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Advancements in Membrane Technology: Standardizations and Innovations in Drinking Water Applications
June 17, 2016
Jarrett Kinslow, PE
Jill Hudkins, PE
● Introduction and Review of
Membrane Technologies
● Membrane Filtration (MF/UF)
Overview, Applications &
Innovations
● Membrane Separation (NF/RO)
Overview, Applications &
Innovations
● Summary
Agenda
SAWS Brackish Groundwater Desalination Approaching Completion (Yesterday)
1
Introduction
Introduction
• Typically, water treatment processes can be broken down into the
following categories:
Chemical
Physical
Biological
• Membrane treatment processes can be generally classified as
physical processes in which constituents are separated from the
raw water.
Increasing regulatory standards
especially regarding disinfectant
by-products and waterborne pathogens
Limited and deteriorating
supplies require the use of
alternative water sources
Growing demand due to
population growth
Technological innovation
leading to development of
low cost, high quality water
treatment solutions
Retrofit of old technology
to protect the public from
aging or underperforming
systems
Membranesoffer costeffectivesolutions
Drivers for Membrane Treatment
Flat Sheet Thin Film Composite (RO/NF)
Support Material
Membrane
Hollow Fiber (MF/UF)
Contaminants
Membrane Types
99.0498.000ppt_4-29-02_djh04.ai
MICROFILTRATION
ULTRAFILTRATION
NANOFILTRATION
RO
Giardia
Salts
SOC’s
NOMHardness
Cryptosporidium
Turbidity
Viruses
Algae
Radionuclides
Bacteria
Asbestos
H2O
Color
Organic Macromolecules
> 0.1 micron
0.1 - .003 micron, >2000 MW
> 0.001 micron, >180 MW
> 0.0001 micron, Ions > 20 AW
Membrane Selection
Membrane Processes
● Membrane Filtration: Size Exclusion (Sieving) Microfiltration, MF Ultrafiltration, UF
● Membrane Separation: Diffusion Controlled Nanofiltration, NF Reverse Osmosis, RO (Low Pressure/Brackish Water) Seawater Reverse Osmosis, SWRO
● Non-Water Permeable: Charge Controlled Processes Electrodialysis, ED Electrodialysis Reversal, EDR
1
Membrane Filtration
● Hollow Fiber Membranes – Bundles or Cassettes
● Microfiltration (MF) Process removes particles / turbidity / bacteria / and protozoa
Pressure Range: 4 - 70 psi
Configuration: Hollow Fiber
● Ultrafiltration (UF) Process removes particles / turbidity / bacteria / protozoa and virus
Pressure Range: 10 - 90 psi
Configuration: Hollow Fiber
Membrane Filtration (MF/UF)
● Various forms are available
Vacuum Driven (submerged in tank)
Pressure Driven (in pressure vessels, normally vertical)
● Typically operates in dead end mode (like a media filter)
● System operates for a prescribed run period (determined by
recovery)
● Concentrate waste from a short duration backwash (backpulse
cycle)
Membrane Filtration (MF/UF)
MF/UF Membranes
• Membranes are manufactured as hollow fibers
• Materials include PP, PVDF, PES, and others
• Most are resistant to high levels of chlorine
• Hollow fibers are engineered to provide a specific pore size
• Hollow strands of porous plastic
fibers with billions of
microscopic pores on the
surface
• The pores are thousands of
times smaller in diameter than a
human hair
• Pores form a physical barrier to
impurities but allow pure water
to pass
UF Membranes = Effective Barrier
MembraneFiber
Electron microscope view of membrane surface
Operating Modes
Outside In
Inside Out, Flow Thru
Inside Out, Dead End
MF/UF Treatment Units
• Hollow fibers are bundled into cassettes for immersed service or enclosed vessel modules
• Operated in inside-out or outside-in and dead end or recirculation modes
• Pressure is applied to the feed or a vacuum is applied to the fibers
● Flux rates decrease with increasing fouling potential
● To Increase Capacity: Add membrane area (more membrane
