Automation of long term chlorine demand measurement of treated waters

In drinking water treatment plants, process evaluation and water quality control are based on standard parameters such as DOG, BDOC, short or long term chlorine demand, oxidation by-products. Chlorine demand is one of the most important parameters because it allows the adjustment of the chlorination rate to maintain a residual concentration of active chlorine and to limit chlorination by-products. According to the results previously observed, the total reaction of chlorine with dissolved organic carbon requires prolonged contact times (several days or several weeks). In order to determine the chlorine demand in the water tanks and in the networks, the laboratory technicians are obliged to use a high chlorine dosage and to follow the decrease of residual chlorine over a very long time. The kinetic model described by Jadas-Hecart et al. (1992) (Water Research 26, 1073) leads to the determination of the long term chlorine demand of water by determining its chlorine consumption as a function of the reaction time and then calculating the kinetic parameters. The use of this kinetic model requires the strict observance of analytical rules in order to avoid any pollution of the samples. In addition to that, these experiments are time-consuming, which greatly limits the number of determinations. According to that, the objective of the present work was to develop an automatic analysis of the chlorine demand in order to reduce the risks of sample contamination while increasing the analytical possibilities. For this purpose, automation of long term chlorine demand measurements was achieved by coupling a Gilson sample changer with a Secomam spectrophotometer. (C) 1997 Elsevier Science Ltd.