ELSEVIER Journal of Biotechnology 43 (1995) Ill- 124 A new balance equation of reducing equivalents for data consistency check and bioprocess calculation A.-P. Zeng zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO GBF - Gesellschajfir Biotechnologische Forschung mbH, Biochemical Engineering Diuision, Mascheroder W eg 1. D-38124 Braunschw eig. Germany Received 19 June 1995; revised 3 August 1995; accepted 8 August 1995 zyxwvutsrqponmlkjihgfedcbaZYXW Abstract The reducing equivalent (RE) balance is a basic equation for data consistency check and calculations of bioprocesses. The macroscopic approach is often used because it does not require detailed knowledge of metabolic pathways. In this work, the conventional Minkevich-Eroshin balance equation is examined with data of anaerobic glycerol conversion by Klebsiella pneumoniae and Clostridium buty ricum as examples. It is shown that the Minkevich-Eroshin equation is very insensitive to measurement errors in products of less dominance and/or with relatively low reductance degree. Relatively large deviations from experimental values are encountered when the Minkevich-Eroshin equation is used for the calculations of these products. To overcome some of these shortcomings an improved RE balance equation is proposed that is based on ‘reductance equations’ of substrate conversion into the individual carbon containing products (including biomass). The proposed new equation significantly improves the performance of the RE balance equation for data consistency check and for the calculations of unknown variables with relatively low reductance degree. The rationale for this is that it considers merely the REs that really participate in the bioreactions. The use of the proposed method requires no detailed knowledge of metabolic pathways and is therefore of macroscopic nature. It can be reduced to the pathway balance equation if the pathways are known. Keywords: Reducing equivalent balance; Data consistency; Process calculation; Glycerol conversion; 1.3~Propanediol 1. Introduction Yield and rate equations are the basis for quantitative analysis, modeling and control of bioprocesses. Among others, the reducing equivalent (RE) balance is an important equation for deriving yield and rate equations (Andrews, 1993). The macroscopic balance approach is often used for this purpose (Minkevich and Eroshin, 1973; Erickson et al., 1978; Roels, 1983). It has also been used for data analysis of indirect measurements (Cooney et al., 19771, for data consistency check (Erickson et al., 1979), and for the detection and rectification of measurement errors (Wang and Stephanopoulos, 1983). In the absence of knowledge about the metabolic pathway of a bioprocess the macroscopic balance approach can give some valuable insights into the process as it can show the channeling of substrate available electron and hence energetic efficiencies (Solomon et al., 1995). For processes, of which the metabolic pathways are known, a balance equation of RE may be established by 016%1656/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0168-1656(95)00122-O