The effects of biochar on physical properties and methane oxidation capacity of cover soils from two Dutch landfills

Designing methane oxidation systems (MOS) requires an understanding of soil physical properties and their changes to create an optimal habitat for methanotrophs. A short-term study was carried out to investigate the suitability of biochar as an additive to improve soil properties for use in MOS. The results from our batch experiments showed the effects of biochar on the particle size distribution, compaction and methane oxidation rates on two Dutch landfill cover soils collected from Braambergen landfill (fine-grained soil) and Wieringermeer landfill (more coarsely grained soil). When soils were amended with 6% (w/w) biochar, the particle size distribution curves shifted to enlarge the median diameter (D50) in both soils. The methane oxidation rate increase was observed only on fined-grained soil with biochar with compaction, but both soils showed reduction in bulk density. Biochar addition enhanced methane oxidation rate in fine-grained soils when moisture content was kept constant at 17.8%, corresponding to a capillary pressure of >1000 hPa. Contrastingly, in coarsely grained soil, cumulated methane oxidation was reduced by 88.5% with biochar addition, despite the median diameter increase by 6%. Possibly, too high capillary pressures inhibited methanotrophic activity. The Procter density (DPr) decreased in both soils, but the optimum water content increased in the fine soil and decreased when biochar was added to the coarse soil. As expected, the biochar improved D50, and optimum water content and methane oxidation in fine-grained landfill cover soil.