Toxicity of Wastewater Treatment Plants (WWTP) effluents before and after disinfection by advanced oxidative processes

Author(s)

Lais Roberta Deroldo Sommaggio

• Document type: Doctoral Thesis
• Press: Rio Claro. 2021-05-25.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro
• Defense date: 2021-04-09
• Advisor: Maria Aparecida Marin Morales; Dânia Elisa Christofoletti Mazzeo

Abstract

The development of new technologies for the treatment of wastewater in Wastewater Treatment Plants (WWTP) is essential for the minimization of the pollution water resources. Among the new technologies, the Advanced Oxidative Processes (AOPs) are highlighted, such as ozonation and ultraviolet radiation (UV) associated with hydrogen peroxide (H2O2). AOPs are based on the use of highly oxidizing species to promote the most effective degradation of pollutants and the disinfection of pathogenic microorganisms from the effluents. The efficiency of the effluent treatment is important for the safe reuse of these waters. However, AOPs can generate toxic compounds that make water reuse unfeasible and compromise the receiving water body. In this sense, the tests carried out with high performance biological indicators are important tools to be used in the evaluation and certification of the toxicity exemption of effluents submitted to AOP. In addition to measuring the disinfectant power of the system used, it is necessary to monitor the possible environmental impacts that these processes may cause. Effluent samples from two WWTPs in the Limeira city, with different characteristics (Municipal WWTP and Unicamp WWTP) and collected in a rainy and dry period were subjected to treatments with ozone or UV/H2O2, for periods of 20 (T1) and 40 (T2) minutes. Different bioassays were used for the evaluation of the samples, before the application of the AOPs and after these treatments. The phytotoxicity of the samples was evaluated by germination and elongation tests of the hypocotyl and radicle in Lactuca sativa. Genotoxicity assays (comet and micronucleus) were performed in human HepG2/C3A cell culture. The mutagenic and estrogenic potentials of the extracts of the samples were evaluated by the Salmonella/microsome assay and Yeast Estrogen Screen (YES), respectively. In addition, a microbiological characterization was carried out to assess the persistent microorganisms in the final effluent of the WWTPs. The results of the microbiological analysis showed that the longer ozonation time and the treatment with UV/H2O2 were efficient for the disinfection of the effluent, according to the tests carried out with the Escherichia coli indicator, with the UV/H2O2 being even more efficient in the disinfection that ozone treatment. Bacillus sp. was the most resistant microorganism identified, being found even after treatments with O3 and UV/H2O2. The results with Lactuca sativa showed inhibition of root growth, for all samples of the Municipal WWTP-dry period. The results of the comet assay showed that the samples from Municipal WWTP-dry period, submitted to UV/H2O2 treatment (T1 and T2), induced significant genotoxic effects in HepG2/C3A cells, when compared to the negative control (NC). Regarding the MN test, a significant MN induction of this elements was observed in all treatments of the Unicamp WWTP and the Municipal WWTP-dry period, when compared to the NC. The presence of nuclear bud was significant for all treatments carried out from Unicamp WWTP and for treatments with UV/H2O2 from Municipal WWTP-dry period. The presence of more than one alteration per cell (composite alterations – e.g. MN and nuclear bud, MN and bridge, among others) was significant for the treatment with UV/H2O2 (T1) of the Municipal WWTP-dry period, when compared to the NC. The evaluation of the total alterations (sum of all events) was significant for all treatments of the Unicamp WWTP; treatments with UV/H2O2 (T1 and T2) from the Municipal WWTP-dry period; and the effluent samples before the application of AOP (O3T2 and UV/H2O2 T2) from the Municipal WWTP-rainy period. Estrogenic activities were observed for most effluents collected before the application of AOP and for effluents collected after treatment with UV/H2O2. The effluents subjected to ozonation did not show estrogenic activity. Regarding the Salmonella assay, mutagenic potential was observed for the TA98 and TA100 strains, with metabolic activation, in the samples treated with UV/H2O2. Based on these results, it was observed that treatment with UV/H2O2 showed greater disinfection power of the samples, but also a greater toxic effect, when compared with O3 the treatment with the O3. Thus, treatments using AOPs must consider not only the disinfectant power of the treatment but the possible impacts that they may have on the environment and human health. (AU)

• FAPESP's process: 16/22483-1 - Toxicity of efluents from wastewater treatments plants (WWTPs), after utilization of advanced oxidation processes, used for disinfection.
• Grantee: Lais Roberta Deroldo Sommaggio
• Support type: Scholarships in Brazil - Doctorate