Abstract
Ozone is an oxidizing agent with a potential for removing complex molecules, including those of difficult microbiological decomposition, such as the molecules found in landfill leachates. This effluent presents high organic content, including recalcitrant molecules. Therefore, this study evaluated the efficiency of ozonation in the treatment of raw leachate at the Primavera landfill, located in Mato Grosso, Brazil. The experiments were carried out using the batch system. The leachate pH value was set at 7 and 10, and the contact times between the gas and the leachate were 20, 40, 60, 80, and 100 minutes. Throughout the study, we analyzed color, turbidity, pH value, chemical oxygen demand (COD), and ultraviolet absorbance at 254 nm (UV abs) of the leachate, both before and after ozonation. Results show that ozonation presented high removal of color, COD and UV abs when pH was 7. In contrast, turbidity removal was higher when the pH value was 10. Regarding contact time, we observed a high removal of color (between 80% and 90%) and UV abs (between 60% and 70%) at 40 minutes, depending on the pH value. Removal was also high for turbidity (approximately 75%) starting at 20 minutes with the pH value at 10, and at 70 minutes with pH at 7. The removal relation within all analyzed parameters (due to ozone consumption) decreased throughout the reaction time. Thus, we concluded that ozonation as a pre-treatment of leachate is indeed satisfactory because of its great capacity for organic material removal.
Highlights
Population growth results in a disorderly growth of cities, mainly in large urban areas, which causes serious problems, especially in regard to the generation of urban waste and its final destination
For the pH at 10, we observed a decrease in the pH value from the beginning of the experiment to its end (Table 1), which, despite being low, indicates the consumption of OH- ions, probably due to its reaction with ozone chain reactions
In neutral pH values there is, basically, ozone reacting with organic matter
Summary
Population growth results in a disorderly growth of cities, mainly in large urban areas, which causes serious problems, especially in regard to the generation of urban waste and its final destination. Landfill leachate has high concentrations of organic matter, chlorides, ammoniacal nitrogen, as well as organic compounds of difficult degradation, such as humic substances and metals, depending on the properties of the residues disposed of in the landfill (Renou et al, 2008; Kawahigashi et al, 2014). When one considers efficient techniques for the decomposition of complex compounds, the ozonation technique stands out, either alone or associated with other processes (advanced oxidation processes/AOPs). It was the technique of choice in this study, and it appears to yield great results in the degradation of recalcitrant molecules (Araújo et al, 2016), as well as in the oxidation and mineralization of organic and inorganic species (Dezotti, 2008). The mentioned technique showed high efficiency in the reduction of biochemical and chemical oxygen demands (BOD and COD, respectively) (Carvalho et al, 2018; Gomes and Schoenell, 2018; Brito and Silva, 2012) and turbidity (Mondardo et al, 2006)
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