Verification of the bisubstrate concept in modelling of the activated sludge process

This investigation was concerned with two problems: (1) verification of the bisubstrate concept proposed by Dold, Ekama and Marais (1980), in which the biodegradable component of wastewater consists of readily and slowly biodegradable fractions, and (2) physical separation techniques for estimating the readily biodegradable fraction. Intensive research, since 1970, into the behaviour of activated sludge systems at the University of Cape Town has culminated in the formulation of a general kinetic model, by Dold and Marais (1986). The model is highly complex, incorporating a number of different processes; however extensive simulation studies have shown that the model simulates the behaviour of activated sludge systems very closely. A crucial concept incorporated in the general model is that the biodegradable fraction of a wastewater can be subdivided into two fractions with sharply different characteristics (bisubstrate concept), a readily biodegradable fraction which is directly utilized by the organism mass at a high rate and a slowly biodegradable fraction which requires to be solubilized extracellularly to readily biodegradable material for subsequent use by .. the organism. Solubilization is hypothesized to be a relatively slow process. These characteristics were inferred from the oxygen utilization rate response of a system fed in a cyclic square wave fashion. No work has been done to verify if substrates of specific chemical structures can be allocated to one or the other of the fractions. One of the objectives of this investigation was to check if pure and mixtures of specific selected substrates reflected these fractions when fed to activated sludge systems. Glucose and maize starch were selected as representative of readily biodegradable and slowly biodegradable substrate respectively. Systems were run under steady state and square wave cyclic state with glucose only, starch only and glucose/starch mixtures. From the steady state response the specific yield values could be determined and the reliability of the data checked by doing mass balances on the COD. From the cyclic response the specific rate constants for growth and solubilization respectively could be determined by trial simulation using the general model and specifying the concentrations of readily and slowly biodegradable fractions equal to the stoichiometric concentrations of glucose and starch in the feed. The constants thus determined were compared with the "standard" constants for municipal wastewaters.

Grantor dc:publisher.institution

Department of Civil Engineering

Year dc:date.issued

1986

Author dc:creator

• Bagg, Wayne Kendall

Advisor dc:contributor.advisor

• Marais, Gerrit van Rooyen

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/7581

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/7581