Exploiting carbon and nitrogen compounds for enhanced energy and resource recovery

A review of microbial desalination cell technology: Configurations, optimization and applications

The availability of drinking water from the current available sources is decreasing due to the high demand and population increase. Seawater is a potential source for drinking water but the current desalination technology is energy intensive, therefore energy efficient desalination technology is desired. In the past decade microbial fuel cells (MFC) were emerged for simultaneous wastewater treatment and bioelectricity generation, in the anodic chamber of MFCs, microbes work as a biocatalyst to generate electrons from the oxidation of the organic compounds (wastewater) and transfer them to the anode electrode. These electrons flow through an external circuit to the cathode electrode where they used to reduce terminal electron acceptors (e.g., oxygen). Microbial desalination cells (MDC) are new potential technique for seawater desalination, in this device energy from wastewater is extracted by using microbes and without any external energy source, water desalination is driven. To convert an MFC to an MDC, a middle chamber is inserted in between the anodic and cathodic chambers of MFC using a pair of anion and cation exchange membranes. This middle chamber works as a desalination chamber in the MDC (Fig. 1). The cations and anions from the desalination chamber moved to the anodic and the cathodic chambers, respectively, due to the cell potential difference between the anode electrode and the cathode electrode; as a result, salts are removed from the saltwater.The first MDC study was reported in 2009 and since then there have been nearly 74 papers published about various aspects of MDC design and development, indicating a strong interest and rapid development of this technology. During this short period of time, various MDC designs were developed for salt removal and wastewater treatment. The desalination chamber volumes were increased from 3 ml to 105 liters and further progress is going on for salt removal and at the same time wastewater treatment. The performance of MDC was investigated using various concentrations of saline water in desalination chamber using industrial or synthetic wastewater in the anodic chamber. Different MDC designs were reviewed here. These developed new MDC designs named as air cathode MDC, stacked MDC (SMDC), up flow MDC (UMDC), recirculated MDC (RMDC), microbial electrodialysis cell (MEDC), submerged microbial desalination- denitrification cell (SMDDC), microbial capacitive desalination cell (MCDC) and osmotic microbial desalination cell (OsMDC). Different anion and cation exchange membranes were compared for power generation and desalination efficiency. This paper also reviews different substrates that have been used in MDCs so far. The MDCs provide an energy self-sustainable system in that water desalination and wastewater treatment conducted by using microbes as catalyst in the anodic chamber. Still the available MDCs were very small in volume that can't meet today's water desalination needs. In the long term operation of MDC, the membrane fouling and electrode stability are still two major problems limiting the development of MDCs. The possibility of scale-up, possible future potentials for synchrony of the MDCs with current desalination techniques were also discussed. Case study with real wastewater in the anodic chamber and real seawater in the desalination chamber were also discussed.AcknowledgementsThis work was made possible by NPRP grant # 6-289-2-125 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.ReferenceSevda, S., Yuan, H., He, Z., Abu-Reesh, I.M., 2015. Microbial desalination cells as a versatile technology: Functions, optimization and prospective. Desalination 371, 9–17. doi:10.1016/j.desal.2015.05.021

Resource recovery from wastewater can be an application niche of microbial desalination cells

By combining the microbial electrolysis cell and the microbial desalination cell, the microbial electrolysis desalination cell (MEDC) becomes a novel device to desalinate salty water. However, several factors, such as sharp pH decrease and Cl(-) accumulation in the anode chamber, limit the MEDC development. In this study, a microbial electrolysis desalination and chemical-production cell (MEDCC) was developed with four chambers using a bipolar membrane. Results showed that the pH in the anode chamber of the MEDCC always remained near 7.0, which greatly enhanced the microbial activities in the cell. With applied voltages of 0.3-1.0 V, 62%-97% of Coulombic efficiencies were achieved from the MEDCC, which were 1.5-2.0 times of those from the MEDC. With 10 mL of 10 g/L NaCl in the desalination chamber, desalination rates of the MEDCC reached 46%-86% within 18 h. Another unique feature of the MEDCC was the simultaneous production of HCl and NaOH in the cell. With 1.0 V applied voltage, the pH values at 18 h in the acid-production chamber and cathode chamber were 0.68 and 12.9, respectively. With the MEDCC, the problem with large pH changes in the anode chamber was resolved, and products of the acid and alkali were obtained.

