A Reduced Model for Microbial Electrolysis Cells

Abstract

Microbial electrolysis cells (MECs) are breakthrough technology of cheap hydrogen production with high efficiency. In this paper differential-algebraic equation (DAE) model of a MEC with an algebraic constraint on current was studied, simulated and validated by implementing the model on continuous-flow MECs. Then sensitivity analysis for the system was effectuated. Parameters which have the predominating influence on the current density and hydrogen production rate were defined. This sensitivity analysis was utilized in modeling and validation of the batch-cycle of MEC. After that parameters which have less influence on MEC were eliminated and simplified reduced model was obtained and validated. Finally, MEC energy productivity was maximized by optimization of operating conditions.

Optimization of Mathematical Modeling of Microbial Electrolysis Cell for the Production of Hydrogen From Sago Wastewater Substrate

“…Replacing the literature value of the substrate concentration in the influent (Si) with the experiment condition, from 2,000 to 476 mg.L -1 resulting to a slightly decreased of the discrepancy of the initial curve with the experimental data (see in Figure 2). These initial values of state variables indicate that the stored energy (i.e., the carbohydrates in the sago effluent) [15, 27,28] is not sufficient for the fermentative bacteria to spontaneously degrade the complex carbon of the substrate into a simple structure, such as acetate [5] as the primary source of free electrons and hydrogen protons due to the significant positive Gibbs free energy of the endothermic reactions [1]. Microbial conversion does not begin until a small external energy greater than the equilibrium electrode potential, identified as ECEF = -0.16 V, is added to the MEC circuit to allow the formation of hydrogen gas at the cathode by reduction and oxidation (redox) [3][4][5].…”

“…The model considered as the allowable range for the oxidation of the organic compounds of the sago wastewater without current losses during electron transfer [16]. At the same time, the energy efficiency decreased exponentially with the increase of the applied potential from 0.1 to 0.8 V, which is the average range required by the MEC to produce the same amount of hydrogen as in water splitting [1], due to the desirable high bioelectrochemical conversion of sago wastewater substrate to hydrogen at a very low external input voltage to the electrode circuit.…”

“…A microbial electrolysis cell (MEC) is an integrated fermentation redox reactor for the production of hydrogen from a variety of organic wastewaters with very low energy input [1][2][3][4][5][6]. However, current performance has not yet reached the point where it can be realized on a large scale [7].…”

“…However, current performance has not yet reached the point where it can be realized on a large scale [7]. The anaerobic environment of the anodic chamber could prevent the MEC from producing oxygen gas and electricity to ensure that hydrogen gas is the final product in the cathodic chamber [1,2,6]. Adopting a dualchamber configuration could effectively minimize the tendency for methane emissions during the microbial reaction [8].…”

“…The use of experimental data is focused on validating the simulation results of the simplified microbial biofilm growth model. The process domains of MEC considered in this study are as follows: (i) a double chamber reactor configuration with a proton exchange membrane as the hydrogen-proton junction; (ii) using as substrate a wastewater sample from a local sago processing mill in Mukah, Sarawak, Malaysia; and (iii) the applied potential (Eapplied) in the range of 0.1 to 0.8 V [1,23,24]. The bioelectrochemical efficiencies such as COD removal efficiency, coulombic efficiency, and energy efficiency [25] were used to evaluate the process limit of the model MEC.…”