Microbial Desalination Cell Research Articles

Effect of initial salt concentrations on cell performance and distribution of internal resistance in microbial desalination cells

Microbial desalination cells (MDCs) are modified microbial fuel cells (MFCs) that concurrently produce electricity and desalinate seawater, but adding a desalination compartment and an ion-exchange membrane may increase the internal resistance (Ri), which can limit the cell performance. However, the effects of a desalination chamber and initial NaCl concentrations on the internal resistances and the cell performances (i.e. Coulombic efficiency (CE), current and power density) of MDCs have yet to be thoroughly explored; thus, the cell performance and Ri distributions of MDCs having different initial concentrations and an MFC having no desalination chamber were compared. In the MDCs, the current and power density generation increased from 2.82 mA and 158.2 mW/m2 to 3.17 mA and 204.5 mW/m2 when the initial NaCl concentrations were increased from 5 to 30 g/L, as a consequence of the internal resistances decreasing from 2432.0 to 2328.4 Ω. And even though the MFC has a lower Ri than the MDCs, lower cell performances (current: 2.59 mA; power density: 141.6 mW/m2 and CE: 62.1%) were observed; there was no effect of improved junction potential in the MFC. Thus, in the MDCs, the higher internal resistances due to the addition of a desalination compartment can be offset by reducing the electrolyte resistance and improving the junction potential at higher NaCl concentrations.

Improving desalination by coupling membrane capacitive deionization with microbial desalination cell

One main obstacle for the development of microbial desalination cell (MDC) is that desalination rate decreases fast when salt concentration in the cell becomes low. To cover this shortage while using less energy to fulfill complete desalination, membrane capacitive deionization (MCDI) was used in this research as the downstream desalination process to further desalinate 1g/L salt water. Single MDC, two MDCs in series and in parallel were used as the power supply to drive the MCDI, and the parallel-configuration system gave the best ECA of 264.8μmol/g, which was a 59% increase compared to that of driven by the potentiostat with the same operational voltage. The desalination rate of the MCDI was as high as 3.7mg/h in one working cycle. MCDI proved to be an effective technology to combine with MDC for complete salt removal.

Microbial Desalination Cell (MDC) in the Presence of Activated Carbon

This report studies the performance of a Microbial Desalination Cell (MDC) in the presence of activated carbon in both the cathode and anode chambers. The large surface area of the activated carbon provides surface for bacterial growth, thereby leading to the formation of a stronger microbial culture through the formation of a biofilm. An MDC of 60 ml total capacity is used to achieve 60 percent desalination within 20 hours. In addition, a maximum mean voltage of 105 mV and a power density of 1.546 mW/m 2 are obtained when a 3.2-k resistor was used. The results of our experiments suggest that the addition of activated carbon to the anodic and cathodic chambers improves MDC performance. This technology has the potential to be used to integrate a waste water treatment plant and a desalination facility.

Effects of salinity anions on the anode performance in bioelectrochemical systems

To study the feasibility to utilize the microbial desalination cell (MDC) to desalinate complex saltwater, the objective of this study was to investigate the effects of different salinity anions on anode performance. Experiments were conducted using three different salinity anions (Cl−, SO42−, and HCO3−) with different concentrations in the anode of two-chamber microbial fuel cell (MFC). Results showed that the supplement of anions, with concentration ranges of 25–50mM for Cl−, 25mM for SO42−, and 25–100mM for HCO3−, into the substrate increased the voltage output of the MFC. With the HCO3− concentrations from 0 to 100mM, the coulombic efficiencies increased from 29% to 44%, and the power densities increased from 465 to 1064mW/m2. At the same conductivity, the electron production in the MFC with the anions was in the order: HCO3−>Cl−>SO42−. The presence of HCO3− enhanced the buffer capacity of the anolyte and maintained the activity of the anode biofilm, in which the dominant species included Geobacter uraniireducens, Desulfofaba fastidiosa, and Mycobacterium fortuitum. This study suggests that the MDC can be used to desalinate complex saltwater to improve wastewater treatment in the anode chamber.

