Influence of ozonation and UV/H2O2 on the genotoxicity of secondary wastewater effluents

The implementation of novel wastewater treatment technologies, including Advanced Oxidation Processes (AOPs) such as ozonation and ultraviolet radiation (UV) combined with hydrogen peroxide (H2O2), can be a promising strategy for enhancing the quality of these effluents. However, during effluent oxidation AOPs may produce toxic compounds that can compromise the water reuse and the receiving water body. Given this possibility, the aim of this study was to evaluate the genotoxic potential of secondary effluents from two different Wastewater Treatment Plants (WWTP) that were subjected to ozonation or UV/H2O2 for periods of 20 (T1) and 40 (T2) minutes. The genotoxic potential was carried out with the Comet assay (for clastogenic damage) and the Micronucleus assay (for clastogenic and aneugenic damage) in HepG2/C3A cell culture (metabolizing cell line). The results of the comet assay revealed a significant increase in tail intensity in the Municipal WWTP (dry period) effluents treated with UV/H2O2 (T1 and T2). MN occurrence was noted across all treatments in both Pilot and Municipal WWTP (dry period) effluents, whereas nuclear buds (NBs) were noted for all Pilot WWTP treatments and UV/H2O2 treatments of Municipal WWTP (dry period). Moreover, the UV/H2O2 (T1) treatment of Municipal WWTP (dry period) exhibited a noteworthy incidence of multiple alterations per cell (MN + NBs). These findings imply that UV/H2O2 treatment demonstrates higher genotoxic potential compared to ozonation. Furthermore, seasonal variations can have an impact on the genotoxicity of the samples. Results of the study emphasize the importance of conducting genotoxicological tests using human cell cultures, such as HepG2/C3A, to assess the final effluent quality from WWTP before its discharge or reuse. This precaution is essential to safeguard the integrity of the receiving water body and, by extension, the biotic components it contains.

Modeling carbonate/bicarbonate and nitrate disturbance during secondary effluent disinfection by UV/H2O2 and UV/ozone

The disinfection of effluents has been considered the main step to inactivate pathogenic organisms to prevent the spread of waterborne diseases. The variation in the matrix composition can lead to the use of inadequate oxidant dose and disturb a correct treatment. The objective of this study was to develop a simple and practical mathematical model to simulate the disturbance of inorganic anions (CO₃^2-/HCO₃^- and NO₃^-) during secondary effluent disinfection by UV/H₂O₂ and UV/O₃. The pathogenic agents chosen for this study were total coliforms and E. coli. To build the mathematical model, a modification of the Chick model (referred to as 'Modified Chick Model') was proposed by employing a weighted average in the calculation of the kinetic constant. Both treatments were affected by the presence of the anions. However, with the highest NO₃^- concentration, less inhibition of disinfection was observed in the UV/H₂O₂. The use of the arithmetic means to calculate the value of k, as indicated by the Chick model, demonstrates a lesser precision in the prediction of the microorganisms' concentrations. On the other hand, using the Modified Chick Model, a better prediction of the inactivation of the microorganisms was obtained, which can be confirmed by the validation performed.

Assessment of phytotoxic potential and pathogenic bacteria removal from secondary effluents during ozonation and UV/H2O2

Wastewater reuse is an important strategy for water resource management. For this reason, the disinfection process must be appropriated, eliminating pathogenic microorganisms. Ozonation (O₃) and UV/H₂O₂ treatments can be used for effluent disinfection, but few studies just address the Escherichia coli quantification. In this study, secondary effluents from two wastewater treatment plants with different characteristics were exposed to O₃ (5 and 10 mg L^-1) or UV/H₂O₂ (H₂O₂: 90 mg L^-1) treatments and evaluated by BD Phoenix ™ 100 (Becton Dickinson, USA) and MALDI-TOF for the characterization of the indigenous microorganisms in the effluents, before and after treatments. Additionally, all the samples were tested for phytotoxicity by Lactuca sativa bioassay. The results showed that the highest ozone dose and the UV/H₂O₂ treatment were effective in removing E. coli. UV/H₂O₂ was more efficient as it eliminated most of the microorganisms. Acinetobacter sp., Aeromonas and Pseudomonas were still found after O₃ treatment. Bacillus sp. was found after O₃ and UV/H₂O₂ treatments. The results with L. sativa showed inhibition of root growth for all dry period (low rainfall) samples of one of the WWTP, due to the high concentration of the phytotoxicity compounds. For environmental and human health safety, treated effluents should be evaluated for their toxic and pathogenic potential before being released into the environment. Pathogens evaluation on treated effluents should cover a wider range of pathogenic microorganisms than those routinely required by legislation.