A New Method for Water Desalination Using Microbial Desalination Cells

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

Organic matter and dissolved salts removal in a microbial desalination cell with different orientation of ion exchange membranes

MICROBIAL DESALINATION CELL: A SUSTAINABLE APPROACH FOR BRACKISH WATER DESALINATION AND WASTEWATER TREATMENT WITH BIOELECTRICITY GENERATION Surajbhan Sevda1, Zhen He2, Ibrahim M. Abu-Reesh*1 1Department of Chemical Engineering, College of Engineering, Qatar University P.O. Box 2713, Doha, Qatar 2Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA *Corresponding author: abureesh@qu.edu.qa Abstract The shortage of the fresh water has become a more and more serious issue because of the rapid increase in human population and resource consumption. Although water is an abundant natural resource available in the earth, only 3% of the water is potable and the other 97 % (seawater) is not potable. To meet the demand for fresh water, desalination processes are used for removing salt from seawater. The major limitation with current desalination processes (membrane or thermal) is the high energy requirement. Therefore, new technologies are required to reduce energy consumption by desalination. Among the new developments, microbial desalination cell (MDC) has a great potential as a low-energy desalination process with significant benefits such as simultaneous wastewater treatment. MDC is a new technology in which salt water can be desalinated without using any external energy source (except that for pumping water). The exoelectrogenic-bacteria in the anode of an MDC oxidize biodegradable substrate in wastewater and transfer the electrons to the anode electrode. Those electrons flow through an external circuit to the cathode electrode where they are used to reduce external electron acceptors such as oxygen. Unlike microbial fuel cell (MFC) from which an MDC is derived, an MDC contains a middle chamber between the anodic and cathodic chambers formed by a pair of anion exchange membrane and cation exchange membranes. This middle chamber works as a desalination chamber like that in an electrodialysis (ED). The potential difference between the anode and cathode electrodes drives the migration of ions out of the desalination chamber, with cations (Na+) migrating to the cathodic chamber and anion (Cl-) moves to the anodic chamber. As a result, salts are removed from the saltwater. MDC technology could be attractive in Qatar and the region because of strong demand for cost effective desalination technologies for desalination of seawater through linking to conventional desalination process, or of brackish water. This paper will introduce the fundamentals and future prospects of MDC technology.

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

Due to unstainable use of natural water resources, alternative water resources such as brackish water and seawater desalination have been an emerging solution. However, development of desalination capacity is limited due to the high energy requirements for removing salt ions from water. Currently, capacitive deionization technology (CDI), following the working principle of supercapacitors, has attracted considerable attention from academia, industry, and government agency. As compared to conventional desalination technologies, CDI has several advantages including low energy consumption, easy regeneration, high water recovery, and no secondary waste. In CDI, by applying an external electric filed between two parallel of nanoporous carbon electrodes (i.e., carbon aerogel, activated carbons, carbon nanotubes, and graphene), ions can be stored at the electrode/solution interface via electrical double layer (EDL) formation. Additionally, microbial desalination cell (MDC) is a new bioelectrochemical technology for seawater desalination with simultaneous electricity generation and wastewater treatment. Basically, a MDC reactor contains an anode chamber, a desalination chamber, and a cathode chamber. In MDC, microorganisms can oxidize organic waters in wastewater to harvest electric energy, and meanwhile, salt ions can be removed during the electricity generating process. In this study, we propose a hybrid electrochemical desalination system for seawater desalination by coupling CDI device with a MDC reactor. As a result, MDC produced electricity with open circuit voltage of 0.8 V and a current of 3 mA by using bacteria to degrade organic contaminants through anode bacterial oxidation and cathode reduction. In MDC, 91% removal of chemical oxygen demand (COD) in synthetic wastewater can be achieved, and the solution conductivity can be reduced from 17,000 µS/cm to about 200 µS/cm. More importantly, CDI device can be driven by electricity harvesting from the two MDCs in parallel, and as the downstream desalination process to further desalinate salt water. The results of this study can demonstrate the feasibility of the integrated electrochemical MDC-CDI system for simultaneous wastewater treatment, power production, and water desalination. .

