Tratamento de lixiviado de aterro sanitário utilizando torre de Air Stripping e adsorção em leito fixo.

Abstract

The treatment of sanitary landfill leachate has become one of the main challenges in the management of urban solid wastes, because this subproduct is heterogeneous and exhibits a complex and variable composition. Thus, this study aimed to evaluate the use of the air stripping and fixed-bed adsorption (FBA) processes in the treatment of leachate produced in a sanitary landfill located in the Brazilian semiarid region. FBA tower and columns were produced using polyvinyl chloride pieces, with dimensions of 1.50 × 0.15 m and 0.70 × 0.05 m (total height × diameter), respectively. The tower was filled with corrugated conduit rings with 0.03 × 0.02 m (length × internal diameter), and fed by an intermittent flux with recirculation and gas (G): liquid (L) ratio of 140. The adsorption columns were packed with a mixture of commercial granular activated carbon (GACc) and calcium bentonite clay (BCc), whose percentages were determined by a factorial planning, and the flux rate varied in the range of 8 to 22 mL min-1 for bed heights of 0.65 m. Five batch experiments (Exp-1, Exp-2, Exp-3, Exp-4, and Exp-5) were conducted in the tower, and the final effluents of Exp-2 (C1), Exp-3 (C2), Exp-4 (C3), and Exp- 5 (C4) were treated in the columns. The G:L ratio was maintained constant during the air stripping process, but the hydrogenionic potential (pH) of leachates was adjusted to 10 ± 1 and 12 ± 1 using commercial lime type I (Exp-2 and Exp-3) and sodium hydroxide analytical reagent grade (Exp-4 and Exp-5), respectively. The performance of the methods evaluated was analyzed by monitoring physico-chemical and phytotoxicological indicators. Based on the results, in the experiments conducted in the tower, the total ammoniacal nitrogen (TAN) removal and the volumetric mass transfer coefficients (kLa) were: 99% and 0.030 h-1 (Exp-1); 98% and 0.061 h-1 (Exp-2); 98% and 0.091 h-1 (Exp-3); 98 % and 0.093 h-1 (Exp-4); and 97% and 0.097h-1 (Exp-5), respectively. The removal and dynamic adsorptive capacities of C1, C2, C3, and C4 decreased with the operation time based on the saturation of the adsorbent bed composed of GACc (75%) + BCc (25%). Thus, the maximum adsorptive capacities (qTh) and Thomas rate constants (KTh) of Cr, Cu, and Ni in FBA columns varied in the following ranges: 0.84–1.59 mg kg-1 and 0.007–0.037 L mg-1 min-1; 4.83–8.45 mg kg-1 and 0.02–0.011 L mg-1 min-1; and 0.32–1.59 mg kg-1 and 0.009–0.067 L mg-1 min-1, respectively. Therefore, the FBA and air stripping methods were efficient and have potential to be used in practical applications, as they removed the TAN, Cr, Cu, and Ni contents to environmentally acceptable contents and significantly reduced the chemical demand of oxygen of the leachate from a sanitary landfill in the semiarid region.