SimpleTreat: a spreadsheet-based box model to predict the fate of xenobiotics in a municipal waste water treatment plant

A non-equilibrium steady state box model is reported, that predicts the fate of new chemicals in a conventional sewage treatment plant from a minimal input data set. The model, written in an electronic spreadsheet (Lotus TM 123), requires a minimum input: some basic properties of the chemical, its emission rate and a few parameters to account for the scale and mode of operation of the plant. Compound properties necessary as input are air-water and sludge solids-water partition coefficients. If these distribution coefficients are not available but the compound is hydrophobic, default values are calculated from input data such as solubility, vapour pressure and octanol-water partition coefficient. Biodegradability data and the degree of dissociation or protonation are the required input data to account for degradation and speciation changes of the chemical in the water phase. The standard output shows the chemical's concentration in effluent and sludge. The presented model, SimpleTreat, is an application of a general purpose box modelling system, SimpleBox. Examples are evaluated and results are compared with measured concentrations.