Dr.Lek Wantha

Water Conditioning Process

Contents Water usage in industries Water sources Water quality related to end-use Water treatment for industrial supply

Water softening Ion exchange process Lime-soda process

Demineralization Desalting or Desalinization

Electrodialysis (ED) Reverse osmosis (RO)

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Water Usage in Industries

Component in products Energy carrying media (heat media), i.e.

steam Cooling media Cleaning Separating & Purification Transportation of raw material & products Mixing Complete reaction

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Water Sources (exclude tap water)

Sea water Salt >>>2.6% by mass NaCl, MgCl2, sulfate Gases>>> N2, O2,CO2

Surface water Flowing in river, cannel Contain of inorganic

and organic compoundsdepend on climatic

Underground water Artesian well Water table well Spring Geysers (hot spring)

Water Sources5

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Water Quality Related to End-use

Inorganic salts Ca2+

Mg2+

Na+

K+

Sulfate carbonate Chloride ion

Organic compounds & dissolved gasses CO2

O2

H2S

Organisms Aquatic animals Aquatic insects Microorganisms

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Water Quality Related to End- use

Water quality parameter

Measurement parameter

pH pHSuspended solid SSTurbidity TurbidityCa2+ and Mg2+ HardnessDissolved ion Conductivity

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Livestock Low bacteria,

<40/100 mL Low toxic

concentration Irrigation

Low dissolved solids, <500 mg/L

Total bacteria, 100,000/100 mL

Low heavy metal

Fish, aquatic life, wide life requirements Low toxic concentration pH near neutral (6.5-

8.5) Low BOD (1-2 mg/L) High DO

Cold: 6-7 mg/L (15 ºC) Warm: 4-5 mg/L (20 ºC)

Low temperature, turbidity

Water quality Requirement for Agriculture

BOD= Biochemical oxygen demandOD = Dissolved oxygen

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Water quality Requirement for

Industries Cooling

Low hardness, 50 ppm of (Mg2+ + Ca2+)

Low corrosivity Food

processing, brewing & soft drinking As public drinking

water, but F- <1 ppm

Thermal power Total Dissolved Solid

(TDS) < 0.1 ppm Public recreational

requirements Free of color, odor,

taste and turbidity Total bacteria,

<1000/100 mL Coliform bacteria

<100/100 mL Low nutrients

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Water quality Requirement for Industries

Public drinking water (treated) No bacteria Low nitrate, nitrite (< 10 ppm) Very low pesticide (none or < 0.05 ppm) Fluoride allowable to 2.4 ppm Toxic substances (below criteria level) TDS < 500 ppm

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Water Treatment for Industrial Supply

Water treatment

Clarification Disinfection Hardness removal (softening)

Physical

methods

Thermal

Distillation

Freezing-out

Chemical

methods

Lime soda process

Phosphat

e process

Physico-chemic

al method

s

Cation

exchange

process

Deaeration

Chemical

Physical

Distillation

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Water treatmentWater

softening

Ion exchange process

Sodium Cation

Exchange

Hydrogen Cation

Exchange

Lime-soda process

Demineralization

Desalinization

Electrodialysis (ED)

Reverse osmosis (RO)

Hydrated lime (Ca(OH)2) Quicklime (CaO)Soda ash (Na2CO3) Caustic soda (NaOH)

Ion exchange processReverse osmosis (RO)Electrodialysis (ED)

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Water Softening

Reduce/remove hardness Hardness

Dissolved salts: Calcium and magnesium Problems

Calcium bicarbonate → Calcium carbonate + Water + Carbon dioxide

Ca(HCO3)2 → CaCO3 + H2O + CO2

deposition of calcium carbonate scale in pipes and equipment

causes corrosion of iron or steel equipment

culprit in forming soap scum

Hardness of WaterCarbonate Hardness

(Temporary hardness)Calcium &

magnesium bicarbonate

Non-Carbonate Hardness

(Permanent hardness)Calcium &

magnesium sulfate

Calcium & magnesium

nitrate

Calcium & magnesium

chloride

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BoilingAdding lime

Adding sodium carbonate

Exchange process

Softening

Adding sodium carbonate

Exchange process

Softening

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Water Softening

Boiling

Adding lime

Adding sodium carbonate

Exchange process

Ca(HCO3)2 + heat CaCO3 +CO2+H2OMg(HCO3)2 + heat MgCO3 +CO2+H2O

Ca(HCO3)2 + Ca(OH)2 2CaCO3 +2H2OMgCl2 + Ca(OH)2 Mg(OH)2 + CaCl2

CaCl2+Na2CO3 CaCo3 + 2NaClMgSO4+Na2CO3+ Ca(OH)2

Mg(OH)2 +CaCo3 + Na2SO4

Ion Exchange Process

Sodium Cation

Exchange

Hydrogen Cation

ExchangeAnion Exchanger

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Ion Exchange Process

Zeolite softening

Ion Exchange Process

Advantages  Ion exchange can be

used with fluctuating flow rates.

Makes effluent contamination impossible.

Resins are available in large varieties from suppliers and each resin is effective in removing specific contaminants.

Limitations  Pretreatment is required

for most surface waters. Waste is highly

concentrated and requires careful disposal.

Unacceptable high levels of contamination in effluent.

Units are sensitive to the other ions present.

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Sodium Cation Exchange

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Hydrogen Cation Exchange

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Anion Exchanger

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Lime-soda Process

Lime = CaO + Soda = soda ash (Na2CO3) Carbonate hardness (temporary)

Ca(HCO3)2 + Ca(OH)2 2CaCO3 +2H2O Mg(HCO3)2 + Ca(OH)2 MgCO3+CaCO3 +2H2O MgCO3+ Ca(OH)2 Mg(OH)2 +CaCO3

Non-carbonate hardness (Permanent) MgCl2 + Ca(OH)2 Mg(OH)2 + CaCl2 CaCl2+Na2CO3 CaCo3 + 2NaCl CaSO4+Na2CO3 CaCo3 + Na2SO4

MgSO4+Na2CO3+ Ca(OH)2 Mg(OH)2 +CaCo3 + Na2SO4

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Types of LimeHydrated lime (Ca(OH)2) quicklime (CaO)

Soda ash (Na2CO3) Caustic soda (NaOH)

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Demineralization Process

Removal of minerals and nitrate from the water Ion exchange:

removal of hardness ions (magnesium and calcium) water demineralization 90% of barium, arsenic, cadmium, chromium,

silver, radium, nitrites, selenium and nitrates can be effectively removed from water

Reverse osmosis Electrodialysis

membrane processes, remove dissolved solids from water using membranes

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Desalting or Desalinization Process

Treatment of highly saline water: sea water 3,500 ppm of dissolved salt

Lowing saline contents < 500 ppm

Two methods Electrodialysis (ED) Reverse Osmosis (RO)

Electrodialysis (ED)25

2Cl- 2e- +Cl2 (g)

2H2O + 2e- 2OH- +H2(g)

Osmosis vs. Reverse Osmosis (RO)

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Osmosis

Direction of water flow

Con

tam

inan

ts

Reverse Osmosis

Direction of water flow

Con

tam

inan

ts

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Sources

http://water.me.vccs.edu/courses/ENV115/lesson9.htm