Desalination by Reverse Osmosis Leili Abkar

Why Desalination ? http://www.popsci.com/article/science/removing-salt-relieve-world%E2%80%99s-thirst https://waterdropblog.files.wordpress.com/2008/06/world_water_final.jpg

Desalination Technology Membrane Electric EDR Pressure MF RO NF UF Thermal MSF MED TVC Desalination : is a process that removes or separate salt from saline water. it produces fresh water at the expenses of energy consumption. It is mainly classified in two groups : membrane and thermal desalination. As you may know , thermal desalination uses heat to boil water and vaporize water then condensation of water give fresh water , main process are MED, TVC, and MSF . Membrane desalination, uses a semi pre- meabale membrane to pass water across the membrane.

Pressure Driven Membrane MF 0.7 bar UF 1-7 bar NF 3.5-16 bar RO 7-69 bar ∆P= Suspended particles can be removed by MF Viroses can be removed by UF MULTIPLE CHARGED IONS BY NF SINGLE CHARGED IONS BY RO Mid-size organic substances, multiple charged ions Bacteria, parasites, particles High molecular substances( ions and proteins), viruses Low molecular substances, single charged ions

Reverse Osmosis History Dr. Sourirajan - 1962 Abbe Nollet -1748 Reverse Osmosis History

1748 : Abbe Nollet observed the phenomenon of Osmosis 1994 : TriSep introduce first “low fouling” membrane, 1995 : Hydranautics introduces first “ energy saving” polyamide membrane, 2002: Koch Membrane System introduces first 18 inch diameter “MegaMagnum” module,

Year Pressure (psi) Relative Flux Rejection (%) Membrane Material 1970’s 435 1 97 Cellulose acetate 1980’s 290 1.9 99 Cross-linked polyamide composite 1987 220 3.0 99.7 Cross-linked aromatic polyamide composite 1988 145 4.2 1996 110 5.6 1999 75 8.0

Osmosis and Reverse Osmosis Phenomenon Water with low concentration has higher chemical potential http://www.chem.ufl.edu/~itl/2045/lectures/lec_i.html

Thin-film, composite membranes RO Membrane Structure RO membranes Asymmetric membranes Thin-film, composite membranes Reverse osmosis membrane separations Chemical nature of the membrane material (almost always a polymer) Physical structure

RO Membrane Structure

Membrane Module Objective : Pack large amount of membrane area into relatively small volume Economical Smaller footprint

Membrane Module Tubular Spiral wound Hollow fibre Plate & frame Tubular Spiral wound Hollow fibre There are 4 basic forms of membrane modules : Plate and frame : usually are used for high suspended solids , ad not in water purification . Consist of a flat sheet membrane , typically two membranes are placed back to back ; then stacked within a frame work for support and there are spacer placed between each plate keep them from sticking together and provide open channel for water to flow trough. Tubular module : typically for high solids, found in the food and biological industries, resemble the heat exchanger shell and tube , with feed water in the tubes and permeate water in the shell. Howllow fiber RO membrane formed in a very small diameter tubes, they resemble human hair and can be as flexible and flow of water is outside in , and the thin layer of RO membrane is on the outside of the membrane.

Membrane Module

How Does Reverse Osmosis Work ?

Performance Parameters Salt rejection% Salt passage % Salt Rejection = Conductivity of Feed Water – Conductivity of Permeate Water Conductivity of Feed ×100 Salt Passage % = (1- Salt Rejection%) How effective the RO membranes are removing contaminants A well-designed RO system with properly functioning RO membranes will reject 95% to 99%

Performance Parameters Recovery % Recovery% = Permeate Flow Rate Feed Flow Rate ×100 The higher the recovery Less water to drain as concentrate Saving more permeate water Recovery is too high Scaling Fouling The % Recovery depends on Feed water chemistry RO pre‐treatment Industrial RO runs anywhere between 50%- 85 %

