Control of External Carbon Addition to Predenitrifying Systems

Abstract

The external carbon dosage control is studied for the predenitrification processes without the on-line controllability of the nitrate recirculation 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 concentration in the anoxic zone at a low set-point. A model-based analysis of the denitrification process reveals that the optimal set-point for the nitrate concentration in the anoxic zone is about 1 mgs˙l−1. Three control laws are designed to control the anoxic zone nitrate concentration at its set-point for different measurement conditions. An effort is made in all the designs to make the control system as simple as possible. This includes the usage of simple control laws and few sensors, which reduces the implementation and maintenance cost of the control system. The analyses and designs are validated by simulation and experimental studies on a full-scale plant.