Indirect Method of Free Chlorine Determination in Wastewater

Dr. Tamás Koltai, Group Leader of Ecology laboratory, ADAMA Agan Ltd., Ashdod, Israel
Dr. Bianca Nitzan, QC laboratory manager, ADAMA Agan Ltd., Ashdod, Israel
Mr. Yosi Goldstein, Head of Group Health, Safety & Environment, ADAMA Ltd., Israel
Prof. Chaim Sheindorf, Environmental Protection Technologies Ltd., Kefar Netter, Israel

Free Chlorine determination in wastewater is part of the requirement of the Israeli Ministry of Environmental Protection. The most acceptable method in the industry is the DPD (N,N-diethyl-p-phenylenediamine) colorimetric method. Free Chlorine immediately reacts with DPD indicator to form a magenta color. The strength of the color is proportional to the concentration measured by a colorimeter. Free Chlorine determination in wastewater is challenging because first the Free chlorine is unstable and needed to be analyzed immediately, secondly the DPD method is not selective to Free Chlorine alone, but bromine, chlorine dioxide etc. are interfering, namely also determined and can give exaggerated chlorine result. The authors present solutions to real wastewater samples to ameliorate the overestimated results of the free chlorine determination.