Recent Developments in Low-Energy

Desalination Technologies:

Forward Osmosis, Membrane Distillation, and

Adsorption Desalination

Gary Amy, Noreddine Ghaffour, Suzana Nunes, Kim Choon Ng

Advances in Desalination

• Materials – Aquaporins (biomimetric membranes)

– Carbon Nanotubes (CNTs)

– Graphene

– Thin Film (inorganic-organic) Nanocomposites

– etc…

• Processes – Forward Osmosis (FO)

– Membrane Distillation (MD)

– Adsorption Desalination (AD)

– Capacitive Deioniniation (CDI)

– etc…

Process Total Energy (kW-h/m3)

Capital Cost ($/m3/d)

Unit Water ($/m3)

Multi Stage Flash/MSF (without waste heat) 55-57 - -

MSF (with waste heat) 10 - 16 1000 - 1500 0.8 -1.0

Multi Effect Distillation/MED (w/o waste heat) 40-43 - -

MED (with waste heat) 6 - 9 900 - 1200 0.6 – 0.8

Sea Water Reverse Osmosis/SWRO 3 - 6 800 - 1000 0.5 – 0.8

SWRO (with energy recovery) 2 - 3 < 800 0.45 – 0.6

Innovative Technologies/Hybridization < 2.0 * < 800 <0.5

(Source: Ghaffour and Ng, 2011)

* Thermodynamically minimum energy requirement for desalination 0.75 kWh/m3; <2.0 kWh/m3 attained by improving efficiency/hybridization

Thermal > SWRO > Innovative processes

Energy Requirements

• Conventional technologies: minimize energy requirements by waste heat, energy recovery

• Thermal desalination energy reduction by co-location with power plant

Wastewater Effluent

(low TDS)

H

H O

H

H O

H

H O

H

H O

H

H O

H

H O

H

H O H

H O

H

H O

H

H O

H

H O

H

H O

H2O

FO Membrane

H

H O

Organic Foulants (Humics, protein, etc.)

Heavy metals (Zn, Pb, Cu, Ni, Cr, Cd,

Mn, etc.)

Pollutants (NO3-, PO4

3-, EDCs, TORCs,

etc.)

H

H O

H

H O

H

H O

H

H O

H

H O

H

H O H

H O

H

H O

H

H O

H

H O

H

H O H

H O

H

H O

H

H O

H

H O

H

H O

H

H O

H

H O

H

H O H

H O

H

H O

H

H O

H

H O

O

Forward Osmosis (FO)

Water transport

driven by osmosis

Objective: Water (only) Extraction

Seawater (high TDS)

Forward Osmosis (FO) RO-like membrane,

but process is osmosis-driven not pressure-driven

Low energy alternative to SWRO Lower salinity or impaired quality

source (e.g. WW) as feed solution; higher salinity draw solution

Research Needs/ Process Improvements

New/better FO Membranes (open support layer; thickness and porosity)

Minimize internal concentration polarization (within support layer)

Assess/minimize fouling/biofouling Novel draw solutions

(seawater vs. synthetic solutions)

RO FO

RO brine

pump

Back pressure regulator

product water

Diluted

DS

Concentrated

DS

Figure 4. A combined FO/RO system

Draw Solution Need high solubility, low cost,

high osmotic pressure solution

Easily separable and reusable

Non-Toxic and eco-friendly

Post Treatment Recovery of product water from

diluted draw solution

Recovery and recirculation of

draw solution (components)

Concentrated feed: treatment

and/or environmental impact?

Need for Novel Draw Solutions

Direct FOD

Indirect FOD

Forward Osmosis

Desalination (FOD)

Company X

• (NaCl as DS with RO recovery)

• FO as Pretreatment RO?

FO

Wastewater

effluent

Concentrated Wastewater

effluent

Seawater

Diluted

seawater

Post-treatment

(lower salinity)

Post-treatment

(concentrated WW)

Forward Osmosis (FO) for Water Desalination and Reuse

in Coastal Cities

• Diluted Draw Solution: LPRO (fate of organic micropollutants & pathogens?)

• Concentrated Feed Solution: Anaerobic Treatment (primary effluent?)

FO Status: Membranes

• FO ≠ RO: Key focus on structure and

support layer, with goal of flux comparable

to RO

• Under development: Thin-film composite

membranes by interfacial polymerization

[Source: Peinemann, Nunes, 2008; Elimelch and Yip, 2010 (bottom)]

Thin-film composite membrane

interfacial polymerisation • New Membranes

• Development of high performance

thin-film composite (TFC)

membranes for FO application

• Polyamide active layer on top of

polysulfone support layer

• Finger like morphologies

FO + Nanoparticles Magnetic nanoparticles (MNPs) as

draw solution in FO

MNPs exert osmotic pressure, easily

recovered from draw solution by

applying magnetic field

FO + High MW Polyelectrolytes High MW polyelectrolytes, separable

by (low pressure) UF

Limitations/Research Needs MNPs and high MW polyelectrolytes'

size distribution, concentration in

draw solution, aggregation and

stability

Osmotic pressure (limited to brackish

water?)

