Abstract
The effects of rice plant varieties and their mechanical pretreatment on anaerobic digestion performances (total methane production potential, the methane production rate, and the lag time) were investigated under the thermophilic condition (55°C). Four rice varieties, three for forage (Oryza sativa L. cv. Leafstar, Kusahonami, and Hamasari) and one for food (Oryza sativa L. cv. Nipponbare), were subject to the investigations. Different anaerobic digestion characteristics were observed with each rice variety: lag time to observe the emergence of methane production of the Leafstar stem was 0.33 day, the shortest among all tested rice varieties. The shortest lag time was likely due to the highest content of starch in the stems of Leafstar. Mechanical pulverization as pretreatment for anaerobic digestion had no effect on the amount of total methane production, methane production rate, and lag time of the Leafstar stems. As for the methane production amount calculated based on biomass productivity, Leafstar was the highest, followed by, in the descending order, Kusahonami, Hamasari, and Nipponbare. The result suggests that forage rice is more suitable as feedstock of anaerobic digestion than common rice. The possibility of dry anaerobic digestion using Leafstar was also confirmed without ammonia inhibition to methane production by a repeated batch anaerobic digestion experiment.
