IN-SITU NUTRIENT SENSORS FOR REAL-TIME CONTROL OF BIOLOGICAL NUTRIENT REMOVAL

The last decade saw a growing acceptance of the use of Nutrient analysers for the measurement of Ammonium, Nitrate and Phosphate. These analysers require installation of sampling systems from the activated sludge tanks to the analysers and more important – they have relatively long response times generated by the sampling systems and the analysers themselves. For real-time control purposes the need for fast responding sensors is obvious, and analysers are therefore mainly used for monitoring of the processes.However, in the middle of the last decade faster responding in-situ sensors for measurement of Ammonium, Nitrate and Phosphate in activated sludge started to appear on the market. The paper describes the status and use of the commercially available in-situ sensors, which are better suited for optimising the nutrient removal as they enable direct use in SCADA control loops.Especially Nitrate in-situ sensors are becoming more and more common – also for control purposes – but in order to really describe and use the dynamics of the nitrification and denitrification processes for efficient Nitrogen removal, fast responding measurements of Nitrate, Nitrite and Ammonium are needed.The development of an in-situ sensor measuring all three Nitrogen components simultaneously and with response time of approximately three minutes is described, as well as the results from the tests in standard solutions and activated sludge.