2 nd Mercosur Congress on Chemical Engineering 4 th Mercosur Congress on Process Systems Engineering 1 MODELING OF PROTEIN HYDROLYSIS KINETIC USING AN ALKALINE PROTEASE FROM BACILLUS LICHENIFORMIS M. Fuentes 1 , C. Thompson 1 , M.C. Mussati 1 , P.A. Aguirre 1,2 and N.J. Scenna 1,3 * 1 INGAR (CONICET-UTN), Avellaneda 3657 (3000) Santa Fe, Argentina. 2 Fac. Ing. Qca., UNL, Santiago del Estero 2829 (3000) Santa Fe, Argentina. 3 Depto. Ing. Qca. - GIAIQ- UTN FRR, Zeballos 1341 (2000) Rosario, Argentina. Abstract. Many industrial and agricultural wastewaters contain appreciable amounts of proteins. Under anaerobic conditions proteins are first hydrolyzed and degraded by proteolytic enzymes into peptides and individual amino acids. The peptides and amino acids are then acidified into volatile fatty acids (VFA), hydrogen, ammonium, and reduced sulfur. The VFA are further converted by acetogens into acetate and H 2 /CO 2 , both of which are lastly converted to methane by methanogens. The aim of this work is to investigate the kinetics of protein hydrolysis for its further application in modeling of anaerobic degradation of complex substrates. A bacterial alkaline serine protease (EC 3.4.21.14, Sigma) from Bacillus Licheniformis, an anaerobic microorganism, is used. Gelatin, which is usually found in meat wastes; albumin, in whey effluents; and soy proteins, were chosen as characteristic molecules to represent the proteins commonly found in waste effluents. A glass stirred tank (batch) reactor (1.5L) was used as experimental device. The Michaelis-Menten type model and a model considering a zero-order hydrolysis with respect to the substrate and a second-order enzymatic denaturalization are investigated to approximate the experimental data obtained by the pH-stat method. By combining the pH-stat and pH drop methods, a hydrolysis conversion of 24% and 15% higher than the experimental values was predicted for gelatin and soy, respectively. The influence of the temperature on the kinetic parameters in the range of 25°C to 50°C was assessed at pH 8. The non-competitive inhibition by VFA was measured during hydrolysis of gelatin. An increase in the acetic acid concentration increases the inhibitory effects. Keywords: Bacterial Protease, Dynamic Modeling, Kinetic Parameters, Protein Hydrolysis. 1. Introduction The bacterial proteases have found wide scale industrial application. Industries in wich proteases are used include the pharmaceutical industry, the leather industry, the manufacturing of protein hydrolizates, the food industry and the waste processing industry. The aim of this work is to study the protein hydrolysis to be considered in the modeling and design of anaerobic treaty systems of a complex substrate in which composition the proteins are present. In general, the reaction rates of enzymatic proteolyses are assumed to follow either Michaelis-Menten or first- order kinetics. Richards (1956), Ottesen (1956), Biszku et al. (1973), Solti et al. (1975) described the enzymatic hydrolysis of peptide bonds by the Michaelis-Menten equation following a pseudo-first order kinetics. First order kinetics is the consequence of a mechanism where the rate controlling step is the first attack on the tertiary structure of the protein (Vorob’ev et al., 1996). González-Tello et al. (1994) considered zero-order hydrolysis with respect to the substrate and second-order enzymatic denaturalization. The substrate and product concentrations in these rate equations are generally expressed either in terms of the number of the hydrolizable peptide bonds or of the degree of hydrolysis (DH). It is important to point out that competition for the active site * To whom all correspondence should be addressed. Address: INGAR -Instituto de Desarrollo y Diseño- Avellaneda 3657 (3000) Santa Fe, Argentina. E-mail: nscenna@ceride.gov.ar