Mathematical modelling of integrated chemical, physical and biological treatment of wastewaters

The development of a kinetic-based model to simulate chemical, physical and biological processes in three phase (gaseous-aqueous-solid) mixed weak acid/base systems is described. The chemical processes are expressed in terms of the kinetics of the forward and reverse reactions for the dissociation of the weak acid/bases. In this approach the H⁺ and all the species of the weak acidfbases of interest are included and the pH is calculated directly from H⁺ via pH = -log (H⁺). The advantage of this approach over the alkalinity/equilibrium chemistry approach is that kinetics are used throughout. Also, the approach is general and can be applied to any combination of mixed weak acid/base systems. The kinetic expressions of the carbonate, phosphate, ammonia, acetate and water systems, including the kinetics of the three phase chemical processes viz. precipitation/dissolution of calcium and magnesium phosphates and carbonates and gas stripping/dissolution of O₂, CO₂ and NH₃, were programmed into the AQUASIM shell package to generate simulation results. The chemical processes part of the model was validated by comparing steady state model predictions with those obtained from equilibrium chemistry based models such as STASOFT I and III (Loewenthal et al., 1986, 1991). Virtually identical results were obtained. The kinetic approach allowed integration of the biological kinetic processes of the IAWQ activated sludge model No 1 (Henze et al., 1987), to extend application of the model to situations where precipitation of minerals, stripping of gasses and biological processes take place in an environment where the pH does not remain constant. Where required the interaction between the chemical species and biological processes was included, e.g. CO₂ uptake for autotrophic nitrifier growth and NH₄⁺ uptake for heterotrophic growth and nitrification. Also, literature information on the effect of pH on the maximum specific growth rates of nitrifiers was included.

Grantor dc:publisher.institution

Department of Civil Engineering

Year dc:date.issued

1998

Author dc:creator

• Musvoto, Eustina Vongai

Advisors dc:contributor.advisor

• Ekama, George A
• Wentzel, Mark C
• Loewenthal, Richard Eric

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/9676

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/9676