Alkalinity,hardness,softening BY Muhammad Fahad Ansari 12IEEM14
Upcoming SlideShare
Loading in...5
×
 

Alkalinity,hardness,softening BY Muhammad Fahad Ansari 12IEEM14

on

  • 2,125 views

Muhammad Fahad Ansari 12IEEM14

Muhammad Fahad Ansari 12IEEM14

Statistics

Views

Total Views
2,125
Views on SlideShare
2,125
Embed Views
0

Actions

Likes
0
Downloads
56
Comments
0

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment
  • The USGS (USGS 2001) defines alkalinity as ‘the capacity of solutes in an aqueous system to neutralize acid” and ANC as “the capacity of solutes plus particulates in an aqueous system to neutralize acid”. Following the 1980’s acid rain surveys the term ANC or acid neutralizing capacity has come into use. In most cases alkalinity and ANC are virtually synonymous. Therefore, strictly speaking: ANC determined on raw, unfiltered samples Alkalinity determined on filtered samples Both are determined by titration with a dilute, strong acid (usually 0.02 – 0.1 N H 2 SO 4 ) to an endpoint of 4.5 – 4.2. Alkalinity and hardness classifications : see Modules 2 - 3 Hardness, in the past, was measured as the capacity of water to precipitate soap when a liquid soap solution was shaken with the water sample to form a lather persisting for 5 minutes (Lind 1985).
  • Eliminating the head space, or air within the container, prevents the exchange of gases between the sample and any air inside the container. EPA recommended holding time is 24 hrs at 4 o C with NO headspace Why just surface sampling ? Only because in most cases the differences between lakes is far greater than the differences between depths in the same lake. We’re usually most interested in classifying lakes into softwater versus hardwater groupings.
  • Wetzel, R. and G. Likens. 2000. Limnological Analyses, 3 rd edition. Springer-Verlag, New York, Inc. APHA.1998. Standard methods for the examination of water and wastewater. American Public Health Association, Washington, D.C. Harder water renders many heavy metals less toxic. Originally, hardness was understood to be a measure of the capacity of water to precipitate soap and it is the magnesium and calcium ions present in the water that do this. Total hardness is defined as the sum of the Ca and Mg concentrations (APHA 1998). Note: The units “mg CaCO 3 ” is rather strange. This is an historical relict from days when alkalinity was predominately measured by drinking water analysts. They were most concerned about maintaining a moderate level of carbonate/bicarbonate alkalinity in the water. Too much leads to excessive marl, the white precipitate that forms in home plumbing systems and poor soap lathering. Too little leads to excessive pipe corrosion.

Alkalinity,hardness,softening BY Muhammad Fahad Ansari 12IEEM14 Alkalinity,hardness,softening BY Muhammad Fahad Ansari 12IEEM14 Presentation Transcript

