Y

In a similar way as shown in Example 5 for each chemical compound, the values of y, DGe, and DHe can be calculated for a large number of relevant compounds. Table 3 contains all relevant stoichiometric and energetic information for growth systems, clearly shown in the following. A point of attention is the finding (Table 3) that for biomass the degree of reduction depends on the N source used in the growth system. For example y = 4.2 for NH4+ and 5.8 for NO— as N source. This is a consequence of the reference definition. The advantage is that the N source disappears from the stoichiometric calculations using y, DGe, and DHe (Examples 7a, 7b, and 8b). The defined reference system is closely related to the generalized degree of reduction as defined by Roels (1) and Erickson et al. (28). It can be seen that for reduced organic compounds y is between 0 and 8 (per C-mol). For inorganic compounds, such an upper limit does not exist (because there is not a normalization per atom). For O2, y is negative ( — 4), which is logical for an acceptor. DGe is related to the conventional redox potential of redox half reactions (DGe1 = — FE0). DGe is calculated using HCO— (the most abundant form of carbon dioxide at pH = 7); DHe has been calculated using CO2 (gas) as reference, to take the large heat effect of HCO— r CO2 (gas) into account.

Table 3. Calculated c, DGe1, and DH Values for Chemical Compounds under Standard Conditions

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