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.
Secondary clarifiers form a crucial component in gravity separation processes mainly in solid-liquid separation. They perform the crucial process of separating the activated sludge from the clarified effluent and also to concentrate the settled sludge. As treatment plants receive increasingly high wastewater flow, conventional sedimentation tanks suffer from overloading problems which result in poor performance. Inlet baffle modification by using an energy dissipating inlet (EDI) was proposed to enhance the performance in the circular clarifiers in Al-Dewanyia wastewater treatment plant. A 3-Dimensional fully mass conservative clarifier model was applied to evaluate proposed tank modification and to estimate the maximum capacity of the existing and modified clarifiers. A Computational Fluid Dynamics (CFD) model was formulated to describe tank performance and design parameters were obtained based on the experimental results. The study revealed that velocity and SS are better parameters than TS, BOD5, and COD to evaluate the performance of sedimentation tanks. Removal efficiencies of suspended solids, biochemical oxygen demand, and chemical oxygen demand were higher in the EDI (Baffle).