Performance Parameters Concentration Factor% High concentration factor High scaling potential Brackish water 3,000 mg/L and CF=5 Brine Salinity = 3,000*5= 15,000 mg/L Sea Water 35,000 mg/L and CF = 2 Brine Salinity = 35,000*2= 70,000 mg/L Concentration Factor = 1 1−Recovery % Recovery Concentration factor 50% 2 75% 4 80% 5 83% 6 87.5% 8

Performance Parameters Flux= Permeate Flow Rate # of RO elements in system x Surface area of each RO element Flux Feed Water Source GFD TDS (mg/L) Sea Water 8-12 35,000 Brackish Surface Water 10-14 1,000-5,000 Brackish Well Water 14-18 5,000-15,000 RO Permeate Water 20-30 <1,000

Operating Condition TFC membrane pH = 2-11 Temperature < 45 C http://www.watertreatmentguide.com/factors_affecting_membrane_performance.htm

How to Design RO System Manually Calculate osmotic pressure of feed water Directly related to operating pressure Determine Silt Density Index (SDI) Fouling indication Must be < 5 to use membrane Choose the proper membrane

Flux×Active Membrane Area Permeate water flow rate No. Membrane Flux×Active Membrane Area Permeate water flow rate No. Pressure Vessels 1-7 No. Membrane

Design Software

Different Design Passes Passes Stages http://puretecwater.com/downloads/basics-of-reverse-osmosis.pdf

Different Design – 2 Stage

Water Treatment Plant http://genesisnanotech.com/tag/water-filtration/

Minimum Required Water Quality Analysis Source Water Minimum Required Water Quality Analysis Water quality and quantity Historic data

Guideline for RO Feed Water Pre-treatment Objective : Make the feed water compatible with RO membrane Poor Pre-treatment: Fouling Biofouling Scaling Guideline for RO Feed Water

Pre-treatment Chemical Mechanical https://www.amtaorg.com/publications-communications/membrane-technology-fact-sheets-summary

Pre-treatment Example A: Selection of pretreatment may impact post treatment. A good example would be if acid is used to lower the pH of the feed water (for reducing scaling potential), the carbonate will convert to the CO2 which may need to be removed with a degasifier process in the post treatment. Example B: If chlorination is used to control microbiological growth in the pretreatment, overfeeding will cause degradation of Thin-Film Composite RO elements.

Pre-treatment Sufficient pre-treatment Conclusion Membrane cleaning 3-4 times per year Membrane life last over 5 years Conclusion No single solution for pre-treatment, Depends on source water quality, seasonal and historical changes

Post treatment Choice and sequence of post treatment Objective : Make the permeate water compatible with distribution system Post-treatment Stabilization, Disinfection, Corrosion control, Degasification and/or air stripping processes Carbon dioxide and hydrogen sulfide gases Choice and sequence of post treatment Regulatory requirements, The design of the system, Finished water quality criteria, Water chemistry

Membrane Desalination Cost https://yatesenvironmentalservices.wordpress.com/category/desalination/

Membrane Desalination Cost 1. Price includes all costs to consumers for treatment and delivery. 2. Cost is based on a family of four using 100 gallons per day per person, for a total monthly use of 12,000 gallons. Cost is based on the average of the “To Consumer” cost shown. 3. Brackish is moderately salty-1,000-5,000mg/L total dissolved solids (TDS). 4. Seawater contains 30,000-35,000mg/L TDS. 5. Cost is for typical urban coastal community in the USA. Costs for inland communities may be higher. 6. Combined supply costs are for the traditional supply augmented with 50% of desalted brackish water, or 10%. of desalted seawater.

Largest SWRO Desalination Plant - 2013 Sorek Desalination plant Capacity: 627,000 m³/d Located at south of Tel Aviv.  Capital Cost: $500 million USD Provides 20% of the Country water demand  16" SWRO membranes in a vertical arrangement