES, thereby enabling water desalination, resource recovery, and valuable substance production. Recently, much attention has been placed on the microbial desalination cells in BESs to drive water desalination, and various configurations have optimized electricity generation and desalination performance and also coupled hydrogen production, heavy metal reduction, and other reactions. In addition, directional transport of other types of charged ions can remediate polluted groundwater, recover nutrient, and produce valuable substances. To better promote the practical application, the use of BESs as directional drivers of ionic substances requires further optimization to improve energy use efficiency and treatment efficacy. This article reviews existing researches on BES-driven directional ion transport to treat wastewater and identifies a few key factors involved in efficiency optimization.

Assessing potential cathodes for resource recovery through wastewater treatment and salinity removal using non-buffered microbial electrochemical systems

The present study evaluates relative functioning of microbial electrochemical systems (MES) for simultaneous wastewater treatment, desalination and resource recovery. Two MES were designed having abiotic cathode (MES-A) and algal biocathode (MES-B) which were investigated with synthetic feed and saline water as proxy of typical real-field wastewater. Comparative anodic and cathodic efficiencies revealed a distinct disparity in both the MES when operated in open circuit (OC) and closed circuit (CC). The maximum open circuit voltage (OCV) read in MES-A and MES-B was about 700mV and 600mV, respectively. Salinity and organic carbon removal efficiencies were noticed high during CC operation as 72% and 55% in MES-A and 60% and 63% in MES-B. These discrete observations evidenced ascribe to the influence of microbial electrochemical induced ion-migration over cathodic reduction reactions (CRR).

Self-Driven Desalination and Advanced Treatment of Wastewater in a Modularized Filtration Air Cathode Microbial Desalination Cell

Microbial desalination cells (MDCs) extract organic energy from wastewater for in situ desalination of saline water. However, to desalinate salt water, traditional MDCs often require an anolyte (wastewater) and a catholyte (other synthetic water) to produce electricity. Correspondingly, the traditional MDCs also produced anode effluent and cathode effluent, and may produce a concentrate solution, resulting in a low production of diluate. In this study, nitrogen-doped carbon nanotube membranes and Pt carbon cloths were utilized as filtration material and cathode to fabricate a modularized filtration air cathode MDC (F-MDC). With real wastewater flowing from anode to cathode, and finally to the middle membrane stack, the diluate volume production reached 82.4%, with the removal efficiency of salinity and chemical oxygen demand (COD) reached 93.6% and 97.3% respectively. The final diluate conductivity was 68 ± 12 μS/cm, and the turbidity was 0.41 NTU, which were sufficient for boiler supplementary or industrial cooling. The concentrate production was only 17.6%, and almost all the phosphorus and salt, and most of the nitrogen were recovered, potentially allowing the recovery of nutrients and other chemicals. These results show the potential utility of the modularized F-MDC in the application of municipal wastewater advanced treatment and self-driven desalination.

Microbial fuel cells and osmotic membrane bioreactors have mutual benefits for wastewater treatment and energy production

This study demonstrates that microbial fuel cells (MFCs) and osmotic membrane bioreactors (OMBRs) can be mutually beneficial when integrated together for wastewater treatment. When connecting MFCs with OMBRs, the solute buildup increased conductivity and buffer capacity, which greatly increased MFC power density from 3 W/m(3) up to 11.5 W/m(3). In turn, the MFCs conditioned and reduced sludge production and therefore reduced forward osmosis (FO) membrane fouling. The MFC-OMBR equipped with new thin-film composite (TFC) membrane showed excellent organic (>95%) and phosphorus removal (>99%) and therefore maintained effluent sCOD below 20 mg/L. However, the nitrogen removal was limited due to the negative surface charge of the thin-film composite membrane and solution chemistry, which led to higher flux of ammonium toward the OMBR draw solution. Further studies are needed to improve nitrogen removal, reduce fouling, and optimize system integration.

Fouling on ion-exchange membranes: Classification, characterization and strategies of prevention and control

The environmentally friendly ion-exchange membrane (IEM) processes find more and more applications in the modern industries in order to demineralize, concentrate and modify products. Moreover, these processes may be applied for the energy conversion and storage. However, the main drawback of the IEM processes is a formation of fouling, which significantly decreases the process efficiency and increases the process cost. The present review is dedicated to the problematic of IEM fouling phenomena. Firstly, the major types of IEM fouling such as colloidal fouling, organic fouling, scaling and biofouling are discussed along with consideration of the main factors affecting fouling formation and development. Secondly, the review of the possible methods of IEM fouling characterization is provided. This section includes the methods of fouling visualization and characterization as well as methods allowing investigations of characteristics of the fouled IEMs. Eventually, the reader will find the conventional and modern strategies of prevention and control of different fouling types.

Analysis of long-term performance and microbial community structure in bio-cathode microbial desalination cells

A microbial desalination cell (MDC) could desalinate salt water without energy consumption and simultaneously generate bioenergy. Compared with an abiotic cathode MDC, an aerobic bio-cathode MDC is more sustainable and is less expensive to operate. In this study, the long-term operation (5500 h) performance of a bio-cathode MDC was investigated in which the power density, Coulombic efficiency, and salt removal rate were decreased by 71, 44, and 27 %, respectively. The primary reason for the system performance decrease was biofouling on the membranes, which increased internal resistance and reduced the ionic transfer and energy conversion efficiency. Changing membranes was an effective method to recover the MDC performance. The microbial community diversity in the MDC anode was low compared with that of the reported microbial fuel cell (MFC), while the abundance of Proteobacteria was 30 % higher. The content of Planctomycetes in the cathode biofilm sample was much higher than that in biofouling on the cation exchange membrane (CEM), indicating that Planctomycetes were relevant to cathode oxygen reduction.