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 O-3/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)-O-center dot) probe compound, we experimentally determined the rate constants of organic matter of the selected waters for their reaction with (OH)-O-center dot (k(OH,DOM)), which varied from 2.0 x 10(4) to 3.5 x 10(4) L mgC(-1) s(-1). Based on these data we calculated (OH)-O-center dot scavenging rates of the various water matrices, which were in the range 6.1-20 x 10(4) 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 Zurich water) the required O-3 dose was roughly 2.3 mg/L, and in the water with the highest scavenging rate (Dubendorf wastewater) it was 13.2 mg/L, corresponding to an energy consumption of 0.035 and 0.2 kWh/m(3), respectively. The use of O-3/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 Zurich water, 0.17-0.75 kWh/m(3) 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)-O-center dot but is transformed efficiently by direct photolysis. (C) 2011 Elsevier Ltd. All rights reserved.