12. • City of Eden Prairie
• City of Minneapolis
• Goodhue County
• MDH
• Palm Beach County, FL
• Port Calcite Collaborative
• SPRWS
• Wisconsin DNR
• Chemco
• Culligan
• Evoqua
• Infilco Degremont
• Merrick
• Tomco
• Westech
Acknowledgements
14. What is hardness?
• Hardness is mineral
content in water that can
form scale.
15. What is hardness?
• It is mostly calcium carbonate
• It is expressed in mg/L as calcium carbonate (CaCO3)
16. What is our goal when softening?
• Moderate in hardness = 90-120 mg/l as CaCO3
• Non-scaling, non-corrosive finished water
• Other goals
17. Can water be too soft?
• Yes!
• Water with low alkalinity is corrosive!
• Utilities with low alkalinity source water add lime too!
18. So, how do we lime soften water?
• Water chemist’s perspective:
• Saturate the water with calcium and carbonates
• Raise pH to and calcium and magnesium
• Re-stabilize the water by lowering the pH
• Filter
Lime
Soda ash
React
Clarify
Re-
Carbonate
Filter
CO2
Mix
19. Operationally, how is that done?
• Add lime, maybe sodium carbonate
• Mix contact and clarify
• Add carbonate & reduce the pH (carbon dioxide)
• Filter and finish
Source Water
Lime slurry
Sludge
CaCO3
CO2
Sludge
Treated water
21. Why are carbonates important?
• Calcium carbonate is very insoluble.
• The solubility is pH and temperature sensitive.
• 10.3 to 10.6 pH
• 150°F (65 °C)
22. Why are carbonates important?
• Carbonate:
• Carbonate, CO3
=
, in very alkaline water
• Bicarbonate,(HCO3
- , in mildly alkaline water
• Carbon dioxide, CO2, is carbonic acid (H2CO3) in acidic to
neutral water
23. Why are carbonates important?
• Carbonate chemistry is well known & determined from:
• Total alkalinity
• pH
• And temperature
24. Do we have to do all that math?
• No. Only for the unusual.
• Labs
• Vendors
• Consultants
• Lime suppliers
25. Calculations simple for natural waters.
• Alkalinity is composed of mainly bicarbonate and
carbonic acid.
• Enables us to estimate lime dosages easily
26. • pH
• Alkalinity
• Temperature
• Calcium (hardness)
Minnesota communities
with central groundwater
softening may use pH,
alkalinity, temperature and
total hardness to operate
softening processes.
What analyses are important?
28. So, how do we calculate the lime dose?
• The carbonic acid + the calcium hardness (in most cases)
• Then convert fromCaCO3 toCaO (56/100)
• And account for the purity of the lime (95% ± CaO)
• Adjust backward to relax treated water quality.
29. What about magnesium?
• Magnesium is much less common in Minnesota
• It is the most common form of non carbonate hardness
• If magnesium hardness > 40, treatment recommended.
• Must raise the pH >>10.5, normally with extra lime.
• Magnesium combines with free hydroxide to form Mg(OH)2.
• Lime dose:
• Carbonic acid + total alkalinity + magnesium hardness +
excess lime dose (40-70 mg/L)
30. What about non-carbonate hardness?
• Non carbonate hardness includes magnesium
• It also includes chlorides, sulfates etc.
• Soda ash will be required
• Lime dose:
• The carbonic acid + the calcium hardness (in most cases)
• Soda ash dose:
• Calcium non-carbonate hardness + magnesium non-
carbonate hardness.
31. • pH
• Alkalinity
• Temperature
• Calcium (hardness)
To summarize: what analyses are important?
32. • pH
• Alkalinity
• Temperature
• Calcium (hardness)
Minnesota communities
with central groundwater
softening may use pH,
alkalinity, temperature and
total hardness to operate
softening processes.
*For surface water and for
groundwater sources
elsewhere, the source water
may be more variable and
require more frequent
adjustment.
What analyses are important?
33. • pH
• Alkalinity
• Temperature
• Calcium (hardness)
• Magnesium*
• TDS*
• Sulfate*
• Anything else from the
last slide that shows up
as unusually high.*
Minnesota communities
with central groundwater
softening may use pH,
alkalinity, temperature and
total hardness to operate
softening processes.
*For surface water and for
groundwater sources
elsewhere, the source water
may be more variable and
require more frequent
adjustment.
What analyses are important?
