Current water desalination techniques are energy intensive and some use membranes operated at high pressures. It is shown here that water desalination can be accomplished without electrical energy input or high water pressure by using a source of organic matter as the fuel to desalinate water. A microbial fuel cell was modified by placing two membranes between the anode and cathode, creating a middle chamber for water desalination between the membranes. An anion exchange membrane was placed adjacent to the anode, and a cation exchange membrane was positioned next to the cathode. When current was produced by bacteria on the anode, ionic species in the middle chamber were transferred into the two electrode chambers, desalinating the water in the middle chamber. Proof-of-concept experiments for this approach, using what we call a microbial desalination cell (MDC), was demonstrated using water at different initial salt concentrations (5, 20, and 35 g/L) with acetate used as the substrate for the bacteria. The MDC produced a maximum of 2 W/m2 (31 W/m3) while at the same time removing about 90% of the salt in a single desalination cycle. As the salt was removed from the middle chamber the ohmic resistance of the MDC (measured using electrochemical impedance spectroscopy) increased from 25 Omega to 970 Omega at the end of the cycle. This increased resistance was reflected by a continuous decrease in the voltage produced over the cycle. These results demonstrate for the first time the possibility for a new method for water desalination and power production that uses only a source of biodegradable organic matter and bacteria.

Two challenges for improving the performance of air cathode, single-chamber microbial fuel cells (MFCs) include increasing Coulombic efficiency (CE) and decreasing internal resistance. Nonbiodegradable glass fiber separators between the two electrodes were shown to increase power and CE, compared to cloth separators (J-cloth) that were degraded over time. MFC tests were conducted using glass fiber mats with thicknesses of 1.0 mm (GF1) or 0.4 mm (GF0.4), a cation exchange membrane (CEM), and a J-cloth (JC), using reactors with different configurations. Higher power densities were obtained with either GF1 (46 +/- 4 W/m(3)) or JC (46 +/- 1 W/m(3)) in MFCs with a 2 cm electrode spacing, when the separator was placed against the cathode (S-configuration), rather than MFCs with GF0.4 (36 +/- 1 W/m(3)) or CEM (14 +/- 1 W/m(3)). Power was increased to 70 +/- 2 W/m(3) by placing the electrodes on either side of the GF1 separator (single separator electrode assembly, SSEA) and further to 150 +/- 6 W/m(3) using two sets of electrodes spaced 2 cm apart (double separator electrode assembly, DSEA). Reducing the DSEA electrode spacing to 0.3 cm increased power to 696 +/- 26 W/m(3) as a result of a decrease in the ohmic resistance from 5.9 to 2.2 Omega. The main advantages of a GF1 separator compared to JC were an improvement in the CE from 40% to 81% (S-configuration), compared to only 20-40% for JC under similar conditions, and the fact that GF1 was not biodegradable. The high CE for the GF1 separator was attributed to a low oxygen mass transfer coefficient (k(O) = 5.0 x 10(-5) cm/s). The GF1 and JC materials differed in the amount of biomass that accumulated on the separator and its biodegradability, which affected long-term power production and oxygen transport. These results show that materials and mass transfer properties of separators are important factors for improving power densities, CE, and long-term performance of MFCs.

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Activated carbon (AC) is a useful and environmentally sustainable catalyst for oxygen reduction in air-cathode microbial fuel cells (MFCs), but there is great interest in improving its performance and longevity. To enhance the performance of AC cathodes, carbon black (CB) was added into AC at CB:AC ratios of 0, 2, 5, 10, and 15 wt % to increase electrical conductivity and facilitate electron transfer. AC cathodes were then evaluated in both MFCs and electrochemical cells and compared to reactors with cathodes made with Pt. Maximum power densities of MFCs were increased by 9-16% with CB compared to the plain AC in the first week. The optimal CB:AC ratio was 10% based on both MFC polarization tests and three electrode electrochemical tests. The maximum power density of the 10% CB cathode was initially 1560 ± 40 mW/m(2) and decreased by only 7% after 5 months of operation compared to a 61% decrease for the control (Pt catalyst, 570 ± 30 mW/m(2) after 5 months). The catalytic activities of Pt and AC (plain or with 10% CB) were further examined in rotating disk electrode (RDE) tests that minimized mass transfer limitations. The RDE tests showed that the limiting current of the AC with 10% CB was improved by up to 21% primarily due to a decrease in charge transfer resistance (25%). These results show that blending CB in AC is a simple and effective strategy to enhance AC cathode performance in MFCs and that further improvement in performance could be obtained by reducing mass transfer limitations.

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Separators are needed in microbial fuel cells (MFCs) to reduce electrode spacing and preventing electrode short circuiting. The use of nylon and glass fiber filter separators in single-chamber, aircathode MFCs was examined for their effect on performance. Larger pore nylon mesh were used that had regular mesh weaves with pores ranging from 10 to 160 mm, while smaller pore-size nylon filters (0.2-0.45 mm) and glass fiber filters (0.7-2.0 mm) had a more random structure. The pore size of both types of nylon filters had a direct and predictable effect on power production, with power increasing from 443 AE 27 to 650 AE 7 mW m À2 for pore sizes of 0.2 and 0.45 mm, and from 769 AE 65 to 941 AE 47 mW m À2 for 10 to 160 mm. In contrast, changes in pore sizes of the glass fiber filters resulted in a relatively narrow change in power (732 AE 48 to 779 AE 43 mW m À2 ) for pore sizes of 0.7 to 2 mm. An ideal separator should increase both power density and Coulombic efficiency (CE). However, CEs measured for the different separators were inversely correlated with power production, demonstrating that materials which reduced the oxygen diffusion into the reactor also hindered proton transport to the cathode, reducing power production through increased internal resistance. Our results highlight the need to develop separators that control oxygen transfer and facilitate proton transfer to the cathode.

During catalytic ozonation, Al2O3-supported catalysts usually have stable structures but relatively low surface activity, while carbon-supported catalysts are opposite. To encourage their synergisms, we designed a Ni-induced C-Al2O3-framework (NiCAF) and reinforced it with a Cu–Co bimetal to create an efficient catalyst (CuCo/NiCAF) with a core–multishell structure. The partial graphitization of carbon adjacent to Ni crystals formed a strong out-shell on the catalyst surface. The rate constant for total organic carbon removal of CuCo/NiCAF (0.172 ± 0.018 min–1) was 67% and 310% higher than that of Al2O3-supported catalysts and Al2O3 alone, respectively. The metals on CuCo/NiCAF contributed to surface-mediated reactions during catalytic ozonation, while the embedded carbon enhanced reactions within the solid–liquid boundary layer and in the bulk solution. Moreover, carbon embedment provided a 76% increase in ·OH-production efficiency and an 86% increase in organic-adsorption capacity compared to Al2O3-supported catalysts. During the long-term treatment of coal-gasification wastewater (∼5 m3 day–1), the pilot-scale demonstration of CuCo/NiCAF-catalyzed ozonation revealed a 120% increase in ozone-utilization efficiency (ΔCOD/ΔO3 = 2.12) compared to that of pure ozonation (0.96). These findings highlight catalysts supported on NiCAF as a facile and efficient approach to achieve both high catalytic activity and excellent structural stability, demonstrating that they are highly viable for practical applications.