Individual treatment processes like biological treatment or ozonation have their limitations for the removal of pharmaceuticals from secondary clarified effluents with high organic matter concentrations (i.e. 17 mg TOC/L). These limitations can be overcome by combining these two processes for a cost-effective pharmaceutical removal. A three-step biological-ozone-biological (BOB) treatment process was therefore designed for the enhanced pharmaceutical removal from wastewater effluent. The first biological step removed 38% of ozone scavenging TOC, thus proportionally reducing the absolute ozone input for the subsequent ozonation. Complementariness between biological and ozone treatment, i.e. targeting different pharmaceuticals, resulted in cost-effective pharmaceutical removal by the overall BOB process. At a low ozone dose of 0.2 g O/g TOC and an HRT of 1.46 h in the biological reactors, the removal of 8 out of 9 pharmaceuticals exceeded 85%, except for metoprolol (60%). Testing various ozone doses and HRTs revealed that pharmaceuticals were ineffectively removed at 0.1 g O3/g TOC and an HRT of 0.3 h. At HRTs of 0.47 and 1.46 h easily and moderately biodegradable pharmaceuticals such as caffeine, gemfibrozil, ibuprofen, naproxen and sulfamethoxazole were over 95% removed by biological treatment. The biorecalcitrant carbamazepine was completely ozonated at a dose of 0.4 g O/g TOC. Ozonation products are likely biodegraded in the last biological reactor as a 17% TOC removal was found. No appreciable acute toxicity towards D. magna, P. subcapitata and V. fischeri was found after exposure to the influents and effluents of the individual BOB reactors. The BOB process is estimated to increase the yearly wastewater treatment tariff per population equivalent in the Netherlands by less than 10%. Overall, the BOB process is a cost-effective treatment process for the removal of pharmaceuticals from secondary clarified effluents.

Ozonation for micropollutant removal from wastewater treatment plant effluent is energy and costintensive because of competition between background organic matter and micropollutants. This study aims to elucidate the interference of different organic matter fractions during the ozonation of micropollutants. Wastewater treatment plant effluent was fractionated using membranes and XAD-8 resin. All membrane and resin fractions were spiked with 18 micropollutants (2 µg/L) and ozonated with 0.25, 0.5 and 1 g O 3 /g TOC. Results show that these fractions differ in their interference with the ozonation of micropollutants. Interference was lower in the smallest size fraction (<1 kDa) than in all other fractions for micropollutants with low and medium ozone reactivity. The hydrophobic neutrals and hydrophilics resin factions showed a high interference for ozonation of micropollutants with medium and high ozone reactivity, respectively. The four parameters that were analyzed (specific UV absorbance at 254 nm, fluorescence, chemical oxygen demand and nitrite) could not elucidate the differences in micropollutant removal. Still, we conclude that understanding the type of organic matter present in the matrix, is essential to optimize micropollutant ozonation and other tertiary micropollutant removal treatments.

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