Effects of pre-chlorination on alum coagulation

Abstract

Chlorine is one of the most important disinfectants for purifying water. Purification of water is a vital concern for mankind since it is directly linked with human welfare. Many treatment plants use surface water sources for supplying of water. But this surface water sources carries exccss amount of amonia, organic matter, turbidity and other impurities due to disposal of untreated waste and wastewater from industria~ commercial and domestic sources. Removal of these impurities from raw water is very difficult and quite impossible by plain sedimentation and even it leads to extra treatment load of the plant. Hence pre-chlorination is performed in those plants to reduce the extra treatment load and higher removal efficiency of organic & inorganic impurities. Saidabad Water Treatment Plant is one example of such pratice. The raw water of Saidabad Water Treatment Plant was used for this study. This study is intended to acquire a better understanding the change of behavior of alum coagulation and sedimentation for use of pre-chlorination in treatment process. Effectiveness of alum coagulation and sedimentation on removing turbidity and color was investigated a wide range in this study in both the cases i.e with and without pre-chlorination condition. Color removal efficiency is significantly higher in case of pre- chlorination condition compared to without pre-chlorination condition. But turbidity removal efficiency IS not significantly higher in case of pre- chlorination condition compared to without pre-cWorination condition. But pre-chlorination has no negative impact on removing turbidity and color. An increase in alum dosage enhances the removal rate of turbidity and color in both the cases. But it is significantly higher in case of pre-chlorination condition compared to without pre-chlorination condition. Above all, pre-chlorination has positive impact on alum coagulation. Turbidity and color removal efficiencies arc directly proportional to contact time of chlorine. [f the contact time 0f chlorine is increased, then turbidity and co [or removal efficiency will be increased and vise-versa. On the other hand, contact time of chlorine is inversely proportional to the amount of applied chlorine doses. If the contact time of chlorine is increased, then comparatively lower amount of chlorine dose will remove same amount of turbidity and color and vise-versa. Ammonia (NH3) concentration of raw water was exhibited a criticality on removing turbidity and color. Removal efficiencies were higher in case of lower ammonia (NH3) concentration of raw water compared to higher ammonia (NH3) concentration of raw water by applying same amount of chlorine doses or same contact time of chlorine. Increase of chlorine dose corresponds to ammonia (NH3) concentration of raw water has no significant impact on turbidity removal but has significant impact on color removal.