Ionic composition and transport mechanisms in microbial desalination cells

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.

Spotlighting of microbial electrodeionization cells for sustainable wastewater treatment: Application of machine learning

Microbial electrodeionization cells (MECs) have been investigated for various potential applications, including the elimination of persistent pollutants, chemical synthesis, the recovery of resources, and the development of biosensors. Nevertheless, MEC technology is still developing, and practical large-scale applications face significant obstacles. This review aims to investigate MEC implementations in sustainable wastewater treatment. Ideas and concepts of MEC technology, the setup of the electrodeionization component, the membranes of MECs, the working mechanism of MECs, and the various microorganisms used in MECs are discussed. Additionally, difficulties and prospective outcomes were discussed. The goal of this review is to support scientists and engineers in fully grasping the most recent developments in MEC technologies and applications.

Application of ZIF-8 nanocomposite membrane in microbial desalination cells for simultaneous heavy metal removal and biofouling prevention

Microbial desalination cells (MDC) syndicate the advantage of physical separation by using membranes to create conditions required for Bioelectrochemical processes for the treatment of various domestic and industrial wastewater, while simultaneously desalinating saline water and generating bioenergy. However, since the introduction of this technology, heavy metal removal has been a challenge, and membrane fouling has become a major bottleneck limiting the optimum performance and efficiency of this technology. This study incorporated the use of ZIF-8 nanocomposite membrane via phase inversion mechanism in MDC for simultaneous heavy metal removal and membrane biofouling prevention. The study was conducted in two MDC systems; MDC-Control (without the ZIF-8 nanocomposite membrane) and MDC with ZIF-8 nanocomposite membrane. The results from the experiment shown that maximum removal efficiency of 85.7%, 84.3%, 84.0%, and 90.61% was obtained for Cu²⁺, Zn²⁺, Pb^2+, and Cd²⁺ respectively in MDC-ZIF-8, while MDC control showed 54.17%, 59.71%, 51.94%, and 54.17%. The results were well fitted to the Langmuir adsorption isotherm with correlation coefficients (R²) > 0.99 in all cases for MDC-ZIF-8. A maximum adsorption capacity (Q_max) of 292 mg g^-1 was attained for all four metal ions in MDC-ZIF-8. Besides, after 38 days of continuous operation with two complete desalination for both systems, the SEM-EDS characterization analysis, polarization characteristics, and power generation revealed antifouling characteristics of ZIF-8 nanocomposite membrane incorporated in MDC. The integration of the ZIF-8 nanocomposite membrane proved to be simultaneously efficient in biofouling prevention and heavy metal removal without jeopardizing the system's ability for wastewater treatment, bioelectricity generation, and desalination processes.

Effect of hydraulic retention time on the electro-bioremediation of nitrate in saline groundwater

Bioelectrochemical systems (BES) have proven their capability to treat nitrate-contaminated saline groundwater and simultaneously recover value-added chemicals (such as disinfection products) within a circular economy-based approach. In this study, the effect of the hydraulic retention time (HRT) on nitrate and salinity removal, as well as on free chlorine production, was investigated in a 3-compartment BES working in galvanostatic mode with the perspective of process intensification and future scale-up. Reducing the HRT from 30.1 ± 2.3 to 2.4 ± 0.2 h led to a corresponding increase in nitrate removal rates (from 17 ± 1 up to 131 ± 1 mgNO₃^--N L^-1d^-1), although a progressive decrease in desalination efficiency (from 77 ± 13 to 12 ± 2 %) was observed. Nitrate concentration and salinity close to threshold limits indicated by the World Health Organization for drinking water, as well as significant chlorine production were achieved with an HRT of 4.9 ± 0.4 h. At such HRT, specific energy consumption was low (6.8·10^-2 ± 0.3·10^-2 kWh g^-1NO₃^--N_removed), considering that the supplied energy supports three processes simultaneously. A logarithmic equation correlated well with nitrate removal rates at the applied HRTs and may be used to predict BES behaviour with different HRTs. The bacterial community of the bio-cathode under galvanostatic mode was dominated by a few populations, including the genera Rhizobium, Bosea, Fontibacter and Gordonia. The results provide useful information for the scale-up of BES treating multi-contaminated groundwater.

