A practical kinetic model that considers endproduct inhibition in anaerobic digestion processes by including the equilibrium constant

Transport and thermodynamics constrain belowground carbon turnover in a northern peatland

“…This level surpasses the theoretical threshold for microbially mediated processes (Schink, 1997) but coincides with the threshold determined for several anaerobic freshwater systems Chin and Conrad, 1995). The small DG r thus did not inhibit methanogenesis in principle but it may have slowed the process, if the dependence of kinetics on DG r near thermodynamic equilibrium is taken into account (Hoh and Cord-Ruwisch, 1996). Homoacetogenesis and fermentative processes, yielding H 2 , DIC, and acetate, finally had to proceed close to the thermodynamic limit of 0 kJ mol À1 substrate at larger depth (Fig.…”

“…Decomposition of organic matter must thus proceed at high DIC and CH 4 concentrations, which may range from 1 to 10 mmol L À1 (Romanowicz et al, 1993;Eilrich, 2002). In analogy to model predictions and observations in technical systems (Hoh and Cord-Ruwisch, 1996), we postulate that these geochemical conditions decrease Gibbs free energy available for methanogenesis towards a critical level and thermodynamically constrain further methanogenic decay of organic matter. The decomposition process would then ultimately be limited by the transport of CH 4 to the atmosphere by diffusion or ebullition of gas bubbles since-in contrast to DIC and intermediates of the decomposition process-no known sinks for CH 4 exist in the peat.…”

“…Utilization of VFAs may proceed close to the thermodynamic limit (Jackson and McInerney, 2002) but À20 to À25 kJ mol À1 (substrate) seem to be required for methanogenesis, which is equivalent to 1/4-1/3 of the energy necessary for ATP generation (Schink, 1997). Such values may be reached in anaerobic environments and slow methanogenesis until biodegradation ceases (Hoh and Cord-Ruwisch, 1996). Also micronutrient availability and toxic effects of decomposition products may affect methanogenesis in peatland soils and have to be considered (Bergman et al, 1999;Basiliko and Yavitt, 2001).…”

Optimal biogas production in a model for anaerobic digestion

“…[12,13], and (H3) is satisfied by Holling type IV (Haldane) functions, [9]. Possible representations of g V and g H are modified Monod functions of the form g(α, β) = g α (α)I (β), where g α is a Monod function and I (β) is a positive, decreasing function, or functions of the form g(α, β) = m α (α − kβ)/(k α + α + μ β β) for (α − kβ) > 0, see [11,16,21]. If k is zero or small, this latter function is approximated by g(α, β) = m α α/(k α + α + μ β β), which also satisfies (H2) and (H4).…”

Sensitivity analysis and parameter estimation in a model of anaerobic waste water treatment processes with substrate inhibition

“…Almost all mesophilic bacteria are very sensitive to changes in pH and they cannot grow when pH is lower than 5.5. VFA accumulation can lead to a drop in pH and in this way it can suppress the microbial growth of all groups microorganisms [3,5,7,10,15]. For simplicity we assume in our model that inhibition by VFA occurs only with respect to methanogenic bacteria.…”