You Said How Many Sludges!? Modeling a Multiple Sludge System for Enhanced Nutrient Removal

As wastewater process models continue to become increasingly more complex, it is important to recognize what level of complexity is needed and in what situations it is appropriate. This level of complexity is governed by the project goals, the treatment process being modeled, what state variables and process rates are needed, and the required degree of calibration. As part of a comprehensive enhanced nutrient removal upgrade project, a whole-plant simulation model of a three-sludge system was developed, calibrated, and verified based on data from two intensive sampling programs. This paper has outlined the development of, and the issues that arose, during the calibration of the model. In particular:One modeling equation was changed to allow the production of soluble organic nitrogen in unaerated reactorsThree separate mass balance issues were discovered in the calibration dataset and decisions were made regarding this data based on assumed behavior, observed behavior, and typical unit process operation.Calibration simulations showed that with the exception of the hydrolysis parameters, the use of updated New General model default parameters from recent literature, coupled with methanol degradation and methylotrophic biomass growth model customization, resulted in modeled behavior consistent with the measured data.It was found that the modeled rate of aerobic hydrolysis had to be reduced to limit the demand for nutrients in the high rate and nitrifying sections of the plant. This reduction was the key to matching the effluent ammonia and soluble phosphate levels in each section of the model.Based on the measured data and the modeled behavior, the best fit to all the data was achieved with an atypical wastewater characterization of 50% particulate inert material.