Consultation document on Octamethylcyclotetrasiloxane(D4): annex 3

Annex 3: Description of wastewater treatment models

ASTreat 1.0 refers to a windows based computer model designed by Procter & Gamble (1999) to determine the chemical removal rates within an activated sludge treatment plant. It assumes a process consisting of a primary clarifier, an aeration tank, a secondary clarifier, a digester and dewatering unit. The program does not contain chemical databases and requires the user to input concentration, chemical properties, and operating conditions. (Crechem 2006)

SimpleTreat 3.0 is a spreadsheet-based fate model for organic chemicals in a conventional activated sludge process. It was originally developed by Struijs et al. (1991) at the Netherlands National Institute for Public Health and the Environment (RIVM) as a simple spreadsheet model based on the OECD SimpleBox approach. Version 3.0 is capable of predicting the removal efficiency of slowly biodegradable and hydrophobic chemicals. (Crechem 2006)

STP Model 1.5 is a windows based computer model developed by the Canadian Environmental Modelling Centre at Trent University. It uses a conventional activated sludge treatment plant and assumes a process consisting of a primary clarifier, an activated sludge aeration basin, and a secondary clarifier. It contains 16 chemicals with partition and biodegradation data, but can be expanded through the addition of user-defined substances. The program requires the user to input chemical properties and facility conditions. (Crechem 2006)

All three models are designed for steady-state conditions. (Crechem 2006)