Lecture3_water purification, ChemEng, KKU, M.Thabuot MEMBRANE: Microfiltration Simple screening mechanism Pore size 0.01 μm - 10 μm  P  0.01 to 0.5 MPa Low pressure process Most effectively remove particles and microorganisms (bacteria) High flux Colloids/Macromole ---> theoretically pass through the membrane 1

Lecture3_water purification, ChemEng, KKU, M.Thabuot MEMBRANE: Microfiltration Any filtration mode Any membrane configuration Needs back flushing and air scour Operating pressure ~ psi Highly automated! Can add coagulants to enhance filtration Can be a good pretreatment for RO or NF 2

Lecture3_water purification, ChemEng, KKU, M.Thabuot Typical MF Membrane System 3

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MEMBRANE: Ultrafiltration Screening and Adsorption Pore size nm  P ~0.1 to 1 MPa Two layers: a thin (0.1 to 0.5 µm), skin layer and a porous substructure support layer Separation of macromolecules Only surface deposition - no internal pore plugging- so, relatively easy to remove, irreversible 5

Lecture3_water purification, ChemEng, KKU, M.Thabuot MEMBRANE: Ultrafiltration Cross flow or transverse flow Any membrane configuration Use re-circulation for high TSS Operating pressures ~ 50 psi Uses back flush to loosen fouling Excellent pretreatment for RO or Posttreatment for ED. 6

Lecture3_water purification, ChemEng, KKU, M.Thabuot UF can replace several conventional processes 7

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MEMBRANE: Nanofiltration NF Removes molecules in the micron range  P ~0.5 to 6 MPa NF is essentially a lower-pressure version of reverse osmosis NF performance characteristics between reverse osmosis and ultrafiltration Nanofiltration: Water softening, removal of organic matter, desalting of organic reaction products. Cross flow or transverse flow Any membrane configuration 9

Lecture3_water purification, ChemEng, KKU, M.Thabuot Desalting Plant 10

Lecture3_water purification, ChemEng, KKU, M.Thabuot MEMBRANE: Reverse Osmosis Spiral wound or hollow fine fiber Pretreatment is critical to success NTU <1, SDI<3 Operating pressures from psi Removes >95-99% TDS Concentrate Stream is 15-25% of flow with 4 to 6 times the TDS. 11

Lecture3_water purification, ChemEng, KKU, M.Thabuot MEMBRANE: Reverse Osmosis Membrane: similar to UF, thin active layer; porous support layer RO has the separation range of to  m Desalination (seawater and brackish water), metal plating effluent treatment, color removal from textile effluents, production of high purity water (boiler feed, electronics, medical, pharmaceutical) 12

Lecture3_water purification, ChemEng, KKU, M.Thabuot Reverse Osmosis force water through membrane force water through membrane removes many contaminants removes many contaminants 13

Lecture3_water purification, ChemEng, KKU, M.Thabuot MEMBRANE: Reverse Osmosis 14

Lecture3_water purification, ChemEng, KKU, M.Thabuot Reverse Osmosis Most common types of RO are: Spiral Wound Hollow Fiber 15

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Lecture3_water purification, ChemEng, KKU, M.Thabuot Hollow fiber: 18

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Lecture3_water purification, ChemEng, KKU, M.Thabuot RO Package System 20

Lecture3_water purification, ChemEng, KKU, M.Thabuot Applications of Micro- and Ultrafiltration Conventional water treatment (replace all processes except disinfection). Pretreat water for R.O and nanofiltration. 21

Lecture3_water purification, ChemEng, KKU, M.Thabuot Applications for R.O. and nanofiltration R.O. application mostly desalination. Nanofiltration first developed to remove hardness 22

Lecture3_water purification, ChemEng, KKU, M.Thabuot RO Package 23

Lecture3_water purification, ChemEng, KKU, M.Thabuot Membrane Fouling Fouling 24

Lecture3_water purification, ChemEng, KKU, M.Thabuot Vibrating shear to prevent fouling Membrane Fouling 25

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Lecture3_water purification, ChemEng, KKU, M.Thabuot Merits and Demerits of Membrane Process Merits It reduces the number of unit processes in treatment systems Potential for process automation and plant compactness Much smaller foot print than the conventional plants of the same capacity Easy scale-up, and expansion 27

Lecture3_water purification, ChemEng, KKU, M.Thabuot Merits and Demerits of Membrane Process Less or no chemical use and provides highest quality water No formation of secondary chemical by-products Less sludge production Water reuse and recycling Demerits Membrane fouling Low membrane life time Low selectivity High capital and operating cost 28

Lecture3_water purification, ChemEng, KKU, M.Thabuot In the ED process a semi-permeable barrier allows passage of either positively charged ions (cations) or negatively charged ions (anions) while excluding passage of ions of the opposite charge. These semi-permeable barriers are commonly known as ion-exchange, ion-selective or electrodialysis membranes. Electrodialysis 29

Lecture3_water purification, ChemEng, KKU, M.Thabuot Electrodialysis 30

Lecture3_water purification, ChemEng, KKU, M.Thabuot Electrodialysis 31

Lecture3_water purification, ChemEng, KKU, M.Thabuot COAGULATION Various sizes of particles in raw water Particle diameterTypeSettling velocity 10 mmPebble0.73 m/s 1 mmCourse sand0.23 m/s 0.1 mmFine sand0.6 m/min 0.01 mmSilt8.6 m/d (10 micron)Large colloids0.3 m/year (1 nano)Small colloids3 m/million year G r a v i t y s e t t l i n g 32

Lecture3_water purification, ChemEng, KKU, M.Thabuot COAGULATION Colloids – so small, gravity settling not possible Metal precipitates are usually colloidal H2OH2O Colloid Colloids have a net negative surface charge Electrostatic force prevents them from agglomeration Brownian motion keeps the colloids in suspension 33

Lecture3_water purification, ChemEng, KKU, M.Thabuot COAGULATION Coagulation is the destabilization of colloids by addition of chemicals that reduce the negative charges The chemicals are known as coagulants, usually higher valence cationic salt (Al3+, Fe3+ etc.) 34

Lecture3_water purification, ChemEng, KKU, M.Thabuot COAGULATION Typical coagulants Aluminum sulfate: Al 2 (SO4) 3.14 H2O Polyaluminum Chloride (PAC): Al 2 (OH) 3 Cl 3 Iron salt- Ferric Sulfate: Fe 2 (SO4) 3 Iron salt- Ferric Chloride: Fe 2 Cl 3 35