THE USE OF PROCESS MODELING TO INVESTIGATE THE PERFORMANCE OF A LARGE INDUSTRIAL WASTEWATER TREATMENT PLANT

The ASM3 model as implemented in the GPS-X wastewater treatment plant simulator was used to model a wastewater treatment plant operated by the Eastman Chemical Company that treats waste from a chemical production plant. The Kingsport plant is a step-feed activated sludge plant with conventional secondary clarification. The composition of the influent waste stream was highly variable during the study period and this required special attention when characterizing the influent in terms of the ASM3 state variables. Although the wastewater temperature was outside the range normally recommended for ASM3, it was found that the default Arrhenius expression and its coefficients were applicable. The autotrophic growth rate was found to be generally low in the Kingsport plant (a value of 0.6 d−1 was used) possibly due to inhibitory substances in the influent. To model the denitrification that was observed in the aeration basins, ASM3 was modified to handle aerobic denitrification. The sludge settling characteristics varied and this required dynamic calibration of the settling model parameters. It was concluded that the model could accurately predict plant performance. The calibrated model was used to conduct a number of ‘what if’ simulations to improve the understanding of the plant and to assess the impact of operational changes, toxic spills, and increased organic and nutrient loadings.