elements in parallel)
● To Increase Recovery: Add pretreatment
● To Increase Quality: Membrane material, pore size
● Recovery limited feed pressure limitations and effectiveness of
backwash cycles
MF/UF System Design Parameters
● Retrofit for Existing Media Filters
● Surface Water Treatment (LT2ESWTR)
● GroundWater Under Direct Influence (GWUDI)
● Pretreatment to RO/NF (Integrated Membrane Systems)
Seawater RO (SWRO)
Brackish Surface Water
Water Reuse (IPR/DPR)
MF/UF Applications
Ultrafiltration Pathogen Removal
4 to 6 micron
0.1 micron pore size
Giardia(4 - 14 microns in diameter) Cryptosporidium
(4 - 6 microns in diameter)
Wastewater Treatment/Reuse
Reclaimed Water
Feed Pump
DisinfectionPermeate
MembraneFiltrationModules
Strainer
Secondary Treatment w/Tertiary Filtration
Secondary Treatment w/Membrane Filtration
Raw
Was
tew
ater
Membrane Filtration System
Membrane Bioreactor
Vacuum Pump
● Commercial offerings are typically proprietary systems ,
packaged by the membrane manufacturer (Pall, GE, Evoqua)
● Most components are not inter-changeable
● Recent market trends are towards standardization of membrane
elements
● Many state regulatory agencies require pilot testing
● Challenge testing
● Direct integrity testing (pressure decay test)
MF/UF Additional Considerations
● Solids and Turbidity Resiliency
● Membrane Fibers
Low Fouling PVDF Membrane Chemistry
Improved Durability of Membrane Fibers
● Membrane Cassettes/Bundles –
Modular Construction and Flexibility for
Expansion
● Encased vs. Submerged Installations
● Enhanced Methods for Maintaining
System Performance (CEB, Mini-Cleans,
CIP)
MF/UF Innovations
MF/UF Market has traditionally been
dominated by suppliers of complete
pre-engineered systems:
● Significant differences in modules,
operational conditions, and cleaning
required custom tailored systems
● Required selection of system supplier
prior to completing the plant design
● Owner often must sole-source future
membrane replacements and future
service/parts
MF/UF Systems - Market Trends
Interchangeable rack MF/UF systems are changing the ways systems are designed and constructed:
● Piping and supporting equipment are designed to work with multiple membrane manufacturers (non-proprietary alternative)
● Allows detailed design to be completed without a final membrane manufacturer selection
● Compatibility with 3-6 different membrane manufacturers
● Improved convergence of suppliers of MF/UF with NF/RO (benefits applications for integrated membrane systems)
MF/UF Systems - Market Trends (cont.)
1
Membrane Separation
●Thin Film, Flat Sheet Membranes – Spiral Wound
●Nanofiltration (NF) Process removes turbidity / virus / color / pesticide / NOM /
pesticide / and hardness
Pressure Range: 70 - 140 psi
Configuration: Spiral Wound Sheet
●Reverse Osmosis (RO) Process removes turbidity / color / pesticide / NOM / pesticide /
hardness / salinity removal / nitrate / arsenic
Pressure Range: 140 - 700 psi
Configuration: Spiral Wound Sheet, Hollow Fiber
Membrane Separation (RO/NF)
Semipermeable
membrane layer~2000 Angstrom
Microporous
polymeric support
Fabric backing
0.2 mm0.008"
Membrane Sheet Surface
Fabric backingPolymeric support
PA membrane surface
Membrane Construction
● Always pressure driven (normally
horizontal pressure vessels)
● Operates in cross flow mode, producing a
constant flow of concentrate (volume
determined by recovery)
● System operates continuously, and the
higher TDS concentrate is produced in
proportion to the permeate flow stream
Membrane Separation (NF/RO)
Reverse Osmosis
● “Reverse” osmosis is achieved by providing adequate pressure to
overcome the osmotic pressure so that the feed water flows from
the more concentrated solution to the “fresh” water side of the
membrane.
