An improved model for predicting the fate of consumer product chemicals in wastewater treatment plants

The WW-TREAT model was developed to predict the fate of consumer product chemicals in primary and activated sludge wastewater treatment plants using independently determined values for the distribution coefficient between sludge solids and liquid, Henry's law constant and biodegradation rate constants. The major difference between this model and previous models is that it assumes the total chemical, not just the dissolved chemical, is available for biodegradation and that sorption to sludge solids increases the time that a chemical is available for biodegradation. The model was validated with monitoring data for four chemicals which possess sorption and biodegradation characteristics that span the range typical of the broader class of consumer product chemicals. Sensitivity analysis revealed that the most important parameters were the plant operating parameter, sludge/solids retention time and the chemical specific parameters, distribution coefficient and biodegradation rate constants. The sludge/solids retention time had its greatest effect when it was less than 9 days and the distribution coefficient had its greatest effect when it was between 100 and 3000 l/kg. The model predicted removal in primary and activated sludge wastewater treatment plants within 5%. Thus, the model can be used as a valuable tool for predicting the fate of consumer product chemicals.