Enhancing desalination and wastewater treatment by coupling microbial desalination cells with forward osmosis

Petroleum refining, not only consumes large quantities of water but also generates large quantities of wastewater. Large quantities of petroleum refinery wastewater are generated worldwide, approximately 3.5–5 m3 of wastewater generated per ton of crude oil processed. This wastewater is considered as a major source of environmental pollution. Various chemical and biologically based technologies have been developed for the treatment of petroleum refinery wastewater such as reverse osmosis, membrane filtration, electrocoagulation, anaerobic tank, anaerobic baffled reactor, aerated filter and bio-contact oxidation. In the last decade, biological treatment methods of petroleum refinery wastewater were developed because of the high cost of chemical treatment methods and these methods are also more environmental friendly.In this study, we demonstrate for the first time that it is possible to remove salt from saltwater and generate electricity while using petroleum refinery wastewater as an anodic substrate in the three chamber microbial desalination cell (MDC). MDC insinuates a new method for treating petroleum refinery wastewater and concurrently salt removal from seawater with bioelectricity generation. MDC was developed from microbial fuel cell (MFCs) concept. In this device, desalination and wastewater treatment are conducted in one system. MDC has an enormous potential as a low-cost desalination process with wastewater treatment and other benefits. MDC is a new technique in which saltwater can be desalinated without using any external energy source. The exoelectrogenic-bacteria are used in MDC reactor to oxidize biodegradable substrate in the anodic chamber and transfer the produced electrons to the anode electrode.In this study, petroleum refinery wastewater was treated in MDC using three different initial salt concentrations of 5 g/l, 20 g/L and real seawater in desalination chamber along with two separate catholyte (phosphate buffer solution and acidified water). All the three chamber MDC operations were carried out in batch mode. The maximum % COD removals of 71 and 64 were obtained using initial salt concentration of 20 g/L with MDC operated with acidified and phosphate buffer solution as catholyte respectively. The maximum desalination efficiency of 19.9% and 19.1 % were obtained in MDC operated with real seawater using PBS and acidified water as catholyte respectively. The scanning electron microscope images investigation confirmed the presence of microbial biofilm on the anode electrode and anion exchange membrane surface. The MDC performed better with acidified water compared to PBS as catholyte. The above obtained results demonstrated the feasibility of using MDC technologies to generate bioelectricity, seawater desalination and simultaneously treat complex petroleum refinery wastewater, although further studies are required to scale up and optimize the process. The MDCs are emerged as a self-energy driven device for wastewater treatment and seawater desalination at the lab scale. But still MDCs needs further research before it can be implemented at large scale. Acknowledgements: This work was made possible by NPRP grant # 6-289-2-125 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.

