PROCESS AUTOMATION OF THE HAGUE SEWAGE-TREATMENT PLANT

The process control of sewage-treatment plants is normally carried out by conventional means. Special circumstances forced the application of a state-of-the-art process automation system for The Netherlands' largest sewage-treatment plant (Houtrust) at The Hague. The plant incorporates the use of oxygen-enriched air for use in the secondary treatment process, and the final settling tanks are constructed one above the other (in two tiers). The automation system is built up with locally-placed process computers, and a central video operating system is included with a data-processing computer; these are interconnected by a data transmission bus of redundant design. The central control system is also connected to the main sewage pumping stations of The Hague district, for collecting data and controlling these stations from the plant. After the start-up of the plant, it took several months of tuning the control system to gain proper process control, the main problem being the influence of pump switching in the intermediate pumping stations on the oxygen supply to the aeration tanks.