Development and testing of surface-based and water-based-diffusion kinetic models for studying hydrolysis and biogas production from cow manure

The hydrolytic step is usually considered the rate limiting step in the biological conversion of ligno-cellulose material into biofuels. Current optimization approach attempts to understand the mechanism of hydrolysis in order to boost production. In this study, the development and testing of a surface-based and a water-based-diffusion kinetic model for modeling biogas production from cow manure was conducted using total solid (TS) loading ranging from 8 to 10% (TS) in batch reactors. Parameter estimation using solver function of the Microsoft Excel Tool Pak revealed that, the second order water diffusion model was superior in predicting biogas production with correlation coefficients ranging from 0.9977 to 0.9995. In addition, the initial surface permeability flux of water (Kspf0) into the organic biomass and fragmentation of particles were observed to be independent events elicited by the action C1 and Cx factors respectively. The initial surface permeability flux of water was observed to increase as solids concentration increased from 8 to 9%TS while, fragmentation constants decreased. Maximum initial surface permeability flux of water (1.78E-05 m3/m2/day) was observed at 9% (TS) with a simultaneous minimization in the fragmentation rate (0.13/day). For optimal production of biofuels, appropriate quantity of C1-factor, the degree of crystallinity and particle size may be critical for efficient conversion.