3 . 0 Advanced Oxidation Processes Literature Review

Organic compounds, including MTBE, have been treated in drinking water using AOPs at several sites across the United States over the past five years. The largest system (3,000 gpm) is a medium pressure H 2 O 2 /MP-UV system installed in Salt Lake City, Utah to remove up to 10 µg/L PCE from drinking water (Crawford, 1999). Other systems are installed in Canada for the removal of N-nitroso dimethyl amine (NDMA) and several are planned for installation at Suburban Water Company (Los Angeles, CA) and La Puente (Los Angeles, CA) (Crawford, 1999). AOPs represent an alternative drinking water treatment option to air stripping (see Chapter 2), GAC adsorption (see Chapter 4), and resin sorption (see Chapter 5) processes, which may be inefficient for MTBE removal in certain cases due to MTBE's relatively low Henry's constant and high solubility. Unlike air stripping and adsorption, which are phase-transfer processes, AOPs are destructive processes. AOPs destroy MTBE and other organic contaminants directly in the water through chemical transformation, as opposed to simply transferring them from the liquid phase into a gas phase (in the case of air stripping) or solid phase (in the case of GAC and resins). However, despite this advantage, there are significant limitations and challenges in the full-scale application of AOPs. In general, AOPs are much less well understood than air stripping and sorption due to the complex chemical and physical processes involved in oxidation reactions. The implementation of AOPs and the determination of their effectiveness are difficult for several reasons. As with all treatment technologies, the effectiveness of AOPs will be largely determined by the specific water quality matrix of the contaminated water. However, in the case of AOPs, the effects of background water quality on contaminant removal are much less well understood than for other technologies. For example, the presence of high bromide concentrations or NOM can result in the formation of regulated oxidation by-products that may cause water quality to deteriorate beyond its initial state of contamination. Similarly, the presence of nitrates, NOM, and carbonates can interfere with the destruction of the target contaminant(s) and ultimately reduce the effectiveness of the selected AOP. In general, most of the technical difficulties associated with AOPs stem from the fact that oxidation processes are non-selective with the potential for significant interference. To compensate for these limitations, more energy or higher chemical dosages may be required, potentially resulting in higher costs. …