Seasonal variations of geochemical parameters for a tropical landfill: Implications for landfill stabilization

Abstract

Landfills stabilization stages depend on parameters such as the age of the landfill, the refuse composition, and the confinement level of the buried material. In the absence of free oxygen, redox reactions (e.g., SO42−, NO3−) and methanogenesis control the decomposition of organic matter. Landfill's stabilization stage is usually assessed by parameters such as pH, biochemical oxygen demand, chemical oxygen demand, dissolved organic carbon, and biogas composition. This study evaluates the stabilization stage of a 50-year-old tropical landfill located in Central Brazil based on physicochemical parameters, dissolved carbon isotope data (δ13C), redox reactions, and concentration of released gases CO2 and CH4. We show that seasonal variations of these parameters are modified by rainwater inflow, which carries free-oxygen into the landfill. An increase in free-oxygen leads to a13C-depletion in carbon isotopic composition of dissolved CO2 and an increase in redox-dependent species such as Fe3+, SO42−, and NO3−. Our data show that most of the landfill has reached the methanogenic stage and that periodic oxygen input by rainwater affects methane production. The studied site is a complex chemical system in which organic matter degradation occurs by aerobic, anaerobic, and methanogenic processes, depending on the recharge susceptibility.