International Journal of Scientific Research and Engineering Studies (IJSRES) Volume 3 Issue 3, March 2016 ISSN: 2349-8862 www.ijsres.com Page 1 Residual Chlorine Decay In Water Distribution Network Gitu.I. Bassey Department of Civil Engineering, University of Nigeria, Nsukka, Nigeria Jerome G. Egbe Department of Civil Engineering, Cross River University of Technology, Nigeria Abstract: The study was undertaken to measure the variational change in residual chlorine decay in water distribution network. A total of 900 water sample were collected at different period of the day for one month, from different ten water sample locations at water stand taps, at the study area in Calabar South Local Government Area of Cross River State, Nigeria. The effect of various Pipe diameter, water sample point distance, change in chlorine concentration with time on residual chlorine and regression model of residual chlorine as a function of dosage, pipe diameter and temperature were investigated. First order decay equation was used to model and analyst the variational change in residual chlorine concentration. It was observed that, the residual chlorine concentration decreases as pipe diameter increases. The loss of chlorine in water was found to be smaller in larger pipe diameter. The residual chlorine concentration decreases as distance increases. A linear relationship was observed to exist between residual chlorine concentration and change in chlorine concentration with time. Furthermore, from the regression model, the R square value, been the coefficient of correlation of the regression, shows that, for morning period 87%, afternoon period 85% and night period 73% of the total variation of the chlorine concentration at the water stand taps was accounted for by dosage, temperature and pipe diameter. This research offers several options and robust approach in addressing chronic water supply in Cross River State and as a guide in planning, simplifying approaches in predicting residual chlorine in pipe of varying diameter and strategizing proper dosing approach for water treatment plant to attain a desirable and durable residual chlorine at water stand taps. Keywords: Residual Chlorine, Water Distribution Network, Pipe diameter, Water sample point distance Calabar, Cross River State. I. INTRODUCTION Modeling and analyzing residual chlorine in water distribution network is very essential in predicting the Variational change in the dosage of chlorine concentration from the ground level water storage reservoir at Cross River State water board to the public water collection stand taps at different location. Chlorine is rated as one of the regularly used disinfectant by water utilities and water service providers to kill and inactivate microorganisms so that they cannot reproduce and infect human hosts. This disinfectant is readily available, cheap, easy to transport, occur in gaseous, liquid and solid form. However, when injecting Chlorine in water and is transported through water pipes of distribution network; it under goes reactions with the bulk water and with the inner pipe wall naturally along the distance of travel. The reactions result in the dissipation and loss of residual chlorine. These phenomenon pose a major threat in weakening the barriers against water safety and create the chances of recontamination. According to world health organization standard, a limit for residual chlorine concentration at public water stand taps was set up to be 0.2 – 0.3mg/L at 30 minute contact time, less than this, the water is not fit for direct consumption (WHO, 1993).Similarly, Lious and Kroon (1987) in their work, reported that on the disinfecting action of chlorine, that when chlorine is added to water, it form hypochlorous acid or hypochlorite ion which have an immediate and disastrous effect on most form of microscopic organism. In a write up by R.O. Connor from Ontario Ministry of the Attorney General report that in May 2000 in Canadian town of Walkerton, that seven people died and more than 2,300 became ill after E-coli and other bacteria related disease infected the town water supply and was concluded that, after the water well was contaminated, the Walkerton disaster could have been prevented if the required residual chlorine had been maintained (Connor., 2002).It was also estimated that 3.4 million people mostly children die every year from water