Ch1 basics

# Ch1 basics - Chapter 1 Basics of Water and Wastewater Dr...

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Chapter 1 Basics of Water and Wastewater Dr. G.H. Chen Department of Civil Engineering HKUST

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Hardness (H) A total concentration of all divalent metallic ions (M 2+ ), such as Ca 2+ , Mg 2+ , Fe 2+ , Cu 2+ , and etc., expressed in mg/L as CaCO 3 Problems of hardness: Excessive soap consumption and scale problem. 50 mg/L 150 mg/L 300 mg/L Soft Moderate Hard Very hard Why hardness use the unit of mg/L as CaCO Why hardness use the unit of mg/L as CaCO 3 ? ?
+ 2 i M q is the equivalent weight of M i +2 2 MW q i 2 i M = + molecular weight Number of valence Formula Formula 50 q M H i 2 i M 2 i × = + + Equivalency: The number of hydrogen, electron that can be transferred in a rxn. M i 2+ = Concentration of the divalent metal i (mg/L)

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Example 1-1 Calculate the hardness of a water sample from the following analytical results: Ion type Concentration (mg/L) Na + 20 Ca 2+ 15 Mg 2+ 10 MW: Na = 23; Ca = 40; Mg = 24.4; Sr = 87.6 g/mole.
Solution 1) Equivalent weight 20 2 40 2 = = + Ca q Ca 2 . 12 2 4 . 24 2 = = + Mg q 8 . 43 2 6 . 87 2 = = + Sr q Mg Sr

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2) Total equivalence ( milli-normal)
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