Anaerobic digestion by a fixed and fluidized hybrid reactor packed with carbon felt

This paper reports the effects of an anaerobic fixed and fluidized hybrid (AFFH) reactor packed with carbon felt on the performance of methanogens supplied with acetate, lactate, and propionate as organic substrates. The reactor had a short start-up time and gave stable degradation. The average removal of dissolved organic carbon was 88%, and the methane production rate was 798 ml/l reactor/day at an organic loading rate of 6.34 g/l reactor/day. After the fluidized bed was taken out and fermentation was continued with only the fixed-bed reactor, the removal of dissolved organic carbon decreased to 62% and the methane production rate decreased to 638 ml/l reactor/day at the same organic loading rate as before. The AFFH reactor performed better than the fixed-bed reactor. Propionate concentrations as high as 10 000 mg/l did not adversely affect methane production. Scanning electron microphotograph indicated that the microbes immobilized on the fluidized carbon felt were mainly coccus- or diplococcus-shaped Methanosarcina-like cells, short rods of Methanosaeta-like cells, and long rods of Methanobacterium-like cells. Methanosarcina-like cells predominated in the fixed carbon felt. The diversity of methanogens in the fluidized carbon felt could play an important role in methane fermentation. These results indicate that an AFFH reactor packed with carbon felt supports effective anaerobic digestion.