Membrane Technology

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MEMBRANE TECHNOLOGY

• Paulus Hartanto

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Membrane Filtration Technology
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Filtration Spectrum
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Cross Flow Filtration
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Dead End Filtration
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Application of membrane processes in water
environment
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Factors affecting membrane performance
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What is membrane ?
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Conventional vs Membrane Filtration
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Classification of membrane processes
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Phases divided by membrane
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Some membrane processes and driving forces
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More common membrane processes
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Flux range trans-membrane pressure in pressure
driven membrane
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Membrane distillation vs Osmotic distillation
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Historical development of membranes
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Classification of filter (membrane)
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Depth filter vs screen filter
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Depth filter
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Screen filter
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Advantages of screen filter
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Absolute vs Nominal rating
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Microporous vs Asymmetric
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Membrane classification (poresize)
Organic macromolecules
Organic compounds
Colloids
Viruses
Dissolved salts
Bacteria
Pollens
Yeasts
0. 1 nm
0.01 mm
0. 1 nm
1 mm
0.1 mm
10 mm
100 mm
RO
Red globule
hair
Smallest microorganisms
Polio virus
visible to naked eye
NF
Nanofiltration
UF
Ultrafiltration
MF
Microfiltration
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Membrane classification (pressure range)
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Rejection Capabilities UF vs MF
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Process combinations
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Membrane classification (driving force)

• Vacuum (Submerged Membranes)
• Compatible with higher solid concentration
• Can be used for retrofit
• High energy demand with air scouring
• Noise evaporation concerns

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Membrane classification (driving force)

• Pressure (Canister Membranes)
• More compact design
• Cannot handle high solid concentration (gt 100
  NTU) for a substantial period of time

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Membrane classification (configuration)

• Open feed channel configuration
• Tubular
• Hollow-Fiber
• Narrow feed channel configuration
• Spiral (Flat sheet)

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Membrane classification (configuration)

• Flat Sheet (Spiral-wound)

Mostly used in Reverse Osmosis Nanofiltration
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Membrane classification (configuration)

• Tubular Membranes (OD gt 3 mm)

Mostly used in Industrial MF
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Membrane classification (configuration)

• Hollow Fiber Membranes (ID lt 1.5 mm)

Mostly used in MF UF
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Membrane classification (Location of membrane)

• Inside-out Membranes

• Outside-In Membranes

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Membranes Applications

• Filtration Low-Pressure membranes (MF/UF) for
  turbidity pathogen removal
• Organic Removal Nanofiltration (NF) for NOM
  removal
• Inland Brackish Desalination RO or NF
• Seawater Desalination RO or 2-stage NF
• Membrane Bioreactor MF/UF MBR

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Membrane vs Sand

• Membrane filtration mechanism
• Sieving/Straining
• Sand filtration mechanism
• Interception, collision, electrostatic attraction
• Straining only happens in cake filtration

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Finished water comparison
Conventional Membranes
Turbidity 0.05 0.3 lt 0.1
Virus removal 2 log gt 4 log
Influent quality change Affected Not affected
Water chemistry change Affected Not affected
Operating conditions change Affected Not affected
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Performance comparison
Conventional Membranes
High feed turbidity Shorter run time Higher pressure (if turbidity is excessive for a long duration)
High feed TOC Not affected Higher pressure, need freq. chemical cleaning
High FeCl3 dose Shorter run time FeCl3 not required
Low feed temp. Not affected Higher pressure or lower output
Capacity increase Shorter run time Higher pressure, need freq. chemical cleaning
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Typical Membrane Filtration Cycle

• Filtration (15 50 minutes)
• Backwash (20 sec 2 min)

(No rinsing, surface wash, or filter-to-waste)
Special Operation/Maintenance

• Chemical Cleaning
• Membrane Repair

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Membrane Fouling (performance)
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Fouling is part of membranes

• All membranes are subject to fouling, no
  exception
• Fouling is acceptable as long as it is reversible
  and manageable (i.e., can be removed in a
  reasonable fashion)

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Potential Fouling MaterialNatural Organic Matter

• NOM with high SUVA
• TOC gt 4 mg/L would be a concern
• Organic fouling is sticky and difficult to
  clean
• Organic may serve as cement to bind other
  particulates and form a strong cake layer
• Caustic cleaning (e.g. NaOH) and strong oxidant
  (e.g. H2O2) are effective for NOM fouling cleaning

