Pretreatment of Secondary Effluents in View of Optimal Ozone-Based AOP Removal of Trace Organic Contaminants: Bench-Scale Comparison of Efficiency and Energy Consumption

Abstract

This study compares the performance of several ozone-based advanced oxidation processes (AOPs), in combination with filtration, in terms of trace organic contaminant (TrOC) removal efficiency and energy and cost requirement. It was shown that the hydroxyl radical (•OH) scavenging rate of the secondary wastewater effluent decreased as a result of an additional pretreatment step, leading to an increase of ozone and •OH exposures at the same ozone dose. Adding filtration such as sand filtration or granular activated carbon filtration (GACF) as a pretreatment increased the removal efficiency of TrOCs by all tested ozone-based AOPs and reduced the minimum effective ozone dose for TrOC elimination. When the applied ozone dose is more than this minimum effective ozone dose, the elimination of TrOCs can be observed. For example, because of the use of anion resin filtration, 17α-ethinylestradiol elimination contributed by the process of ozone-based AOP increased from 34.6 to 42.1% at an ozone dose of 1.0 g O3/g dissolved organic carbon. Ozone-based AOPs coupled with filtration as a pretreatment were found to be more cost-efficient than the single AOPs at all ozone dose levels. The energy consumption of ozone-based AOPs was decreased by more than 25% when applying GACF as a pretreatment. In comparison with other filtration techniques, the pretreatment of secondary effluents by GACF before ozonation was proven to be the most cost-effective method for TrOC elimination.