Desalination by membrane technology – state of the art and future trends

Desalination by membrane technology –state of the art and future trends Dr. Matthias Rothe and Oliver Hentschel ProMinent GmbH Im Schuhmachergewann 5-11, D-69123 Heidelberg Tel. +49 (6221) 842-0, Fax. +49 (6221) 842-1900 O.Hentschel@prominent.de www.prominent.com

Content Basics and state of the art membrane filtration Applications for desalination by membranes Future trends for membrane desalination

1. Basics and state of the art membrane filtration • Membrane filtration: removal of particles and salts ensuring lowest operating costs • physical process using semi-permeable membranes • 4 technologies depending on the size of the particles/molecules to be removed • Microfiltration • Ultrafiltration • Nanofiltration • Reverse Osmosis

Nanofiltration and Reverse Osmosis Nanofiltration and Reverse Osmosis are the only membrane technologies to remove ions/salts from water ! How does it work ?

Osmosis water column corresponding to osmotic pressure diluted solution concentrated solution semipermeable membrane

Reverse Osmosis pressure diluted solution concentrated solution semipermeable membrane

Development of Reverse Osmosis Membranes 1960 1970 1980 - 2014 • cellulose acetate membranes • lifetime about 6 months • pH range: 4 - 8 • salt rejection:up to 90-95% • polyamide hollow fibre modules • lifetime about 5 years • pH range: 4 - 11 • salt rejection:up to 96-98% • less sensitive against bacteria • thin film composite membrane • lifetime about 10 years • pH range: 2 – 11, for cleaning: 1 - 12 • salt rejection: up to 99.8% • stability up to 45°C • sanitary membr. 90°C • less sensitive against bacteria/biofilm

Thin film composite membrane Polyamide ultrathin barrier layer (approx. 0.1-0.2µm) Polysulfone micro-porous support (approx. 40µm) Polyester non-woven web Carrier (approx. 120µm)

Crossflow membrane filtration

Thin film composite membrane module http://www.youtube.com/watch?v=YlMGZWmh_Mw&feature=player_embedded

Water temperature influence on reverse osmosis • increased water temperature • reduction of water viscosity • increased permeate production • but:decreased salt rejection

Operation pressure influence on reverse osmosis The higher the pressure the more permeate flow is produced The salt rejection will be better, also

Recovery of membrane systems 100% raw water 75% permeate P R K 25% drain to waste Recovery [%] = Output : Input = (Permeate flow / raw water flow) x 100 Typical recoveries: 70-80% for desalination of tap water 35-45% for desalination of sea water

Typical reverse osmosis system 12 10 11 11 9 2 4 17 13 2 2 5 7/8 15 3 6 16 20 1 16 1. particle filter 2. pressure gauge 3. solenoid valve incl. check valve 4. pressure switch 5. thermometer 6. high-pressure pump 7. pressure vessel 8. membrane 9. conductivity probe 10. controller incl. conductivity measurement 11. flow meter permeate 12. 3-wayvalve 13 13 10 18 19 13. ball valve 14. flow meter concentrate 15. 3-wayvalve 16. flow meter concentrate recycle 17. sample valve 18. cleaning tank 19. cleaning pump 20. check valve 13

Typical reverse osmosis system 4 2 3 6 5 1 1 pressure vessels incl. membranes 2 switch cabinet with RO control unit 3 cleaning tank 4 flow meter permeate + concentrate 5 particle filter 6 conductivity sensor permeate

Overall design of a membrane system Post-treatment depending on application Pre-treatment depending on the feed water‘s quality: filtration and chemical conditioning as a minimum

Applications for desalination by membranes • Tap water desalination(typically up to 1.000 mg/l of feed water salinity) • Brackish water desalination(typically 1.500 – 8.000 mg/l of feed water salinity) • Sea water desalination(typically more than 35.000 mg/l of feed water salinity)

Applications for Reverse Osmosis • industrial water • desalination of tap water • boiler water for steam production • dilution water for juice- and softdrink production • bottled water • … • potable water production • desalination of brackish and sea water • reduction of nitrate • reduction of fluoride • reduction of arsenic

Desalination of tap water (installation example) 3x tap water desalination 1.200 m³/day, total 3.600 m³/day,process water for paintshop of KIA motors

Future trends for membrane desalination nano-coating structures on the active membrane layer, advantages: • anti-fouling properties are improved

Future trends for membrane desalination • Increase in permeability • less energy is needed at improved salt rejection rates • first membranes with nano-coating are commercially available now http://www.nanoh2o.com/technology/video

Future trends for membrane desalination • decreased energy consumption • membrane desalination with renewable energies like solar power …

Future trends for membrane desalination • … or wind energy:

Future trends for membrane desalination • Combination of membrane technologies, e.g. Micro- and Ultrafiltration (MF/UF) as pre-treatment followed by reverse osmosis, advantages: • Smaller footprint of complete water treatment plant which leads to smaller buildings • Better quality water of pre-treatment e.g. in comparison to classical sand filters • Reverse osmosis after MF/UF can be designed much more aggressive because of higher filtrate quality. This saves investment and operation costs on the reverse osmosis downstream

Future trends for membrane desalination • Energy recovery on sea water desalination systems has moved from turbines to pressure exchangers. They reduce energy consumption of a sea water desalination units by 50-60% !

Cost considerations • Energy consumption depend on: • Salinity and permeate quality • Recovery Rate • Feed Water Temperature • Membrane Type and Aging (Fouling/Scaling) • Pump Type and Configuration

Energy consumption of large SWTP Source: Watereuse: Seawater desalination Power consumption

Typical Range of SWRO Facility Costs Source: Watereuse: Seawater desalination Power consumption

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Desalination by membrane technology – state of the art and future trends