Comparison of the efficiency of *OH radical formation during ozonation and the advanced oxidation processes O3/H2O2 and UV/H2O2.

Comparison of advanced oxidation processes (AOPs) can be difficult due to physical and chemical differences in the fundamental processes used to produce OH radicals. This study compares the ability of several AOPs, including ozone, ozone+H2O2, low pressure UV (LP)+H2O2, and medium pressure UV (MP)+H2O2 in terms of energy required to produce OH radicals. Bench scale OH radical formation data was generated for each AOP using para-chlorobenzoic acid (pCBA) as an OH radical probe compound in three waters, Lake Greifensee water, Lake Zurich water, and a simulated groundwater. Ozone-based AOPs were found to be more energy efficient than the UV/H2O2 process at all H2O2 levels, and the addition of H2O2 in equimolar concentration resulted in 35% greater energy consumption over the ozone only process. Interestingly, the relatively high UV/AOP operational costs were due almost exclusively to the cost of hydrogen peroxide while the UV portion of the UV/AOP process typically accounted for less than 10 percent of the UV/AOP cost and was always less than the ozone energy cost. As the *OH radical exposure increased, the energy gap between UV/H2O2 AOP and ozone processes decreased, becoming negligible in some water quality scenarios.