Conversion of landfill composite to activated carbon as an approach to sustainable landfill management

Landfilling of municipal solid waste is a major waste disposal method, especially in developing countries despite its pressing environmental challenges. Reuse of the landfill composite has been suggested as a sustainable management option that could limit its negative effect. This research evaluated the compositional trend and characteristics of landfill composites with depth in order to assess its suitability as a precursor for activated carbon. A bulk system classification was used during analysis of the composite parameters (‘more degraded’ and ‘less degraded’ components). Both landfills had similar waste constituents, but varied in relation to moisture, TOC, and heavy metals contents. The elemental and chemical constituents of an active and a closed landfill were compared using Fourier transform - infrared (FTIR) spectroscopy, scanning electron microscope/energy-dispersive X-ray (SEM/EDX) spectroscopy, and proximate analysis. The two 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 respectively. A single step chemical activation process of precursor was applied involving irradiation with microwave energy and KOH as the activation agent. The average percentage yield of activated carbon (AC) from active landfill precursor was higher than that from closed landfill for all three depths of sampling (upper, 23.8 and 19.3 %; mid, 52.4 and 34.7 %; lower 35.7 and 27.0 %). Methylene blue adsorption capacity and BET surface analysis indicated adsorption capacity and surface area of AC from degraded precursor increased with depth. All AC conformed to a multilayer adsorption model and a pseudo second order kinetic. Carbonyl and hydroxyl groups were the major functional group on the surface of activated carbon. The AC properties indicated that precursors from both landfills are potentially suitable for generation of adsorbent suitable for removal of cationic dyes and pollutants.