Ozone-microbubble-enhanced oxidation of pharmaceuticals and personal care products in municipal secondary effluents

Abstract

Microbubble aeration can greatly improve ozonation by enhancing ozone transfer and subsequent hydroxyl radical formation. Here, we applied microbubble ozonation to treat pharmaceuticals and personal care products (PPCPs) in several municipal secondary effluents. Compared with conventional ozonation, microbubble ozonation efficiently eliminated both ozone-reactive and ozone-resistant PPCPs and greatly reduced the ozone doses in the complex water matrixes of the secondary effluents. In addition, compared with millibubble ozonation, the removal of chemical oxygen demand (COD) increased by 32.0%–67.2% at 60mg/L ozone dose during microbubble ozonation. The carbon emission of microbubble ozonation varied in different water matrix, and was 47–76% less than that of millibubble ozonation. The oxidizing capacity ratio of microbubble to millibubble for PPCPs was between 1.26 to 3.50 times, and ozone-resistant PPCPs removal was enhanced more than ozone-reactive PPCPs by microbubble ozonation. Specifically, the oxidizing capacity ratio of microbubble to millibubble for carbamazepine (ozone-reactive) was 1.30 to 2.43 times, whereas that for N,N-diethyl-3-tolumide (ozone-resistant) was 1.88 to 3.50 times. Microbubble ozonation also greatly decreased the UV absorbance and fluorescence for all of the water samples. The UV absorbance at 254, 280, and 320nm decreased by 64.0%–83.8%, and the fluorescence peak intensity decreased by more than 94%. Surrogates for the removal of PPCPs and COD were evaluated and compared. This study provides new insights into the application of microbubble ozonation to control PPCPs in secondary effluents.