MODELING THE FATE OF METALS IN MUNICIPAL WATER-POLLUTION CONTROL PLANTS

A solution of seven metal salts was dosed into batch and continuous-fl ow dynamic wastewater experiments at bench- and pilot-scale to calibra te a computer-based mathematical model for predicting the fate of meta ls in municipal water pollution control plants (WPCPs). The model acco unts for both precipitation and sorption onto primary and secondary sl udges, and predicts the concentrations of metals in the primary sludge , return activated sludge, and secondary clarifier effluent. In dynami c step experiments, six of seven metals were removed substantially (55 -99%) by the pilot activated sludge system. Lead and chromium were rem oved to the greatest extent while nickel was least removed. With the e xception of nickel, a large fraction of the effluent metal concentrati ons were in particulate form. Below the solubility limits, a linear so rption model generally was able to simulate the observed effluent resp onse to a step input. Sampling at a full-scale WPCP was conducted for testing the steady-state model's predictive capability. Except for lea d, the predicted effluent concentrations agreed well with observed val ues.