In the past decades, microbial fuel cells (MFCs) have been intensively studied in order to provide sustainable and environmentally friendly wastewater treatment concurrent with energy harvesting. A highly porous, highly efficient, light-weight, and inexpensive 3D sponges consisting of interconnected carbon nanotubes (CNTs) were developed as anodes of MFCs in order to allow more efficient microbe-to-anode electron transfer that are key to the operation of MFCs. The MFCs equipped with the 3D CNT sponge anode generates high power densities of 2150 Wm–3 (per anode volume) or 170 Wm–3 (per anode chamber volume), comparable to those of commercial 3D carbon felt electrodes under the same conditions (1). The high performances are due to excellent charge transfer between CNTs and microbes, which is evident by the 13 times lower charge transfer resistance compared to that of carbon felt. The 3D CNT sponges produced here has low cost (∼$0.1/gCNT) and high production rate (3.6 g/hr) compared to typical production rate of 0.02 g/hr of other CNT-based materials (1). The high production rate and low cost of this highly efficient electrode material can make MFCs more feasible to be scaled up for various applications such as desalination of seawater or saline water. Also, other electrode materials were compared to the 3D CNT sponge in evaluating the efficiency of the MFC and extending the use of these electrode materials to a field of microbial desalination cell (MDC).Once MDCs are applied to the desalination process, there are several challenges that need to be addressed. First, a pH gradient forms between anode and cathode chambers (due to proton accumulation in the anode chamber and hydroxyl ion accumulation in the cathode chamber). In addition, chloride ion accumulation inhibits the activities of electrochemically active microbes. Together these activities degrade the overall performance of the system. Recirculation of the anolyte and catholyte provides one solution to addressing this challenge. However, this approach results in lower Coulombic efficiency. Here, we studied to develop a modified three-chamber configuration where part of the anode chamber and part of the cathode chamber are directly connected through a cation exchange membrane, thus partially allowing transport of protons between the chambers, and thereby limiting the drop in pH, while still maintaining charge differences that drive Cl– and Na+ ions to move from seawater to the anode and cathode chambers. Practical MDCs require continuous or batch-mode feeding of wastewater into the anode chambers of the system, thus accumulated chloride ions will be simply flushed out or diluted due to the influx of new wastewater or catholyte. This aspect will mitigate the impacts of the chlorine ion accumulation problem. Also, a pivotal performance limitation centers on the cathode catalyst layer owing to sluggish kinetics of the oxygen reduction reaction and several transport losses. On the cathode side, expensive precious metal catalysts have been used in conventional systems to overcome the slow reactions on the electrode. Platinum and Pt-based electrocatalysts, commonly used in the electrodes, not only contribute to high fuel cell cost but also lead to durability concerns in terms of Pt cathode oxidation, catalyst migration, loss of electrode active surface area, and corrosion of the carbon support. So, this study used Pt-free 3D carbon-based cathode for MDC system.Reference[1] Celal Erbay, Gang Yang, Paul de Figueiredo, Reza Dadr, Choongho Yu, Arum Han, “Three-dimensional porous carbon nanotube sponges for high-performance anodes of microbial fuel cells”, Journal of Power Sources, (2015), 177–183.

Utilization of coconut shell carbon in the anode compartment of microbial desalination cell (MDC) for enhanced desalination and bio-electricity production

Bioelectricity production in photosynthetic microbial desalination cells under different flow configurations

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 2.06W/m3 with open circuit voltage (OCV) of 0.942V was produced in 42days. When initial NaCl concentration was 2g/L, the desalinization rate was about 15.5mg/(L·h) in the first 24h, 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).

