Optimization of Pretreatment for Seawater Reverse Osmosis

Dr. Young Chul Choi (Director of R&D)

Mizu Dela Cruz, & Dr. Chunwoo Lee

Doosan Hydro Technology

Content

1 INTRODUCTION

2 PRETREATMENT OPTION

4 DOOSAN’S PERFORMANCE RECORD

3 COST COMPARISON

5 DOOSAN’S EFFORT

6 CONCLUSION

1. INTRODUCTION

Contracted/Forecast Desalination Technology

RO Process Failure Attribution

79%

� “Most SWRO failures are actually

pretreatment failures and that most

pretreatment failures are biofouling

related” (Water Desalination Report, Vol

46, Num 32)

� The desalination market has

grown dramatically in recent

years, and seawater reverse

osmosis technology is leading

this growth

ORGANIC FOULING

SEM micrograph showing EPS

Blanket of EPS

Irreversible attachment

Maturation

Detachment

Reversible attachment

Transport to a surface

(http://www.juliantrubin.com/encyclopedia/microbiology/biofilm.html)

Applied Microbiology (2002) 59: 629-640

INORGANIC FOULING

Iron coagulant fouling

Particulate (silt) fouling

Calcium carbonate fouling

RED TIDE

•Abnormal proliferation of red

colored phytoplankton.

•The source of red tide blooms are

not fully understood

During 2008 ~ 2009, ‘red tide events’ forced

many desalination plants closure.

•Red-tide algae can be easily broken

by the shear force of pump or

through chlorination.

CLEANING OF FOULED SYSTEM

Cartridge filter

replacement

ChlorinationBackwash

CEB & CIP

CIP or

Membrane

replacement

PRETREATMENT – MEDIA FILTRATION

□□□□ Proven technology

Intake pump

Feed Tank Feed Filter pump

Permeate

Concentrate

High Pressure pump SWROBooster pump

Cartridge Filter

Dual Media Filter 1st

stage

Intake screens

8

□□□□ Lower O&M cost compared to

membrane filtration

□□□□ Larger footprint requirement

□□□□ Effluent water quality is highly

dependent on feed water quality

PRETREATMENT – MEMBRANE FILTRATION

□□□□ Produce constant quality of

filtrate

Intake Pump

Feed tank Filter Feed pump

Permeate

Concentrate

High Pressure pump SWRO

Booster pump

Cartridge Filter

Ultrafiltration

Intake Screen

□□□□ Provide a higher quality of

filtrate compared to the media

filtration

□□□□ Higher operational costs due to

membrane replacement and

chemical consumptions

PRETREATMENT – DISSOLVED AIR FLOTATION

□□□□ Dissolved air flotation

(DAF) removes

particulate foulants such

as oil, grease, and other

contaminants by flotation

with micro size air

bubblesbubbles

□□□□ Recent project requires

the dissolved air flotation

to combat the red tide

problems.

DAF PILOT OPERATION EXPERIENCE

Case Pretreatment Configuration

1

DAF Pressurized DMF Gravity DMF

2

DAF Gravity DMF Pressurized DMF

PRETREATMENT OPTIONS

PretreatmentIntake

SWRO

Post

treatment

DAF Gravity DMF Pressurized DMF

3

DAF Gravity DMF

4

DAF Gravity DMF Gravity DMF

5

DAF Pressurized DMF Pressurized DMF

6

DAF UF

COST COMPARISON

40

60

80

100

120

% C

OS

T B

AS

ED

ON

CA

SE

1

CAPEX

OPEX

TOTAL

40

60

80

100

120

% C

OS

T B

AS

ED

ON

CA

SE

1

CAPEX

OPEX

TOTAL

0

20

40

CASE1

(DAF + P.DMF +

G.DMF)

CASE2

(DAF + G.DMF

+ P.DMF)

CASE3

(DAF + G.DMF)

CASE4

(DAF + G.DMF

+ G.DMF)

CASE5

(DAF + P.DMF +

P.DMF)

CASE6

(DAF + UF)

% C

OS

T B

AS

ED

ON

CA

SE

1

0

20

40

CASE1

(DAF + P.DMF +

G.DMF)

CASE2

(DAF + G.DMF

+ P.DMF)

CASE3

(DAF + G.DMF)

CASE4

(DAF + G.DMF

+ G.DMF)

CASE5

(DAF + P.DMF +

P.DMF)

CASE6

(DAF + UF)

% C

OS

T B

AS

ED

ON

CA

SE

1

□□□□ Total cost is sum of CAPEX and OPEX.

□□□□ The lowest pretreatment process is combining DAF and gravity DMF.

□□□□ 25% of total cost increase is found for Case 6.

DOOSAN’S PERFORMANCE RECORD

Fujairah, UAE (06.01’ ~ 12.04’)

170,000 m3/day

Pretreatment

Gravity DMF

DOOSAN’S PERFORMANCE RECORD

Shuaibah Ph.3, KSA (07.07’~02.09’)

150,000 m3/day

Seawater quality

Temperature (ºC) 25 ~35

TDS (mg/L) 43,300

Turbidity (NTU) < 2

Pretreatment

Pressurized DMFPressurized DMF

DOOSAN’S PERFORMANCE RECORD

Jeddah, KSA (07. 09’ ~ 09.12’ )

240,000 m3/day

Pretreatment

Gravity DMF

Intake,

Pretreatment

RO, Potable

Remineralization

DOOSAN’S PERFORMANCE RECORD

Shuwaikh, Kuwait (03.08’~09.10’)

(Under construction)

136,000 m3/day

Seawater quality

Temperature (ºC) 15 ~35

TDS (mg/L) 44,667

Turbidity (NTU) < 50

PretreatmentPretreatment

DAF + UF

DOOSAN’S PERFORMANCE RECORD

Ras Az Zawr, KSA (09.10’~03.14’)

(Singed Contract)

RO: 310,000 m3/day

Seawater quality

Temperature (ºC) 18 ~38

TDS (mg/L) 47,000

Turbidity (NTU) 5~12

PretreatmentPretreatment

DAF + Gravity DMF

DOOSAN’S EFFORT

Doosan is continuously contributing R&D efforts to improve SWRO and its

pretreatment by conducting pilot studies.

- Capacity: Up to 654 m3/d- Mobilized Unit

- Capacity: Up to 1490 m3/d- Gravity and pressurized operation

enabled- Different underdrain can be tested

- Mobilized Unit- Three membranes tested simultaneously- Remote controlled operation

- Capacity: Up to 98 m3/d - Mobilized Unit -Three trains in one skid

- Remote controlled operation

□Membrane fouling is related to pretreatment failures.

□ UF shows higher CAPEX than single stage gravity DMF, while it has

lower CAPEX than dual stage DMF configurations.

□ UF presents a higher OPEX compared to conventional filtration

(DMF) as a SWRO pretreatment.

□ DAF and gravity DMF configuration provides the lowest total price.

Conclusions

□ DAF and gravity DMF configuration provides the lowest total price.

However, other conditions need to be considered to select the proper

pretreatment process for SWRO.

□ Doosan has broad experience on various pretreatment options for

mega size SWRO projects.

□ Doosan invests heavily in R&D to improve SWRO pretreatments and

provide better desalination plant to clients.