Abstract—A quadratic model (p＜0.0001) was developed by using a central composite design of 50 experimental runs (42 non-center + 8 center points) to assess the efficiency of background chlorine residuals in combating accidental microbial episodes in a scaled-up distribution network (DN) (rig). A known amount of background chlorine residuals were maintained in the DN and a required number of bacteria, Escherichia coli K-12 strain, was introduced by an injection port in the pipe-loop system. Samples were taken at various time intervals at different pipe lengths. A spread-plate count was performed to count the bacterial number. Microbial concentration and time (p ＜0.0001), pipe length (p＜0.022), background chlorine residuals (p＜0.07) and time2 (p＜0.09) were observed as significant factors. The model that was developed was significant. The ramp function of variables shows that, at the microbial count of 10^6, at 0.76 L/min, with a pipe length of 133 meters, a back ground residual chlorine of 0.16mg/L was enough for the complete inactivation of a microbial episode in approximately 18 minutes.
Index Terms—Central composite design (CCD), distribution network, Escherichia coli, residual chlorine.
S. Rasheed and I. Hashmi are with the Institute of Environmental Sciences and Engineering, School of Civil and Environmental Engineering, National University of Sciences and Technology, Islamabad, Pakistan (e-mail: firstname.lastname@example.org, email@example.com).
Q. Zhou, G. K. Kim, and L. Campos are with University College London, London, UK (e-mail: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org).
Cite:S. Rasheed, I. Hashmi, Q. Zhou, J. K. Kim, and L. C. Campos, "Combating Accidental Microbial Episodes by Back-Ground Chlorine Residuals in a Scaled-up Distribution Network (Rig) Using a Central Composite Design (CCD)," International Journal of Environmental Science and Development vol. 6, no. 2, pp. 122-127, 2015.