Biological ensilage additives as pretreatment for maize to increase the biogas production

Several biological ensilage additives were tested on maize substrate for their effect on biogas production and preservation of ODM content. In general, the addition of some biological additives and subsequent storage for 7 weeks could enhance the biogas and biomethane production per ODM when compared to the untreated sample. A common microbial inoculent containing homo-fermentative and hetero-fermentative bacteria (Bonsilage Mais®), had no beneficial effect on biogas and biomethane production compared with the non-treated sample (−12.7% and −13.1% per ODM, respectively). More complex additives with hetero- and homo-fermentative activity (Silasil Energy®) as well as enzymes (Sil-all 4 × 4®) or bacteria and yeasts (Microferm®) did effectively increase the biogas production per ODM (respectively with 11.8, 10.1 and 14.7%). Losses in ODM content were minor in all samples. These results might indicate that more divergent biological additives involving yeasts or enzymes during ensiling are preferred as maize preservation tools for anaerobic digestion instead of a spontaneous ensilage population or to add only homo- and hetero-fermentative strains. The nature of the additive might enhance the hydrolysis step in the anaerobic digestion process by decomposing complex carbohydrate structures.