Potential of composite adsorbent comprising peat, limestone, zeolite, and activated carbon for the treatment of diffused soluble contaminants

This study aimed to develop a novel composite adsorbent combining peat (PS), limestone (LS), zeolite (ZEO), and activated carbon (AC), with ordinary Portland cement (OPC) as a binder (40% by weight), for the simultaneous removal of ammoniacal nitrogen (NH₃-N) and chemical oxygen demand (COD) from stabilized landfill leachate. The composite was characterized using X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, and pH at zero-point charge (pHzpc). The material exhibited high SiO₂ and CaO content, functional groups (e.g., Si–O-Si, N–H, O–H, C–O, C–N, and O–C.), a rough and heterogeneous surface morphology, a surface area of 105.96 m²/g, and a pHzpc of 11.25. Batch experiments determined optimal adsorption conditions: 200 rpm shaking speed, 120-min contact time, pH 7, particle size of 2.36–3.35 mm, and dosage of 57 g/L. The Langmuir isotherm model provided the best fit for NH₃-N and COD adsorption with adsorption capacities of 26.18 mg/g and 47.39 mg/g, respectively (R² = 0.9941 and 0.9814). Kinetic studies indicated pseudo-second-order kinetics, suggesting chemisorption as the rate-limiting process. These findings demonstrate the composite (PS, LS, ZEO, and AC) potential as an efficient and sustainable adsorbent for treating stabilized landfill leachate. Further studies should focus on evaluating the performance of composite adsorbents for the removal of NH₃-N, COD, or other pollutants from mining industry, domestic, or combined effluents, as well as their potential application in air pollution control.