Vacuum ultraviolet irradiation for natural organic matter removal

Low pressure mercury vapour lamps were used alone and in combination with hydrogen peroxide (H₂O₂) to investigate the removal of natural organic matter (NOM) from highly coloured surface water, high in total organic carbon (TOC). A potential benefit of vacuum ultraviolet (VUV) irradiation is additive-free degradation of NOM by hydroxyl radicals rather than concentration and subsequent disposal problems associated with many conventional techniques. For mineralization and chromophore removal the UV/VUV/H₂O₂ combination was most effective, followed by UV/VUV. Photooxidation alone was inappropriate because small (but much greater than normal UV disinfection doses) and intermediate doses increased chlorine demand, trihalomethane formation potential, nitrite, hydrogen peroxide and low molecular weight carbonyl compound concentrations. Subsequent biological treatment reduced the chlorine reactivity significantly, by removal of oxidized NOM intermediates. Low molecular weight carbonyl compound concentrations in the water increased significantly on irradiation, and differences in their speciation indicated that different reaction mechanisms were dominant in different treatments. Trihalomethane (THM) distribution shifted to more highly brominated compounds as the NOM concentration decreased with treatment. Results from this preliminary study indicate that NOM can be removed from water by VUV irradiation combined with biological treatment leading to improved drinking water quality.