Multi-population model of a microbial electrolysis cellOrganic matter conversion to hydrogen in a microbial electrolysis cell (MEC) offers a number of advantages in comparison to H 2 production by water electrolysis, which requires a significant energy input, and to fermentative H 2 production, which has a limited yield of not more than 25%.1À3 Intensive MEC research in recent years has led to significant improvements in the volumetric rate of H 2 production, cathode materials, MEC design, and operating conditions, yet the overall performance remains relatively low. 2,4 One solution for the complex problems posed by MEC research is to develop a mathematical model that can describe the dynamics of chemical oxygen demand (COD) consumption and H 2 production in a MEC. This model can then be used to optimize the MEC operational parameters and design, thus facilitating the development of a full-scale MEC-based wastewater treatment process. Although several microbial fuel cell (MFC) models have been developed 5À9 and an anodic compartment model has been recently presented, 10 to our best knowledge a MEC model capable of simulating H 2 production from complex organic matter has not yet been reported. However, MFC models that can describe the competition between electricigenic and methanogenic microorganisms for acetate have already been presented. 5,7,11 The anaerobic degradation process has also been extensively studied and modeled (e.g., 12À14).This work presents a simple dynamic model of a MEC developed with the objective to simulate H 2 production from wastewater for process design, optimization, and control applications. Furthermore, the model application is illustrated by analyzing the influence of the substrate feed rate (organic load) and applied voltage on COD removal and H 2 production.' MATERIALS AND METHODS Analytical Methods. Chemical oxygen demand of synthetic wastewater (sWW) was estimated according to Standard Methods.
15Both total COD (tCOD) and soluble COD (sCOD) values were analyzed. Acetate, propionate, and butyrate were analyzed using a gas chromatograph. The total concentration of volatile fatty acids (VFAs) was calculated with respect to the COD equivalent of each component. Gas production in the MEC anodic and cathodic chambers was measured online using glass U-tube bubble counters interfaced with a data acquisition system. The gas composition was measured using a gas chromatograph. A detailed description of all analytical methods used in the study can be found in Tartakovsky et al.
16MEC Design, Operation, and Characterization. Three membraneless MECs (MEC-1, MEC-2, and MEC-3) with 50-mL anodic and H 2 -collection compartments were constructed from nylon plates. The anodes were made of 5-mm-thick carbon felt measuring 10 cm Â5 cm (SGL Group, Wiesbaden, Germany). Gas diffusion cathodes with a Ni load of 0.2À0.3 mg cm À2 were used in all MECs and prepared as described in Manuel et al. ABSTRACT: This work presents a multi-population dynamic model of a microbial electrolysis cell (MEC). The model ...