FUGACITY ANALYSIS AND MODEL OF ORGANIC-CHEMICAL FATE IN A SEWAGE-TREATMENT PLANT

Expressions are developed in fugacity format for the partitioning, transport, and transformation processes encountered by an organic chemical in a secondary sewage treatment plant (STP). A mass balance model is developed for correlating and predicting the steady-state phase concentrations, the process stream fluxes, and the fate of organic chemicals in a STP. Input data are the chemical's properties and the plant's design and operating parameters. The model is algebraically simple, robust, and can be run on a personal computer. The relative amounts of chemical that are likely to be stripped or volatilized, sorbed to sludge, biodegraded, and discharged in the effluent water can be assessed. Results obtained by applying the model to screen the fate of 12 chemicals compare satisfactorily with data from full-scale plants. The most critical and uncertain variable is the biodegradation rate constant and its dependence on biomass concentration. It is believed that the fugacity analysis provides useful insights into chemical fate in a STP and that with further calibration and validation the model will be useful for correlation and prediction purposes.