Challenges of using ensiled sorghum in anaerobic co-digestion with beef cattle manure: Effects on process stability and nutrient recovery

Abstract

This study evaluated the performance of anaerobic co-digestion (ACoD) of manure from confined beef cattle with Bolivian giant sorghum under batch conditions. Sorghum was tested in fresh and ensiled forms, with and without panicles, to assess process stability, biogas and methane production, and the agronomic quality of the resulting digestate. Treatments with fresh sorghum showed performance similar to that of anaerobic mono-digestion of manure, with stable operation and high methane yields. In contrast, ensiled sorghum led to process instability, characterised by volatile fatty acid accumulation, VA/TA ratios above 2.0, and reduced methane production. The treatment with ensiled sorghum, including panicles, exhibited the lowest stability and produced digestate with reduced nitrogen, phosphorus, and potassium contents. These results demonstrate that, although ensiling ensures biomass preservation, it can negatively affect process stability and nutrient recovery in batch ACoD systems. Adjustments to substrate proportions or process configurations are required to enable the efficient use of ensiled energy crops.