Microbial desalination cells (MDCs) are bioelectrochemical systems using electroactive bacteria to generate energy simultaneously cleaning wastewater and desalinating water. This sustainable technology addresses pollution issues and water shortage using an environmentally friendly solution that aids in desalination as well as wastewater treatment. This research focuses on the effectiveness of microbial desalination cells (MDCs) in concurrently treating wastewater and removing salt from water. The study seeks to determine whether MDCs offer a viable, environmentally friendly method for purifying water while generating energy. The MDC setup incorporated three distinct chambers: anode, desalination, and cathode. Wastewater samples were placed in the anode and cathode compartments, while the desalination chamber contained saline water. A digital multimeter was employed to regularly monitor and log the generated voltages. The microbial community was examined through 16S rRNA gene sequencing techniques. Organic matter elimination was quantified by measuring total organic carbon (TOC) levels. The MDC operated for 30 days continuously. The microbial desalination cell (MDC) produced bioelectricity, effectively desalinated water, and broke down organic molecules during its 30-day running. This suggests that since the voltage generation peaked at 638 mV and then stabilized at 460 mV, the electrochemical activity has been constant. From 46.2 mS/cm to 10.1 mS/cm, the desalination chamber's electrical conductivity (EC) fell drastically, clearly removing the ions. A decline in sodium chloride (NaCl) concentration-from 29 mg/L to 7 mg/L-also proved a sign of effective desalination. Better organic degradation was shown by the cathode chamber reaching 99.9% while the anode chamber attained a total organic carbon (TOC) removal rate of 97.2%. Desalination mostly depends on selective ion exchange across cation and anion membranes; microbial biofilm adaptation helped in the slow development of voltage. These findings suggest that since they efficiently mix the processes of wastewater treatment, desalination, and power generation, MDCs are a reasonably sustainable technology. The Microbial Desalination Cell (MDC) effectively desalinated water and treated wastewater having a peak voltage of 638 mV and a drop in NaCl concentration from 29 mg/L to 7 mg/L. With TOC removal in the anode at 97.2% and the cathode at 99.9%, the system proved excellent in both desalination and organic matter degradation. Furthermore, found to be unique from NCBI-recognized species was the microbiome found in Iraqi municipal effluent. Microbial Desalination Cells (MDCs) have many advantages over conventional desalination techniques like reverse osmosis, including being able to cleanse wastewater and simultaneously generate renewable electricity with far reduced energy usage. Constant challenges are improving ion exchange efficiency, honing interactions between microbial communities, and increasing technological scale. Improving MDC performance and incorporating it into whole energy and water management systems is the main emphasis of research nowadays. This could be a perfect choice for encouraging more environmentally friendly energy sources and lessening the consequences of world water shortage.

Chapter 5 - Microbial desalination cell based wastewater treatment and resource recovery: Various challenges

Microbial Desalination Cell (MDC) represents an innovative technology which accomplishes simultaneous desalination and wastewater treatment without external energy input. MDC technology could be employed to provide freshwater with low-energy input, for example, in remote areas where organic wastes (i.e. urban or industrial) are available. In addition, MDC technology has been proposed as pre-treatment in conventional reverse osmosis plants, with the aim of saving energy and avoiding greenhouse gases related to conventional desalination processes. The use of oxygen reduction (i.e. O2 + 2H2O +4e-  4 OH-, E0’ = 0.815 V, pH=7) was usually implemented as cathodic reaction in most of the MDCs reported in literature, whereas other strategies based on liquid catholytes have been also proposed, for example, ferro-ferricyanide redox couple (i.e. Fe(CN)63- + 1e-  Fe(CN)64-, E0 = 0.37 V). As the MDC designs in the literature and operation modes (i.e. batch, continuous, semi-continuous, etc.) are quite different, the available MDC studies are not directly comparable. For this reason, the main objective of this work was to have a proper comparison of two similar MDCs operating with two different catholyte strategies, and compare performance and desalination efficiencies. In this sense, this study compares the desalination performance of two laboratory-scale MDCs located in two different locations for brackish water and sea water using two different strategies. The first strategy consisted of an air cathode for efficient oxygen reduction, while the second strategy was based on a liquid catholyte with Fe3+/Fe2+ solution (i.e. ferro-ferricyanide complex). Both strategies achieved desalination efficiency above 90% for brackish water. Nominal desalination rates (NDR) were in the range of 0.17-0.14 L·m-2·h-1 for brackish and seawater with air diffusion cathode MDC, respectively, and 1.5-0.7 L·m-2·h-1 when using ferro-ferricyanide redox MDC. Organic matter present in wastewater was effectively removed at 0.9 and 1.1 kg COD·m-3·day-1 using the air diffusion cathode MDC for brackish and sea water, respectively, and 7.1 and 19.7 kg COD·m-3·day-1 with a ferro-ferricyanide redox MDC. Both approaches used a laboratory MDC prototype without any energy supply (excluding pumping energy). Pros and cons of both strategies are discussed for subsequent upscaling of MDC technology.

Life cycle assessment of a microbial desalination cell for sustainable wastewater treatment and saline water desalination

Ionic composition and transport mechanisms in microbial desalination cells