Design of Ultrafiltration plants for safe drinking water Frans Knops Mark Steggink Irene Körbl

Contents 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

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)

ultrafiltration

Designing an UF system Information required: Feed Quality: Capacity: 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

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

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

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

Membrane fouling and cleaning Types of fouling on UF membranes: Cake formation Pore blocking Adsorption Concentration Polarization

Membrane fouling and cleaning Cleaning modes: Backwash (BW) Relaxation Chemical Enhanced Backwash (CEB) Clean-In-Place (CIP)

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.

Membrane fouling and cleaning UF cleaning chemicals * It is important to check back with UF supplier on chemical compatibility and dosage

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

TESTING AND VALIDATING 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.

TESTING AND VALIDATING 4MS The 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

TESTING AND VALIDATING 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)

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 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

TESTING AND VALIDATING Testing during operation Testing methods Direct integrity testing: pressure decay airflow Performance testing: spiking with indicator substance non-spiked (naturally present matter)

TESTING AND VALIDATING Virus Like Particles (4.3 – 6.0 log) versus MS2 Phages (6.6 – 8.2 log) VLP is conservative

New developments HFW1000 color UFC – Xiga / Aquaflex

Hollow fiber nanofiltration Virus Like particles Virus Like Particles (5.1 log)

ULTRAFILTRATION Drinking water production

Roetgen, Germany UF product flow rate 145.000 m3/d

Lower selatar water works, singapore UF product flow rate 260.000 m3/d

Goteborg vatten, sweden UF product flow rate 186.000 m3/d

Thank you for your attention!