CT4471 Drinking water I
Dr.ir. S.G.J. Heijman nanofiltration and reverse osmosis Nanofiltration and reverse osmosis Contents
1. Introduction 2. Theory 3. Membrane modules 4. Applications 5. Design 6. Fouling control Introduction
Size, µm 0.001 0.01 0.1 1.0 10 100 1000 Approximate molecular 100 200 1000 10000 20000 100000 500000 weight Viruses Bacteria Relative size of Dissolved salts Algae materials in water Metal ions Humus acids Cystes Sand
Clay Silt ΔP [bar] Conventional filtration processes 0.01 Micro filtration 0.05 Treatment Ultra filtration 0.1 process Nanofiltration 5 Reverse osmosis 30 ED and EDR
Metal ions Dissolved salts Viruses Bacteria Cryptosporidium Arsenic Calcium salts Contagious Giardia Salmonella Nitrate Sulfate salts Hepatitis Nitrite Magnesium salts Shigellosis Protozoa Cyanide Aluminum salts Vibrio cholera Cystes Introduction •Bacteria •Virusses •Multivalent •Monovalent salts salts
Microfiltration MF + - - -
Ultrafiltration + + - - UF
Nanofiltration + + + - NF
Reversed Osmosis + + + + RO
October 16, 2007 4 Introduction Introduction
• Spiral wound membrane Modules
• Spiral wound membranes Introduction
• Principle slow sand filtration
v = 0.10 m/h d = 0.15 – 0.35 mm
October 16, 2007 8 Introduction • Slow sand filtration
slow sand filtration
October 16, 2007 9 Introduction
• Parallel MF/SSF
Problems: 1. Fouling 2. Packing
flux = 0.01 m/h
October 16, 2007 10 Introduction
• Traditional RO/NF - fouling
spacers
Concentrate channel Permeate channel
October 16, 2007 11
Turbulent flow across membranes Introduction
• Filtration process and particle size Particle size pressure MWCO flux [nm] [bar] [m3/m2·h] Micro filtration > 100 < 1 0.04 - 0.2 Ultra filtration 10 - 100 < 2 1000 - 10000 0.08 - 0.2 Nano filtration 1 - 2 5 - 10 200 - 500 0.02 - 0.08 Reverse osmosis0.2 - 1 15 - 60 100 0.01 - 0.04
MWCO = Molecular Weight Cut Off = 90% of organic molecules is removed Contents
1. Introduction 2. Theory 3. Membrane modules 4. Applications 5. Design 6. Fouling control Theory water
• Principle NF/RO product = 80% of supply water membrane concentrate = 20% of s s supply water n le io u c d e r e l o flow across te lv o m s membrane wa o s is r c id d a lo m l concentrate is 5 times more o c concentrated compared to the feed water Theory
• Reverse Osmosis ??
pure salt water water
semi-permeable membrane Theory
• Osmotic balance osmotic pressure ΔΠ
pure salt water water
semi-permeable membrane Theory
Pressure ΔP−ΔΠ • Reverse osmosis
pure salt water water
semi-permeable membrane Theory
Qf, Pf, cf Qc, Pc, cc
Qp, Pp, cp
Mass balance water: Qf = Qc + Qp Qp Recovery γ = Qf
Mass balance salt: Qf·cf = Qc·cc + Qp·cp 1 cccf=⋅ , c p≈ 0 1− γ cp Retention Ret=− 1 cf Theory
Reverse osmosis nanofiltration parameter Sea water Brackish water Ground water T [°C] 25 25 25 3 cf [g/m ] 35000 2000 100 γ [−] 0.3 0.8 0.8 ΔP [bar] 55 25 10
Ro [-] 0.995 0.95 0.85 η [−] 0.7 0.7 0.7
ηrec [−] 0.7 0.7 0.7 πf [bar] 30 1.7 0.1 Δπ [bar] 36 5.1 0.5 ΔP-Δπ [bar] 19 20 9.5 R [-] 0.994 0.85 0.55 3 cp [g/m ] 210 300 45 E [kWh/m3] 7.2 1.2 0.5 3 Erec [kWh/m ] 2.5 0.1 0.05 Theory
• Concentration • polarisation
October 16, 2007 20 Contents
1. Introduction 2. Theory 3. Membrane modules 4. Applications 5. Design 6. Fouling control Membranes structure
Homogenous
Asymmetric
Composite
Liquid Membrane modules
Tubular membranes 20 - 200 m2/m3
Plate and frame membranes 400 - 600 m2/m3
Spiral wound membranes 900 - 1000 m2/m3
Hollow fiber membranes until 12000 m2/m3 Modules
• Tubular membranes Modules
• Spiral wound membrane Modules
• Hollow fiber membranes Modules
October 16, 2007 27 Contents
1. Introduction 2. Theory 3. Membrane modules 4. Applications 5. Design 6. Fouling control Applications RO