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.

Overcoming organic matter limitation enables high nutrient recovery from sewage sludge reject water in a self-powered microbial nutrient recovery cell

In order to meet the global demand of fertilizers for food production, there is an urgent need to recover macronutrients (such as NH₄⁺, PO₄^3-, Ca²⁺, K⁺, and Mg²⁺) from non-conventional sources (e.g., waste streams). Sludge reject water - a by-product produced during the dewatering of anaerobically-stabilized sewage sludge - is considered an ideal feedstock for bioelectrochemical nutrient recovery due to its high nutrient content. However, its low readily available organic matter and alkalinity usually limit electric current generation, resulting in low nutrient recovery. Here, we designed and operated self-powered microbial nutrient recovery cells (MNRCs) to test whether or not the addition of high-strength livestock wastewater could improve the macronutrients recovery from sludge reject water into a liquid concentrate. MNRCs fed with sludge reject water exhibited a low current density generation of 0.98 ± 0.31 A/m³ with approximately 24 ± 2% reduction in chemical oxygen demand (COD) concentration. The NH₄⁺ removal was only 37.1 ± 11% with an up-concentration factor of ~0.43 ± 0.15. Macronutrients recovery and up-concentration were optimized by mixing sludge reject water with livestock wastewater, which its content varied from 10 to 30%. Consequently, the current output and NH₄⁺ up-concentration factor were remarkably increased, peaking at 14.10 ± 1.14 A/m³ and 2.19 ± 0.51, respectively, for MNRCs fed with sludge reject water:livestock wastewater = 70%:30% (v:v). Detailed analysis of the liquid concentrate revealed that it could be efficiently used as a liquid fertilizer to replace chemical fertilizers with comparable agricultural productivity at a lower cost. These results suggest that the MNRC can promote self-powered, chemical-free macronutrients recovery from sludge reject water (and other low-strength wastewater, too) by controlling the availability of organic matter in waste streams.

A Review on Ion-Exchange Membrane Fouling during the Electrodialysis Process in the Food Industry, Part 1: Types, Effects, Characterization Methods, Fouling Mechanisms and Interactions

Electrodialysis (ED) was first established for water desalination and is still highly recommended in this field for its high water recovery, long lifetime and acceptable electricity consumption. Today, thanks to technological progress in ED processes and the emergence of new ion-exchange membranes (IEMs), ED has been extended to many other applications in the food industry. This expansion of uses has also generated several problems such as IEMs' lifetime limitation due to different ageing phenomena (because of organic and/or mineral compounds). The current commercial IEMs show excellent performance in ED processes; however, organic foulants such as proteins, surfactants, polyphenols or other natural organic matters can adhere on their surface (especially when using anion-exchange membranes: AEMs) forming a colloid layer or can infiltrate the membrane matrix, which leads to the increase in electrical resistance, resulting in higher energy consumption, lower water recovery, loss of membrane permselectivity and current efficiency as well as lifetime limitation. If these aspects are not sufficiently controlled and mastered, the use and the efficiency of ED processes will be limited since, it will no longer be competitive or profitable compared to other separation methods. In this work we reviewed a significant amount of recent scientific publications, research and reviews studying the phenomena of IEM fouling during the ED process in food industry with a special focus on the last decade. We first classified the different types of fouling according to the most commonly used classifications. Then, the fouling effects, the characterization methods and techniques as well as the different fouling mechanisms and interactions as well as their influence on IEM matrix and fixed groups were presented, analyzed, discussed and illustrated.

