Efficiency and energy requirements for the transformation of organic micropollutants by ozone, O3/H2O2 and UV/H2O2

The energy consumptions of conventional ozonation and the AOPs O3/H2O2 and UV/H2O2 for transformation of organic micropollutants, namely atrazine (ATR), sulfamethoxazole (SMX) and N-nitrosodimethylamine (NDMA) were compared. Three lake waters and a wastewater were assessed. With p-chlorobenzoic acid (pCBA) as a hydroxyl radical (•OH) probe compound, we experimentally determined the rate constants of organic matter of the selected waters for their reaction with •OH (kOH,DOM), which varied from 2.0 × 104 to 3.5 × 104 L mgC-1 s-1. Based on these data we calculated •OH scavenging rates of the various water matrices, which were in the range 6.1-20 × 104 s-1. The varying scavenging rates influenced the required oxidant dose for the same degree of micropollutant transformation. In ozonation, for 90% pCBA transformation in the water with the lowest scavenging rate (lake Zürich water) the required O3 dose was roughly 2.3 mg/L, and in the water with the highest scavenging rate (Dübendorf wastewater) it was 13.2 mg/L, corresponding to an energy consumption of 0.035 and 0.2 kWh/m3, respectively. The use of O3/H2O2 increased the rate of micropollutant transformation and reduced bromate formation by 70%, but the H2O2 production increased the energy requirements by 20-25%. UV/H2O2 efficiently oxidized all examined micropollutants but energy requirements were substantially higher (For 90% pCBA conversion in lake Zürich water, 0.17-0.75 kWh/m3 were required, depending on the optical path length). Energy requirements between ozonation and UV/H2O2 were similar only in the case of NDMA, a compound that reacts slowly with ozone and •OH but is transformed efficiently by direct photolysis. © 2011 Elsevier Ltd.