Miniplant experiments showed precipitation of the components cinnamic acid, aldehyde, and alcohol from the liquid phase, because their concentration exceeded the saturation concentration. Especially the low water saturation concentration of cinnamic acid led to precipitation. In order to be able to simulate substance precipitation and dissolution in the aqueous phase and thus achieve a higher model depth, a storage term\(\dot{n}\)precipitation,i is introduced for any given component i. In every time step of the dynamic simulation, the concentration of each component in the aqueous phase is compared to the saturation concentration of that same component. If the concentration exceeds the saturation concentration, the overlap is stored in the storage term, from which it can dissolute again at lower concentrations.
The mass balance of each component in the aqueous phase is therefore described through differential equations in dependency on the reactions of the respective enzymes, the feed streams, mass transfer to the organic phase, and the precipitated amount in each time step. Equation (6) shows the generalized form of the mass balance for any given component i in the volume specific form. Equations (7) and (8) show the modified forms of the mass balance for the cofactors NADH and NAD+ respectively, considering the auto-oxidation of NADH instead of the non-existing precipitation of the cofactors.