Lower methane emissions from full-scale stockpiles of the solid fraction of separated digested slurry with biochar amendment

Abstract

Field application of biochar can be challenging due to loss through dust release and uneven spreading, and incorporation of biochar into organic fertilisers has been proposed as a practical application strategy. If biochar is added to the solid fraction prior to field application, it must be incorporated before or during storage, making its effect on storage emissions important to investigate. This study investigated how biochar addition to the solid fraction from separated digestate affected emissions during storage. Emissions from two full-scale stockpiles were determined over 85 days using the backward Lagrangian stochastic dispersion model combined with up- and downwind concentration measurements. One stockpile was amended with 10% (w/w) biochar, while the other was unamended. The CH 4 emissions were consistently lower from the biochar-amended stockpile during both covered and uncovered periods. Higher oxygen concentrations across depths and elevated core temperatures in the biochar-amended stockpile indicate improved aeration and enhanced aerobic degradation. Emissions of N 2 O and NH 3 were below measurable levels in both treatments. To the best of current knowledge, this is the first field-scale study to quantify the effect of biochar amendment on gas emissions from stockpiled solid fractions of anaerobically digested slurry. The results provide field-scale evidence that biochar enhances gas diffusion and shifts decomposition towards aerobic pathways, suppressing methanogenesis without increasing NH 3 or N 2 O emissions. These findings advance the state of the art beyond small-scale and composting studies by demonstrating that the effect of biochar on CH 4 emissions is detectable and consistent at full scale under practical field conditions.