KINETIC-BASED MODEL FOR MIXED WEAK ACID BASE SYSTEMS/

This paper describes the development of a simple kinetic model for mix ed weak acid/base systems in the model, the weak acid/base equilibria are formulated in terms of the kinetics of the forward and reverse rea ctions for the dissociation of the weak acid/bases. The parameter (com pound) H+ is also explicitly included in the model, so that pH can be calculated directly. The weak acid/bases included are water, carbonate , ammonium, phosphate and short-chain fatty acids. However, the approa ch used to develop the model is general, and can be applied to include any other weak acid/base of importance. Precipitation of CaCO3 and ga seous exchange of CO2 also have been included. The model and the appro ach on which it is based have been validated by comparing model predic tions to those obtained from equilibrium-chemistry-based models; good correlation was obtained. Compared to the equilibrium chemistry approa ch to modelling mixed weak acid/base system, the kinetic approach offe rs several advantages. In particular, the use of kinetics will facilit ate integration of the weak acid/base model with other kinetic models (biological chemical or physical). For example, the model presented he re can be readily integrated with the existing biological kinetic mode ls for wastewater treatment systems, to extend application of these mo dels to situations where an estimate for pH is essential. Furthermore by providing an estimate for pH and for the species making up the weak acid/bases, the model will simplify inclusion of chemical and physica l processes, where these are of importance.