Integração dos processos de coagulação-floculação, foto-fenton e/ou fotocatálise para o tratamento de efluentes de pesticidas

Abstract

Industrial effluents from pesticides have high toxicity associated with their high organic load, as well as high levels of turbidity, suspended solids and color. Due to the complexity and toxicity of this kind of effluent, the objective of this work was to evaluate the combination of coagulation-flocculation-decanting and advanced oxidation (photo-Fenton and/or heterogeneous photocatalysis) as treatment alternatives for this type of matrix. The present study consists of the treatment of an industrial effluent of pesticides, consisting of a mixture of the pesticides ametrine (ATT), atrazine (ATZ), imidacloprid (IMD) and tebuthiuron (TBH) in concentrations of 403, 2153, 2936 and 3354 mg L-1, respectively. Firstly, the study of the best coagulant for the pre-treatment was analyzed, with Fe (NO3)3 at 8 mmol L-1 at pH adjusted to 4.0. Under such conditions, there was a 99% color and turbidity removal, 65% COD, 27% BOD and 56% TOC. For pesticides, 72%, 98%, 82% and 39% for AMT, ATZ, IMD and TBH, respectively. However, this process was inefficient to remove the soluble organic fraction and toxicity, being necessary the integration with other processes, such as photo-Fenton and/or photocatalysis. Firstly, different types of iron sources, Fe(NO3)3, FeSO4, FeOx, FeCit, FeEDTA, FeEDDS and FeNTA complexes were analyzed in a concentration of 2 mmol L-1. Other operational parameters were also evaluated, such as FeOx and FeCit complex concentrations (0.5, 1.0, 2.0 and 3.0 mmol L-1) and the influence of the binder replacement on the process. Among the conditions evaluated, the best results were obtained using 2 mmol L-1 concentration of the FeOx iron complex, without replacing the binder, with 2000 mg L-1 of H2O2. There was a removal of 86%, 34%, 95% and 87% for AMT, ATZ, IMD and TBH, respectively. For comparison purposes, experiments employing the heterogeneous photocatalysis using TiO2 P25 were also carried out in the same supernatant after the physical-chemical treatment, obtaining better results with 150 mg L-1 of TiO2 and 2000 mg L-1 of H2O2, reaching 73%, 25%, 71%, 37% degradation for AMT, ATZ, IMD and TBH, respectively. Therefore, this study shows the importance of combination of two or more processes for the treatment of complex matrices, such as an industrial effluent containing pesticides, since the physico-chemical process is effective for the reduction of turbidity, color and suspended solids, while the photo-Fenton process and/or photocatalysis is efficient for the degradation of the organic matter.