Possibility of utilizing natural coagulants (Trigonella foenum-graecum and Astragalus gossypinus) along with alum for the removal of turbidity

Abstract

Water, especially drinking water, might need to be treated before being utilized. Coagulants play a significant role in water treatment. In spite of having adverse effects on human health, aluminum sulfate, alum and other chemical coagulants are commonly used in coagulation processes. Utilization of natural and herbal materials such as quince seeds, fleawort, tragacanth, starch and yeast as coagulant aids has been experimentally investigated in this study. The aims of the present paper are: (1) to determine the optimal dose of Trigonella foenum-graecum (fenugreek) and Astragalus gossypinus (tragacanth) seeds as coagulant aids along with alum for the coagulation of raw water from Minab water treatment plant) located 7 km away from Bandar Abbas–Minab road at the east of Bandar Abbas in Iran, with a total area of 11.5 ha) and (2) to study their influence on reducing the water turbidity at a pilot scale. According to the obtained results, the optimum amount of alum (without additives) was calculated as 35 mg/L for water with the initial turbidity of 70–75 NTU, as the average turbidity interval. Using A. gossypinus and T. foenum-graecum seeds as coagulant aids, the optimum amount of alum reached 22 mg/L. The performance of A. gossypinus, as a coagulant aid, was much better in low concentrations. It was used in doses of 0.25, 1 and 2 mg/L along with 20, 22 and 28 mg/L of alum for low, intermediate and high turbidity levels (28, 70 and 120 NTU) and led to turbidity removal percentages of 85, 94.5 and 96.4, respectively. The optimum amounts of T. foenum-graecum seeds for the three mentioned turbidity levels were calculated as 1, 2 and 4 mg/L. The turbidity removal percentages of 91.5, 95.7 and 97.8 were obtained using the mentioned amounts of T. foenum-graecum seeds along with 20, 22 and 25 mg/L of alum, respectively. Similar results were obtained by using both additives along with alum.