(c)殘餘色度考量、以及去除溶解性五價砷時，何者效率較佳？

2. 試計算下列水質之總硬度(以 mg/L as CaCO3 表示)：鈣離子(分子量 = 40.1 g/mole) = 30.0 mg/L、鎂離子(分子量 = 24.3 g/mole) = 5.0 mg/L、鈉離子(分子量 = 23.0 g/mole) = 11.5 mg/L、鉀離子(分子量 = 39.1 g/mole) = 13.0 mg/L、碳酸氫根離子(分子量 = 61.0 g/mole) = 84 mg/L、硫酸根離子(分子量= 96.1 g/mole) = 48 mg/L、氯離子(分子量 = 35.5 g/mole) = 13 mg/L。