Abstract
In this study, we focused on the rice straw collection systems for co-digestion with sewage sludge at the Nagaoka Wastewater Treatment Plant. The collection period for rice straw in this area was between September and October, and rice straw was collected usually 6 to 8 times in that period. The amount of collectable rice straw in October was 68% of that in September, because the rice straw in October was stuck to the surface of paddy. In addition, the collection unit was generally composed of 3 participants. If the collection period was 2 days, then the amount of maximum collectable rice straw for the unit was about 24 Mg (water content, 20%), and the collection was accomplished using the “maximum collection system”. However, if the period was more than 2 days, the amount was 39.2 Mg (3 days) or 58.8 Mg (4 days), and the collection was accomplished using the “minimum farm machines system”. The reason was that collection at the first cite and turning over at the second cite were performed at same time in “minimum farm machines system”. At Nagaoka Wastewater Treatment Plant, 1916 Mg of rice straw (water content, 20%) is required for co-digestion with sewage sludge. The number of participants and farm machines for the collection of 1916 Mg of rice straw was as follows : 42 participants and 14-15 farm machines for the “minimum farm machines system” ; 36 participants, 14-15 farm machines, and 24 rakes for the “maximum collection system” ; and 57 participants and 19-20 farm machines for the “twice turning over system”.
