Anaerobic model for high-loaded or high-temperature digestion – additional pathway of acetate oxidation

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Current digestion models cannot properly simulate processes that are operated under high loadings or high temperatures. A modification to existing models has been implemented by adding important missing degradation pathways, to accommodate these high loaded and high temperature anaerobic systems without artificially recalibrating the model parameters. This degradation pathway relies on the use of an alternate acetate oxidizing mechanism that is more tolerant to ammonia than the aceticlastic pathway. Inhibition values have been estimated and a logistic function has been used to apply ammonia inhibition. The model also relates metabolic activity to unionised species such as undissociated acetic acid as substrate (though not obligatory for all organisms) and unionized ammonia as inhibitor. The model also incorporates all important chemical species and activity coefficients in the equilibrium chemistry module (such as the phosphate buffer), resulting in more accurate pH predictions which is crucial for proper modeling of CO and NH stripping. This model can now be used to simulate processes that are operated under conditions where free ammonia inhibition can be an important factor for process efficiency and substrate conversions.