Water Conditioning Process Dr.Lek Wantha

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)

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

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 compounds depend on climatic Underground water Artesian well Water table well Spring Geysers (hot spring)

Water Sources

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

Water Quality Related to End- use Water quality parameter Measurement parameter pH Suspended solid SS Turbidity Ca2+ and Mg2+ Hardness Dissolved ion Conductivity

Water quality Requirement for Agriculture 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 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 BOD= Biochemical oxygen demand OD = Dissolved oxygen

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

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

Water Treatment for Industrial Supply Clarification Disinfection Hardness removal (softening) Physical methods Thermal Distillation Freezing-out Chemical methods Lime soda process Phosphate process Physico-chemical methods Cation exchange process Deaeration Chemical Physical

Water treatment Water softening Demineralization 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 process Reverse osmosis (RO) Electrodialysis (ED)

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

Calcium & magnesium bicarbonate Hardness of Water Carbonate Hardness (Temporary hardness) Calcium & magnesium bicarbonate Non-Carbonate Hardness (Permanent hardness) Calcium & magnesium sulfate Calcium & magnesium nitrate Calcium & magnesium chloride Softening Boiling Adding lime Adding sodium carbonate Exchange process Softening Adding sodium carbonate Exchange process

Water Softening Adding lime Boiling Adding sodium carbonate Exchange process Ca(HCO3)2 + heat  CaCO3 +CO2+H2O Mg(HCO3)2 + heat  MgCO3 +CO2+H2O Ca(HCO3)2 + Ca(OH)2  2CaCO3 +2H2O MgCl2 + Ca(OH)2  Mg(OH)2  + CaCl2 CaCl2+Na2CO3  CaCo3  + 2NaCl MgSO4+Na2CO3+ Ca(OH)2  Mg(OH)2  +CaCo3  + Na2SO4 Sodium Cation Exchange Ion Exchange Process Hydrogen Cation Exchange Anion Exchanger

Ion Exchange Process Zeolite softening

Ion Exchange Process Advantages Limitations 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.

Sodium Cation Exchange

Hydrogen Cation Exchange

Anion Exchanger

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

Types of Lime Hydrated lime (Ca(OH)2)  quicklime (CaO) Soda ash (Na2CO3)  Caustic soda (NaOH)

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

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) 2H2O + 2e- 2OH- +H2(g) 2Cl-  2e- +Cl2 (g)

Osmosis vs. Reverse Osmosis (RO) Direction of water flow Contaminants Reverse Osmosis Direction of water flow Contaminants

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