Limitations of biochemical methane potential testing in forecasting farm-scale digester performance under psychrotrophic conditions

This study evaluated the extent to which laboratory-scale biochemical methane potential (BMP) assays predict actual methane production in a full-scale tubular anaerobic digester operating under psychrotrophic conditions. The 8 m³ farm-scale digester, situated in a cold, high-altitude climate, was retrofitted with passive solar heating, resulting in an average sludge temperature of 21.5 ± 1.2°C. In contrast, the mean ambient temperature was kept at 10.6 ± 1.4°C. BMP tests were conducted using the digester influent and effluent as substrate and inoculum, respectively, at mesophilic (35 ± 2°C) and psychrotrophic (23 ± 2°C) temperatures. The methane yield in the full-scale system (0.36 Nm³ CH₄ kg^-¹ VS), operated at an average temperature of 21.5°C, significantly exceeded the values obtained in the batch BMP tests (0.19 Nm³ CH₄ kg^-¹ VS at 35°C and 0.18 Nm³ CH₄ kg^-¹ VS at 23°C). No statistically significant correlation was found between laboratory and field data. These findings show the limited predictive power of BMP testing for farm-scale digester performance in decentralized, low-temperature environments.