Physicochemical and microbiological characteristics of waste foundry sand used in landfills

Biodegradation of solid waste is a process that depends on the characteristics of waste and soil, and these characteristics may create a waterproof barrier in the landfill, changing its performance. Some residues, such as waste foundry sand (WFS), whose final destination is the sanitary landfill, can create waterproofing and alter the performance of the landfill. This study was carried out to test this hypothesis by evaluating two prototypes composed of layers of organic residues, one covered by a mixture of 30% clay soil + 70% WFS and the other covered only with clay soil, monitored for 24 months. The generated leachate was analyzed regarding the parameters of chemical oxygen demand (COD), pH and electrical conductivity. In addition, after the monitoring period, semi-undeformed samples were collected for quantification of microorganisms and physical-chemical analysis (pH, electrical conductivity, moisture content and images with scanning electron microscopy). In the soil prototype, there was the formation of a waterproofing barrier in its deepest layer (soil₃). Factors such as the clay-mineral portion, moisture content (33,18%) and amount of microorganisms influenced this formation (650.000 and 15.000 CFU/g bacterial and fungal biomass, respectively), showing that WFS avoids the formation of this waterproofing barrier, as indicated for covering organic waste in landfills.