A ten liter stacked microbial desalination cell packed with mixed ion-exchange resins for secondary effluent desalination.

The architecture and performance of microbial desalination cell (MDC) have been significantly improved in the past few years. However, the application of MDC is still limited in a scope of small-scale (milliliter) reactors and high-salinity-water desalination. In this study, a large-scale (>10 L) stacked MDC packed with mixed ion-exchange resins was fabricated and operated in the batch mode with a salt concentration of 0.5 g/L NaCl, a typical level of domestic wastewater. With circulation flow rate of 80 mL/min, the stacked resin-packed MDC (SR-MDC) achieved a desalination efficiency of 95.8% and a final effluent concentration of 0.02 g/L in 12 h, which is comparable with the effluent quality of reverse osmosis in terms of salinity. Moreover, the SR-MDC kept a stable desalination performance (>93%) when concentrate volume decreased from 2.4 to 0.1 L (diluate/concentrate volume ratio increased from 1:1 to 1:0.04), where only 0.875 L of nonfresh water was consumed to desalinate 1 L of saline water. In addition, the SR-MDC achieved a considerable desalination rate (95.4 mg/h), suggesting a promising application for secondary effluent desalination through deriving biochemical electricity from wastewater.

Application Driven Fundamental Research on Microbial Electrochemical Technologies: From Components to System

Microbial electrochemistry is the study and application of interactions between microbial cells and electron conductors (electrodes). For a long time this field of bioelectrochemistry has been the interest of only fundamental researchers. This has significantly changed during the last decade, in which microbial electrochemistry gained increasing interest from applied researchers and engineers. Among other types of potential application, these researchers developed microbial fuel cells (MFCs), microbial electrolysis cells (MECs) and microbial desalination cells (MDCs) – electrochemical systems that utilize the organic load in wastewater to produce electric power, to produce chemical compounds or to desalinate salt water, respectively. However, the great majority of research on full systems is still being performed at laboratory scale (less than 1 L reactor volume) and technical or even pilot scale studies are rare. Rationally the majority of current studies do not focus on the system scale, but on the advancement of components, e.g. electrodes and membranes, and the investigation of fundamental processes of these components, e.g. interactions in microbiomes formed at electrodes, aiming at their subsequent engineering. However, system scale studies have clearly revealed a substantially higher degree of complexity and thus achievements on the component scale often cannot be simply transferred.Therefore, we advocate that the most important issue is wisely merging fundamental research at the component scale with full system development. In this presentation we will illustrate on selected, recent examples the rationale of our appeal, spanning from very fundamental aspects like the development of high-performance electrode materials via the removal of micropollutants from wastewater at laboratory scale to a recent technical scale demonstrator and its performance in cleaning municipal wastewater and nitrogen recovery.

Tetramethylammonium hydroxide production using the microbial electrolysis desalination and chemical-production cell

The aim of this study was to investigate the feasibility of tetramethylammonium hydroxide (TMAH) production using the microbial electrolysis desalination and chemical-production cell (MEDCC). With 1.0 g/L acetate in the anode chamber and tetramethylammonium chloride solutions with different concentrations in the desalination chamber, TMAH could be efficiently produced in the cathode chamber of MEDCC. With an applied voltage of 1.0 V, the concentration of TMAH reached 0.087 M within 17.5 h, with current efficiency of 52–58%. The electrical energy consumed for the TMAH production using the MEDCC was 0.76 kWh/kg, which was only 5–12% of that for the electrolysis and electrodialysis process. With the high value of TMAH produced in a friendly environment with low energy consumption, the MEDCC should be a potentially valuable method for the chemical production in practice.

