Activated sludge model

Activated sludge model is a generic name for a group of mathematical methods to model activated sludge systems. The research in this area is coordinated by a task group of the International Water Association (IWA). Activated sludge models are used in scientific research to study biological processes in hypothetical systems. They can also be applied on full scale wastewater treatment plants for optimisation, when carefully calibrated with reference data for sludge production and nutrients in the effluent.

Around 1983 a task group of the International Association on Water Quality (one of the associations that formed IWA) was formed. They started creating on a generalised framework for mathematical models that could be used to model activated sludge for nitrogen removal.^[1][2] One of the main goals was to develop a model of which the complexity was as low as possible and simple to represent, though still able to accurately predict the biological processes. After four years, the first IAWQ model, named ASM1 was ready and incorporated a basic model taking into account chemical oxygen demand (COD), bacterial growth, and biomass degradation.

An activated sludge model consists of:

• state variables: these include the different fractions of COD, biomass and different types of nutrients, both organic and inorganic
• a description of the dynamic processes: lists the different biological processes that are modelled, together with their formulae
• parameters: variables that describe the circumstances of the biological system, such as growth and decay rate, half-saturation coefficient for hydrolysis, etc.