Chlorine contact tank in water and waste water treatment plant suffer from a lack of efficiency disinfected treated water, which discharge to the rivers and they need a large amount of chlorine for the purpose of disinfection as a result of the presence of dead zones in the basins of chlorine as well as the need to contact a long more than exact standard specifications for the tanks disinfection time. This study deal with optimal performance basin mixing chlorine, which is located at the beginning of Chlorine contact tank of waste water treatment plant in the city of Nasiriyah in Dhi Qar, which is located south of the province of Iraq. In this paper, the use of computational fluid dynamic model in the numerical analysis for the purpose of finding the optimum performance of the chlorine mixing tank with the help of the program FLUENT 6.3.26 and program GAMBIT 2.3.16. Also in this study was used User Defined Function for the purpose of improvements of mixing chlorine. Where the results of the study showed that the ideal rotational speed of the mixer is 140 rpm as well as the results showed Numerical Model that can reduce chlorine dose to 5 mgliter, which is the optimum concentration of chlorine to be supplied for wastewater disinfect and is identical to the Iraqi specifications water sanitation, which discharge to the Euphrates River. In this study the best contact time of chlorine which give the best performance for mixing was 20 seconds.
Chlorine is considered as one of the most important disinfectants because of its availability in a wide form and in acceptable cost. Measurements of residual chlorine are very essential to assure the presence of disinfection at various locations of the water distribution system. The aim of the present work is to find the residual chlorine concentrations in potable water which leaves Tikrit University water supply plants. pH-, water temperature and water turbidity are also measured. Sixty samples of tap water are tested during November 2009 till April 2010. The results show that range of residual chlorine is 0.2-4mg/l) and most of the measured values are higher than the maximum permissible limit according to Iraqi standards( 417/1974 ) The data indicated that pH is within the range of (7-8.2) and there is no clear relationship between pH and residual chlorine concentration. It is found that there an inverse proportionality between residual chlorinean and temperature . Same trend is found between residual chlorine and turbitiy. The Conductivity and total dissolved solid of drinking water was within the permitted level by the Iraqi standers