Avaliação isolada e integrada dos processos de coagulaçãofloculação- decantação e foto-Fenton para o tratamento de chorume

Abstract

Landfill leachate contains a variety of contaminating substances organic and inorganic, dissolved and at suspension, such as humic and fulvic acids, xenobiotics, metals (Hg2+, Pb2+, Cd2+, Cu2+, Zn2+, Cr3+/Cr6+) and ammoniacal nitrogen, which give it characteristics of low biodegradability, high organic load and toxicity. In the face of concern about the damages that this composition may cause to the environment and to animal and plant, the use and combination of new treatment technologies has a high research interest. In the first part of this work, interfering factors in the removal of dissolved organic carbon (DOC) of leachate by the photo-Fenton process, it’s the coupling of treatments were evaluated. Firstly, the isolated application of the photo-Fenton process was employed, evaluating the influence of the concentration of Fe2+ (25, 50, 100 and 200 mg L-1) on DOC removal efficiency, obtaining better results in the presence of 100 mg L-1 of Fe2+. However, a long treatment time (20 h) and high consumption of hydrogen peroxide was required. Then, the influence of two coagulant ions (Al3+ and Fe3+) was evaluated as well as different dosages in the removal of the apparent color, turbidity and DOC by the coagulation-flocculation process in the leachate matrix at pH 3. It was defined as the best coagulant and dosage, 240 mg L-1 of Fe3+, which resulted in 60, 80 and 11%, respectively, of apparent color, turbidity and DOC removals. The influence of the matrix composition (SO42- and Cl- ions and presence of color and turbidity) in the photo-Fenton process was also evaluated. For this, the isolated or combined precipitation of the SO42- and Cl- ions with Ba2+ and Ag+, respectively, as well as the application of a coagulation-flocculation pretreatment using Fe3+ in the leachate were carried out. It was observed that the photo-Fenton process in the absence of inorganic ions resulted in a kinetic 2.4 times better, consuming half of the amount of oxidant when compared to the treatment of the raw leachate, with greater interference of sulfate ions. On the other hand, applying coagulation-flocculation pretreatment using Fe3+ and in sequence photo-Fenton process, resulted in a similar efficiency in the treatment of raw leachate (70-77% DOC removal), with only 17% of the time and 7% of the consumption of H2O2. In a second step, a protocol was evaluated for the treatment of landfill leachate by the integration of coagulation flocculation, filtration stage for the elimination of suspended material and solar photo-Fenton process at pH close to neutrality. The coagulation-flocculation process was applied at natural pH of the raw leachate (7.9), evaluating different concentrations of the coagulating agents - Fe3+ or Al3+ and salts of different anions (Cl-, NO3- and SO42-). Improved turbidity removal efficiency (66%) was obtained using 4.4 mmol Al3+ L-1 (119 mg Al3+ L-1) as nitrate salt. Afterwards, the photo-Fenton process was applied to the supernatant aiming to the degradation of residual DOC, being evaluated two iron-FeOx and FeCit complexes, as iron sources and, pH influence. Better results were obtained using FeOx after adjusting the pH of the effluent to 5.0 and membrane filtration, thus promoting 68% of DOC removal. In these conditions the organic fraction removal by GC-FID was also evaluated, where it was verified the degradation of the organic compounds of greater carbonic chain in compounds of lower carbonic chain. Using this treatment protocol, it was possible to remove 86% DOC, being an alternative treatment for this type of effluent.