1. Desalinization of sea or brackish water - high costs: ( 1.0 euro /m3 till 3.5 euro /m3 sea water) - examples: Heineken Greenhouse agriculture 2. Split flow membrane filtration - costs: 50 euro cents/m3 product - example: Na+/Cl- Andijk (PWN)
3. Direct treatment of surface water - removal of micro organisms, organic compounds, hardness and salts - examples: Application RO • Treatment Heemskerk (PWN)
50% 50% IJssel lake ACF Ultrafiltration
Micro sieves AOP Reverse osmosis Fe3+ Ca(OH)2 Coagulation Dune infiltration
Sedimentation Aeration Rapid filtration Rapid filtration Softening Rapid filtration
Drinking water Application RO
• Treatment Heemskerk (PWN)
October 16, 2007 31 Application RO • Treatment Heemskerk (PWN)
October 16, 2007 32 Application RO
October 16, 2007 33 Performance NF/RO
Removal percentage [%] NF RO
Pesticides > 90% > 95%
DOC > 90% > 95%
Hardness (Ca2+, Mg2+) > 90% > 99%
+ - - Salts (Na , Cl , NO3 ) 50 - 70% > 90 %
Disinfection - bacteria, viruses > 99.99% > 99.99% - Giardia, Cryptosporidium > 99.99% > 99.99% Application NF
1. Split flow membrane filtration for softening and removal of organic compounds - alternative for softening and activated carbon filtration - examples: colored ground water bank filtration water pretreatment for infiltration (IB) - costs: 35 euro cents/m3 product
2. Direct treatment of surface water - removal of micro organisms, organic compounds and hardness Application NF • Treatment anaerobic groundwater 100%
Anaerobic GW 56% 44% Candle filter
nanofiltration Concentrate 45% discharge Conventional 11% treatment Conditioning 45% Permeate storage 45%
RWK 89% Contents
1. Introduction 2. Theory 3. Membrane modules 4. Applications 5. Design 6. Fouling control Design
Membrane ΔP PI TI unit TI Raw water Product Micro filter
HCl/H2SO4/AS FIC
Concentrate Design • Membrane staging Christmas tree staging
PC Supply Concentrate Product
Circulation PC Concentrate Supply
Product Design
• Staging 22-11-5 Design
October 16, 2007 41 Design
• Standard design standard design: 6 elements/vessel 2 stages (staging 2:1) Design
• Recent research Design
• Production per element maximum: 0.918 conventioneel:conventional: 0.723 0,91 0,86 0,81 0,76 1 stage 0,71 6:1 0,66 5:1 4:1 Staging (m3/h/element) 0,61 3:1 Element production 0,56 2:1 0,51 1:1 1 2 3 4 5 6 7 Elements/vessel Design Optiflux®
Addapted pressure vessel with special connector
October 16, 2007 45 Contents
1. Introduction 2. Theory 3. Membrane modules 4. Applications 5. Design 6. Fouling control Fouling control
Pre-treatment Optimali- cleaning sation process conditions Particles ++ - + Scaling - ++ +/- Biofouling ++ +/- ? Organic fouling + ++ +
October 16, 2007 47 Fouling control: scaling
October 16, 2007 48 Fouling control: scaling
• Process design: • module design • staging • operational parameters: • cross flow velocity • flux • recovery • acid or anti-scalant
October 16, 2007 49 Fouling control: scaling
October 16, 2007 50 Fouling control: scaling
• Spiral wound membranes Fouling control: scaling
• Staging: increasing cross-flow velocity in second stage Fouling control: scaling
• Process design: • module design • staging • operational parameters: • cross flow velocity • flux • recovery • acid or anti-scalant
October 16, 2007 53 Fouling control: scaling
October 16, 2007 54 Fouling control: scaling
October 16, 2007 55 Fouling control: scaling Permeate Permeate feed
Concentrate
Sr BaSO4[-] 8
6
4
2
0 0 2 4 6810 12
October 16, 2007 Element56 # Fouling control: scaling
• Process design: • module design • staging • operational parameters: • cross flow velocity • flux • recovery • acid or anti-scalant
October 16, 2007 57