Comparative characterization of closed and active landfill composites using spectroscopic and proximate techniques

INTRODUCTION: Effective utility of mixed waste in the landfills lies before its complete degradation rather than after landfill closure. The elemental and chemical constituents of an active and a closed landfill composite were compared using Fourier transform - infrared (FTIR) spectroscopy, scanning electron microscope / energy-dispersive X-ray (SEM/EDX) spectroscopy, and proximate analysis in order to determine potential alternative uses.

METHOD: Landfill sites were systematically gridded into seven cells according to RCRA USEPA guidelines. Three samples were obtained from each cell at upper (0-15cm), mid (16-35cm) and low- (36-50cm) depths, both during the dry and wet seasons. The dried samples were separated by size into composites of less degraded (S> 0.63mm) and more degraded (S<0.63mm) components and homogenised.

Proximate parameters (ash, volatile and fixed carbon) of samples were determined by ASTM D3174-5 methods. An Alpha attenuated total reflectance -FTIR spectrometer (Bruker) and X-Max SEM/EDX Instruments were used to evaluate the functional and elemental properties.

RESULTS: both landfills had similar major elemental constituents representing 96.5% and 98.4% of elemental composition for the closed (O > C > Si> Fe > Ca >Al) and active(C > O > Si > Al > Ca > Fe) landfill samples. Cluster analysis revealed that elemental similarities were more influenced by the level of composite degradation (more degraded / less degraded) than by depth or seasonal variations. FTIR absorption peaks of both landfill samples indicated mineralised waste constituent with some distinguishing peaks peculiar to each landfill. The average ash content (>51%) of the waste in both landfills was above the level considered suitable for energy recovery from waste.

DISCUSSION: The absence of major organic peaks precludes use of the waste for soil enrichment and anaerobic digestion feeds, but not for landfill covering. These findings, from rapid and amenable spectroscopic techniques, inform strategic management decisions for landfills.