Operational Cost Optimization Modeling for Conventional Activated Sludge Process

Energy and solids processing cost accounts for 40% of the total operation and maintenance costs in wastewater treatment facilities. This indicates the potential for saving operation and maintenance costs through the process optimization. The limitations of most cost optimization studies carried out in the past are either these studies could not be applied to existing facilities as the objective function includes both construction and operational cost or the operational costs ignores pumping or solids processing costs or operational cost uses empirical cost curves ignoring actual equipment data. In this study an optimization model was developed to minimize the total operational cost of a conventional activated sludge system taking into consideration energy costs associated with pumping and aeration, solids processing cost, and the equipment system data while satisfying the effluent requirements and process stability criteria. The cost optimization model developed has been minimized using an optimization technique called, the simulated annealing (SA) method. In order to demonstrate the usefulness of the model, a case study has been presented for a typical hypothetical conventional activated sludge treatment system 18,900 m3/d (5 Mgal/d) in size, and the cost savings have been compared with the operational costs of the traditional operation of the plant under standard rules. A sensitivity analysis was also performed to study the impact of the variation in unit energy and sludge processing costs on optimum operational parameters.