1 Chapter 10 Water Treatment 10 1 The EPA provides reports sometimes referred to as consumer confidence reports that explain where your drinking water comes from and whether there are any contaminants in the water Go to this information at the Local Drinking Water Information page of EPA s Web site http www epa gov safewater dwinfo index html Look up the utility that serves your university and the largest city near your hometown What is the source of water Are there any violations If so are they for physical biological or chemical constituents Solution Students responses will vary Solutions Manual prepared by Ziad Katirji and Heather E Wright Wendel Environmental Engineering Fundamentals Sustainability Design James R Mihelcic and Julie Beth Zimmerman John Wiley Sons New York 2009 2 10 2 Jar testing was performed using alum on a raw drinking water source that contained an initial turbidity of 20 NTU and an alkalinity of 35 mg L as CaCO3 The optimum coagulant dosage was determined as 18 mg L with a final turbidity of 0 25 NTU Determine the quantity of alkalinity consumed as CaCO3 Solution Each 1 mg L of alum consumes 0 5 mg L of alkalinity as CaCO3 18 mg L alum 0 5 mg L alkalinity 9 mg L alkalinity consumed 1 mg L alum Or Molecular weight of alum Al2 SO4 3 14H2O equals g moles therefore alkalinity consumed equals mg 1 g 1 mole L 6 mole HCO3 18 L 1000 mg 594 g mole 1 mole 1 eqv of alk 50 g CaCO3 1 mole HCO3 1 eqv of alk 0 009 g L as CaCO3 9 mg L as CaCO3 Solutions Manual prepared by Ziad Katirji and Heather E Wright Wendel Environmental Engineering Fundamentals Sustainability Design James R Mihelcic and Julie Beth Zimmerman John Wiley Sons New York 2009 3 10 3 Jar tests were performed on untreated river water An optimum dose of 12 5 mg L of alum was determined Determine the amount of natural alkalinity mg L as CaCO3 consumed If 50 106 gal day of raw water are to be treated determine the amount of alum required kg yr Solution 12 5 mg L alum 12 5 0 5mg L alkalinity 6 25mg L alkalinity consumed 1mg L alum mg gal 3 78 L 365 day kg kg alum 50 106 6 862 300 L day gal year 10 mg yr Solutions Manual prepared by Ziad Katirji and Heather E Wright Wendel Environmental Engineering Fundamentals Sustainability Design James R Mihelcic and Julie Beth Zimmerman John Wiley Sons New York 2009 4 10 4 A source water mineral analysis shows the following ion concentration in the water Ca2 70 mg L Mg2 40 mg L HCO3 250 mg L as CaCO3 Determine the water s carbonate hardness noncarbonated hardness and total hardness Solution mg 100 g CaCO3 mole mg 164 2 L L 24 4 g Mg mole mg 100 g CaCO3 mole mg Ca2 concentration as CaCO3 70 175 2 L 40 g Ca mole L Mg2 concentration as CaCO3 40 Total Hardness Mg2 conc as CaCO3 Ca2 conc as CaCO3 164 mg L 175 mg L Total Hardness 339 mg L as CaCO3 Carbonate Hardness 250 mg L as CaCO3 175 mg L Ca2 75 mg L Mg2 Mg2 concentration is the difference between HCO3 and Ca2 Noncarbonate Hardness 164 mg L 75 mg L Noncarbonate Hardness 89 mg L Solutions Manual prepared by Ziad Katirji and Heather E Wright Wendel Environmental Engineering Fundamentals Sustainability Design James R Mihelcic and Julie Beth Zimmerman John Wiley Sons New York 2009 5 10 5 Calculate the lime dosage required for softening by selective calcium removal for the following water analysis The dissolved solids in the water are CO2 17 6 mg L Ca2 63 mg L Mg2 15 mg L Na 20 mg L Alk HCO3 189 mg L as CaCO3 SO42 80 mg L Cl 10 mg L What is the finished water hardness Solution Determine the chemical concentration as CaCO3 Chemical Conc MWCaCO3 MW mg L CO2 17 6 100 44 Cations Ca 2 63 100 40 Mg 2 15 100 24 4 Na 20 100 23 Anions Alk HCO3 SO42Cl 80 10 100 96 100 35 5 Conc mg L As CaCO3 40 157 5 61 5 87 306 189 83 28 300 Carbonate Hardness 157 5 31 5 189 mg L as CaCO3 Noncarbonate Hardness 61 5 31 5 30 mg L as CaCO3 Total Hardness 157 5 61 5 219mg L as CaCO3 Ca OH 2 required to react with CO2 40 mg L as CaCO3 Ca OH 2 required to react with Ca HCO3 2 157 5 mg L as CaCO3 Dosage of lime required for selective calcium removal is 40 157 5 197 5 mg L as CaCO3 Finished water hardness Mg carbonate hardness left noncarbonate hardness 31 5 30 61 5 mg L as CaCO3 Further treatment with lime is possible a dosage of 63 mg L as CaCO3 will remove the 31 5 mg L as CaCO3 of Mg carbonate hardness The noncarbonate hardness also can be removed by using 30 mg L lime as CaCO3 and then use soda ash with concentration of 30 mg l as CaCO3 Solutions Manual prepared by Ziad Katirji and Heather E Wright Wendel Environmental Engineering Fundamentals Sustainability Design James R Mihelcic and Julie Beth Zimmerman John Wiley Sons New York 2009 6 10 6 A municipality uses green energy and treats 15 106 gal day of a groundwater containing the following CO2 17 6 mg L Ca2 80 mg L Mg2 48 8 mg L Na 23 mg L Alk HCO3 270 mg L as CaCO3 SO42 125 mg L Cl 35 mg L The water is to be softened by excess lime treatment Assume that the soda ash is 90 percent sodium carbonate and the lime is 85 percent weight CaO Determine the lime and soda ash dosages necessary for precipitation softening kg day Solution Chemical Conc mg L MWCaCO3 MW Conc mg L As CaCO3 CO2 17 6 100 44 40 Ca 2 80 100 40 200 Mg 2 48 8 100 24 4 200 Na 23 100 23 100 Cations 500 Alk HCO3 270 SO42125 100 96 130 Cl 35 100 35 5 100 Anions 500 Ca HCO3 2 200 mg L as CaCO3 Mg HCO3 2 270 200 70 mg L as CaCO3 MgSO4 200 70 130 mg L as CaCO3 Lime required 30m g L is added for pH adjustment mg CaCO3 mg CaCO3 mg CaCO3 mg CaCO3 mg CaCO3 200 2 70 130 30 40 L L L L L 56 g mole CaO 15 106 gal 3 78 L kg bulk lim e Kg 20 172 kg 100 g mole CaCO3 106 mg 0 85 kg CaO day gal Soda ash required mg CaCO3 106 mg Na2CO3 mole kg 15 106 gal 130 100 mg CaCO mole 106 mg L day 3 3 78L kg bulk soda ash 8 681 kg gal 0 9 kg sodium carbonate Solutions Manual prepared by Ziad Katirji and Heather E Wright Wendel Environmental Engineering Fundamentals Sustainability Design James R …