Enhanced water desalination efficiency in an air-cathode stacked microbial electrodeionization cell (SMEDIC)

A microbial desalination cell was developed that contained a stack of membranes packed with ion exchange resins between the membranes to reduce ohmic resistances and improve performance. This new configuration, called a stacked microbial electro-deionization cell (SMEDIC), was compared to a control reactor (SMDC) lacking the resins. The SMEDIC+S reactors contained both a spacer and 1.4±0.2mL of ion exchange resin (IER) per membrane channel, while the spacer was omitted in the SMEDIC-S reactors and so a larger volume of resin (2.4±0.2mL) was used. The overall extent of desalination using the SMEDIC with a moderate (brackish water) salt concentration (13g/L) was 90–94%, compared to only 60% for the SMDC after 7 fed-batch cycles of the anode. At a higher (seawater) salt concentration of 35g/L, the extent of desalination reached 61–72% (after 10 cycles) for the SMEDIC, compared to 43% for the SMDC. The improved performance was shown to be due to the reduction in ohmic resistances, which were 130Ω (SMEDIC-S) and 180Ω (SMEDIC+S) at the high salt concentration, compared to 210Ω without resin (SMDC). These results show that IERs can improve performance of stacked membranes for both moderate and high initial salt concentrations.

Desalination combined with copper(II) removal in a novel microbial desalination cell

A novel four-chamber microbial desalination cell (FMDC) was proposed to treat synthetic Cu(II)-containing wastewater in the cathode chamber and simultaneously desalinate brine or seawater in the desalination chamber. In this study, two anion exchange membranes (AEMs) and one cation exchange membrane (CEM) were used as separators between the four different function chambers of the FMDC. Below a pH value of 3.0, the maximum current density was 2.0A/m2 with the initial Cu2+ concentration of 800mg/L and an external resistance of 10Ω. The copper removal rate, salt removal rate and total desalination rate, all conducted simultaneously, were 94.1±1.2%, 43.9±0.9% and 5.1±0.6mg/h in a batch-fed cycle, respectively. Scanning electron microscope–energy dispersive spectrometer (SEM–EDS) analysis indicated that the Cu(II) was reduced to Cu2O plus Cu, which deposited on the cathode surface. These results suggested a novel approach to remove and recover Cu(II) from Cu(II)-containing wastewater and to desalinate salt water by using an FMDC reactor.

Biodegradation and bioelectricity generation by Microbial Desalination Cell

This study highlights the application potential of Microbial Desalination Cell in effective bioremediation of dye house effluent by biodecolourisation of industrial dyes. The study showed, for the first time, that the dye house effluent could be used as an organic substrate in MDC, achieving biodecolourisation of effluent along with considerable desalination and power production. Utilization of these wastes in MDC can protect the environment from dye-containing wastewater contamination and the treated water can be reused for other purposes. Two bacterial strains, a novel isolate Bacillus subtilis moh3 and a MTCC strain Aeromonas hydrophila subsp. hydrophila 8049 were used for decolourisation of two model dyes-Malachite Green (C.I.42,000) and Sunset Yellow (C.I.15,985). Decolourisation of dyes by these cultures was studied in batch cultures and optimized the growth conditions. The same cultures when used in Microbial Desalination Cell, achieved complete biodecolourisation along with considerable desalination (62.2 ± 0.4% and 57.6 ± 0.2%) and power production.

Microbial desalination cell for enhanced biodegradation of waste engine oil using a novel bacterial strain Bacillus subtilis moh3

Microbial desalination cell (MDC) is a bioelectrochemical system developed recently from microbial fuel cells (MFCs), for producing green energy from organic wastes along with desalination of saltwater. MDC is proved to be a better performer than MFC in terms of power output and chemical oxygen demand removal, with desalination as an additional feature. This study investigates the application potential of MDC for integrated biodegradation of waste engine oil. This study showed, for the first time, that waste engine oil could be used as an organic substrate in MDC, achieving biodegradation of engine oil along with considerable desalination and power production. Utilization of these wastes in MDC can protect the environment from waste engine oil contamination. Indigenous oil-degrading bacteria were isolated and identified from engine oil contaminated sludge. Degradation of waste engine oil by these novel isolates was studied in batch cultures and optimized the growth conditions. The same cultures when used in MDC, gave enhanced biodegradation (70.1±0.5% ) along with desalination (68.3±0.6% ) and power production (3.1±0.3 mW/m2). Fourier transform-infrared spectroscopy and gas chromatography-mass spectrometry analyses were performed to characterize the degradation metabolites in the anolyte of MDC which clearly indicated the biodegradation of long chain, branched and cyclic hydrocarbons present in waste engine oil.

