Adsorption of pollutants in sanitary landfill leachate using granular activated carbon and bentonite clay

Organic and inorganic pollutants in sanitary landfill leachates are harmful to the environment and human health and must be removed before reaching receptive waterbodies. Thus, this study aimed to determine the adsorption capacity of granular activated carbon (GAC) mixed with bentonite clay (BC) for the removal of chemical oxygen demand (COD), ammoniacal nitrogen (N–NH3), and total chromium (Cr) from the leachate generated in the Sanitary Landfill of Campina Grande, Paraíba, Brazil. Different compositions of these materials were tested, and the best one was determined based on central composite rotational design (CCRD) type 22. From this result, batch adsorption tests (isotherm and kinetics) were conducted using an adsorbing material:leachate ratio of 1:10, agitated at 130 rpm at 26°C ± 2°C. The isothermal behavior of the adsorption process was evaluated using linear, Langmuir, and Freundlich models, whereas the sorption mechanisms and rates were evaluated by pseudo-first-order and pseudo-second-order kinetic models. The CCRD results indicated that the best composition for the batch adsorption tests was 75% GAC + 25% BC. The maximum adsorption capacities obtained were approximately 29.00, 2.60, and 0.78 mg g–1 and the removal efficiencies were 80%–94%, 16.8%–30.4%, and 96.7%–99.7%, for COD, N–NH3, and Cr, respectively. The Freundlich model exhibited the best adjustment for COD, N–NH3, and Cr. Moreover, the pseudo-first-order kinetic model exhibited an acceptable adjustment only to COD, whereas the pseudo-second-order kinetic model was better adjusted to N–NH3, and Cr results.