Design of Ultrafiltration plants
for safe drinking water
Frans Knops
Mark Steggink
Irene Körbl
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CONTENTS
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INTRODUCTION
ULTRAFILTRATION
DESIGNING AN UF SYSTEM
COMPONENTS OF AN UF PLANT
MEMBRANE FOULING AND CLEANING
TESTING AND VALIDATING FOR DRINKING WATER
NEW DEVELOPMENTS
EXAMPLES OF POTABLE WATER UF PLANTS
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INTRODUCTION
WHAT IS A MEMBRANE?
‐ A membrane is a selective physical barrier used to separate a stream (gases or liquids
and slurries) into its components based on their permeability through the barrier.
COMMON MEMBRANES PROCESSES FOR WATER TREATMENT:
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Microfiltration (MF)
Ultrafiltration (UF)
Nanofiltration (NF)
Reverse Osmosis (RO)
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ULTRAFILTRATION
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DESIGNING AN UF SYSTEM
INFORMATION REQUIRED:
• Feed Quality:
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Capacity:
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Micro biological removal efficiency
Removal of organics and color
Other considerations:
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Nominal flow
Peak flow
Required filtrate quality:
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Non ionics: turbidity, TSS, COD, TOC, color, silica
Ionics: dissolved metals, alkalinity, silica
Others: temperature, pH
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Redundancy
Footprint
COMPONENTS OF AN UF PLANT
COMPONENTS OF AN UF PLANT
• Pre-treatment
• Pre-screen
• UF skid
• Chemical dosing unit(s)
• Neutralisation unit
• Backwash unit
• CIP unit
• Post treatment (disinfection, RO etc)
• Membrane integrity test unit
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COMPONENTS OF AN UF PLANT
PRE-TREATMENT
• Pre-treatment is installed to:
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Typical UF pre-treatment processes:
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Remove particular foulants that UF is susceptible to. (e.g. Mn, Fe, FOG)
Reduce size of UF plant by reducing TSS load.
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DAF  removal /reduction of FOG, COD and TSS
Green sand filter  Mn and Fe removal, reduce TSS
Coagulation/Flocculation  Reduce TSS load, remove oxidised Fe and Mn
Activated carbon (GAC/PAC)  colour, odour, TOC
Oxidation  oxidation of Mn and Fe, reduction of TOC
COMPONENTS OF AN UF PLANT
CHEMICAL DOSING UNITS
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For pH adjustment, CEB, in-line coagulant dosing and chemical
neutralisation
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Typical dosing sets required:
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Considerations:
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In-line coagulation: FeCl3, alum, PACl + pH adjustment
CEB: Caustic + NaOCl + acid
Neutralisation: Reducing agent (SBS) + acid/caustic
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Chemical dosing sets should be overdesigned to cater for deterioration in
chemical stock concentration and fluctuating water quality
MEMBRANE FOULING AND CLEANING
TYPES OF FOULING ON UF MEMBRANES:
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Cake formation
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Pore blocking
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Adsorption
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Concentration Polarization
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MEMBRANE FOULING AND CLEANING
CLEANING MODES:
• Backwash (BW)
• Relaxation
• Chemical Enhanced Backwash (CEB)
• Clean-In-Place (CIP)
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MEMBRANE FOULING AND CLEANING
BACKWASHING
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Reverse the flow of filtrate at higher flux for short duration to flush out foulants from membrane surface and pores.
Effective against surface foulants, loose cake layer and partially effective against adsorbed foulants.
RELAXATION
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Short stoppages of filtration. (air scouring may run concurrently).
Loosen cake layer and loosely attached foulants.
CHEMICAL ENHANCED BACKWASH
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Chemical cleaning involving a short soak duration.
Effective against adsorbed foulants.
CLEAN-IN-PLACE
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Long duration, chemical cleaning involving recirculation-soak cycles.
Use for recovery cleaning or with specialised chemicals for particular foulants.
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MEMBRANE FOULING AND CLEANING
UF CLEANING CHEMICALS
* It is important to check back with UF supplier on chemical compatibility and dosage
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TESTING AND VALIDATING
One of the main requirements of governments and drinking water companies
worldwide in providing drinking water: public safety
REQUIRED REMOVAL
• Bacteria (e.g. Fecal bacteria)
• Protozoa (e.g. Cryptosporidium and giardia)
• Viruses (e.g. Enteric viruses like hepatitis)
DIRECTIVES
• WHO
• European directive
• Long term 2 surface water treatment (USA)
APPROVALS
• Potable water approvals: UK, USA, F, D, NL, AUS, JAP, CN, RU
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TESTING AND VALIDATING
EUROPEAN DIRECTIVE
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COUNCIL DIRECTIVE 98/83/EC on the quality of water intended for human
consumption (Drinking Water Directive or DWD)
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For drinking water contact materials no harmonized EU regulations yet.
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Four EU Member States France, Germany, the Netherlands and the United
Kingdom Great Britain (4MS) announced in January 2011 that they have
formalized arrangements to work together on this important aspect of the
regulatory frameworks they have in place to ensure the hygienic safety of
drinking water.
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TESTING AND VALIDATING
4MS
The 4MS intend to adopt common, or directly comparable, practices for:
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Acceptance of constituents used in materials in contact with drinking water
(4MS Common Positive List(s))
Testing of materials
Use of common test methods and
setting acceptance levels
Specification of tests to be applied
to products
Reviewing factory production control
and setting audit testing requirements
Assessing the capabilities of
certification and testing bodies
Transition period several years, in the meantime still national approvals required
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TESTING AND VALIDATING
Validating for safe use: leaching of toxic chemicals
Leaching
• USA
• UK
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F
D
NL
CN
RU
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NSF Std.61 (membrane module)
DWI reg.31 (membrane module)
WRAS (ancillaries)
ACS (membrane module plus chemicals)
KTW, W270 DVGW (membrane fibers)
KIWA ata (membrane module)
MoH (membrane module)
Federal Service (membrane module)
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TESTING AND VALIDATING
Testing for removal efficiency of microbiology
Challenge Testing
• USA:
CDPH approval as Alternative Filtration Technology
Demonstration study with membrane module to show
microbiological reduction of 0.5 μm microspheres (conservative
Cryptosporidium/Giardia surrogate) and MS2 virus
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In-house: Challenge testing with membrane module to show microbiological
reduction of MS2 virus
Non-Destructive Performance Test (Intern)
Demonstrates the Cryptosporidium/Giardia removal capability of the membrane
module.
• Diffusive Airflow Test
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TESTING AND VALIDATING
Testing during operation
Testing methods
• Direct integrity testing:
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Performance testing:
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pressure decay
airflow
spiking with indicator substance
non-spiked (naturally present matter)
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TESTING AND VALIDATING
Virus Like Particles (4.3 – 6.0 log)
versus
MS2 Phages (6.6 – 8.2 log)
VLP is conservative
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NEW DEVELOPMENTS
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HOLLOW FIBER NANOFILTRATION
Virus Like particles
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Virus Like Particles (5.1 log)
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ULTRAFILTRATION
DRINKING WATER PRODUCTION
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ROETGEN, GERMANY
UF product flow rate 145.000 m3/d
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LOWER SELATAR WATER WORKS, SINGAPORE
UF product flow rate 260.000 m3/d
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GOTEBORG VATTEN, SWEDEN
UF product flow rate 186.000 m3/d
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THANK YOU FOR YOUR ATTENTION!
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