  • Alkalinity, Hardness,& Lime/Soda Ash Softening BY Muhammad Fahad Ansari 12IEEM14
  • General Considerations 1. Its capacity to neutralize acids or its buffering capacity. 2. 3 major classes of materials A. Bicarbonates, HCO3- - pH 4.0 ≤ pH 8.3 B. Carbonates, CO3- - >pH 8.3 < pH 10 C. Hydroxide, OH- - > pH 10.0
  • Sanitary Significance1. Lime/Soda Ash Softening2. Effects on Coagulant Dosing3. Total Dissolved Solids compliance4. Industrial Wastes Discharges5. Calcium Carbonate Stability
  • Method of Analysis1. Phenolphthalein Alkalinity A. Phenolphthalein indicator Acrobat Document B. pH 8.3 endpoint of titration C. Measures Carbonates and Hydroxide ions2. Total Alkalinity A. Bromcresol green or Methyl Orange indicator B. pH 4.5 endpoint of titration C. Measures Bicarbonates
  • Methods of Expressing1. Phenolphthalein Alkalinity as CaCO3 P. Alk. = ml 0.02N sulfuric acid (1000/ml sample) = mg/L as CaCO32. Total Alkalinity as CaCO3 T. Alk. = ml 0.02N sulfuric acid X (1000/ml sample) = mg/L as CaCO33. Hydroxide, Carbonate, and Bicarbonate Alkalinity as CaCO 3
  • Alkalinity RelationshipsTitration OH- CO3- HCO3- Result Alkalinity as Alkalinity as Alkalinity as CaCO3 CaCO3 CaCO3 P=0 0 0 TP<1/2 T 0 2P T-2PP=1/2 T 0 2P 0P>1/2 T 2P – T 2(T- P) 0 P=T T 0 0
  • Standard Solutions General Considerations 1. Saves Time in calculating results 2. Selection of Proper Normality is convenient * 1 mg/ml or 1000mg solution * 1/eq.wt., example: Alkalinity as CaCO3 = 0.02 N 3. Preparation of Solution of Proper Normality * Material of Known purity is weighed & transferred to volumetric flask * Purchase Solutions of known Normality
  • Preparation of 1N Acid Solution* Sulfuric acid used for Alkalinity Test 1 GMW = 98 g pure H2SO4 = 2.016 g H+ 1 GMW/2 = 49 g pure H2SO4 = 1.008 g H+ Acid is 96% pure, then 49/0.96 = 51 g = 1.008 g H+ Make 5% stronger = 51 X 1.05 = 53.5 g Procedure: Weigh about 53g of conc. acid into a small beaker on Trip balance. Place 500 ml of distilled water in 1-liter graduated cylinder And add the acid to it. Rinse the contents of the beaker into the cylinder With distilled water, and add water to the 1-liter mark. Mix by pouring Back and forth from the cylinder into a large beaker. Cool to room temp.
  • Primary Standard* Sodium Carbonate is a convenient primary standard MW = 106 of Na2SO3 1EW or 1N = 53g/L when reacting with H2SO4 to pH 4.5, T. Alk endpoint Preparation of 0.02 N Acid or N/50 can be made from 1N based on ml X N = ml X N Example: ml X 1.0 = 1000 X 0.02 ml = 20
  • Alkalinity and hardness -what is it? Alkalinity: a measure of the ability of a water sample to neutralize strong acid – Expressed as mg CaCO3 per liter or micro- equivalents – Alkalinities in natural waters usually range from 20 to 200 mg/L Hardness: a measure of the total concentration of calcium and magnesium ions – Expressed as mg CaCO3 per liter
  • Alkalinity and hardness -how to sample Usuallycollected at the surface in lakes (0 to 1m depth) Keep the sample cool (4oC refrigerated) and out of direct sunlight
  • Alkalinity and hardness- why measure? Thealkalinity of natural waters is usually due to weak acid anions that can accept and neutralize protons (mostly bicarbonate and carbonate in natural waters). – Usually expressed in units of calcium carbonate (CaCO3) The ions, Ca and Mg, that constitute hardness are necessary for normal plant and animal growth and survival. Hardness may affect the tolerance of fish to toxic metals.
  • Introduction to Hardness * Causes & Sources of Hardness Cations causing Anions hardness Ca++ HCO3- Mg++ SO4= Sr++ Cl- Fe++ NO3- Mn++ SiO3=* Source – Rain contact with soil and rock formations
  • Sanitary Significance* Reasons to Soften 1. Reduce Soap Consumption 2. Improve Aesthetics of Water 3. Hot Water Heaters last longer* Reasons not to Soften 1. Expensive Process 2. May be less healthy 3. Competes with health related costs
  • Method of Analysis* EDTA – Ethylenediaminetertraacetic Acid Method * EDTA complexes Ca & Mg * Eriochrome Black T serves as an indicator when EDTA is in excess of the complexed hardness ions. * Color change is from red to blue
