Abstract
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.