Study on Evaluation of On-Line Free Chlorine Sensors in Water Supply Facilities

Chlorination of treated drinking water has been widely used to prevent microbial contamination or waterborne diseases caused by reverse siphon or cross pipe connection in pipe networks. Continuous residual chlorine test is required to ensure the safety of drinking water against pathogenic microbes. With development of sensor technology, i.e., easy operation, lower operating cost, and no discharge of reagent, on-line chlorine sensors have been widely used in water supply facilities. Although the device has many advantages, it also has a little practical problems related with reliability in measurement reading due to disturbing materials and difference in N,N-diethyl-p-phenylenediamine (DPD) principle. The performance of on-line chlorine sensor differs significantly according to their manufacturers. The objective of the study was to evaluate the performance and the characteristics of 5 sensors which were used in water supply facilities in Seoul Metropolis at the moment. One was sensor with reagent and the other four sensors were no-reagent type. The effect of combined chlorine and pH to free chlorine was investigated with one reagent type sensor and four no-reagent type sensors. The authors concluded that the on-line free chlorine sensors were affected by combined chlorine and pH. No-reagent type sensors calibrated for pH were not affected pH while sensors not calibrated were affected significantly by pH fluctuation. With sufficient chlorination, all the sensors tested recorded similar free chlorine concentration. But insufficient chlorination with much combined chlorine shows different result according to the sensors which means the effect of combined chlorine. The important parameters to be checked in evaluating on-line chlorine sensor applied for water supply facilities are pH and combined chlorine. This paper was presented at the 8th Annual Water Distribution Systems Analysis Symposium which was held with the generous support of Awwa Research Foundation (AwwaRF).