Effects of number of cell pairs on the performance of microbial desalination cells

Microbial desalination cells (MDCs) use the electrical current generated by microbes to simultaneously treat wastewater, desalinate water, and produce bioenergy. However, current MDC systems transfer salts to the treated wastewater and affect wastewater's beneficial use. A microbial capacitive desalination cell (MCDC) was developed to address the salt migration and pH fluctuation problems facing current MDCs and improve the efficiency of capacitive deionization. The anode and cathode chambers of the MCDC were separated from the middle desalination chamber by two specially designed membrane assemblies, which consisted of cation exchange membranes and layers of activated carbon cloth (ACC). Taking advantage of the potential generated across the microbial anode and the air-cathode, the MCDC was capable of removing 72.7 mg total dissolved solids (TDS) per gram of ACC without using any external energy. The MCDC desalination efficiency was 7 to 25 times higher than traditional capacitive deionization processes. Compared to MDC systems, where the volume of concentrate can be substantial, all of the removed ions in the MCDC were adsorbed in the ACC assembly double layer capacitors without migrating to the anolyte or catholyte, and the electrically adsorbed ions could be recovered during assembly regeneration. The two cation exchange membrane based assemblies allowed the free transfer of protons across the system and thus prevented significant pH changes observed in traditional MDCs.

Desalination of actual wetland saline water associated with biotreatment of real sewage and bioenergy production in microbial desalination cell

Microbial desalination cells (MDCs) have great potential as a cost-effective and green technology for simultaneous water desalination, organic matter removal and energy production. The aim of this study was to compare the performance of a MDC under batch and continuous feeding conditions. Hence, power and current output, coulombic efficiency, electron harvest rate, desalination rate and COD removal were calculated during the operation. According to the obtained results, the MDC performance exhibited some changes when the reactor switched from batch to continuous mode. The continuously operated MDC indicated a maximum power density of 15.9 W.m-3 and an average salt removal rate of 80%. In comparison, the batch MDC demonstrated the maximum power density and average salt removal rate of 13.9 W.m-3 and 68.1%, respectively. In addition, 83.7% of COD was removed in the continuously fed MDC at a hydraulic retention time of two days, which was 13.8% more than amount of COD removed in MDC under a two days batch process. The obtained results revealed that enrichment of anolyte under controlled continuous feeding conditions would relatively improve the MDC performance.

ABSTRACTImproving 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.

The world's largest demonstrator of a revolutionary energy system in desalination for drinking water production is in operation. MIDES uses Microbial Desalination Cells (MDC) in a pre-treatment step for reverse osmosis (RO), for simultaneous saline stream desalination and wastewater treatment. MDCs are based on bio-electro-chemical technology, in which biological wastewater treatment can be coupled to the desalination of a saline stream using ion exchange membranes without external energy input. MDCs simultaneously treat wastewater and perform desalination using the energy contained in the wastewater. In fact, an MDC can produce around 1.8 kWh of bioelectricity from the energy contained in 1 m3 of wastewater. Compared to traditional RO, more than 3 kWh/m3 of electrical energy is saved. With this novel technology, two low-quality water streams (saline stream, wastewater) are transformed into two high-quality streams (desalinated water, treated wastewater) suitable for further uses. An exhaustive scaling-up process was carried out in which all MIDES partners worked together on nanostructured electrodes, antifouling membranes, electrochemical reactor design and optimization, life cycle assessment, microbial electrochemistry and physiology expertise, and process engineering and control. The roadmap of the lab-MDC upscaling goes through the assembly of a pre-pilot MDC, towards the development of the demonstrator of the MDC technology (patented). Nominal desalination rate between 4-11 Lm-2h-1 is reached with a current efficiency of 40 %. After the scalability success, two MDC pilot plants were designed and constructed consisting of one stack of 15 MDC pilot units with a 0.4 m2 electrode area per unit. This book presents the information generated throughout the EU funded MIDES project and includes the latest developments related to desalination of sea water and brackish water by applying microbial desalination cells. ISBN: 9781789062113 (Paperback) ISBN: 9781789062120 (eBook)

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±5mWm−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.

Reduction of organic compounds in petro-chemical industry effluent and desalination using Scenedesmus abundans algal microbial desalination cell

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±7mWm−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.

Sources of organic matter in seagrass-colonized sediments: A stable isotope study of the silt and clay fraction from Posidonia oceanica meadows in the western Mediterranean