Water
1,500 mg/L 100 mg/L
Dia
ph
ragm
P>PO
Length: 1 m, 40 “
Diameter: 200 mm, 8”
Membrane Element Dimensions
Feed
Concentrate
Product
Membrane
Permeate
Carrier
Brine Spacer
RO/NF Membrane Element
Feed
Concentrate
Permeate
Head End Adapter R.O. Element
InterconnectorO-rings Brine Seal
Pressure Vessel
Retaining Ring
Head Seal Thrust Cone
RO/NF Pressure Vessel Assembly
44 gpm feed
22 gpm permeate
22 gpm concentrate
Pressure Vessel Flow-streams
Interconnector
End plate
Trust ring
Connector -adaptor
Pressure vessel
Feed or concentrate port
Section of RO element
Element Cross-Section
Reverse Osmosis System Schematic
FinishedWater
RawWater
Pretreatment
High Pressure Pumps
Post Treatment
Permeate
Concentrate toDisposal
Membrane Treatment Stage 1
Stage 2
Raw Water Blend
● Flux rates decrease with increasing fouling potential
● To Increase Capacity: Add membrane area (more pressure
vessels in parallel)
● To Increase Recovery: Concentrate Staging - 1st stage
concentrate becomes 2nd stage feed
● To Increase Quality – Permeate Staging – 1st stage permeate
becomes feed to 2nd Pass
● Recovery limited by limiting salts and/or feed pressure limitations
(energy costs)
RO/NF System Design Parameters
● Membrane Softening (NF)
● Color / Organics Removal (NF, Stage 2 DBPR)
● Brackish Water (BWRO)
● Nitrate Removal
● Arsenic Removal
● Industrial Water Treatment (Boiler, Manufacturing, ect.)
● High Purity / Ultrapure Water
● Seawater Desalination (SWRO)
● Water Reuse (LPRO)
● Food & Beverage, Bottled Water
NF/RO Applications
Membrane Softening vs. Lime Softening
Fin
ish
ed
Wat
er
Pretreatment High Pressure Pumps
Post Treatment
Permeate
Concentrate to Disposal
MembraneSoftening SkidsStage 1
Stage 2
Raw Water Blend
Solids Contact Unit (Softener)
Rapid Media Filtration
Blending Basin
Lime/PolymerLime-Soda Ash Process
Raw Water w/Hardness, Color, Iron Nitrates and Organics
Membrane Softening Process
Dissolved Inorganic Solutes (Brackish GW)
FinishedWater
RawWater
Pretreatment High Pressure Pumps
Post Treatment
Permeate
Concentrate to Disposal
NF/RO Membrane SkidStage 1
Stage 2
Raw Water Blend
Blending Basin
Existing Treatment Process
Reverse Osmosis Treatment Process
● Commercial offerings are standardized with inter-changeable
vessels and membrane elements
● Systems packaged by Membrane OEMs
● State regulatory agencies may accept membrane projections
(software), some still require pilot testing
● Method of concentrate disposal
NF/RO Additional Considerations
NF/RO Innovations
● Energy Reduction
Low Energy (Higher Permeability)
Membranes
Optimized Feed Channel Spacers
Energy Recovery Devices
● Process Optimizations
Fouling Resistant Membranes
Improved Pretreatment Chemicals
High Recovery RO Designs
(Concentrate Minimization)
Multi-ported Pressure Vessels
Center Feed Vessels (Nanofiltration)
Port St. Lucie Energy Recovery Device
NF/RO Innovations
● Product Innovations
Large Diameter Elements
High Surface Area Elements
(Automated Manufacturing)
Interlocking Membrane
Elements
8” element vs. 16” element
● Membrane technology is rapidly becoming more
mainstream throughout the US
● Costs can be competitive with conventional
treatment
● Membrane technology continues to evolve with
innovation
● Pilot Scale and Demonstration Scale Testing is
always beneficial
Summary