Investigation of biogeochemical landfill covers incorporating different biochars and alkaline industrial byproducts for landfill gas mitigation: A column experiment study
Gaurav Verma, Krishna R. Reddy, Stefan J. Green
Abstract
Fugitive emissions of methane (CH 4 ) and carbon dioxide (CO 2 ) from municipal solid waste (MSW) landfills pose significant environmental risks if not captured. To address this, researchers at the University of Illinois Chicago developed a biogeochemical cover (BGCC) comprising a biochar-amended soil (BAS) layer and a basic oxygen furnace (BOF) slag layer to simultaneously mitigate CH 4 and CO 2 . Previous laboratory experiments with BGCC comprising pinewood-derived biochar (PW)-amended soil and BOF slag (BGCC-PWBOF) demonstrated substantial potential for CH 4 and CO 2 mitigation. However, reliance on PW biochar and BOF slag may face challenges due to limited availability near landfill site location, which motivated the investigation of BGCC, which consists of different biochar and alkaline materials. Therefore, this study compared two BGCC configurations-one with rice husk biochar and cement kiln dust (BGCC-RHCKD) and another with pinewood biochar and BOF slag (BGCC-PWBOF)-against a conventional soil cover (SC) system in a laboratory column experiment. All three covers were exposed to synthetic landfill gas across four phases with varying CH 4 influx rates. Surface emissions and gas concentrations were continuously monitored. After the experiment, the covers were dismantled, and samples from multiple depths were collected for physico-chemical characterization, microbial community analysis, and batch tests to determine CH 4 oxidation rates and residual carbonation capacity. Results showed that under moderate CH 4 influx rates (20.77–22.80 g CH 4 /m 2 -day) in Phase 1, BGCC-RHCKD and SC achieved peak CH 4 removal efficiencies of 67.3 % and 74.2 %, respectively. The CKD layer in BGCC-RHCKD maintained 100 % CO 2 removal across all phases without breakthrough, whereas BOF slag in BGCC-PWBOF experienced breakthrough after 16–22 days due to desiccation. The highest CH 4 oxidation rates reached 2042.8 μg CH 4 /g-day (BGCC-RHCKD), 455.3 μg CH 4 /g-day (BGCC-PWBOF), and 372.1 μg CH 4 /g-day (SC) and were strongly correlated with the relative abundance of methylotrophic bacteria, especially Methylobacter luteus , in 16S rRNA gene amplicon profiles. Overall, the BGCC-RHCKD system offers an effective solution for mitigating both CH₄ and CO₂ emissions, while the SC system is effective for CH₄ emissions. • Biogeochemical cover (BGCC) demonstrates potential to mitigate fugitive landfill gas emissions of methane and carbon dioxide. • BGCC consists of biochar-amended soil overlain by a CO 2 sequestration layer • Different biochars and alkaline industrial byproducts in the BGCC were tested through column experiments. • Two BGCC configurations: (1) rice husk biochar with cement kiln dust, and (2) pinewood biochar with BOF slag were compared to a soil cover (SC). • BGCC comprising rice husk and cement kiln dust mitigated CH 4 and CO 2, while the SC system is effective for CH₄ emissions. • Rates of methane oxidation were positively correlated with the percentage of microbial communities that were methylotrophs, as assessed by 16S rRNA gene amplicon sequencing.