Effect of conservation time and addition of lactic acid bacteria on the biogas and methane production of corn stalk silage

The effects of ensiling and baling processes, of the application of silage additives and of the storage period of corn stalks on methane production have been assessed through anaerobic digestion batch experiments, in order to evaluate the storage efficacy of corn stalks used as feedstock in biogas plants. Ensiling has proved to be a good method for corn stalk preservation for methane production, as it helps to maintain low pH values of the biomass and reduce volatile solid losses during storage, even for longer periods than 3 months. It has been shown that ensiling does not affect the cumulative methane production of corn stalks but does improve the methane production rate at the beginning of the process. This can be attributed to an increase in ethanol during ensiling, which favours the rapid start of anaerobic digestion. Corn stalks inoculated with lactic acid bacteria have shown similar pH and slightly higher lactic and acetic acid contents than untreated ones, but these changes have not had a practical effect on methane production. Dry baled corn stalks have shown a lower methane production than ensiled stalks, due to the respiration process that takes place in the field during the wilting period and to the reduction in degradability, because of drying. Nevertheless, the choice of an adequate harvest chain of corn stalks is very important in order to obtain higher energy efficiency from ensiled corn stalks than from dry conservation. If the harvested biomass per hectare is very low, ensiled corn stalks could be an inefficient way of managing this biomass for methane production.