Experimental, economic, and life cycle carbon footprint assessment of low-cost adsorbents for siloxane removal from landfill gas

Siloxane impurities in landfill gas (LFG) pose a significant challenge for downstream processing equipment used in energy recovery. This study investigated the adsorption capacity, cost, and environmental impact of five low-cost adsorbent materials: biochar, clinoptilolite, hydrochar, diatomaceous-earth, and crushed glass. Gravimetric analysis was used to determine the adsorption capacity of these materials for octamethylcyclotetrasiloxane (D4). The results were then used to conduct a technoeconomic analysis (TEA) and life cycle assessment (LCA), comparing the selected adsorbents with activated carbon (AC), a commonly used adsorbent for siloxane removal. The TEA revealed that the cost of LFG purification with clinoptilolite, biochar, and AC was $0.035, $0.034, and $0.033/m³, respectively, for the base case studied. The cradle-to-gate LCA showed that clinoptilolite had significantly lower carbon emissions compared with the other adsorbents, both per kg of D4 captured and per kg of adsorbent produced. The potential fate of siloxanes after adsorption was discussed, emphasizing the importance of proper treatment and disposal of spent adsorbents. Surface modification techniques were recommended to enhance the adsorption capacity and regeneration of clinoptilolite, potentially reducing cost and carbon emissions in LFG purification. These findings highlight the potential of low-cost adsorbents for sustainable LFG purification.