Impact of catalyst load, chemical oxygen demand and nitrite on disinfection and removal of contaminants during catalytic ozonation of wastewater

Abstract

Calcium-silicate mineral Polonite® and aluminum-based catalyst (AL-1010S), previously identified as promising materials for catalytic ozonation, were used as catalysts to investigate the impact of some operating conditions (ratio ozone feed concentration to catalyst load) and wastewater characteristics (chemical oxygen demand - COD and nitrite - NO2 concentration) on the disinfection and removal of contaminants of emerging concern (CECs) during catalytic ozonation of wastewater. Tests conducted in synthetic wastewater using two different ozone gas concentration (4 and 8 g (nm3)) and 6 different catalyst loads provided ratios of 0.08, 0.11, 0.16, and 0.32. Results from the experiments indicated that the ratio of 0.11 was optimal and reached residual disinfection below 2 MPN mL−1 from the initial concentration of 5 ± 2 × 105 MPN mL−1 and removal of atrazine (ATZ) above 80% from the initial concentration of 100 ± 10 μg L−1 for an ozone dose of 41–45 mg L−1. Catalytic ozonation with the selected materials enhanced disinfection and ATZ removal from synthetic wastewater (SWW) in comparison to non-catalytic ozonation by making the treatment performance less sensitive to increased chemical oxygen demand (COD) and nitrite (NO2) in the matrix. Validation of the results in real wastewater effluents confirmed that catalytic ozonation enhanced disinfection. Catalytic ozonation using Polonite® and AL-1010S provided residual bacteria level of 0.6 ± 0.42 MPN mL−1 and 0.29 ± 0.41 MPN mL−1, while non-catalytic ozonation lead to an average residual bacteria level of 1.26 ± 0.09 MPN mL−1 for the same range of transferred ozone dose. However, under the conditions tested, a limited number of CECs were extracted at levels above the limits of quantification and further validation work required to evaluate the performance of catalytic ozonation for the removal of CECs.