Increased dairy farm methane concentrations linked to anaerobic digester in a five-year study

Organic waste materials are sources of anthropogenic methane (CH₄ ) emissions. Anaerobic digestion (AD) is a technology that produces biogas from organic waste materials, and CH₄ is the primary component of biogas. Unintended emission of CH₄ from biogas facilities could undercut the environmental benefits of this technology. The objective of this study was to determine if the implementation of an AD system affected ambient CH₄ concentrations ([CH₄ ]) on a commercial dairy farm over 5 yr, from before installation into full operation. Concentrations at 4.5-m height on a tower receiving wind that originated from various directions, comprising components of the dairy farm such as the AD facility, crop fields, or main barn, were measured using a closed-path tunable diode laser trace-gas analyzer. In 2012 and 2013, the first 2 yr of AD operation, [CH₄ ] was not significantly different than pre-AD levels in 2011 (2.04 ± 0.01 μl L^-1 ). However, mean [CH₄ ] increased to 2.47 ± 0.03 and 2.48 ± 0.04 μl L^-1 in 2014 and 2015, respectively, and the occurrence of high [CH₄ ] (>10 μl L^-1 ) increased from <0.05% in Year 1 (pre-AD) to 12% in Years 4 and 5. These elevated concentrations were related to an increased use of food waste feedstocks over time and suggest that the biogas system was a source of fugitive CH₄ emissions. Food waste materials have a high biogas potential and are a valuable resource that require appropriate facility design and management to fully harness their benefits.