Feed S

olu

tion

(low

er

osm

otic

pre

ssure

)

Dra

w S

olu

tion

(hig

her

osm

otic

Pre

ssure

)

Osmosis

(Source Chung, 2011)

The Ammonium-Carbonate Direct Desalination System (Elimelich, 2010)

Limitations:

• Energy Input

(if no waste heat)

• Residual Ammonia

• Carbonate Scaling

Pressure Retarded Osmosis

(PRO): A Special Case of FO

PRO • Pressure created by flow

of freshwater into salt water

• Pressure used to run a turbine

Blue energy

• In Norway,

River Water and Seawater

Research Questions • Develop PRO Membrane (PRO FO)

• Improve Power Efficiency (W/m2)

• Identify Applications

• Desalination Brine & Wastewater Effluent

• Piloting/Up-Scaling

Theoretical Yields

*

Membrane Distillation (MD)

http://www.purity.se/company/technologies.html High hydrophobicity

High thermal stability

High porosity

Chemical stability

Hot

Feed

Cold

Permeate

Membrane:

1 KwH/m3 w/ waste heat (PUB)

Membrane Distillation (MD) Evaporation process involving hydrophobic membrane Water vapor transported through membrane Temperature driven (lower than conventional distillation) Can be coupled with waste heat, or solar (solar-MD) MD applicable to extreme salinity (e.g.. Arabian Gulf) Little or no effect on flux Potential Application: MSF Brines; Produced Water

Research Needs Improved MD membranes, increased flux (85 LMH with 99.95% salt rejection with fabricated nanofiber membranes)

Reduce temperature polarization (through spacers) Process modeling and scale-up

Feed 90°C

60°C

Distillate

30°C

Distillate

60°C

Concentrate

Me

mb

ran

e

(Source: Ghaffour 2011, Tzahi Y. Cath 2008)

Flat sheet Hollow fiber Nanofiber

Materials:

- Commercial and new

membranes (higher flux)

Module design and lab-scale

performance testing

Pilot testing (scale-up): MSF Brine, Produced Water

FO + MD FO and MD integrated, FO is

employed to draw water from

dilute feed solution to concentrate

solution, and MD is used to

recover water from draw solution,

permitting recycling

Research Needs Feasibility/optimization of FO-MD

hybrid process in water treatment

and in desalination

Improved FO and MD membranes

to increase flux, minimize fouling

(Source: Chung, 2011)

Osmosis Heat

+ F

eed S

olu

tion

(low

er

osm

otic

pre

ssure

)

Dra

w S

olu

tion

(hig

her

osm

otic

Pre

ssure

)

Osmosis

Silica Gel (hydroscopic)

Water Vaporization

(at the Evaporator)

Silica Beads

Adsorption Desorption

(by Solar heat)

Condensed water Vapor

(at the Condenser)

Adsorption Desalination (AD) using Silica Gel

Adsorption and Desorption

AD Mesaporous

adsorbent, such as silica, is used to adsorb water vapor,

Heat (solar energy) is used to desorb water

Produces two useful effects (cooling and water desalination) with low temperature heat input (~65oC)

Low energy (1.4 kWh/m3 ) usage and no moving parts

Economical

Process kWh/m3* US$/m3

Thermal 6 -16 0.60-1.00

Membrane 3 - 6 0.45- 0.80

AD 1.4-1.9 0.29-0.30

* Total energy (includes thermal and electrical)

3 prototypes in Saudi Arabia and Singapore

1 commercial prototype in Poland

(Wroclaw University of Technology)

3 large Adsorption Desalination and Cooling

(ADC) planned for KSA

Saudi Arabia –KAUST, 10Rtons Solar Powered Singapore -45Rtons Each, Solar Powered Singapore –NUS 10Rtons, Waste Heat Prototype

Reaction

bed tower

Evaporator

Condenser

Purified

water

storage tank Reaction

bed tower

1

2 3

4

5

d d

H

( PCT/SG2009/ 000223, filing No. 61/226,783, No.: 61/297,347, PCT/SG2012/000076)

Microbial Fuel Cell (MFC) Covert chemical energy to electrical energy (bioelectricity) Two chambers, anode (oxygen starved /anaerobic) and cathode (oxygen rich/aerobic) Substrate (e.g., wastewater) introduced to anaerobic chamber, oxidized and releases electrons Electrons migrate toward cathode, in aerobic chamber

Microbial Desalination Cell (MDC) Third chamber, ions move from middle chamber to balance charge, due to protons produced by bacteria at the anode, protons removed at the cathode (Source: Bruce Logan, Penn State University)

What does this have to do w/ desalination? Third Cell with Electrodialysis (ED) Membranes:

Anion (AEM) and Cation (CEM) Exchange Membranes

Knowledge Gaps Opportunity for low-energy desalination

Proof of concept in batch-mode

Next, continuous mode & pilot scale

Most ED membranes developed for

brackish, not seawater, desalination

Use of novel ion-exchange membranes

Possible fouling of membranes

Presently limited to 90% TDS reduction

with single ED

New, multiple stacks (Stacked MDC,

SMDC) with ion exchange membranes, up

to 98% reduction

Use of wastewater vs. simple substrate

(integrated desalination & WW treatment)

MDC-RO Hybrids (Source Logan, 2011)

Technology Integration Energy Recovery + Wastewater Treatment + Water Reuse

A Technology Roadmap for Low-Energy (-Cost) Desalination

Current

3.0 – 4.0 kWh/m3

Near Horizon

< 2.0 kWh/m3

Far Horizon:

Approach

1.0 kWh/m3

• Forward Osmosis (FO)

• Membrane Distillation (MD)

• Adsorption Desalination (AD)

• Microbial Desal. Cell (MDC)

• Microbial Osmotic FC (MOFC) • Seawater

Reverse Osmosis

(SWRO)

http://wdrc.kaust.edu.sa

Beyond Electrodialysis (ED)…

Electrodeionization (EDI) Similar to ED but also includes mixed-bed

ion-exchange resins between anion and cation membranes (to facilitate ion removals)

Capacitive Deionization (CDI) External electric charge applied on pair of

electrodes to feed water; ions migrate towards electrode of opposite charges and adsorb; in regeneration cycle, electric charge is turned off, adsorbed ions are released

Key Research Need Application to higher salinity waters

(seawater) What is salinity niche?