Introduction: Colloidal materials and suspended solids cause turbidity in water. To remove turbidity, clarification method is used that includes processes of coagulation, flocculation, and sedimentation. Due to the long duration of coagulation process, coagulant aids are applied. Despite the favorable efficiency of synthetic polyelectrolytes as a coagulant aid, due to their harmful effects on human health, in this process, natural organic polymers are used instead.
Materials and Methods: In this research, the use of tragacanth as a natural organic coagulant aid was studied instead of synthetic polymers in water turbidity removal along with alum and poly aluminum chloride. To compare the experiments with natural conditions, Karun River water was analyzed. To complete these studies, the effects of several factors such as tragacanth concentration, the concentration of alum and poly aluminum chloride, and pH changes in average and low turbidity were investigated. Optimum pH for turbidity removal was determined by jar testing.
Results: The results showed that the best pH to remove turbidity was from 5.5 to 7, with the efficiency of 97.3%. At pH = 6 and at the concentration of 30 mg/L, poly ammonium chloride had maximum efficiency (90%). Using tragacanth with concentrations of 1 and 4 mg/L along with alum at a concentration of 40 mg/L leads to turbidity removal of 81.75%.
Conclusion: Using 2 and 4 mg/L of tragacanth, a significant removal efficiency is achieved in low and average turbidity. pH = 7 leads to the most efficient use of tragacanth coagulant aid.