A kinetic study on methanogenesis by attached biomass in a fluidized bed

Abstract

The objective of this study is to estimate growth kinetic constants and the concentration of “active” attached biomass in an anaerobic fluidized bed, which decomposes acetic, propionic and butyric acids. The fluidized bed was operated as a methanogenic reactor with synthetic zeolite as support media. The reactor was supplied with synthetic wastewater (1000 mg COD l −1), a mixture of the above-mentioned volatile fatty acids (VFA), in the range of hydraulic retention time (HRT) from 0.25 to 2 days. After the effluent has reached a steady state in quality, batch experiments in the bed reactor were conducted using acetic, propionic and butyric acids as substrate in order to investigate the decomposition characteristics of each substrate by the attached biomass. Detached biomass from the support media was also served to batch experiments under the completely mixed condition in order to estimate parameter values of the growth kinetics of the bacteria. The changes of fatty acid concentrations with time were expressed with the Monod growth model. The two kinetics parameters, maximum specific growth rates and saturation constants, and “active” biomass concentrations were obtained by the curve fitting method. The comparison of the measured concentration of volatile suspended solids (VSS) and protein with the estimated “active” biomass concentrations indicated that a large amount of inert organic matter exists in the attached growth reactor.