2-methylisoborneol (MIB) and geosmin are two compounds that lead to unpleasant tastes and odors (T&O) in drinking water. These compounds are often detected during or following seasonal algal blooms that can result from a combination of factors including warm temperatures and nutrient loading into water catchments through agricultural run-off. The combined use of ultraviolet (UV)-light and hydrogen peroxide, a process known as UV-oxidation, is a recognized approach to mitigating T&O problems brought on by MIB and geosmin.
To date, a number of water treatment facilities have adopted UV-oxidation for this purpose, and performance data has been collected from a recently completed North American UV-oxidation installation. The results demonstrated that UV-oxidation can remove well over 90% (1-log) of MIB while treatment with hydrogen peroxide alone (no UV) showed negligible levels of treatment. In addition to performance testing, a competitive life cycle analysis (LCA) analysis approach was taken to evaluate the global warming potential (GWP) of various T&O treatment technologies and UV-oxidation had 46.2% lower greenhouse gas (GHG) emissions compared to an alternative treatment approach which used carbon adsorption. The GWP of UV-oxidation was also compared with ozone, and a 7.9% lower GHG emission was observed by using UV-oxidation.
It was also recognized that removal of residual hydrogen peroxide upstream of a distribution system was necessary to ensure ongoing compliance with local drinking water standards. With this in mind, bench scale testing with granular activated carbon (GAC) and biological activated carbon (BAC) filtration demonstrated that empty bed contact times of as low as two minutes were effective at removing greater than 98% of residual H2O2 after UV-oxidation treatment with BAC often demonstrating improved residual removal efficiency over GAC. This suggested that frequent changeouts of filter beds are not necessary when using activated carbon for the quenching of residual H2O2.
This presentation will highlight the various technical, economic and environmental features and benefits of UV-oxidation when applied for the treatment of T&O compounds.