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

Microbial desalination cells (MDCs) are being developed as a low-energy desalination technology. Most MDCs in the previous studies contained one cell pair (CP, a pair of cation and anion exchange membranes) and very few had multiple CPs (<5). The effect of the number of CPs on the MDC performance has not been well understood. Herein we examined the current generation, desalination, and water recovery in a bench-scale MDC containing up to 10CPs, fed with salt water containing either 35 or 5gL−1 NaCl. It was found that current generation decreased with more CPs, while the charge transfer efficiency increased; the highest value of 450% was achieved with 10CPs when treating 35gL−1, which also yielded the highest salt removal rate of 90.8±8.3mgh−1. Applying an external voltage of 0.8V greatly increased current generation and salt removal rate, and decreased the desalination time from 12 to 4h. Water loss tended to be more serious and water recovery became lower with more CPs and/or lower salinity of the salt water. The results suggest that both desalination performance and water recovery should be evaluated when developing the MDC technology.

Microbial electrolysis desalination and chemical-production cell for CO2 sequestration

Mineral carbonation can be used for CO2 sequestration, but the reaction rate is slow. In order to accelerate mineral carbonation, acid generated in a microbial electrolysis desalination and chemical-production cell (MEDCC) was examined to dissolve natural minerals rich in magnesium/calcium silicates (serpentine), and the alkali generated by the same process was used to absorb CO2 and precipitate magnesium/calcium carbonates. The concentrations of Mg(2+) and Ca(2+) dissolved from serpentine increased 20 and 145 times by using the acid solution. Under optimal conditions, 24 mg of CO2 was absorbed into the alkaline solution and 13 mg of CO2 was precipitated as magnesium/calcium carbonates over a fed-batch cycle (24h). Additionally, the MEDCC removed 94% of the COD (initially 822 mg/L) and achieved 22% desalination (initially 35 g/L NaCl). These results demonstrate the viability of this process for effective CO2 sequestration using renewable organic matter and natural minerals.

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

Two microbial desalination cells (MDCs), MDC-1 having anion exchange membrane (AEM) near anode and cation exchange membrane (CEM) near cathode and MDC-2 having CEM near anode and AEM near cathode were used for removal of total dissolved solids (TDS) and chemical oxygen demand (COD) from wastewater. Performance of MDCs was evaluated at different catholyte pH (8.0 and 3.0) using 0.2 g/L of KMnO4 as catholyte under dissolved salt concentrations of 8, 20, and 30 g/L in the middle chamber. Maximum Coulombic efficiency in MDC-1 (15%) and MDC-2 (11%) was observed at acidic catholyte pH. Highest TDS removal was obtained in MDC-1 (50%) having AEM near anode at higher salt concentration in middle chamber and acidic catholyte pH. Slightly lesser TDS removal was observed with alkaline catholyte pH. However, COD removal was more in MDC-2 (91%), where CEM was placed near anode.

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.

The near-future integration of microbial desalination cells with reverse osmosis technology

The combined negative effect of both fresh water shortage and energy depletion has encouraged the research to move forward to explore effective solutions for water desalination with less energy consumption.

