Enhanced Landfill Methane Oxidation Using Activated Biochar

Biochar, a solid porous product derived from waste biomass, has garnered profound attention from the geoenvironmental engineers in the recent years, due to its ability to absorb wide range of gaseous and liquid phase contaminants. One important application of biochar that has been explored recently is the use in landfill cover soil to enhance microbial methane oxidation. The unique properties of biochar such as high-internal porosity, high-moisture retention, and presence of recalcitrant carbon compounds offer conducive environment for the methane oxidizing microbes to proliferate and thrive in the long-term exposure to landfill methane, thereby enhancing aerobic methane oxidation and mitigating landfill methane emissions. Although biochar has shown promising potential to enhance methane oxidation, the addition of inert biochar in the landfill cover soil leads to an initial lag phase due to the time required for microbial acclimation and may result in lower methane oxidation rates in comparison to the soil alone which has already been exposed to the landfill gas. However, once the microbes are acclimated, the effect of biochar kicks in and transcends the capacity of soil alone to oxidize landfill methane. This paper investigates reduction of the initial lag phase caused by addition of inert biochar using an activated biochar. Activated biochar was prepared by soaking biochar in a methanotrophic bacterial consortium isolated from a landfill cover soil. Several series of laboratory batch and column experiments were performed with activated biochar amended soil, non-activated biochar amended soil, and unamended soil to quantify methane oxidizing potential. DNA based 16S rRNA gene amplicon sequencing was performed to characterize and compare the microbial community. The activated biochar amended soil showed higher methane oxidation rates and efficiency from the beginning of the incubation in batch and column experiments in comparison to the non-activated biochar amended and unamended soils. The cumulative methane uptake of 10% non-activated biochar amended soil was lower than the unamended soil until initial 50 days of batch incubation which increased rapidly thereafter. The carbon dioxide generation and significant increase in methylotrophic relative abundance confirmed methane oxidation. Overall, the activated biochar showed promising potential to reduce the initial lag phase and enhance microbial methane oxidation in landfill cover soil.