Gasification biochar from biowaste (food waste and wood waste) for effective CO₂ adsorption

Biochar is newly proposed as an innovative and cost-effective material to capture CO₂. In this study, biochar was produced from feedstock mixtures of food waste and wood waste (i.e., 20%:80% WFW20, 30%:70% WFW30 and 40%:60% WFW40) by gasification. The two biochar adsorbents containing the highest percentage of food waste, i.e., WFW40-K and WFW40-KC, were activated by KOH and KOH + CO₂, respectively. The biochar adsorbents were then tested for CO₂ adsorption at room temperature of 25 °C by using a volumetric sorption analyzer. The WFW20 showed the highest CO₂ adsorption capacity, while higher percentage of food waste in the feedstock was unfavorable for the CO₂ adsorption. The presence of N and S on the biochar surface was the primary contributor to the high CO₂ uptake on WFW20. The development of micropores by KOH activation significantly increased the CO₂ adsorption on WFW40-K, but KOH + CO₂ activation could not further increase the development of micropores and subsequent CO₂ adsorption. Moreover, WFW40-K showed >99% recyclability during 10 consecutive adsorption-desorption cycles. The biochars derived from biowaste (food waste and wood waste) could be effective adsorbents for CO₂ capture by providing green solution for food waste recycling.