Efficiency and energy requirements for the transformation of organic micropollutants by ozone, O 3/H 2O 2 and UV/H 2O 2

Abstract

The energy consumptions of conventional ozonation and the AOPs O 3/H 2O 2 and UV/H 2O 2 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 ( k OH,DOM), which varied from 2.0 × 10 4 to 3.5 × 10 4 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 × 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 Zürich water) the required O 3 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/m 3, respectively. The use of O 3/H 2O 2 increased the rate of micropollutant transformation and reduced bromate formation by 70%, but the H 2O 2 production increased the energy requirements by 20–25%. UV/H 2O 2 efficiently oxidized all examined micropollutants but energy requirements were substantially higher (For 90% pCBA conversion in lake Zürich water, 0.17–0.75 kWh/m 3 were required, depending on the optical path length). Energy requirements between ozonation and UV/H 2O 2 were similar only in the case of NDMA, a compound that reacts slowly with ozone and •OH but is transformed efficiently by direct photolysis.