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Design of Ultrafiltration plants for safe drinking water

Frans KnopsMark StegginkIrene Körbl

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CONTENTS1) INTRODUCTION2) ULTRAFILTRATION 3) DESIGNING AN UF SYSTEM 4) COMPONENTS OF AN UF PLANT 5) MEMBRANE FOULING AND CLEANING 6) TESTING AND VALIDATING FOR DRINKING WATER7) NEW DEVELOPMENTS8) 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:‐ 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:

» Non ionics: turbidity, TSS, COD, TOC, color, silica» Ionics: dissolved metals, alkalinity, silica » Others: temperature, pH

• Capacity:» Nominal flow» Peak flow

• Required filtrate quality:» Micro biological removal efficiency» Removal of organics and color

• Other considerations:» Redundancy» Footprint

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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:

» Remove particular foulants that UF is susceptible to. (e.g. Mn, Fe, FOG)» Reduce size of UF plant by reducing TSS load.

• Typical UF pre-treatment processes:» 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

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COMPONENTS OF AN UF PLANT

CHEMICAL DOSING UNITS• For pH adjustment, CEB, in-line coagulant dosing and chemical neutralisation

• Typical dosing sets required:»In-line coagulation: FeCl3, alum, PACl + pH adjustment»CEB: Caustic + NaOCl + acid»Neutralisation: Reducing agent (SBS) + acid/caustic

• Considerations:» Chemical dosing sets should be overdesigned to cater for deterioration in

chemical stock concentration and fluctuating water quality

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MEMBRANE FOULING AND CLEANING

TYPES OF FOULING ON UF MEMBRANES:• Cake formation• Pore blocking• Adsorption• 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• 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• Short stoppages of filtration. (air scouring may run concurrently).• Loosen cake layer and loosely attached foulants.

CHEMICAL ENHANCED BACKWASH• Chemical cleaning involving a short soak duration.• Effective against adsorbed foulants.

CLEAN-IN-PLACE• 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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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

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EUROPEAN DIRECTIVE

• COUNCIL DIRECTIVE 98/83/EC on the quality of water intended for human consumption (Drinking Water Directive or DWD)

• For drinking water contact materials no harmonized EU regulations yet.

• 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

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4MSThe 4MS intend to adopt common, or directly comparable, practices for:

• 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

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Validating for safe use: leaching of toxic chemicals

Leaching• USA NSF Std.61 (membrane module)• UK DWI reg.31 (membrane module)

WRAS (ancillaries)• F ACS (membrane module plus chemicals)• D KTW, W270 DVGW (membrane fibers)• NL KIWA ata (membrane module)• CN MoH (membrane module)• RU Federal Service (membrane module)

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TESTING AND VALIDATING

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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

• 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

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Testing during operation

Testing methods• Direct integrity testing: pressure decay

airflow• Performance testing: spiking with indicator substance

non-spiked (naturally present matter)

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Virus Like Particles (4.3 – 6.0 log)versus MS2 Phages (6.6 – 8.2 log)

VLP is conservative

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TESTING AND VALIDATING

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UFC – Xiga / Aquaflex

HFW1000 color

NEW DEVELOPMENTS

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Virus Like particles

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HOLLOW FIBER NANOFILTRATIONVirus Like Particles (5.1 log)

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ULTRAFILTRATIONDRINKING WATER PRODUCTION

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ROETGEN, GERMANY

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UF product flow rate 145.000 m3/d

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LOWER SELATAR WATER WORKS, SINGAPORE

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UF product flow rate 260.000 m3/d

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GOTEBORG VATTEN, SWEDEN

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UF product flow rate 186.000 m3/d

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THANK YOU FOR YOUR ATTENTION!

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