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Team:SCAU-China/MFC,MDC-device
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Introduction of MDC
Microbial Desalination Cell (MDC) is a new method of water desalination which is similar to water dialysis but without external energy input. This desalination process is driven by current and potential generated by bacteria in the Microbial Fuel Cell (MFC) (Kim and Logan 2013) (Fig.1)1. The energy in domestic wastewater ranges from 1.8 to 2.1 kWh/m3 and suffices most of energy demand in water desalination (3~4 kWh/m3) using reverse osmosis.
Fig. 1 Schematic diagram for ionic separation in microbial desalination cells, (A) three-chamber design and (B) stacked ion-exchange membrane design with three dilute and concentrate cell pairs.
The MDC consists of anion exchange membranes (AEM) and cation exchange membranes (CEM), a desalination chamber, a two-chamber MFC and a connecting chamber. Because of the depletion of proton in the cathode chamber, cations move from the desalination to cathode chamber. The AEM prevents positive charged ions from leaving the anode chamber so charge is balanced by anions leaving the desalination chamber. As results, the ions in the desalination chamber are removed and the water is desalinated (Mehanna, Saito et al. 2010)2.
The ionic separation is repeated in every cell pair, the desalination effect is magnified by the number of cell pairs in the stack. For example, 100 pairs of sodium and chloride ions are separated for every electron transfer in a 100-cell paired electrodialysis stacks. The internal resistance was so large that the authors concluded that an MDC with more than 1.5 cell pairs (2 diluted and 1 concentrate chambers) would not be more efficient. A new developed electrodialysis stack make it possible to substantially increase the extent and efficiency of desalination, and allow high power densities through the minimization of Ohmic resistances in the stacks (Figs.2, 3)3.(Kim and Logan 2011)
◇The connecting chamber consists of a 90º turn for water influx and efflux and a same size lumen as electrode chamber.
◇Intermembrane distance (or cell width) was held constant by a piece of polyethylene mesh (10 × 10 cm2) 1.3 mm thick, with each cell having a rectangular cross section (4 × 2 cm2) (Figs. 2, 3). The dilute solution was introduced from the cathode side and flowed serially through every dilute cell 4(Hatzell and Logan 2013).
◇Anode is a non-waterproof carbon cloth with an active area of 28 cm2 (3 cm in diameter).
◇Cathode is a platinum (0.5 mg 60% Pt/C on the water side) coated carbon cloth with 5 diffusion layers (on the air side).
◇The dilute and concentrated water are introduced from the connecting chamber. The synthetic seawateand diluted water is controlled in fix flow rate (1 mL/min).
Kim, Y. and B. E. Logan (2011). Series Assembly of Microbial Desalination Cells Containing Stacked Electrodialysis Cells for Partial or Complete Seawater Desalination. Environmental Science & Technology 45 (13): 5840-5845.
Kim, Y. and B. E. Logan (2013). Microbial desalination cells for energy production and desalination. Desalination 308 (0): 122-130.
Mehanna, M., T. Saito, J. Yan, M. Hickner, X. Cao, X. Huang and B. E. Logan (2010). Using microbial desalination cells to reduce water salinity prior to reverse osmosis. Energy & Environmental Science 3 (8): 1114-1120.
Fig. 1 Schematic diagram for ionic separation in microbial desalination cells, (A) three-chamber design and (B) stacked ion-exchange membrane design with three dilute and concentrate cell pairs.
The ionic separation is repeated in every cell pair, the desalination effect is magnified by the number of cell pairs in the stack. For example, 100 pairs of sodium and chloride ions are separated for every electron transfer in a 100-cell paired electrodialysis stacks. The internal resistance was so large that the authors concluded that an MDC with more than 1.5 cell pairs (2 diluted and 1 concentrate chambers) would not be more efficient. A new developed electrodialysis stack make it possible to substantially increase the extent and efficiency of desalination, and allow high power densities through the minimization of Ohmic resistances in the stacks (Figs.2, 3)3.(Kim and Logan 2011)
(a) |
(b) |
(c)
Fig. 2 (a) Schematic design for the novel electrodialysis stack, (b) The configuration of the thin gasket, (c) A 4 cell-pair MDC in our project. |
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(a) |
(b) |
| Fig3. Construction of the gaskets used to direct the flow. | |
MDC construction
◇The cathode (170 mL) and anode (170 mL) chambers were cylindrical with a cross-sectional area of 28 cm2.◇The connecting chamber consists of a 90º turn for water influx and efflux and a same size lumen as electrode chamber.
◇Intermembrane distance (or cell width) was held constant by a piece of polyethylene mesh (10 × 10 cm2) 1.3 mm thick, with each cell having a rectangular cross section (4 × 2 cm2) (Figs. 2, 3). The dilute solution was introduced from the cathode side and flowed serially through every dilute cell 4(Hatzell and Logan 2013).
◇Anode is a non-waterproof carbon cloth with an active area of 28 cm2 (3 cm in diameter).
◇Cathode is a platinum (0.5 mg 60% Pt/C on the water side) coated carbon cloth with 5 diffusion layers (on the air side).
◇The dilute and concentrated water are introduced from the connecting chamber. The synthetic seawateand diluted water is controlled in fix flow rate (1 mL/min).
References
Hatzell, M. C. and B. E. Logan (2013). Evaluation of flow fields on bubble removal and system performance in an ammonium bicarbonate reverse electrodialysis stack. Journal of Membrane Science 446 (0): 449-455.Kim, Y. and B. E. Logan (2011). Series Assembly of Microbial Desalination Cells Containing Stacked Electrodialysis Cells for Partial or Complete Seawater Desalination. Environmental Science & Technology 45 (13): 5840-5845.
Kim, Y. and B. E. Logan (2013). Microbial desalination cells for energy production and desalination. Desalination 308 (0): 122-130.
Mehanna, M., T. Saito, J. Yan, M. Hickner, X. Cao, X. Huang and B. E. Logan (2010). Using microbial desalination cells to reduce water salinity prior to reverse osmosis. Energy & Environmental Science 3 (8): 1114-1120.
