A Highly Efficient Methanol Dosage Controller for Multi-stage WRRFs

A new model-based methanol dosage controller for multi-stage Water Resource Recovery Facilities (WRRF) is presented and compared with classic control approaches. The new controller uses self-tuning observer models to predict the concentration of methanol consuming organisms (methylotrophs) and subsequently the remaining methanol concentration in the denitrification zone effluent. This information is used in methanol dosage controllers to reduce methanol over-dosage if the mass of methylotrophs is insufficient to make use of the dosed methanol. This bleeding of methanol into the downstream aeration zones causes additional chemical costs, increases oxygen demand, and produces additional sludge. It is shown that classic methanol dosage controllers cannot prevent over-dosage and that the presented control solution (i) reduces the likelihood of over-dosage, (ii) leads to cost savings in comparison with classic controllers, and (iii) increases the control authority of the dosage controllers by minimizing the grow-in time of methylotrophs.