Organic Micropollutant Treatment by Pre-Ozonation and Activated Carbon

Abstract

Inadequate treatment of wastewater effluent is one of the major point sources of pollution of organic micropollutants (OMPs) into aquatic environments. Wastewater treatment plants need to be upgraded to reduce OMP contamination. Recently, the combination of pre-ozonation and granular activated carbon (GAC) filtration has been proposed as a potential OMP treatment method. The aims of this study are to examine the treatment efficiency of selected OMPs, the effects of an ozonated feed water (second clarifier effluent) on GAC adsorption, effects of ozonation on GAC bed life and to identify the dosages of ozone for the design of a pilot plant. Batch adsorption experiments were conducted. The results show that combining the two treatment methods lead to higher elimination/removal rates of the target compounds. The data obtained in the study was used to plot adsorption isotherms and breakthrough curves to investigate the effect of ozonation on GAC bed life. The study found that ozonation reduces the adsorption capacity of the GAC for the selected compounds. Increasing the ozone dosage from 0.2 to 0.4gO3/gDOC further lowers the adsorption capacity. However, at 0.8gO3/gDOC, the adsorption capacity improves. Consequently, according to COMSOL simulations based on the LDF model, ozonation of the feed water at dosages 0.2 and 0.4 gO3/gDOC results in the breakthrough point occurring earlier than without ozonation. However, a later breakthrough point is obtained with a dosage of 0.8gO3/gDOC. This is likely due to the effect of low post-ozonation concentrations outstripping the effects of a poorer adsorption capacity. Therefore, an ozone dose of 0.8g/gDOC is recommended for the pilot plant while a lower dose could be examined to confirm the findings in this study. Further research is recommended to assess the behaviour of the oxidation by-products and their removal efficiency by GAC filtration.