Natural organic matter removal by enhanced photo-oxidation using low pressure mercury vapour lamps

High efficiency, low pressure mercury vapour lamps producing radiation at the wavelengths of 254 plus 185 nm and 254 nm only, were used to investigate the H2O₂ enhanced photo-oxidation of natural organic matter (NOM). NOM is a problem in drinking water for a number of reasons: aesthetics; it provides an energy source for the growth of microorganisms in the distribution system; and reacts with chlorine to produce potentially harmful disinfection by-products. One promising oxidant for the removal of NOM from drinking water is the hydroxyl radical. The aim of this work was to investigate the kinetics, mechanisms, and feasibility of treatment of a highly coloured natural water by H2O₂ enhanced UV (254 nm alone or with 185 nm). Kinetic models were applied to the data as a tool to understand the mechanisms and give a basis for process scale-up. Electrical energy per order criteria were used to determine the most efficient process. Irradiation by 254 plus 185 nm was found to be more efficient than 254 nm alone for low H₂O₂ doses, although at higher doses the performance of the two systems became similar. Size exclusion chromatography revealed three distinct fragmentation patterns for the different processes.