successful long-term operation results of seawater ro plant by using hollow fiber...

SUCCESSFUL LONG-TERM OPERATION RESULTS OF

SEAWATER RO PLANT BY USING HOLLOW FIBER TYPE

CTA-RO MEMBRANE MODULES

Toshitaka TANAKA

Desalination Membrane Dept.,

TOYOBO CO., LTD., Japan

October 18, 2017

Water Arabia

Background

Serious water-shortage

Membrane

Deterioration

18% Element

Deterioration

4%

Fouling 77% Biofouling

43% Organic

15%

Colloids

22%

Scale

13%

Khedr, Desalination & Water Reuse, 10/3 (2000) 8-17

(2/17)

Demand for desalinated water is increasing.

Seawater RO membrane desalination plants

Advantage: Saving energy

Problem: Fouling

(biological fouling)

Skin layer : 5 mm

Support layer : 45 mm

Pressure Vessel

RO Element

RO Module HU10255MI

Features of CTA Hollow-Fiber RO Module

Hollow Fiber RO Membrane

Outer dia. : 140 mm, Inner dia. : 55 mm

(3/17)

(4/17)


Structural Advantage

Cross winding

arrangement

Cross winding arrangement of hollow fiber

bundles can minimize pressure loss and

uniform water flow.

Space between hollow fibers is remarkably

large, so fouling matter can pass through

very easily

Large membrane

surface area

Millions of hollow-fibers are wound

into element configuration.

Compared to spiral wound

membrane element, hollow-fiber

membrane element has about

10 times larger surface area.

Much larger surface area

allows much less surface fouling.

(5/17)


Material Advantage

“Control biological fouling with chlorine disinfectant”

Hollow-fiber RO membrane made from CTA has a superior chlorine

tolerance compared to Polyamide membranes, and it enables direct

injection of chlorine disinfectant to RO modules.

The disinfection operation mode can also be optimized by continuous

chlorine injection (CCI) or intermittent chlorine injection (ICI).

Chlorine Injection to RO Membrane

1. Dechlorination before RO inlet to prevent deterioration of the membranes

from happening due to oxidation.

2. AOC (Assimilable Organic Carbon) problem has been reported.

ICI (Intermittent Chlorine Injection)

1. Intermittent chlorine injection directly injects chlorine disinfectant to RO

modules in order to prevent biological fouling on the membrane.

2. Membranes have to be resistant to chlorine.

Seawater Pretreatment

Sodium Meta

Bisulphite (SBS) ;

Continuous

Chlorine

HPP RO module


Chlorine SBS;

Intermittent

injection

HPP RO module

Dechlorination Operation

(6/17)

Investigation on the Optimization of ICI Condition

(7/17)

Lag phase is for at least 6

hours from the incubation

start

0 3 6 9 12 15 18 21 24

Growth Time in Seawater [hr]

To

tal B

acte

ria C

ou

nts

[C

FU

/ml]

Lag Phase Logarithmic Phase

Initial counts: 104 CFU/mil level

Initial counts: 103 CFU/mil level101

102

103

104

105

106

Bacteria counts of 105

CFU/ml level became

below the detection limit

in 30 minutes after

chlorine injection.

0 10 20 30 40 50 60

Time after Injection of Chlorine [min]

To

tal B

acte

ria C

ou

nts

[C

FU

/ml]

101

102

103

104

105

106

Residual Chlorine: 0.5 mg/L

Residual Chlorine: 0.2 mg/L



Detection limit : 20 CFU/mL

Result of growth rate of bacteria in the seawater from the Red Sea

Result of sterilization of bacteria by chlorine

Summary of Bacteria Count Test

1. 104 to105 level of total bacteria counts became under the detection level

when the bacteria were exposed to 0.2 to 0.5 mg/l of residual chlorine for

30 minutes or more.

2. The number of bacteria stayed the same during “Lag phase” for at least 6

hours, after that, the number of bacteria increased exponentially. Even if

bacteria increased during “Logarithmic Phase" , 1-hour chlorine injection

every 24 hour could constrict the biofouling.


Sodium Meta

Bisulphite (SBS) Chlorine Intermittent

injection

HPP RO module

Dosing (example);

0.2~0.5 mg/L

for 1hr/24hr ~

Intermittent Chlorine Injection (ICI)

(8/17)

Chlorine Consumption during ICI

Result at actual SWRO plantICI condition : about 0.5 mg/L (target value) for 1hr/24hr

(9/17)

Chlorine consumption*1

during ICI was high

Fouling potential

became high

*1 Chlorine consumption

means the difference between

R-Cl conc.*2 of RO inlet and

R-Cl conc. of RO outlet

*2 R-Cl conc. means “Residual

chlorine concentration”.

