Biogas Production from Maize Grains and Maize Silage

The main objective of this work was anaerobic digestion of maize grains and maize silage and biogas production from these crops. Maize grains were treated using one-stage and two-stage anaerobic techniques; using hydrolysis and acidification as the first stage and methanogenesis as the second stage. Processing nonacidified maize grains in an anaerobic reactor is more stable, though the anaerobic degradation start-up period is longer, specific production of biogas is lower and excess sludge production is higher as from acidified maize grains. Maximum specific biogas production was 0.72 m·kg of volatile suspended solids – VSS (nonacidified maize) (at 35oC) and 0.770 m·kg VSS (acidified maize) during anaerobic digestion of maize grains. At average yield of 9 t·ha of dry maize 5,450 Nm·ha of methane can be generated from nonacidified maize and 5,828 Nm·ha methane from acidified maize grains. Due to low nitrogen content in maize silage, anaerobic digestion of maize silage is rather unstable. Alkali or complementary substrates with higher nitrogen content (e.g. excess sludge from wastewater treatment plant or manure) can be used for anaerobic process stabilization. Maximum measured biogas specific production from maize silage reached 0.655 m·kg VSS. At average yield of 30 t·ha of the dry maize silage 9,058 Nm·ha of methane can be generated.