Development of a Highly Efficient Membrane-Based Wastewater Management System for Thermal Power Plants Xiao Wang, Palitha Jayaweera, Elisabeth Perea, Richard Callahan, and Indira Jayaweera*

Summary: The main goal of the proposed research is to introduce SRI-based polybenzimidazole (PBI) hollow-fiber membranes (HFMs) for flue gas desulfurization (FGD) wastewater (WW) treatment and Selenium (Se) release control. The PBI membranes are resistant to fouling and can be operated under substantially harsher conditions than those tolerated by commercial membranes. Success of this project will result in an effluent control system that reduces freshwater withdrawal by removing hazardous compounds and reusing the recovered water. Contact: Indira S. Jayaweera, Sr. Staff Scientist/ Sr. Program Manager, indira.jayaweera@sri.com, +1-650-859-4042

Background of Flue Gas Desulfurization Wastewater (FGD WW) Treatment and Selenium (Se) Pollution Control

1. Water Requirements for Existing and Emerging Thermoelectric Plant Technologies. DOE/NETL, 2008. 2. Journal of the Air & Waste Management Association, 51 (2011) 1676-1688. 3. Journal AWWA, 100 (2008) 76-89.

Wet FGD

- Limestone-forced Oxidation - Limestone-inhibited Oxidation - Jet-bubbling Reactor - Lime - Magnesium-enhanced Lime - Dual Alkali - Seawater

Once-through

- Sodium Sulfite - Magnesium Oxide - Sodium Carbonate - Amine

Regenerable

Element/Ions in Untreated FGD

Wastewater Concentration (ppm)

Boron (B) 100 - 600 Calcium (Ca) 300 - 1000

Magnesium (Mg) 1000 - 4000 Potassium (K) 45 Sodium (Na) 500 Chloride (Cl-) 10000 - 25000 Nitrate (NO3

-) 1-400 Selenium (Se) 1-10 Sulfate (SO4 2-) 3000 - 20000

PC power plant with cooling and wet FGD 1

Comparison of the costs of MLD and ZLD.3

Minimum Liquid Discharge (MLD)3

• Membrane-based MLD is a more economical process than zero-liquid discharge (ZLD).

• The last 5% of ZLD is costly.

0 70 95 100 Water Recovery (%)

ZLD

Cost

of W

ater

Rec

over

y ($

/m3)

Primary Wastewater Reuse Minimal Liquid Discharge (MLD)

$12-13/1000 gal

$4-6.6/1000 gal

Selenium Chemistry 4-6

• For adults, the recommended daily Se intake is 55 mg, and the upper limit is 400 mg.

• Se toxicity: Se(+IV) < Se(+VI) < Se(-II). • Environmental Protection Agency (EPA) criterion: acute

concentration (20 ppb) and chronic concentration (5 ppb). • In FGD WW, Se is present as Se(+VI) and Se(+IV).

1 2 3 4 5 6 7 8 9 10 11 12 13 14

H2SeO3 HSeO3- SeO3

2-

HSeO4- SeO4

2-

pH

Se(+IV)

Se(+VI)

Speciation of Se in Aqueous Solution

H2Se HSe- Se(-II)

*In a nanofiltration (NF) membrane with negative surface charge, this area leads to higher rejection .

4. Talanta, 154 (2016) 474-480. 5. Aquatic Life Ambient Water Quality Criterion for Selenium – Freshwater, EPA, 2016. 6. Applied Geochemistry, 11 (1996) 797-802. 7. Science of the Total Environment 521–522 (2015) 246–260. 8. Water Research, 71(2015) 274-281. 9. Geochimica et Cosmochimica Acta, 206 (2017) 236–253. 10. Environmental Science and Pollution Research 22 (2015) 3127-3137. 11. Biotechnology Advances 34 (2016) 886–907. 12. Membrane Separation Technology in Carbon Capture, Chapter 3, 60. 13. Nature Communication, 4:2344 (2013).

