CONTROL OF EXTERNAL CARBON ADDITION TO PREDENITRIFYING SYSTEMS

The external carbon dosage control is studied for the predenitrificati on processes without the online controllability of the nitrate recircu lation flow. The control objective is to minimize the external carbon use while keeping the average effluent nitrate concentration below its standard. The proposed strategy is to control the nitrate concentrati on in the anoxic zone at a low set-point. A model-based analysis of th e denitrification process reveals that the optimal set-point for the n itrate concentration in the anoxic zone is about 1 mg.l(-1) Three cont rol laws are designed to control the anoxic zone nitrate concentration at its set-point for different measurement conditions. An effort is m ade in all the designs to make the control system as simple as possibl e. This includes the usage of simple control laws and few sensors, whi ch reduces the implementation and maintenance cost of the control syst em. The analyses and designs are validated by simulation and experimen tal studies on a full-scale plant.