Controlling Salinity
March 02, 2017
Val S. Frenkel, Ph.D., P.E., D.WRE
What is Salinity?
Total Dissolved Solids (TDS):
•  Sodium
•  Chloride
•  Hardness
•  Sulfate
•  Other inorganic trace minerals
–  (Si, P, K, B, etc.)
What is Salinity?
Chemical Formula: Na- + Cl+
= NaCl
Atomic Weight: 22.99 + 35.45 = 58.44
Low Sodium – Na < 50 mg/l
Low Sodium – NaCl < 50/22.9 x 58.44 < 127.1 mg/l
Low Sodium – TDS < 180 mg/l (assuming NaCl ~ 70% of TDS)
WHO Standard Drinking Water TDS < 500 mg/l
4
Do we need to control salinity ?
5
RO System
6
Reverse Osmosis Desalination Process Schematic
Feed
Water
Structure
PreTreatment
Solids
Disposal
Reverse Osmosis
Energy
Recovery
Brine
Disposal
Water
Conditioning
Product
Water
7
Energy Consumption by Desalination
Desalination
Energy
8
Reverse Osmosis Desalination Process Schematic
90-95% of Entire Energy
Feed
Water
Structure
PreTreatment
Solids
Disposal
Reverse Osmosis
Energy
Recovery
Brine
Disposal
Water
Conditioning
Product
Water
9
Typical Breakdown of Desalination Cost, %
Seawater
Brackish water
Fixed costs
35 %
50 %
Energy
45 %
15 %
Labor
5%
10 %
Membrane s
replacement
5%
5%
Maintenance
7%
10 %
Consumables
3%
10 %
Energy Consumption by RO
§  Kinetic energy for desalination
process caused by membrane losses
§  Kinetic system energy losses
§  Kinetic energy losses caused by
membrane fouling
§  Osmotic energy
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Osmosis
Reverse Osmosis
Pacific Ocean
TDS = 35,000 mg/l
Osmotic Pressure = 350 psi
No external pressure
Concentrated
Solution
Diluted
Solution
RO reject at R=50%, TDS = 67,000 mg/l
Osmotic Pressure = 670 psi
Operational Pressure = 750 - 850 psi
External pressure
Concentrated
Solution
100 mg/l TDS = 1 psi
Diluted
Solution
12
RO Desalination Technology Growth Trends
New Technologies and New RO Concepts
Growth
Energy
Recovery
RO Membrane
Improvements,
New Materials
1960
1990
RO Membrane
Improvements,
System Design
Optimization,
Large Diameter RO,
Pre-Treatment MF/UF, DAF,
Nano-RO
2020?
Time
13
ForwardOsmosis-FO
FOMembrane
Water
Draw
Solu5on
NH3/CO2
Concentrate
Draw
Solu5on
Recovery
Treated
Water
14
PressureRetardedOsmosis-PRO
PowerGenerator
ConcentratedSalty
WaterIN
FreshWaterIN
DilutedSaltyWater
OUT
Membrane
Membrane
ConcentratedFreshWater
OUT
15
Permeate
Pump
Feed Water
Aerobic Tank
Anoxic Tank
Air
RAS
WAS
MBR Driven by Permeate Pump
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Permeate
Pump
Feed Water
Aerobic Tank
Anoxic Tank
RAS
Air
WAS
MBR Driven by Permeate Pump
Feed Water
Forward Osmosis
Concentrate from RO
Diluted Concentrate
from FO
Aerobic Tank
Anoxic Tank
Air
RAS
WAS
MBR Driven by Forward Osmosis
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Water Consumer
WATER
WWTP/MBR
WASTEWATER
Reverse
Osmosis
Water
Supply
Sea/Ocean
Combina5onofReverseOsmosiswithForwardOsmosis
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Water Consumer
WATER
WWTP/MBR
WASTEWATER
Reverse
Osmosis
Water
Supply
Sea/Ocean
Combina5onofReverseOsmosiswithForwardOsmosis
19
Water Consumer
WWTP/MBR
WASTEWATER
Forward Osmosis
WATER
Reverse
Osmosis
Water
Supply
Sea/Ocean
Combina5onofReverseOsmosiswithForwardOsmosis
20
Water Consumer
WWTP/MBR
WASTEWATER
Forward Osmosis
WATER
Reverse
Osmosis
Water
Supply
Sea/Ocean
Combina5onofReverseOsmosiswithForwardOsmosis
21
Water Consumer
WWTP/MBR
WASTEWATER
Forward Osmosis
WATER
Reverse
Osmosis
Water
Supply
Sea/Ocean
Combina5onofReverseOsmosiswithForwardOsmosis
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Summary
Salt is associated with energy. Removing salt from the water
requires energy, the more salt concentration, the more energy
is required.
Desalination by Reverse Osmosis (RO) has
become one of the key technologies for desalinating water.
Combination of RO technology with the newer processes may
accelerate development of RO and newer processes at the
same time providing significant energy savings to desalinate
water.
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