Efficient wastewater disinfection using a novel microwave discharge electrodeless ultraviolet system with ozone at an ultra-low dose.

Microwave discharge electrodeless lamp (MDEL) is a novel ultraviolet (UV) light source. Synergistic disinfection using UV light emitted by MDEL (MWUV) coupled with ozone (O) at an ultra-low dose was investigated. Escherichia coli and Bacillus subtilis were deactivated more effectively by MWUV/O than by either MWUV or O alone. MWUV/O treatment using an O concentration of 0.4 mg/L gave an E. coli inactivation rate of 5.52 log. The photoreactivation degree and rate of E. coli were lower after inactivation by MWUV/O treatment than after MWUV treatment alone. The maximum photoreactivation rates after the MWUV/O and MWUV treatments were 2.90% and 16.08%, respectively. MWUV/O disinfection also inhibited dark resurrection of E. coli and gave a maximum dark resurrection rate of 0.0036%. Electron paramagnetic resonance spectroscopy indicated that more hydroxyl radicals were generated during MWUV/O treatment. Scanning electron microscopy and laser confocal scanning microscopy observations indicated that O played a key role in breaking down the cell structure. MWUV/O treatment gave a good disinfection effect on fecal coliform bacteria in actual domestic wastewater. The results indicated that inactivation of bacteria can be more effectively achieved by MWUV treatment with O.