The kinetics of anaerobic digestion of farm wastes

Abstract

The conversion of animal excreta and similar feedstocks to biogas in single-stage, continuous-flow anaerobic digesters running in steady-state conditions can be described in terms of undegradable material and hydrolysis and fermentation of two solid components plus conversion of acid and hydrogen plus carbon dioxide to methane. These reactions, while linked in provision of substrates for the different bacterial groups, can be regarded as separate continuous-cultures, each with one limiting substrate, but with nitrogen in excess. The substrate utilisations can then be described by simple kinetic equations applicable to bacterial growth in pure-culture chemostats. The degradation of solids is the overall rate-limiting reaction and the use of two biodegradable solids, distinguished more by particle size than by chemical composition, explains some apparent anomalies in solids degradation and gas production at different retention times. While the general principles apply to any waste, the values of constants used in the equations depend on the solids in a particular feedstock. Temperature effects on digestion are explained by using a recentlysuggested formula for modification of the maximum growth rates of the bacteria with temperature. This distinguishes between mesophilic and thermophilic digestions. Inhibitory effects of ammonia and high input solids concentrations can also be described by modification of maximum bacterial growth rates.

Biochemical, morphological, and yield responses of lady's finger plants to varying ratios of palm oil mill waste (decanter cake) application as a bio-fertilizer

“…Additionally, it compares well with the 0.07-0.08 day −1 reported by Kang et al (2014) for digesting dairy manure at 35 °C. Nevertheless, it is generally within the value (0.08 day −1 ) reported by Hobson (1983) for slowly degradable cow slurry. Although the impact of temperature is obvious the culture adapted well to the new substrate at 20 °C.…”

Mathematical modelling of anaerobic digestion of biomass and waste: Power and limitations

“…Based on the implementation of Mosey [32] and Hobson [42], the hydrogenotrophic methanogenesis component was included in the models, which, in normal situations, accounts for about 30% of the CH 4 production. The inclusion of H 2 as a variable introduces a subtle system of balances in the model.…”

Enzymatic hydrolysis of polysaccharide‐rich particulate organic waste

“…Numerous kinetic models have been used to describe the hydrolytic kinetics, including the chemical first-order model (Eastman and Ferguson, 1981), the biological first-order model (Valentini et al, 1997), the half-order biomass kinetic model (Rozzi and Verstraete, 1981), the A-order biomass kinetic model (Valentini et al, 1997), the Michaelis-Menten equation (Valentini et al, 1997), the Monod equation (Hobson, 1983), the Haldane equation (Andrews and Graef, 1971), the Contois model (Henze et al, 1995), the ChenHashimoto model (Chen and Hashimoto, 1980), the two phase model (Vavilin et al, 1996), the step diffusion equation (Cecchi et al, 1990), the shrinking core model (Negri et al, 1993), the flux model (Terashima and Lin, 2000), and the surface-based kinetic model (Sanders et al, 2000). In fact, the hydrolytic models were all useful, according to data of these cited authors, and some were equally effective as each other (Cecchi et al, 1990;Valentini et al, 1997;Vavilin et al, 1996).…”