Berrigan- Softening_April-4-2016-Minnesota-AWWA-Metro-District

John K. Berrigan, Jr., PE

TKDA

Lime softening

Introduction

• El Paso, TX

• 10 mgd

• Excess lime treatment

• Virus kill primary purpose

• Secondary TOC, metals

• Follows full water reclamation

• For aquifer replenishment

Photos Courtesy of Zimpro

Introduction

• Davie, FL

• 4 mgd design build

• Enhancement of softening

• Iron

• Hardness

• Sulfide

• TOC

• Pretreatment

• Cascade aeration

• Post treatment

• Ion exchange (TOCO

• Fluoride

• Chloramine

Courtesy of Town of Davie (above) Tonka Water (below)

Introduction

• Palm Beach County, FL #8

• 10 mgd design build

• Enhancement of softening

• Iron

• Hardness

• Sulfide

• TOC

• Pretreatment

• Cascade aeration

• Post treatment

• Ion exchange

• Fluoride

• ChloramineCourtesy of Palm Beach County (above) Tonka Water (below)

Outline

• Lime softening chemistry and basics

• Lime softening chemistry detail

• Examples

• Softening processes

• Softening clarifiers and reactors

• Softening processes in Minnesota:

• Lime

• Recarbonation

• Dewatering

• Additional benefits of lime softening

• Wrap-up

Recommended Resources

Sources

Recommended Resources

• 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

Add lime

Mix

Let sit

Add bubbles

Filter

Enjoy

Lime softening chemistry basics

What is hardness?

• Hardness is mineral content in water that can form scale.

What is hardness?

• It is mostly calcium carbonate

• It is expressed in mg/L as calcium carbonate (CaCO3)

What is our goal when softening?

• Moderate in hardness = 90-120 mg/l as CaCO3

• Non-scaling, non-corrosive finished water

• Other goals

Can water be too soft?

• Yes!

• Water with low alkalinity is corrosive!

• Utilities with low alkalinity source water add lime too!

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

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

Carbonates

Calcium hardness

Magnesium Hardness

Calculating the lime requirement

Examples

Lime softening chemistry detail

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)


• 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


• Carbonate chemistry is well known & determined from:

• Total alkalinity

• pH

• And temperature

Do we have to do all that math?

• No. Only for the unusual.

• Labs

• Vendors

• Consultants

• Lime suppliers

Calculations simple for natural waters.

• Alkalinity is composed of mainly bicarbonate and carbonic acid.

• Enables us to estimate lime dosages easily

• 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?

How do we calculate lime dose for calcium?

So, how do we calculate the lime dose?

• The carbonic acid + the calcium hardness (in most cases)

• Then convert from CaCO3 to CaO (56/100)

• And account for the purity of the lime (95% ± CaO)

• Adjust backward to relax treated water quality.

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)

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.

• pH

• Alkalinity

• Temperature


To summarize: what analyses are important?

• pH

• Alkalinity

• Temperature



*For surface water and for groundwater sources elsewhere, the source water may be more variable and require more frequent adjustment.


• pH

• Alkalinity

• Temperature


• Magnesium*

• TDS*

• Sulfate*

• Anything else from the last slide that shows up as unusually high.*


*For surface water and for groundwater sources elsewhere, the source water may be more variable and require more frequent adjustment.


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

Eden Prairie Example

Examples

Practice

Examples


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


* As CaCO3

Minneapolis Example

Example Problems

Practice

Examples


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


* As CaCO3

Escanaba Example

Examples

Practice

Examples


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 10

Na, mg/L 5 40 5 100

Sulfate, mg/L 20 50 100 80


* As CaCO3

Palm Beach County, FL

Processes

Lime

Excess lime

Lime-soda ash

Some like it hot

Lime & lime-soda ash softening processes

Configurations

Single stage

Two stage

Split feed

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

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 disposalBackwash

supply

Treated water

Softening Processes – Single Stage Lime Soda


Filtration

Source water

Lime slurry

Recycle

Sludge

CaCO3

CO2



supply

Treated water

Soda ash

Softening Processes – Two Stage Lime Soda

First Stage

Excess LimeRecarbonation

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

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

Softening Processes – Hot Lime Soda @ 150°F


Filtration

Source water

Lime slurry

Recycle

Sludge

CaCO3

CO2



supply

Treated water

Soda ash

Softening clarifiers or reactors

History

Conventional clarifiers

Solids contact clarifiers

High rate clarifers

Very high rate clarifers

175 years of lime softened drinking water

• Lime softening has origins in 1841 treating Thames River water for its bactericidal properties.

• Companies founded by Drs. John Van Norstrand Dorr (1904) and Edwin Letz Oliver (1907) merged as Dorr Oliver 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 and Texas for hardness reduction.

Softening Processes – Circular Clarifier

Courtesy Westech

Softening Processes – Contact Clarifier

Courtesy Westech

Softening processes – Spaulding Clarifer

Courtesy AWWA

Softening processes – Spaulding Clarifier

Courtesy AWWA

Softening Processes – High Rate

Courtesy Infilco Degremont

Softening Processes – Very High Rate

Courtesy Infilco Degremont

Softening processes in Minnesota

Lime softening

Other types of softening

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 Water Works Courtesy Saint Paul Regional Water Services

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

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

What is it good for?

Absolutely everything.

Lime

Lime is made from limestone

Heated in an oxygen starved furnace

A process called calcining

Lime

Largest high-calcium limestone quarry

Rogers City, Michigan

Original lime kiln process

Red Wing lime kiln

Lime production

Limestone in

Lime out

Burner

Blower

Lime kiln in operation

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

What do you get if you add clay to limestone

and send it through the same (calcining) process?

Bonus Question

What do you get if you add clay to limestone

and send it through the same (calcining) process?

Cement

Bonus Question

• 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

• Lime slaking deserves its own session.

• Quicklime must be slaked from CaO 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

Calculating the carbon dioxide requirement

Equipment

Recarbonation

Calculating the Carbon Dioxide Requirement

Process Carbon Dioxide Dose

Lime

(Calcium Hardness)

Initial alkalinity – initial calcium hardness + residual

calcium hardness*

Excess Lime

(Calcium and Magnesium

Hardness)

Initial alkalinity – initial calcium hardness + residual

calcium hardness +excess lime dose + residual

magnesium hardness*

Lime – Soda

(Noncarbonate hardness)

Initial alkalinity + soda ash dose – initial calcium

hardness + residual calcium hardness*

Excess Lime – Soda(Magnesium noncarbonate hardness)


hardness + residual calcium hardness +excess

lime dose + residual magnesium hardness*

Excess Lime – Soda 1st Stage

2nd Stage

Excess lime dose + residual magnesium hardness


hardness + residual calcium hardness *

* Converted from CaCO3 to CO2 (44/100)

• Direct injection

• Pressurized solution feed

Recarbonation Equipment

Most have recessed plate and frame

presses

Cycle time 90 minutes

Cake dryness 40%

Compressed air

Sizing feed pumps

Sludge disposal issues

Sludge dewatering

• Magnesium

• Calcium

• Iron

• Manganese

• Strontium

• Barium

• Radium

• Others

• Uranium

• Total organic carbon

Additional benefits of lime softening

Outline

• Lime softening chemistry and basics

• Lime softening chemistry detail

• Examples

• Softening processes

• Softening clarifiers and reactors

• Softening processes in Minnesota:

• Lime

• Recarbonation

• Dewatering

• Additional benefits of lime softening

• Wrap-up

Berrigan- Softening_April-4-2016-Minnesota-AWWA-Metro-District

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