An estimation method of decay coefficients of anaerobic bacteria involved with methanogenesis is experimentally discussed from the aspect that decay phenomena have an important role in biofilm development and its composition.
Attached biomass in a methanogenic fluidized bed was collected and incubated for more than 100 days without any substrate addition. During the incubation, batch tests of substrate consumption were conducted to estimate each concentration of “active” biomass which decomposes acetate, propionate or butyrate. The growth increment in bacteria during the batch tests was taken into consideration, when the “active” biomass concentrations were estimated. In addition, the biomass concentrations were corrected by subtracting biomass increment due to the production of fatty acids from decomposition of biomass decayed during incubation. Neglecting the increments of the biomass during the batch tests and incubation caused a significant error in the estimation of decay coefficients.
The decay cefficients of acetate, propionate and butyrate decomposing bacteria were estimated at 0.014, 0.015 and 0.024 [day^-1] , respectively, based on the decrease in “active” biomass concentrations with incubation time. The coefficients are available to investigate the accumulation of inactive biomass in the anaerobic biofilm.