Piggery wastewater treatment is one environmental challenge for Japanese tiny pig farmers. Dry anaerobic digestion would be promising technology because digestion occurs at low water content (ca. 80%) without liquid digestate generation. However, this process requires an expensive pump or mixer for feedstock and inoculum mixing in continuous system. This study focused on the batch operation and stirring frequency for more simple operation. Batch dry-thermophilic anaerobic co-digestion of rice straw and pig urine was conducted. During digestion, stirring was conducted at different frequencies (no stirring(Do), 1 time every 1 day(D_1), 3 days(D_3) and 7days(D_7)) in the air. Results showed that more frequent stirring decreased CH4 yield. CH4 yield at D_0 was similar with D_3 and D_7, while both CH_4 generation rate and CH_4 yield at D_1 were 65% of those of Do. Methanogens inhibited by the oxygen exposure with stirring should be considered as an important inhibition factor. These suggest that effective digestion is possible on the batch operation without any stirring during the digestion.
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