Performance and regeneration of a sustainable composite adsorbent in fixed-bed columns for landfill leachate treatment

Abstract

The present study was primarily designed to develop a novel composite material composed of peat, limestone, zeolite, and activated carbon (PS-LS-ZE-AC) and to evaluate its simultaneous effectiveness in removing ammoniacal nitrogen (NH₃-N) and chemical oxygen demand (COD) from stabilised landfill leachate. Batch-scale adsorption analyses were performed to identify the optimum compositional ratios, with PS-AC were classified as hydrophobic adsorbents, with the optimum ratio identified as 1.5:2.5. LS-ZE were classified as hydrophilic adsorbents, with the optimum ratio determined as 15:25. The optimal proportion of hydrophobic to hydrophilic adsorbents was determined to be 4:4, as this ratio demonstrated superior adsorption performance for NH₃-N and COD. Characterization of composite was carried out using XRF, FTIR, and SEM. XRF analysis revealed that the main constituents were present in high concentrations of CaO and SiO₂. The composite adsorbents contained several dominant functional groups, notably O–C, C–N, Si–O–Si, O–H, N–H, and C–O. SEM testing demonstrated rough and heterogeneous porous surface of the composite adsorbent. The effects of shaking speed and dosage were examined in conjunction with the reduction of NH₃-N and COD. Fixed-bed columns (FBCs) adsorption experiments indicated reduction efficacy of NH₃-N and COD achieving 99% and 98%. An increase in flowrate resulted in shorter breakthrough and saturation times. The experimental results showed significantly more correlation with the Thomas and Yoon-Nelson compared to Adams-Bohart model. The composite adsorbent was reusable following regeneration with 0.5 M NaCl solution at pH 12, and adjusting using 1 M NaOH, achieving adsorption capacities of NH₃-N and COD 34.13 mg/g and 33.22 mg/g. These findings highlight the efficacy of PS-LS-ZE-AC-based composite adsorbents in treating stabilized landfill leachate.