  • Types of Hardness* Calcium and Magnesium Hardness * Total Hardness – Calcium Hardness = Magnesium Hardness* Carbonate and Noncarbonate Hardness * When alkalinity < Total Hardness, CO3 Hardness = T. Alkalinity * When alkalinity ≥ Total hardness, CO3 Hardness = T. Hardness * CO3 hardness removed by boiling or lime (Temporary Hardness) * Noncarbonate Hardness (permanent) = T. Hardness – CO3 Hardness* Pseudo-Hardness * Associated with Na+ which causes soap consumption but not considered part of hardness.
  • Effective Lime/Soda Ash Water Softening ByDouglas Rittmann, Ph.D., P.E.Water/Wastewater Consultant Presented to CE 5345 On Sept., 2006
  • Water SofteningI. Introduction A. Reasons to Soften 1. Reduce Soap Consumption 2. Improve Aesthetics of Water 3. Hot Water Heaters last longer B. Reasons not to Soften 1. Expensive Process 2. May be less healthy 3. Competes with health related costs
  • Water SofteningII. What is Hardness? A. Hardness Classifications a. Soft Water = 0 to 70 mg/L b. Moderate Hardness = 71 to 150 mg/L c. Hard Water = > 150 mg/L B. 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 CaCO3 a. Removed by Boiling b. Removed by Lime D. Non-Carbonate Hardness = T. Hardness – T. Alkalinity a. Unaffected by boiling b. Removed by Soda Ash
  • Water SofteningIII. Methods of Softening A. Lime-Soda Ash Chemistry 1. 1st Stage Treatment (Lime only) a. Carbon Dioxide Removal (< 8.3 pH) * CO2 + Ca(OH)2 CaCO3 + H2O b. Carbonate Hardness Removal * Ca + 2HCO3 + Ca(OH)2 2CaCO3 + 2H2O(pH 8.3-9.4) * Mg + 2HCO3 + Ca(OH)2 CaCO3 + Mg + CO3 + 2H2O(pH >10.8) c. Magnesium Hardness Removal (>pH 10.8) * Mg + CO3 + Ca(OH)2 CaCO3 + Mg(OH)2 * Mg + SO4 + Ca(OH)2 Ca + SO4 + Mg(OH)2 2. 2nd Stage Treatment (Soda Ash) * Ca + SO4 + Na2CO3 Na2SO4 + CaCO3 * Ca + Cl2 + Na2CO3 CaCO3 + 2NaCl
  • IV. Chemical Analyses Interpretations A. Calcium Alkalinity = Ca Hardness or T. Alkalinity whichever is smaller B1. Magnesium Alkalinity = Mg. Hardness if T. Alkalinity > or = than total hardnessB2. Magnesium Alkalinity = Total Alkalinity – calcium hardness if total alkalinity is > than calcium hardness but less than total hardness. C. Sodium alkalinity = total alkalinity – total hardness D. NCH = Total Hardness – Total Alkalinity ( If Mg Alkalinity present then no Ca NCH) Analyses Water #1 Water #2 Water #3 Total Hardness 300 300 300 Calcium 200 200 200 Hardness Mg Hardness 100 100 100 Total Alkalinity 150 250 350 Interpretations Water #1 Water #2 Water #3 Calcium Alkalinity 150 200 200 Mg. Alkalinity None 50 100 Sodium Alkalinity None None 50 Ca N.C. 50 None None Hardness Mg. N.C. 100 50 none
  • Water SofteningV. Theoretical versus Practical A. Theoretical Solubility of Ca & Mg: Mg(OH)2 = 9 mg/L Solubility CaCO3 = 17 mg/L Solubility Total = ~ 26 mg/L Solubility B. Practical Minimum Total Hardness = 50 to 80 mg/L Example: Calculate the hydrated lime (100%), soda ash, and carbon dioxide requirement to Reduce the hardness of a water with the following analysis to about 50 to 80 mg/L by the excess Lime-soda ash process. Analyses: Total Hardness = 280 mg/L as CaCO3 Mg++ = 21 mg/L Alkalinity = 170 mg/L as CaCO3 Carbon Dioxide = 6 mg/L Lime Requirement: Carbon Dioxide = (6) (56) / (44) = 8 Alkalinity = (170) (56) / (100) = 95 Mg ++ = (21) (56) / (24.3) = 48 Excess Lime = = 35 Total CaO required = 186mg/L Soda Ash Requirement: NCH = 280 – 170 = 110 mg/L Soda Ash (Na2CO3) = (110) (106) / (100) = 117 mg/L
  • Water Softening  Hardness is an important water quality parameter in determining the suitability of water for domestic and industrial uses – Hard waters require considerable amounts of soap to produce foam – Hard waters produce scale in hot-water pipers, heaters and boilers Ca2+ + 2HCO3- → CaCO3 (s) + CO2 (g) + H2O  Groundwater is generally harder than surface water  Principal cations causing hardness and the major anions associated with them (in decreasing order of abundance in naturalWater Treatment Chemistry Water Softening 29 waters)