Application of microbial electrochemical technologies for the treatment of petrochemical wastewater with concomitant valuable recovery: A review

Petrochemical industry is one of the major and rapidly growing industry that generates a variety of toxic and recalcitrant organic pollutants as by-products, which are not only harmful to the aquatic animals but also affects human health. The majority of the components of petrochemical wastewater (PW) are carcinogenic, genotoxic and phytotoxic in nature; hence, this complex wastewater generated from different petrochemical processes should be efficiently treated prior to its disposal in natural water bodies. The established technologies like advanced oxidation, membrane bioreactor, electrocoagulation and activated sludge process employed for the treatment of PW are highly energy intensive and incurs high capital and operation cost. Moreover, these technologies are not effective in completely eliminating petroleum hydrocarbons present in PW. Thus, to reduce the energy requirement and also to transform the chemical energy trapped in these organic matters present in this wastewater into bioelectricity and other value-added products, microbial electrochemical technologies (METs) can be efficaciously used, which would also compensate the treatment cost by transforming these pollutants into bioenergy and valuables. In this regard, this review elucidates the feasibility and application of different METs as an appropriate alternative for the treatment of PW. Furthermore, the numerous bottlenecks towards the real-life application and commercialization of pioneering METs have also been articulated.

An overview of brine management: Emerging desalination technologies, life cycle assessment, and metal recovery methodologies

This study examines which management methods are the most recent and advanced in managing rejected brine generated from desalination plants. It also provides up-to-date information regarding the most adequate technologies that generate a minimum quantity of rejected brine via the use of minimization techniques and analyzes the method of direct disposal that has lately received noticeable improvements. It further discusses the reuse of discarded brine to recover valuable goods and sequestration of carbon dioxide. Sustainability is an important parameter that needs consideration to achieve uninterrupted operation of the discarded brine management to achieve the least environmental, social, and economic aftermath. To properly deal with any environmental issues related to brine disposal, different methods are implemented so that, in the end, higher water recovery is achievable from the desalination processes, namely brine minimization and rejection technologies (pressure retarded osmosis, microbial desalination cell technology), membrane-based technologies (vibratory shear enhanced processing, forward osmosis, electrodialysis, electrodialysis reverse, and electrodialysis metathesis, pervaporation method, thermal-based technologies (wind-aided intensified evaporation, brine concentrators, ohmic evaporator, membrane distillation, multi-stage flash distillation. This review also critically examined the two conventional approaches commonly used in life cycle assessment (LCA), when evaluating the ecotoxic effect of discarded brine. It intends to discuss the currently available methods and propose an improved method for evaluating the toxicity potential of brine on the aquatic ecosystem originated from seawater desalination plants. The Group-by-Group method takes into consideration the demerits of the two methods of the traditional method of LCA or chemical-specific approach as it provides a more holistic coverage for complicated brine to be disposed of. Recently, attention has been focused on recovering valuable metals from the discharged concentrated brine waste. Certainly, attaining marketable products from the discharged concentrated brine would offer an economic benefit and reducing the whole desalination costs. Ion imprinting polymers have potential applications in metal recovery from brine. Finding selective, more efficient, and less expensive imprinted polymers for extraction/pre-concentration of valuable ions is a vital and challenging task. Lastly, the brine should be seen as a resource and not as a waste to attain sustainability in its management approaches. Hybrid processes would be highly recommended to get the absolute transformation of the discarded brine from desalination processes to more valuable constituents.

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.

A comprehensive review of nutrient-energy-water-solute recovery by hybrid osmotic membrane bioreactors

Hybrid osmotic membrane bioreactor (OMBR) takes advantage of the cooperation of varying biological or desalination processes and can achieve NEWS (nutrient-energy-water-solute) recovery from wastewater. However, a lack of universal parameters hinders our understanding. Herein, system configurations and new parameters are systematically investigated to help better evaluate recovery performance. High-quality water can be produced in reverse osmosis/membrane distillation-based OMBRs, but high operation cost limits their application. Although bioelectrochemical system (BES)/electrodialysis-based OMBRs can effectively achieve solute recovery, operation parameters should be optimized. Nutrients can be recovered from various wastewater by porous membrane-based OMBRs, but additional processes increase operation cost. Electricity recovery can be achieved in BES-based OMBRs, but energy balances are negative. Although anaerobic OMBRs are energy-efficient, salinity accumulation limits methane productions. Additional efforts must be made to alleviate membrane fouling, control salinity accumulation, optimize recovery efficiency, and reduce operation cost. This review will accelerate hybrid OMBR development for real-world applications.

