수소생산을 위한 생물전기화학반응기의 성능향상방안

Abstract

Microbial electrolysis cells (MECs) are capable of converting the chemical energy of organic waste into hydrogen gas. In MECs, an additional voltage is supplied to the cell and by lowering cathode potential, protons are reduced at the cathode to produce hydrogen gas. In present study, several experiments were performed to investigate lower-cathode cost materials for MECs and to enhance the performance of a scale-up MEC. Firstly, performance of a wire type cathode with a reduced Pt loading was assessed by comparing with a disk type cathode that has 7 times larger surface area than that of the wire type cathode. Secondly, different types of tubular anion exchange membranes (AMI and EDC) were evaluated for developing a scale-up tubular MEC. Thirdly, the optimal anion exchange membrane (EDC) was used to make membrane cathode assembly in a continuous-flow tubular MEC and seawater was evaluated as a catholyte to replace phosphate buffer solution in the cathode chamber. The summarized results of this study are as follows. 1. Although the wire type cathode has 1 cm^(2) surface area with sufficiently low Pt loading (0.02 mg Pt/cm^(2)), the performance of the MECs equipped with the wire type cathodes showed similar or better performances than that of the disk type cathodes (7 cm^(2), 0.5 mg Pt/cm^(2)) at various sodium acetate concentrations in terms of coulombie efficiency (CE), hydrogen production rates (Q), cathodic hydrogen recovery r_(cat)), energy recovery (ηE). The result of Electrochemical Impedance Spectroscopy (EIS) showed that film resistance and polarization resistance of the wire type cathode were lower than those of the disk type cathode because of thiner catalyst layer and high current density. 2. In order to find the optimum membrane cathode assembly in the tubular reactor, the performances of AMI and EDC membranes were evaluated. COD was completely removed in both reactors but MECs with EDC showed better performance in terms of CE, Q, r_(cat), and ηE than MECs with AMI. Also, EIS results showed the internal resistance of EDC was higher than that of AMI. 3. A continuous-flow tubular MEC was operated with the EDC membrane. At initial phase, PBS was used as a catholyte solution and after 3 days of the operation, artificial seawater was supplied to the cathode chamber instead of PBS. Similar performances were achieved in both conditions in terms of current density, COD removal, r_(cat) and and Q but energy efficiency with PBS was 8% higher than that with artificial seawater. When using artificial seawater, calcium and magnesium ions were removed by 59% and 53%, respectively. This shows that bioelectrochemical system can be used as a pretreatment step for seawater desalination to prevent inorganic fouling on reverse osmosis (RO) membrane.