Journals Proceedings

Abstract

Activated sludge process control is a major challenge to plant operators given the need for correct balance of parameters to achieve plant optimum conditions. A good example is a correct Mixed Liquor Suspended Solids (MLSS) balance necessary to retain the Food to Microbe (F/M) ratio within the desired range. In this regard, mathematical models play an important role in assisting plant process control. Thus, a research on a full scale activated sludge nutrient removal plant was carried out in Harare, Zimbabwe at Firle Sewage Treatment Works (FSTW) Unit 4. The main objective was to investigate opportunities for optimizing nutrient removal through the use of BioWin Simulator. This paper presents the results of calibration, simulation and validation of the BioWin modeling tool for optimum nutrient removal from a study carried out during the period 2012 to 2015 at FSTW. BioWin Simulator is complex because it attempts to simulate simultaneously biological processes of different organisms in addition to being built-up from a large number of model parameters with only few being able to be measured directly. To overcome this challenge the International Association on Water Quality (IWAQ) approach was used. In accordance with this approach a stepwise procedure starting with sludge composition and production, nitrification and finally denitrification was used. Critical attention was on the plant model set-up before any detailed measurement and calibration program started in order to reduce tedious cycles. To validate the model, data was collected for periods comparable with the period from which data for input and calibration was obtained. The initial simulation did not predict well the effluent quality, thus data reconciliation and plant revisits were conducted. This assisted in detecting where potential errors in the process could have been made. By using this method the number of components that need to be analyzed and the number of analyses was reduced. After validation the model predicted Chemical Oxygen Demand (COD), Total Nitrogen (TN) and Total Phosphate (TP) effluent concentrations reasonably well. Thus, it was concluded the calibrated simulator could be used to inform operations and for process control.