Production of modified biochar to treat landfill leachate using integrated microwave pyrolytic CO2 activation

Abstract Improper handling of leachate in landfills leads to leakage to the surrounding environment and pollute soil surface, runoff water and groundwater among other. A new approach that integrates self-purging microwave pyrolysis and pyrolytic activation was developed to transform empty fruit bunch (EFB), being a plentiful waste in oil palm plantation, into microwave modified biochar (MB). The performance of steam and CO2 as activating agent was contrasted, and the subsequently produced MB was then applied to treat actual landfill leachate via batch and continuous adsorption operation. Using a single-mode microwave system, the pyrolysis approach integrating steam or CO2 activation showed a high heating rate and process temperature of up to 170 °C/min and 600 °C, respectively. However, MB produced via CO2 activation (MB-CO2) showed significantly higher surface area (95.6 m2/g) and mass yield (92.0 wt%) compared to that produced via steam activation (MB-Steam) (29.3 m2/g of surface area, 84.0 wt% of mass yield). The volatile matter of both MB-CO2 and MB-Steam were low at 19.0–22.0 wt% leading to MB with high content of fixed carbon (69.3–72.0 wt%). Compare to MB-steam, the treatment with MB-CO2 in fixed bed column (10 g) achieved a better adsorption efficiency of NH3-N up to 5.0 mg/g and 43.0 mg/g of COD. Our findings demonstrate that microwave pyrolysis combined with CO2 activation is an auspicious technique preferable to steam activation for the generation of desirable MB from oil palm waste to treat hazardous landfill leachate.