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Potential Fouling MaterialParticulate/Colloids

• Inorganic particles alone would not cause much
  fouling
• Inorganic particle cake layer could be easily
  removed by backwash
• Excessive turbidity could clog membrane fiber
  lumens
• Inorganic particles mixed with NOM could cause
  substantial fouling
• Organic colloids could cause significant fouling
  and could be difficult to clean

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Potential Fouling MaterialInorganic Material

• Precipitation of Ca, Mn, Mg, Fe, and Al could
  cause significant fouling
• Fine inorganic colloids (lt 0.05 mm) could clog
  membrane pores and cause fouling
• Prefer a negative Langelier Index
• Acid, EDTA, SBS cleaning could be effective for
  inorganic fouling

Langelier Index Actual pH Saturation
pH Saturation pH 2.18 - logCa2 - logHCO3-
L.I. gt 0 Oversaturated (tend to
precipitate) L.I. lt 0 Undersaturated (tend to
dissolve more)
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Potential Fouling MaterialSynthetic Polymers

• Polymers used for coagulant/filter aids
  backwash water treatment
• Presence of polymers in feed water could cause
  dramatic fouling, and sometimes irreversible
• Free residual polymer is worse than
  particle-associated polymer
• Cationic polymers are worst
• Some polymers can be easily cleaned with chlorine
  and therefore are consider compatible with
  membranes

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Fouling Mitigation Pretreatment

• Reduce TOC level (lt 4 mg/L)
• Reduce Turbidity (lt 5 NTU)
• Reduce Hardness (lt 150 mg/L)
• Avoid substantial change in water chemistry, such
  as pH and other pretreatment chemicals
• Prevent Oil and Polymers from entering the feed
  water

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Fouling MitigationOperation

• Use crossflow if turbidity is high (For
  Inside-out membranes)
• Bleed a portion of the concentrate to avoid solid
  buildup
• Operate at a lower flux (lower TMP)
• Enhance pretreatment

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Fouling MitigationCleaning Strategy

1. Frequent BW (shorter filtration cycle)
2. Longer BW duration
3. Higher BW pressure
4. Add cleaning chemicals in BW water
5. Frequent chemical cleaning

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Membrane CleaningMembrane Fouling Mechanisms

• Organic Inorganic
• Particulate Soluble
• Various Mechanisms
• Surface Pore
• Adsorption, precipitation, coagulation

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Membrane Cleaning

• Hydraulic Cleaning (1030 minutes)
• Water/Air Backwash
• Air Scouring
• Water Flushing
• Chemical Cleaning (18 weeks)
• Free Chlorine (Sodium Hypochlorite)
• Acid/Base
• Other strong oxidants, such as H2O2
• Reducing agent, such as SBS
• Chelating chemicals, such as EDTA
• Proprietary Chemicals (surfactants)

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Summary of Fouling Material Cleaning Chemicals
Cleaning Chemical For Fouling Material
NaOCl Biological NOM Synthetic polymers
Acids (HCl, H2SO4, Citric Acid) Inorganic deposits
NaOH NOM
Sodium bi-sulfite (SBS) Reducible metals (Fe, Mn)
H2O2 NOM
EDTA Metals
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Membrane Integrity
Membrane Integrity
Membrane failure is rarely catastrophic less
serious than microbial penetration of rapid sand
filter beds.

• Membranes fail incrementally one fiber at a
  time.
• Statistically, individual fiber breaks are
  insignificant to the overall microbial water
  quality.

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Membrane Integrity Monitoring

• On-Line Turbidity Monitoring
• 0.08 NTU 95 of the time, 0.1 NTU max.
• On-Line Particle Count
• Baseline establishment (lt 50 particles/mL)
• Sensitivity Number of fiber breakage?
• Pressure Holding Test
• Virus Seeding Test (UF)

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The Secret of Membranes
Fouling Index
Cleaning Water Quality
High Production High Recovery
Manageable
Problematic

• Finding the balance point between
  Fouling-Enhancers and Fouling Reducers is the KEY!

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Take Away Points

• Membranes Offers a Wide Range of Applications
• Membrane is a Mature Technology
• A Successful Membrane Operation Depends on
• The Selection of an Appropriate System
• Optimized Operating Conditions/Protocols that
  Yield Manageable Membrane Fouling
• Experience Design Engineer

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The End