  • Water Hardness Hardness expressed in mg/L as CaCO3 mg/L CaCO3 Degree of hardness 0-75 Soft 75-150 Moderately hard 150-300 Hard 300 up Very hard Methods of determination – Calculation (see example) Hardness (mg/L) as CaCO 3 = M 2+ (mg/L) x 50 / EW of M 2+ – EDTA titrimetric method M2+ + Eriochrome Black T (blue) → (M · Eriochrome Black T)complex (wine red) Water softening is needed when hardness is above 150-200 mg/L; Hardness 50-80 is acceptable in treated Chemistry Water Treatment water Water Softening 30
  • Lime-Soda [Ca(OH) 2 -Na 2 CO 3 ] Process:Recarbonation by bubbling CO 2 aftersoftening  Recarbonation is usually required after lime-soda process  Why? – To prevent super-saturated CaCO3 (s) and Mg(OH)2 (s) from forming harmful deposits or undesirable cloudiness in water at a later time CaCO3 (s) + CO2 + H2O Ca2+ + 2HCO3- MgCO3 (s) + CO2 + H2O Ca2+ + 2HCO3- – To neutralize excessively high pH caused by Na2CO3 OH- + CO2 HCO3-
  • Lime - Soda AshSoftening Advantages 􀂄 potential for significantly reducing total dissolved solids 􀂄 removes hardness 􀂄 lime added to process is removed precipitates soluble iron and manganese (groundwater) 􀂄 disinfection 􀂄 aids in coagulation
  • Lime - Soda Ash Softening Disadvantages 􀂄 large quantities of sludge 􀂄 sodium remains after adding soda ash (however, hardness removed by soda ash is usually a small percentage of total hardness)
  • Water SofteningA. Reasons to Soften 1. Reduce Soap Consumption 2. Improve Aesthetics of Water 3. Hot Water Heaters last longerB. Reasons not to Soften 1. Expensive Process 2. May be less healthy 3. Competes with health related costs
  • IV. Chemical Analyses Interpretations A. Calcium Alkalinity = Ca Hardness or T. Alkalinity whichever is smaller B1. Magnesium Alkalinity = Mg. Hardness if T. Alkalinity > or = than total hardnessB2. Magnesium Alkalinity = Total Alkalinity – calcium hardness if total alkalinity is > than calcium hardness but less than total hardness. C. Sodium alkalinity = total alkalinity – total hardness D. NCH = Total Hardness – Total Alkalinity ( If Mg Alkalinity present then no Ca NCH) Analyses Water #1 Water #2 Water #3 Total Hardness 300 300 300 Calcium 200 200 200 Hardness Mg Hardness 100 100 100 Total Alkalinity 150 250 350 Interpretations Water #1 Water #2 Water #3 Calcium Alkalinity 150 200 200 Mg. Alkalinity None 50 100 Sodium Alkalinity None None 50 Ca N.C. 50 None None Hardness Mg. N.C. 100 50 none
  • Water SofteningV. Theoretical versus Practical A. Theoretical Solubility of Ca & Mg: Mg(OH)2 = 9 mg/L Solubility CaCO3 = 17 mg/L Solubility Total = ~ 26 mg/L Solubility B. Practical Minimum Total Hardness = 50 to 80 mg/L Example: Calculate the hydrated lime (100%), soda ash, and carbon dioxide requirement to Reduce the hardness of a water with the following analysis to about 50 to 80 mg/L by the excess Lime-soda ash process. Analyses: Total Hardness = 280 mg/L as CaCO3 Mg++ = 21 mg/L Alkalinity = 170 mg/L as CaCO3 Carbon Dioxide = 6 mg/L Lime Requirement: Carbon Dioxide = (6) (56) / (44) = 8 Alkalinity = (170) (56) / (100) = 95 Mg ++ = (21) (56) / (24.3) = 48 Excess Lime = = 35 Total CaO required = 186mg/L Soda Ash Requirement: NCH = 280 – 170 = 110 mg/L Soda Ash (Na2CO3) = (110) (106) / (100) = 117 mg/L
  •  Pb. Result of chemical analysis of a sample of raw water is given below:Ca++=80mg/lNa+=2.5 m.eq/lTotal alkalinity=80mg/lTotal hardness=120mg/lSO-4=20mg/lCl-=140mg/lNO3-=5mg/lPrepare bar chart program of raw water.Estimate the quantity in kg/day of CaO(90%) and Soda ash as (95% ) to softener 4 million liters of this water.
  • Ion ExchangeIon exchange is an adsorption phenomenonwhere the mechanism of adsorption iselectrostatic. Electrostatic forces hold ions tocharged functional groups on the surface of theion exchange resin. The adsorbed ions replaceions that are on the resin surface on a 1:1 chargebasis. For example:
  • Applications of ion exchange in water & wastewater• Ca, Mg (hardness removal) exchange with Na or H.• Fe, Mn removal from groundwater.• Recovery of valuable waste products Ag, Au, U• Demineralization (exchange all cations for H all anions for OH)• Removal of NO3, NH4, PO4 (nutrient removal).
  • Ion Exchangers (types)• Natural: Proteins, Soils, Lignin, Coal. Metal oxides, Aluminosilicates (zeolites)(NaOAl2O3.4SiO2).• Synthetic zeolite gels and most common-polymeric resins (macroreticular, large pores).