34. Examples
Practice
Examples
Eden Prairie Minneapolis Escanaba, MI Palm Beach
County, FL
Flow, mgd 30 100 1 50
Temp °C 10 25 7 15
pH 7.5 7.8 6.8 6.9
Alk., mg/L* 320 250 200 140
Ca, mg/L* 250 200 250 220
Mg, mg/L* 20 25 150 80
Na, mg/L 5 40 5 100
Sulfate, mg/L 20 50 100 100
Chloride mg/L 5 20 5 120
* As CaCO3
35. Examples
Practice
Examples
Eden Prairie Minneapolis Escanaba, MI Palm Beach
County, FL
Flow, mgd 30 100 1 50
Temp °C 10 25 7 15
pH 7.5 7.8 6.8 6.9
Alk., mg/L* 320 250 200 140
Ca, mg/L* 250 200 250 220
Mg, mg/L* 20 25 150 80
Na, mg/L 5 40 5 100
Sulfate, mg/L 20 50 100 100
Chloride mg/L 5 20 5 120
* As CaCO3
44. What determines the process?
Process Calcium
Hardness
Magnesium
Hardness
Non-carbonate
Hardness
Free CO2
High
Lime X
Excess Lime X X
Lime – Soda Ash X X
Excess Lime – Soda Ash X X X
Split treatment (2-Stage) X X X
45. Softening processes – single stage lime
Contact Clarification Recarbonation Granular Media
Filtration
Source Water
Lime slurry
Recycle
Sludge
CaCO3
CO2
Sludge Filter backwash to
reclaim or disposal
Backwash
supply
Treated water
46. Softening Processes – Single Stage Lime Soda
Contact Clarification Recarbonation Granular Media
Filtration
Source water
Lime slurry
Recycle
Sludge
CaCO3
CO2
Sludge Filter backwash to
reclaim or disposal
Backwash
supply
Treated water
Soda ash
47. Softening Processes –Two Stage Lime Soda
First Stage
Excess Lime
Recarbonation
Source water
Lime slurry
Recycle
Sludge
CaCO3
CO2
Sludge
Source water
Soda ash
Recycle
Sludge
CaCO3
CO2
Sludge
Second Stage
Soda Ash
Recarbonation
To Filtration
48. Softening Processes –Two Stage Split Flow
First Stage
Excess Lime
Source water
Lime slurry
Recycle
Sludge
CaCO3
Soda ash
Recycle
Sludge
CaCO3
CO2
Sludge
Second Stage
Soda Ash
Recarbonation
To Filtration
49. Softening Processes – Hot Lime Soda @ 150°F
Contact Clarification Recarbonation Granular Media
Filtration
Source water
Lime slurry
Recycle
Sludge
CaCO3
CO2
Sludge Filter backwash to
reclaim or disposal
Backwash
supply
Treated water
Soda ash
50. Softening clarifiers or reactors
History
Conventional clarifiers
Solids contact clarifiers
High rate clarifers
Very high rate clarifers
51. 175 years of lime softened drinking water
• Lime softening has origins in 1841 treatingThames River
water for its bactericidal properties.
• Companies founded by Drs. JohnVan Norstrand Dorr
(1904) and Edwin Letz Oliver (1907) merged as DorrOliver
in 1931 and invented the contact clarifier.
• In 1936, the Spaulding contact clarifier begins operation in
Springfield, IL and adopted by many major US cities.
• In the 1960’s lime softening became prominent for
industrial and municipal water treatment in the Midwest,
Florida andTexas for hardness reduction.
60. Who treats with lime softening in the metro?
Community Type of Softening
Bloomington Conventional Solids Contact
Eden Prairie Conventional Solids Contract
Minneapolis Spaulding Clarifier
Richfield Very High Rate
Saint Paul Spaulding Clarifier
White Bear Lake Conventional Solids Contact
City Lime Softening Process
Courtesy Minneapolis WaterWorks Courtesy Saint Paul RegionalWater Services
61. Who else in Minnesota?
Community Type of Softening
Mankato Very high rate
Moorhead Conventional solids contact
Saint Cloud High rate
Ion Exchange Excelsior, Forest Lake, St. Bonifacius…
Reverse Osmosis Examples: Hutchinson, St. Peter, Lincoln-Pipestone…
City Softening Process
62. What is Lime?
Description
Where it’s used
How it’s Made
How it’s purchased
What does it cost
Lime
How is it handled
Storage
Feeders
Slakers
63. What is it good for?
Absolutely everything.
Lime
64. Lime is made from limestone
Heated in an oxygen starved furnace
A process called calcining
Lime
71. Lime is made from limestone
Heated in an oxygen starved furnace
A process called calcining
Calcium Carbonate (CaCO3) + Heat =
Calcium Oxide (CaO or quick lime) + Carbon Dioxide (CO2)
Lime
72. What do you get if you add clay to limestone
and send it through the same (calcining) process?
BonusQuestion
73. What do you get if you add clay to limestone
and send it through the same (calcining) process?
Cement
BonusQuestion
74. • Granular (pebble) or powdered
• AWWA Standard B-202 and NSF 61
• Bulk by rail car and truck.
• Silos to 15’ in diameter 36’ high
(factory built) to roughly 70 tons.
• A truckload is 23 tons of quicklime, 20
tons of slaked lime.
• Carmeuse, Graymont, Linwood
Mining, Mississippi Mining (survey?)
• Prices range from $150/ton to
$320/ton (survey?)
Lime sources and shipment
75. • Lime slaking deserves its own session.
• Quicklime must be slaked fromCaO to Ca(OH)2
• Slurry Slakers
• Paste Slakers
• Ball mill Slakers
• Each method has its benefits and disbenefits
• Operation takes into consideration
• Lime / water ratio
• Residence time
• Slaking temperature
• Lime quality / grit removal
Lime shipment and storage
79. Most have recessed plate and frame
presses
Cycle time 90 minutes
Cake dryness 40%
Compressed air
Sizing feed pumps
Sludge disposal issues
Sludge dewatering
80. • Magnesium
• Calcium
• Iron
• Manganese
• Strontium
• Barium
• Radium
• Others
• Uranium
• Total organic carbon
Additional benefits of lime softening