Comparison of Technologies for Se Removal7

• Efficiency: ~100% removal, <10 ppb • Long resident time • pH and temperature dependent • High cost of chemicals and waste

disposal

Chemical Reduction8 Coagulation Ferrihydrite Precipitation9

• Efficiency: <5 ppb • Ineffective for SeO4 2-

• Influenced by other anions • pH dependent (4-6) • Extra cost for solid waste disposal

Electrocoagulation10

• Efficiency: ~ 98% removal • High energy consumption • Extra cost for electrolyzer construction

and electrode replacement

Biological Method11

• Efficiency: <10 ppb • Cheap and adaptable to various wastewaters • More energy to remove oxygen in wastewater • Remobilization of bio-reduced selenium • Interference of other oxyanions (e.g., nitrate,

sulfate)

• Efficiency: varies widely • Low cost • Not suitable for high levels of

contaminants • pH and temperature dependent • Ion-competitive effects • Extra cost for regeneration and disposal

of exhausted absorbents

Ion Exchange and Absorption12 Membrane Separation 13

• Efficiency: >95% • pH independent • Removes other pollutants

simultaneously • Operational cost is comparatively

high

Our Approach

FGD Recycle

FGD

Waste Heat 32oC to 70 oC

High Pressure RO

Low Pressure RO

Hydrocyclone

Concentration Disposal

Clean Water Recovery

Salt Precipitates Blowdown

Makeup water

Research focus

MLD Strategy Proposed by SRI

The main goal is to develop innovative effluent water management practices at coal-fired energy plants; we will also:

•Test the SRI seawater desalination PBI hollow-fiber membranes (HFMs) for separating sulfates and selenium from an FGD WW simulant and then from real-world FGD WW.

•Use the data to design and model the optimized membrane unit arrangement for reduced energy operation.

•Fabricate high-strength PBI HFMs suitable for processing high-salinity (high-osmotic pressure) brines at an industrial site.

Cooperative agreement grant with U.S. DOE: − Contract No. DE-FE0031552 Period of Performance: − 12/19/2017 – 06/18/2020 Funding: − U.S. Department of Energy: $639,949 − Cost share: $160,000 − Total: $799,949 NETL Project Manager: − Anthony Zinn: anthony.zinn@netl.doe.gov Principal Investigator: − Indira Jayaweera: indira.jayaweera@sri.com

NETL • Funding and technology oversight SRI • PBI membrane development • Membrane testing Enerfex, Inc. • Membrane system modeling

PBI Performance Products, Inc. • PBI dope source Generon, IGS • Membrane fabrication site OLI Systems • Optional partner

Project Budget and Team

Membrane Separation Based on Polybenzimidazole Hollow-fiber Membranes (PBI HFMs)

http://diagram.premamaz.com/reverse-osmosis-diagram/

• Pressure driven process (200-1000 psi) to overcome osmosis pressure

• Solution diffusion mechanism: RO membrane is assumed to be nonporous, and transport is by diffusion between the interstitial space of polymer chains or polymer nodules

• Donnan effect: works in charged membranes • Reverse osmosis is the best known method for

removing dissolved hardness

Reverse Osmosis (RO) Technology

Repel

Hollow-fiber Membrane Spiral-wound Flat-sheet Membrane

Advantages of Hollow-fiber Membranes • No need for spacers • Self-supporting structure • Able to permeate channel • High surface area per unit of membrane module volume: spiral-wound packing density is 800 m2/m3

while hollow fiber is 6000 m2/m3 (reported by Lux Research, Inc.)

SRI PBI module

Hollow-fiber vs. Spiral-wound Membranes

J. Membr. Sci. 362 (2010), 202-210

PBI vs. Other Membrane Materials

N

N

N

N

H

H

n

PBI molecular structure

RO Membrane Materials Property Reference

PBI

Superior thermal stability: Tg=450oC, degradation at 450oC in air, continuous operating temperature up to 250oC

High mechanical strength Outstanding chemical resistance Excellent chlorine resistance.

Fire Mater. 26(2002),155–

168

Cellulose Triacetate

• Low thermal resistance (<30oC) • Low chemical resistance (working pH=2-8)

Poor chlorine resistance Desalination

326(2013), 79-95 Polyamide • Poor chlorine resistance

FGD and Advantages of Minimum Liquid Discharge (MLD)

PBI HFM

Fabrication of Polybenzimidazole Hollow-fiber Modules

550 µm

265 µm 100 µm 100 nm

100 nm

Nano open pores on shell surface

Interconnected porous structure in support layer

Barrier layer on lumen surface

1 µm

96.75

96.80

96.85

96.90

96.95

97.00

0.00

2.00

4.00

6.00

8.00

10.00

12.00

5000 7000 9000 11000 13000 15000

Reje

ctio

n (%

)

Flux

(LM

H)

TDS (ppm)

Test @ 400 psi

Flux (LMH)

Rejection (%)

Composition of Feed Solution (TDS=~1500)

Salt Concentration (ppm) Ions Concentration

(ppm)