Comparison of the removal of monovalent and divalent cations in the microbial desalination cell

Microbial desalination cell (MDC) is a promising technology to desalinate water and generate electrical power simultaneously. The objectives of this study were to investigate the desalination performance of monovalent and divalent cations in the MDC, and discuss the effect of ion characteristics, ion concentrations, and electrical characteristics. Mixed salt solutions of NaCl, MgCl2, KCl, and CaCl2 with the same concentration were used in the desalination chamber to study removal of cations. Results showed that in the mixed salt solutions, the electrodialysis desalination rates of cations were: Ca2+ >Mg2+>Na+>K+. Higher ionic charges and smaller hydrated ionic radii resulted in higher desalination rates of the cations, in which the ionic charge was more important than the hydrated ionic radius. Mixed solutions of NaCl and MgCl2 with different concentrations were used in the desalination chamber to study the effect of ion concentrations. Results showed that when ion concentrations of Na+ were one-fifth to five times of Mg2+, ion concentration influenced the dialysis more profoundly than electrodialysis. With the current densities below a certain value, charge transfer efficiencies became very low and the dialysis was the main process responsible for the desalination. And the phosphate transfer from the anode chamber and potassium transfer from the cathode chamber could balance 1%–3% of the charge transfer in the MDC.

Microbial Desalination Cell Combined with Capacitive Deionization/Membrane Capacitive Deionization to Desalinate Seawater

Microbial desalination cell (MDC) was considered inefficient to desalinate salt water with low salt concentration, therefore, the feasibility of using capacitive deionization (CDI) and membrane capacitive deionization (MCDI) as a post-processing technologies for MDC was investigated in this study, as well as the possibility of using MDC as the power supply for CDI and MCDI. The internal resistances of MDC with different salt concentration, the desalination rate and fresh water yield during a typical desalination cycle under initial salt concentration of 35 g/L were investigated in order to find out the deadline salt concentration for the MDC to desalinate effectively. The internal resistance increased from 21.7 to 602 Ω as the concentration of salt water decreased from 35 g/L to 0.1g/L. The salt water volume increased from 42 to 48 ml when the salt concentration decreased from 35 to 15 g/L, then decreased to 38 ml at the end of one desalination cycle when the salt concentration achieved 0.05 g/L due to the salt gradient (osmotic pressure). The maximum desalination rate during one typical desalination cycle in our experiment reached 5.65 mg/h when salt concentration decreased from 27.26 to 26.32 g/L, while the minimum desalination rate was 0.534 mg/h when salt concentration decreased from 0.38 to 0.05 g/L. It was concluded that MDC was not suitable to desalinate salt water with salt concentration less than 1 g/L. When CDI and MCDI were used as the post-processing technologies for MDC, a better performance in term of electrosorption capacity was obtained from MCDI with an influent salt concentration of 1 g/L. The experimental result also showed that the electrosorption capacity of MCDI with MDC as power supply was more than that with potentiostat as power supply at 0.8V, this suggests that MDC could be an alternative power supply for MCDI.

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.

Long-term investigation of fouling of cation and anion exchange membranes in microbial desalination cells

The fouling of ion exchange membranes in microbial desalination cells (MDCs) was investigated through an eight-month operation. Multiple MDCs were set up by using cation (CEM), anion (AEM), and/or proton (Nafion) membranes. The MDCs exhibited relatively constant reduction of conductivity of artificial seawater during the testing period (46.3±6.3% in the CEM-MDC and 78.7±0.8% in the Nafion-MDC in an operating cycle). However, the current generation decreased from 99 to 56A/m3 in the CEM-MDC after 250days, and from 97 to 46A/m3 in the Nafion-MDC after 130days, indicating the presence of membrane fouling. Theoretically the MDCs removed 6.7–12.1kgTDS/m3/d with a high charge transfer efficiency of 230–440%, suggesting that electric current was not the only factor to drive desalination; water dilution played an important role in conductivity reduction as well. It was observed that the AEM contained significant biofouling, resulting from wastewater and microbial growth on organic compounds migrating across the membrane, while the CEM had substantial inorganic scaling, mainly consisting of calcium and magnesium. The membrane resistance of the CEM increased more significantly than that of the AEM, indicating that CEM needs more maintenance during MDC operation.