Urban wastewater treatment by ozonation: Disinfection by-products and toxicity assessment
K.J. Castañeda Retavizca, Kris O’Dowd, Eva Jambrina-Hernández, Samira Nahim–Granados, Patricia Plaza‐Bolaños, S. Malato, María Inmaculada Polo-López, S C Pillai, I. Oller
Abstract
The capability of ozonation for the simultaneous elimination of organic microcontaminants (OMCs) and pathogens naturally present in the secondary effluent of an urban wastewater treatment plant has been investigated assessing different doses of ozone (0.2, 0.3 and 0.4 g O 3 L −1 h −1 ). The quantification of intermediates, disinfection byproducts (DBPs), and water toxicity (cytotoxicity, phytotoxicity and ecotoxicity bioassays), have been also evaluated. Ozonation performance was studied at pilot plant scale, obtaining 80 % degradation of OMCs. The inactivation of E. coli and total coliforms was directly proportional to the ozone doses, and the detection limit (1 CFU 100 mL −1 ) was attained after a consumption of 0.3 and 0.4 g O 3 L −1 h −1 , respectively. The generation of bromate was related to the ozone dose, exposure time and bromide concentration present in the target wastewater. Bromoform concentration increased as a function of ozone dose, decreasing then more rapidly at higher ozone doses. Concentration of chlorinated haloacetic acids (HAAs) remained constant due to low reactivity with O 3 and brominated HAA increased with O 3 dose and time due to the bromide presence in the wastewater. The evaluation of cytotoxicity revealed cell viability higher than 80 %, and for phytotoxicity, the root growth index did not change during the ozonation treatment, both indicating non-toxic effect. The analysis of Aliivibrio fischeri toxicity at the end of the treatment time with 0.4 g O 3 L −1 h −1 showed an inhibition effect, due to the presence of different DBPs, however, with 0.3 g O 3 L −1 h −1 a stimulation effect was observed. • The risks associated to disinfection and decontamination with O 3 were evaluated. • DBPs such as trihalomethanes and haloacetic acids were analyzed. • The presence of DBPs did not show toxicity effects. • UWWTP secondary effluents treated by O 3 are safe for reusing in agriculture.