The molybdenum blue method was prepared according to the standard method for the examination of water and wastewater [5]. A 5 N of sulfuric acid was prepared from diluted 35.0 mL of concentrated H2SO4(Carlo ERBA, Italy)to 250.0 mL with de-ionized water. The potassium antimonyl tartrate solution was prepared by dissolve 0.2743 g of K(SbO)C4H4O6•1/2H2O (Riedel-de Haen, Germany)in 100.0 mL de-ionized water. The ammonium molybdate solution was prepared by dissolve 4.0 g of (NH4)6Mo7O24•4H2O (Ajax Finechem, Australia)in 100.0 mL de-ionized water. The ascorbic acid solution was prepared by dissolve 1.76 g of C6H8O6(RANKEM, India) in 100.0 mL
de-ionized water. The above solutions were mixed by the ratio of 10:1:3:6 (molybdenum blue solution)