Anaerobic digestion of maize focusing on variety, harvest time and pretreatment

The methane potential of six varieties of fresh maize (whole plant) harvested at three different times and of maize silage (whole plant) in two particle size distributions was experimentally determined in batch assays. Fresh maize gave the highest methane yield/hectare at late harvest (6270 m3 CH4 (104 m2)−1). The methane yield/wet weight (WW) increased from 80 (early harvest) to 137 m3 CH4 (t WW)−1 (late harvest). Maize harvested at different times, or different varieties of maize had similar specific methane production/volatile solids content (m3 CH4 (kg VS)−1). The measured yield m3 CH4 (kg VS)−1 was 84% of the theoretical methane potential. The estimated ethanol yield was between 2.5 and 3.5 t ethanol (104 m2)−1. The energy yield was 62 and 19–22 MWh (104 m2)−1 if fresh maize (whole plant) is used for methane or ethanol production respectively. Reducing the particle size of maize silage to an average size of approximately 2 mm increased the methane yield m3 CH4 (kg VS)−1 by approximately 10%.