用醋酸盐和丁酸盐进行产电的单室微生物燃料电池(英文).pdf

Production of Electricity from Acetate or Butyrate Using a Single-Chamber Microbial Fuel CellH O N GL I U ,†S H A O A NC H E N G ,†A N D B R U C EE .L O G A N *, † , ‡Department of Civil and Environmental Engineering, and The Penn State Hydrogen Energy (H2E) Center, The Pennsylvania State University, University Park, Pennsylvania 16802Hydrogen can be recovered by fermentation of organic material rich in carbohydrates, but much of the organic matter remains in the form of acetate and butyrate. An alternative to methane production from this organic matter is the direct generation of electricity in a microbial fuel cell (MFC). Electricity generation using a single-chambered MFC was examined using acetate or butyrate. Power generated with acetate (800 mg/L) (506 mW/m2or 12.7 mW/ L) was up to 66% higher than that fed with butyrate (1000 mg/L) (305 mW/m2or 7.6 mW/L), demonstrating that acetate is a preferred aqueous substrate for electricity generation in MFCs. Power output as a function of substrate concentration was well described by saturation kinetics, although maximum power densities varied with the circuit load. Maximum power densities and half-saturation constants werePmax) 661 mW/m2andKs) 141 mg/L for acetate (218 Ω) andPmax) 349 mW/m2andKs) 93 mg/L for butyrate (1000 Ω). Similar open circuit potentials were obtained in using acetate (798 mV) or butyrate (795 mV). Current densities measured for stable power outputwerehigherforacetate(2.2A/m2)thanthosemeasured in MFCs using butyrate (0.77 A/m2). Cyclic voltammograms suggested that the main mechanism of power production in these batch tests was by direct transfer of electrons to the electrode by bacteria growing on the electrode and not by bacteria-produced mediators. Coulombic efficiencies and overall energy recovery were 10-31 and 3-7% for acetate and 8-15 and 2-5% for butyrate, indicating substantial electron and energy losses to processes other than electricity generation. These results demonstrate thatelectricitygenerationispossiblefromsolublefermentation end products such as acetate and butyrate, but energy recoveriesshouldbeincreasedtoimprovetheoverallprocess performance.IntroductionHarvesting products from wastewater in order to make the processmoreeconomicalandsustainableisthenextfrontier in wastewater treatment (1, 2). Hydrogen production from wastewater by biological fermentation has drawn much attentionasamethodofproducingavaluableproductduring treatmentofwastewaterscontaininghighconcentrationsofcarbohydrates (3-7). One mole of glucose can theoretically be converted into 12 mol of hydrogen, but the maximum yieldviaknownfermentationroutesisonly4molofhydrogen when acetate is the sole byproduct. While the maximum efficiencyofhydrogenproductionistherefore33%,typically only 15% of the energy is recovered as hydrogen (2, 8) with the remainder of the organic matter present as fatty acids and alcohols. To improve the economics of hydrogen production from wastewater,additionalprocessesareneededtorecoverythe remaining energy. One approach is to link hydrogen pro- duction with methane production by using a two-stage process (2). Although two-stage anaerobic treatments have been used to make methane, it has not yet been proven outside of the laboratory that hydrogen can be recovered at high concentrations from the first stage using actual waste- waters. A second approach is to use phototrophic bacteria to recover additional hydrogen from the byproducts of hydrogenfermentation(9,10).Althoughsolarenergyisfree, the availability of sufficient land area and the instability of sufficientsolarenergyattheplantwouldmakesuchaprocess difficult for wastewater treatment applications. A third approach is to recover the remaining energy directly as electricity in a microbial fuel cell (MFC). While electricity productionhasbeenshowninMFCsusingglucoseoracetate, much remains to be done in order to use this technology for wastewater treatment. Bacteriapresentinwastewater,anaerobicreactorsludges, andmarinesedimentshavebeenshowntoproduceelectricity in a MFC (11-14). Bacteria that have been identified to be capable of making electricity in fuel cells, most of which are metal-reducing bacteria, include Geobacter sulfurreducens (15, 16), Geobacter metallireducens (13, 16), Shewanella putrefaciens(17,18),Clostridiumbutyricum(19),Rhodoferax ferrireducens(20),andAeromonashydrophila(15).Ithasalso been recently shown that electricity generation in an MFC resulted in large part from the production of mediators, or electron shuttles, by a microbial community consisting of primarily three bacteria: Alcaligenes faecalis, Enterococcus faecium, and Pseudomonas aeruginosa (12). Many MFCs contain two chambers (16-18, 20). One chambercontainselectrochemicallyactivebacteriagrowing under anaerobic conditions that grow as a biofilm attached to the anode. The other chamber is kept aerobic by sparging water with air and contains the cathode. The two chambers are typically separated by a proton excha。