Removal of hexavalent chromium in dual-chamber microbial fuel cells separated by different ion exchange membranes

An ion exchange membrane (IEM) is an important component in dual-chamber microbial fuel cells (MFCs) to separate cathodic chromium from anode bacteria to avoid toxicity. Common used IEMs (e.g., BPM, CEM, PEM, AEM) have different ionic transfer abilities which could influence MFC performance and chromium removal. Additionally, to distinguish chromium "removal" or "reduction" by MFCs, the chromium removal in this study was further analyzed into cathodic reduction, adsorption on the membrane and permeation through membrane to the anode chamber. It was found that BPM achieved the best performance in removing hexavalent chromium (99.4 ± 0.2 %) and balancing pH and conductivity in both chambers, followed by AEM (97.9 ± 0.8 %) and CEM (95.6 ± 0.8 %), while PEM can not well maintain pH and conductivity leading to the worst anode performance and lowest chromium removal efficiency. However, the adsorption of chromium on the AEM accounts for 91.1 ± 0.7 %, which was much higher than the other three membranes. The permeation of chromium through the membrane were all lower than 0.2% which can be ignored. SEM and EDS results showed that chromium deposits and bacteria were detected on the membrane facing cahtode and anode, respectively, indicating that membrane scaling and fouling were inevitable and happened within 24 h operation.

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.

Biofouling of membranes in microbial electrochemical technologies: Causes, characterization methods and mitigation strategies

The scope of the review is to discuss the current state of knowledge and lessons learned on biofouling of membrane separators being used for microbial electrochemical technologies (MET). It is illustrated what crucial membrane features have to be considered and how these affect the MET performance, paying particular attention to membrane biofouling. The complexity of the phenomena was demonstrated and thereby, it is shown that membrane qualities related to its surface and inherent material features significantly influence (and can be influenced by) the biofouling process. Applicable methods for assessment of membrane biofouling are highlighted, followed by the detailed literature evaluation. Finally, an outlook on e.g. possible mitigation strategies for membrane biofouling in MET is provided.

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.

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).

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.

Bioelectricity inhibits back diffusion from the anolyte into the desalinated stream in microbial desalination cells

Microbial desalination cells (MDCs) taking advantage of energy in wastewater to drive desalination represent a promising approach for energy-efficient desalination, but concerns arise whether contaminants in wastewater could enter the desalinated stream across ion exchange membranes. Such back diffusion of contaminants from the anolyte into the desalinated stream could be controlled by two mechanisms, Donnan effect and molecule transport. This study attempted to understand those mechanisms for inorganic and organic compounds in MDCs through two independently conducted experiments. Donnan effect was found to be the dominant mechanism under the condition without current generation. Under open circuit condition, the MDC fed with 5 g L(-1) salt solution exhibited 1.9 ± 0.7%, 10.3 ± 1.3%, and 1.8 ± 1.2% back diffusion of acetic, phosphate, and sulfate ions, respectively. Current generation effectively suppressed Donnan effect from 68.2% to 7.2%, and then molecule transport became more responsible for back diffusion. A higher initial salt concentration (35 g L(-1)) and a shorter HRT (1.0 d) led to the highest concentration gradient, resulting in the most back diffusion of 7.1 ± 1.2% and 6.8 ± 3.1% of phosphate and sulfate ions, respectively. Three representative organic compounds were selected for test, and it was found that organic back diffusion was intensified with a higher salt concentration gradient and molecular weight played an important role in compound movement. Principal component analysis confirmed the negative correlation between Donnan effect and current, and the positive correlation between molecule transport and concentration gradient related conditions.

