Real-time optimization of wastewater treatment plants via constraint adaptation

Abstract

An important requirement of wastewater treatment plants (WWTPs) is compliance withthe local regulations on effluent discharge, which are going to become more stringent in the future.The operation of WWTPs exhibits a trade-off between operational cost and effluent quality, whichprovides a scope for optimization. Process optimization is usually done by optimizing a model of theprocess. However, due to inevitable plant-model mismatch, the computed optimal solution is usuallynot optimal for the plant. This study represents the first attempt to handle plant-model mismatchvia constraint adaptation (CA) for the real-time optimization of WWTPs. In this simulation study,the "plant" is a model adopted from the BSM1 benchmark, while a reduced-order "model" is usedfor making predictions and computing the optimal inputs. A first implementation uses steady-statemeasurements of the plant constraints to adjust the model in the optimization framework. A fast CAtechnique is also proposed, which adjusts the model using transient measurements. It is observedthat, even in the presence of significant plant-model mismatch, the two proposed techniques are ableto meet the active plant constraints. These techniques are found to reduce the pumping and aerationenergy by 20%, as compared to that adopted in BSM1.