The inactivation of Escherichia coli was investigated with two types of underwater electrical discharge systems such as pulsed electrical discharge (PED) and dielectric barrier discharge (DBD). The DBD system consisted of a quartz tube and a coaxial discharging electrode, which was submerged in biologically contaminated water. In the underwater PED system, the electrical discharge starting from the tip of submerged tubular discharging electrode propagated downward and the direction of working gas injected through the discharging electrode was also downward. The inactivation performances of the underwater electrical discharge systems were comparatively examined with experimental variables including working gas type, the mode of operation, electrical energy and treatment time. With air or oxygen as a working gas, the DBD system showed much better inactivation performance than the PED system, but with nitrogen the PED system was superior, suggesting that these two types of underwater electrical discharge systems are different in dominant inactivation mechanisms. The inactivation by the DBD could be best characterized by the ozonation, and the contribution of the UV irradiation was minor. An operation at lower electric power (the DBD case) or at lower pulse repetition rate (the PED case) consumed less electrical energy for the inactivation, but it required longer inactivation time.
주제어 : 아이소프로필알코올, 아세톤, 플라즈마-촉매, 산화철, 산화구리Abstract : This work investigated the plasma-catalytic decomposition of isopropyl alcohol (IPA) and the behavior of the byproduct compounds over monolith-supported metal oxide catalysts. Iron oxide (Fe2O3) or copper oxide (CuO) was loaded on a monolithic porous α-Al2O3 support, which was placed inside the coaxial electrodes of plasma reactor. The IPA decomposition efficiency itself hardly depended on the presence and type of metal oxides because the rate of plasma-induced decomposition was so fast, but the behavior of byproduct formation was largely affected by them. The concentrations of the unwanted byproducts, including acetone, formaldehyde, acetaldehyde, methane, carbon monoxide, etc., were in order of Fe2O3/α-Al2O3 < CuO/α-Al2O3 < α-Al2O3 from low to high. Under the condition (flow rate: 1 L min -1 ; IPA concentration: 5,000 ppm; O2 content: 10%; discharge power: 47 W), the selectivity towards CO2 was about 40, 80 and 95% for α-Al2O3, CuO/α-Al2O3 and Fe2O3/α-Al2O3, respectively, indicating that Fe2O3/α-Al2O3 is the most effective for plasma-catalytic oxidation of IPA. Unlike plasma-alone processes in which tar-like products formed from volatile organic compounds are deposited, the present plasma-catalyst hybrid system did not exhibit such a phenomenon, thus retaining the original catalytic activity.
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