Novel Self-driven Microbial Nutrient Recovery Cell with Simultaneous Wastewater Purification

Conventional wastewater purification technologies consume large amounts of energy, while the abundant chemical energy and nutrient resources contained in sewage are wasted in such treatment processes. A microbial nutrient recovery cell (MNRC) has been developed to take advantage of the energy contained in wastewater, in order to simultaneously purify wastewater and recover nutrient ions. When wastewater was circulated between the anode and cathode chambers of the MNRC, the organics (COD) were removed by bacteria while ammonium and phosphate (NH₄⁺-N and PO₄³⁻-P) were recovered by the electrical field that was produced using in situ energy in the wastewater without additional energy input. The removal efficiencies from wastewater were >82% for COD, >96% for NH₄⁺-N, and >64% for PO₄³⁻-P in all the operational cycles. Simultaneously, the concentrations of NH₄⁺ and PO₄³⁻ in the recovery chamber increased to more than 1.5 and 2.2 times, respectively, compared with the initial concentrations in wastewater. The MNRC provides proof-of-concept as a sustainable, self-driven approach to efficient wastewater purification and nutrient recovery in a comprehensive bioelectrochemical system.

Integrated experimental investigation and mathematical modeling of brackish water desalination and wastewater treatment in microbial desalination cells

Desalination of brackish water can provide freshwater for potable use or non potable applications such as agricultural irrigation. Brackish water desalination is especially attractive to microbial desalination cells (MDCs) because of its low salinity, but this has not been well studied before. Herein, three brackish waters prepared according to the compositions of actual brackish water in three locations in Israel were examined with domestic wastewater as an electron source in a bench-scale MDC. All three brackish waters could be effectively desalinated with simultaneous wastewater treatment. The MDC achieved the highest salt removal rate of 1.2 g L(-1) d(-1) with an initial salinity of 5.9 g L(-1) and a hydraulic retention time (HRT) of 0.8 d. The desalinated brackish water could meet the irrigation standard of both salinity (450 mg L(-1) TDS) and the concentrations of major ionic species, given a sufficient HRT. The MDC also accomplished nearly 70% removal of organic compounds in wastewater with Coulombic efficiency varied between 5 and 10%. A previously developed MDC model was improved for brackish water desalination, and could well predict salinity variation and the concentrations of individual ions. The model also simulated a staged operation mode with improved desalination performance. This integrated experiment and mathematical modeling approach provides an effective method to understand the key factors in brackish water desalination by MDCs towards further system development.

Simultaneous Desalination of Sea water and Electricity Production with New Membrane Technology, Air-Cathode Microbial Desalination Cells

Water and energy shortages, has increased the need for methods that can provide low energy for desalination of sea water. Microbial desalination cell is one of the most important of these methods. In this study we use air cathode MDC for desalination of seawater. The maximum voltage, power and current density was 607mV, 521mW/m2 and 858mA/m2 (25mM PBS) and 701mV, 695mW/m2 and 992mA/m2 (50mM PBS) respectively. During the period of the voltage generation in 50mM PBS was about 1.5 times of 25mM PBS. Under this situation, EC of seawater with initial electrical conductivity declined by 48.31±3% (25mM PBS) and 46.71±2.73% (50mM PBS). As well as decrease of salt from sea water in the middle chamber, EC in synthetic wastewater and catholyte slightly increased. So that Change percent of EC in synthetic wastewater was 44.20 ± 11.94(25mM PBS) and 27.94 ± 3 (50 mM PBS) and in catholyte was 211.66 ± 22.41(25mM PBS) and 119.24 ± 11.25 (50 mM PBS) respectively. These results show that the MDC can also be used as a pretreatment to reverse osmosis; simultaneously the energy required in this process is also partly meet.

