Comparative evaluation of biochemical methane potential of various types of Ugandan agricultural biomass following soaking aqueous ammonia pretreatment

The feasibility of pretreatment involving soaking in aqueous ammonia (SAA) for the anaerobic digestion (AD) of eight different types of agricultural biomass of Ugandan origin was investigated. Moderate pretreatment temperatures of 60 and 90 °C were employed, and the NH₃ concentration, solid-to-liquid ratio, and pretreatment time were fixed at 15.0% (w/w), 1:6, and 6 h, respectively. The delignification efficiencies of the SAA pretreatment ranged from 51.1 to 76.6%, and the maximum value was observed for maize bran pretreated at 90 °C. Biochemical methane potential experiments proved that the breaking of the complex bonds of lignin made fermentable sugars easily accessible to microorganisms. In all cases, the SAA pretreatment enhanced the methane potential of the eight types of Ugandan biomass compared with its untreated counterparts. The pretreated maize bran exhibited the highest methane yield of 291.5 mL CH₄/g COD, which is 83.1% of the theoretical conversion. SAA followed by AD is useful for employing Ugandan agricultural biomass as a renewable energy source.