Sistema de lagoas de estabilização e lagoa aerada para redução da carga orgânica e nitrogênio de percolado de aterro sanitário

Abstract

Sanitary landfills are one of the appropriate forms of final disposal of solid waste. These, during the degradation process, produce a leachate with a large amount of organic and inorganic pollutants and, before being discarded or reused, they must go through treatment to achieve the release standards by law. Among the types of treatments, the system of stabilization ponds associated with aerated ponds. This system is appropriate for effluents with a high concentration of organic matter, it is easy to apply and has cheaper operating costs. However, in most cases, the effluent from the ponds does not meet the release standards and need a post-treatment, usually physicochemical, charging the ponds of the pre-treatment in order to adapt the effluent to the standards required by the post-treatment. The main objective of this study was to measure, on a real scale, the pre-treatment by a system of stabilization ponds and aerated pond to reduce the organic load and nitrogen of the leachate from the landfill of Maceió (AL). Based on secondary data obtained by the company who manages the landfill, a qualitative and quantitative analysis of the last five years of operation of the enterprise was carried out. In addition, collections and physical-chemical analyzes of the effluents from the 4 lakes that compose the pre-treatment system were also carried out. The qualitative and quantitative analysis of the leachate evidenced that its generation is higher in the rainy season when compared to the dry season, inasmuch as it is influenced by precipitation. It was observed that during this same period the concentrations of COD and BOD increased when compared to the values in the dry period. The predominant form of nitrogen is the ammoniacal and the concentrations of N-Amoniacal, N-nitrite, N-nitrate, alkalinity and the pH values were not influenced by the precipitation, being more related to the phase of anaerobic degradation of the landfill, which is currently in the methanogenic phase. During the period of analysis, the lagoons that make up the pre-treatment presented an average efficiency of 41.33 % in the removal of color and 80.60 % in the removal of turbidity. With respect to COD and BOD, the removal efficiencies were 51.68 % and 76.14 %. For the removal of ammoniacal nitrogen, the treatment system showed an efficiency of 87.0 %, but with high concentrations of N-nitrite and N-nitrate, in the pre-aerated and aerated lagoons. As practically 85% of the nitrogen in the raw leachate is in the ammoniacal form, the ammonification process in the anaerobic lagoon is incipient, and showed a 17% reduction of N-ammoniacal, probably by volatilization. In the aerated lagoons, the ammoniacal nitrogen was being converted to nitrite and nitrate through nitrification. Finally, the pre-treatment achieved removal efficiencies greater than 50%, but still not enough to meet all the release standards set by CONAMA Resolution No. 430/2011.