Removal and fate of trace organic compounds in microbial fuel cells

This study focused on understanding and characterizing the removal of trace organic compounds (TOrCs) in microbial fuel cells (MFC). 26 TOrCs with broad physicochemical properties were spiked in synthetic wastewater. Single-chamber air-cathode MFC (SMFC) and double-chamber air-cathode MFC (DMFC) were constructed to provide combined or separated oxidation/reduction environments for TOrCs removal. The study showed that TOrCs removal processes involved both sorption and biodegradation. For neutral TOrCs, the removal efficiency was affected primarily by the biodegradability probability and hydrophobicity of the compounds, while electrostatic interactions played an additional role in the MFCs as the removal of positively charged TOrCs was generally higher than negatively charged TOrCs. The presence of TOrCs showed negligible impact on MFC power generation, likewise the operation of MFCs had marginal effect on TOrCs removal, except longer residence time in MFCs improved biological removal performance.

Pluggable microbial fuel cell stacks for septic wastewater treatment and electricity production

Septic tanks and other decentralized wastewater treatment systems play an important role in protecting public health and water resource for remote or developing communities. Current septic systems do not have energy production capability, yet such feature can be very valuable for areas lack access to electricity. Here we present an easy-to-operate microbial fuel cell (MFC) stack that consists a common base and multiple pluggable units, which can be connected in either series or parallel for electricity generation during waste treatment in septic tanks. Lab studies showed such easy configuration obtained a power density of 142±6.71mWm(-2) when 3 units are connected in parallel, and preliminary calculation indicates that a system that costs approximately US $25 can power a 6-watt LED light for 4h per day with great improvement potential. Detailed electrochemical characterizations provide insights on system internal loss and technology advancement needed.

High performance spiral wound microbial fuel cell with hydraulic characterization

The understanding and development of functioning systems are crucial steps for microbial fuel cell (MFC) technology advancement. In this study, a compact spiral wound MFC (swMFC) was developed and hydraulic residence time distribution (RTD) tests were conducted to investigate the flow characteristics in the systems. Results show that two-chamber swMFCs have high surface area to volume ratios of 350-700m(2)/m(3), and by using oxygen cathode without metal-catalysts, the maximum power densities were 42W/m(3) based on total volume and 170W/m(3) based on effective volume. The hydraulic step-input tracer study identified 20-67% of anodic flow dead space, which presents new opportunities for system improvement. Electrochemical tools revealed very low ohmic resistance but high charge transfer and diffusion resistance due to catalyst-free oxygen reduction. The spiral wound configuration combined with RTD tool offers a holistic approach for MFC development and optimization.

Shale gas produced water treatment using innovative microbial capacitive desalination cell

The rapid development of unconventional oil and gas production has generated large amounts of wastewater for disposal, raising significant environmental and public health concerns. Treatment and beneficial use of produced water presents many challenges due to its high concentrations of petroleum hydrocarbons and salinity. The objectives of this study were to investigate the feasibility of treating actual shale gas produced water using a bioelectrochemical system integrated with capacitive deionization-a microbial capacitive desalination cell (MCDC). Microbial degradation of organic compounds in the anode generated an electric potential that drove the desalination of produced water. Sorption and biodegradation resulted in a combined organic removal rate of 6.4 mg dissolved organic carbon per hour in the reactor, and the MCDC removed 36 mg salt per gram of carbon electrode per hour from produced water. This study is a proof-of-concept that the MCDC can be used to combine organic degradation with desalination of contaminated water without external energy input.

Bioelectrochemical desalination and electricity generation in microbial desalination cell with dewatered sludge as fuel

Microbial desalination cells (MDCs) with common liquid anodic substrate exhibit a slow startup and destructive pH drop, and abiotic cathodes have high cost and low sustainability. A biocathode MDC with dewatered sludge as fuel was developed for synergistic desalination, electricity generation and sludge stabilization. Experimental results indicated that the startup period was reduced to 3d, anodic pH was maintained between 6.6 and 7.6, and high stability was shown under long-term operation (300d). When initial NaCl concentrations were 5 and 10g/L, the desalinization rates during stable operation were 46.37±1.14% and 40.74±0.89%, respectively. The maximum power output of 3.178W/m(3) with open circuit voltage (OCV) of 1.118V was produced on 130d. After 300d, 25.71±0.15% of organic matter was removed. These results demonstrated that dewatered sludge was an appropriate anodic substrate to enhance MDC stability for desalination and electricity generation.