CaSO4 2511 Ca2+ 3272

CaCl2 7029 Mg2+ 1908

MgCl2 7553 Na+ 681

NaCl 1731 Cl- 11191

Total 18824 SO4 2- 1773

Our PBI HFM is comparable to the best commercial product

Point Material Reference Do DowEX (cellulose triacetate) Desalination 102 (1995) 225-234

Du1 Permasep B-10 (polyamide) Desalination 126 (1999) 33-39 Du2 Permasep B-9 (polyamide) Desalination 48 (1983) 1-16 T-1 Hollosep MH10255 (Cellulose triacetate) Desalination 125(1999) 55-64

T2 Hollosep HA8130 (Cellulose triacetate) Journal of Membrane Science 236 (2004) 1—16

HF1 Dual layer (Polyethersulfone/polyamide) Environ. Sci. Technol. 46(2012), 7358−7365

HF2 Dual layer (Polyester/polyamide) Environ. Sci. Technol. 47(2013), 7430−7436

HF3 Electrospun fibers (polyacrylonitrile) Journal of Membrane Science 363 (2010) 195–203

Test with ~2000 ppm NaCl solution@400 psi at room temperature

Previous Test

Preliminary Test

Inside-out HF (Negatively-charged Barrier Layer)

100 µm 209 µm

496 µm

100 nm

1 µm 100 nm

Barrier layer on shell surface

Interconnected porous structure in support layer

Micro open pores on lumen surface

Test @ room temp (TDS=~5000)

Pressure Module #1 Module #2

Flux Rejection Flux Rejection 300 1.52 98.4 1.26 98.8 400 1.81 99.0 1.59 99.1

Test @ 50 oC (TDS=~5000)

Pressure Module #1 Module #2

Flux Rejection Flux Rejection 300 1.95 98.7 1.73 98.9 400 2.66 99.0 2.21 99.0

Outside-in HF (Positively-charged Barrier Layer)

100 nm

71.9 nm 84.4 nm

0.000

0.005

0.010

Reje

ctio

n (%

)

PBI HF (SRI)

Permeability

Perm

eabi

lity (L

/(m2 h

psi)

)

Hollosep (Toyobo)90

92

94

96

98

100

Rejection

-50

-40

-30

-20

-10

0

10

Per

cent

age

(%)

Change of water permeability Change of water-salt selectivity

PBI hollow fibers LCLE (DOW) BW30 (DOW)

86

87

88

89

90

91

92

93

94

95

96

97

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Reje

ctio

n (%

)

Flux

(L/m

2 hr

)

pH

Flux(L/m2 hr) Rejection (%)

4.9 6.9 9.2 10.0 9.9 7.9 4.9

Superior chlorine resistance 15

(Chlorine exposure: 4,000 ppm· h, pH=11, Feed solution: 2,000 ppm NaCl)

Ultra-thin PBI barrier layer Higher selectivity at low pH value

14. Desalination 125(1999) 55-64 15. J. Membr. Sci., 451(2014), 205-215

Performance is comparable to the commercial HF 14

Previous Test

Preliminary Test

Two Different Types of Hollow-fiber Membranes (HFMs) and Their Performance

Conclusions

Both operational cost and energy consumption will be significantly decreased by the use of reverse osmosis (RO) technology in flue gas desulfurization wastewater (FGD WW) management approaches.

Among the existing technologies, membrane separation, especially using RO, is the most promising way to remove Se and other heavy metals in FGD WW.

The hollow-fiber (HF) format reduces membrane module size and operational cost relative to spiral-wound membranes.

Inside-out HF can provide both high flux and rejection comparable to that of commercial flat-sheet membranes.

Outside-in HF can tolerate harsh operating conditions, and its separation performance is comparable to that of commercial membranes.

Acknowledgements The authors wish to acknowledge:

• The DoE Project Manager

• The SRI Team and Partners

• The DoE for current funding (DE-FE0031552)

• Previous Funding from, the KACST, Riyadh, National Energy Technology Laboratory (NETL) of the U.S. Department of Energy (Contract No. DE-FE0012963), and the Office of Naval Research (ONR) of the US Department of Defense (Contract No. N00014-10-C-0059).

Disclaimer This poster includes an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by tradename, trademark, manufacturer, or otherwise does not necessarily constitute or imply endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

5. Large fiber module

2. Crosslinking

3. Post treatment

4. Potting

4” diameter module containing 10,000 fibers (Gas-separation PBI membrane elements are pictured)

1. Fiber Spinning