2 Water Softening I. Introduction A. Reasons to Soften 1. Reduce Soap Consumption2. Improve Aesthetics of Water3. Hot Water Heaters last longerB. Reasons not to Soften1. Expensive Process2. May be less healthy3. Competes with health related costs
3 Water Softening II. What is Hardness? A. Hardness Classifications a. Soft Water = 0 to 70 mg/Lb. Moderate Hardness = 71 to 150 mg/Lc. Hard Water = > 150 mg/LB. T. Hardness, mg/L, as CaCO3 = (Ca X 2.5) + (Mg X 4.12)(MW=100) (40 X 2.5 = 100) (24.3 X 4.12 = 100)C. Carbonate Hardness as CaCO3 = T. Alkalinity as CaCO3a. Removed by Boilingb. Removed by LimeD. Non-Carbonate Hardness = T. Hardness – T. Alkalinitya. Unaffected by boilingb. Removed by Soda Ash
5 IV. Chemical Analyses Interpretations A. Calcium Alkalinity = Ca Hardness or T. Alkalinity whichever is smallerB1. Magnesium Alkalinity = Mg. Hardness if T. Alkalinity > or = than total hardnessB2. Magnesium Alkalinity = Total Alkalinity – calcium hardness if total alkalinity is > thancalcium hardness but less than total hardness.C. Sodium alkalinity = total alkalinity – total hardnessD. NCH = Total Hardness – Total Alkalinity ( If Mg Alkalinity present then no Ca NCH)AnalysesWater #1Water #2Water #3Total Hardness300Calcium Hardness200Mg Hardness100Total Alkalinity150250350InterpretationsWater #1Water #2Water #3Calcium Alkalinity150200Mg. AlkalinityNone50100Sodium AlkalinityCa N.C. HardnessMg. N.C. Hardnessnone
6 Water Softening V. Theoretical versus Practical A. Theoretical Solubility of Ca & Mg:Mg(OH)2 = 9 mg/L SolubilityCaCO3 = 17 mg/L SolubilityTotal = ~ 26 mg/L SolubilityB. Practical Minimum Total Hardness = 50 to 80 mg/LExample: Calculate the hydrated lime (100%), soda ash, and carbon dioxide requirement toReduce the hardness of a water with the following analysis to about 50 to 80 mg/L by the excessLime-soda ash process.Analyses: Total Hardness = 280 mg/L as CaCO3Mg = 21 mg/LAlkalinity = 170 mg/L as CaCO3Carbon Dioxide = 6 mg/LLime Requirement: Carbon Dioxide = (6) (56) / (44) = 8Alkalinity = (170) (56) / (100) = 95Mg = (21) (56) / (24.3) = 48Excess Lime = = 35Total CaO required = 273 mg/LSoda Ash Requirement: NCH = 280 – 170 = 110 mg/LSoda Ash (Na2CO3) = (110) (106) / (100) = 117 mg/L
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