A comprehensive review of microbial electrochemical systems as a platform technology

Microbial electrochemical systems (MESs) use microorganisms to covert the chemical energy stored in biodegradable materials to direct electric current and chemicals. Compared to traditional treatment-focused, energy-intensive environmental technologies, this emerging technology offers a new and transformative solution for integrated waste treatment and energy and resource recovery, because it offers a flexible platform for both oxidation and reduction reaction oriented processes. All MESs share one common principle in the anode chamber, in which biodegradable substrates, such as waste materials, are oxidized and generate electrical current. In contrast, a great variety of applications have been developed by utilizing this in situ current, such as direct power generation (microbial fuel cells, MFCs), chemical production (microbial electrolysis cells, MECs; microbial electrosynthesis, MES), or water desalination (microbial desalination cells, MDCs). Different from previous reviews that either focus on one function or a specific application aspect, this article provides a comprehensive and quantitative review of all the different functions or system constructions with different acronyms developed so far from the MES platform and summarizes nearly 50 corresponding systems to date. It also provides discussions on the future development of this promising yet early-stage technology.

Competitive migration behaviors of multiple ions and their impacts on ion-exchange resin packed microbial desalination cell

Mixed ion-exchange resins packed microbial desalination cell (R-MDC) could stabilize the internal resistance, however, the impacts of multiple ions on R-MDC performance was unclear. This study investigated the desalination performance, multiple ions migration behaviors and their impacts on R-MDCs fed with salt solution containing multiple anions and cations. Results showed that R-MDC removed multiple anions better than multiple cations with desalination efficiency of 99% (effluent conductivity <0.05 ms/cm) at hydraulic retention time of 50 h. Competitive migration order was SO4(2-)>NO3(-)>Cl(-) for anions and Ca(2+)≈Mg(2+)>NH4(+)>Na(+) for cations, jointly affected by both their molar conductivity and exchange selectivity on resins. After long-term operation, the existence of higher concentration Ca(2+) and Mg(2+) caused the electric conductivity of mixed resins decrease and scaling on the surface of cation-exchange membrane adjoined with cathode chamber, suggesting that R-MDC would be more suitable for desalination of water with lower hardness.

Microbial desalination cell with capacitive adsorption for ion migration control

A new microbial desalination cell with capacitive adsorption capability (cMDC) was developed to solve the ion migration problem facing current MDC systems. Traditional MDCs remove salts by transferring ions to the anode and cathode chambers, which may prohibit wastewater beneficial reuse due to increased salinity. The cMDC uses adsorptive activated carbon cloth (ACC) as the electrodes and utilizes the formed capacitive double layers for electrochemical ion adsorption. The cMDC removed an average of 69.4% of the salt from the desalination chamber through electrode adsorption during one batch cycle, and it did not add salts to the anode or cathode chamber. It was estimated that 61-82.2mg of total dissolved solids (TDS) was adsorbed to 1g of ACC electrode. The cMDC provides a new approach for salt management, organic removal, and energy production. Further studies will be conducted to optimize reactor configuration and achieve in situ electrode regeneration.

Long-term performance and characterization of microbial desalination cells in treating domestic wastewater

Microbial desalination cell represents a new technology for simultaneous wastewater treatment, water desalination, and energy production. This study characterized the long-term performance of MDC during wastewater treatment and identified the key factors that caused performance decline. The 8-month operation shows that MDC performance decreased over time, as indicated by a 47% decline in current density, a 46% drop in Columbic efficiency, and a 27% decrease in desalination efficiency. Advanced electrochemical, microscopy, and spectroscopy analyses all confirmed biofouling on the anion exchange membrane, which increased system resistance and reduced ionic transfer and energy conversion efficiency. Minor chemical scaling was found on the cation exchange membrane surface. Microbial communities became less diverse at the end of operation, and Proteobacteria spp. was dominant on both anode and AEM fouling layer surface. These results provide insights into the viability of long-term MDC operation on reactor performance and direct system development through membrane optimization.