Handbook Biological Wastewater Treatment - Design of Activated Sludge Systems

Introduction

In this chapter, a quantitative model is developed that describes the removal of organic material in the activated sludge system and its consequences for the principal parameters of the process:

• Effluent quality
• Excess sludge production
• Oxygen demand

The model is applicable to all aerobic suspended sludge treatment systems, which include the different versions of the conventional activated sludge system, sequential batch reactors, carrousels and aerated lagoons. It will be demonstrated that the model can easily be extended to include the processes of nitrogen removal and phosphorus removal, while it is also shown that the model remains valid when it is used for sewage that has received anaerobic pre-treatment. Most of the concepts presented in this section have been developed at the University of Cape Town (UCT) in South Africa and form the backbone of the activated sludge models as developed by the specialist group of the International Water Association (IWA; 1986, 1994 and 2000).

In summary, the main advantages of this simplified steady state activated sludge model are:

Contents of this section

Influent- and biomass composition Differentiation of influent COD into several fractions, based on differences in biodegradability and physical characteristics Identification of the different biomass fractions that make up the suspended solids in the bioreactor Introduction and use of a COD mass balance Read more....	Model development Development of a steady state model that predicts the sludge composition, oxygen demand, and excess sludge production Summary of all model equations on both concentration- and mass basis Presentation of a calibration method for the main model parameters Read more....
Model applications Determination of excess sludge mass and -composition Determination of required biological reactor volume Determination of nutrient demand Temperature effect Comparison of the design parametres sludge age and F/M ratio Control of the sludge age Read more....	Determination of oxygen uptake rate Determination of the oxygen uptake rate Critical oxygen concentration Effect of reactor hydraulics and the absorption of atmospheric oxygen Relaxation effect of the oxygen sensor Read more....
General model of the activated sludge system Development of a general model that dispenses with the requirements of assumed ideality and a steady state situation Model calibration using OUR measurements (respirometrics). Evaluation of the impact of non-ideal system behaviour on the modelling results of the ideal general and steady state models	Aeration Theoretical principles of aeration Effect on the value of the oxygen saturation concentration and the oxygen transfer coefficient of: Impurities Local atmospheric pressure Submergence level of diffusors Sludge concentration Calculations for sizing of surface aeration and diffused aeration systems, including blower calculations Experimental methods to determine the values of the oxygen transfer constant, oxygen transfer capacity and oxygen transfer efficiency
System configurations Discussion of common configurations for activated sludge systems: conventional activated sludge systems (completely mixed and plug-flow) carrousels sequencing batch reactors	We regret that the sections on the "General model of the activated sludge system", "Aeration" and "System Configurations" are not available as a free online resource. If you want to know more, please purchase the handbook. More info ?

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