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

0 5 10 15 20 25Time [Month]

Re

sid

ua

l c

hlo

rin

e c

on

ce

ntr

ati

on

[mg

/L]

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Inc

rea

se

of

dif

fere

nti

al p

res

su

re

[ba

r/d

ay

]

R-Cl conc. in RO inlet <Feed>R-Cl conc. in RO outlet <Brine>Increase of DP (moving average)

0

100

200

300

400

500

600

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Actu

al

perm

eate

qu

ality

[ m

S/c

m]

Dif

fere

nti

al

pre

ssu

re [

bar]

Time [Month]

Differential pressure

Actual permeate qualityCriteria for chemical cleaning

Operation Result of ICI

Result of Site Test at Addur SWRO Plant in Bahrain (Arabian Gulf)

Stable Permeate quality

・ICI condition: from 1hr/24hr to 1.5hr/24hr, 0.3 mg/l as R-Cl conc.

・Addition of periodic continuous 24-hour chlorine injection

Maintaining of differential pressure at low level

ICI can effectively prevent biological fouling

(10/17)

Initial ICI condition: about 0.3 mg/L (target value) for 1hr/24hr

0

100

200

300

400

500

600

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1 2 3 4 5 6 7 8 9

Ac

tua

l P

erm

ea

ter

qu

ality

[m

S/c

m]

Dif

fere

nti

al p

res

su

re [b

ar]

Time [Month]

Differential Pressure

Actual permeate qualityCriteria for chemical cleaning


Results of site test at Al-Jubail SWRO plant in Saudi Arabia (Arabian Gulf)

ICI is effective against biological fouling

(11/17)

Initial ICI condition: about 0.3 mg/L (target value) for 1hr/24hr

Differential pressure

was maintained at

low pressure level

ICI condition: 1hr per 24 hrs,

R-Cl conc. Fluctuated between 0.2 to 0.5 mg/L

Actual permeate quality was at the low level

Optimization of ICI

Condition during ICI Assumption Countermeasure

A small amount of

chlorine-consuming

matters was in RO

module

No need to

change the ICI

condition

A great amount of

chlorine-consuming

matters was present in

RO module or RO inlet.

Required

Change of chlorine injection frequency

Addition of periodic continuous 24-hour chlorine injection

*2 During ICI, it is desirable R-Cl conc. of RO brine/permeate is more than 0.05 mg/L (less than 0.10 mg/L).

Improvement method

(12/17)

*1 R-Cl conc. means “Residual Chlorine concentration”.

Feed Pressure

Brine Pressure

R-C

l co

nc.

R-C

l co

nc.

R-C

l co

nc.

RO membrane

Feed Pressure

Brine Pressure

R-C

l co

nc.

R-C

l co

nc.

R-C

l c

on

c.

RO membrane Chlorine-

consumption

Differential Pressure (Stable)

Differential Pressure (Increase)

Operation Result of ICI(13/17)

0

200

400

600

800

1,000

0.0

0.5

1.0

1.5

2.0

Pe

rme

ate

TD

S [

mg

/L]

Dif

fere

nti

al

pre

ss

ure

[ba

r]

Differential Pressure Permeate TDS

0

50

100

150

200

250

300

0 1 2 3 4 5 6 7 8 9 10Co

lon

y c

ou

nts

fo

r R

O

bri

ne

wa

ter

[CF

U/m

L]

Time [Month]

During SBS Injection During R-Cl Injection

Results of Site Test at Jeddah SWRO Plant (Red Sea)

Conductivity was stable during test period.

Colony counts of brine under ICI was at low-enough level.

ICI is a very effective disinfection method

ICI condition: 0.2~0.4 mg/L for 1hr/8hr

0.0

1.0

2.0

3.0

4.0

5.0

Diffe

ren

tia

l P

ressu

re

[bar]

0

500

1,000

1,500

2,000

0 10 20 30 40 50 60

Perm

eate

TD

S [

mg

/L]

Time [Month]


Jeddah Phase-2 SWRO Plant for 5-Year Operation (Red Sea)

ICI is applied as a basic disinfection method to all SWRO plants using

hollow fiber CTA based RO membranes.

ICI condition: 0.2~0.4 mg/L for 1hr/8hr

(14/17)

Product TDS satisfied the plant specification during 5-year guarantee

operation without membrane replacement.

Differential Pressure was maintained at a low level. Once a year citric

acid cleaning was enough.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

1-Jan 2-Mar 2-May 2-Jul 1-Sep 1-Nov 1-Jan 2-Mar 2-May 2-Jul 1-Sep 1-Nov 1-Jan

Dif

fere

nti

al

Pre

ss

ure

[b

ar]

Date

Operation Result of optimization of ICI condition

(15/17)

ICI condition:

0.3 mg/L for 1hr/8hrICI condition:

0.5 mg/L for 1hr/24hr

Chemical cleaning :

4 times/year

Chemical cleaning:

2 times/year

The stable RO operation has been achieved by appropriately adjusting

the ICI condition depending on the quality of RO feed water.

Result at an actual SWRO plant in Saudi Arabia (Arabian Gulf)

Haql (SWCC)- 4,400m3/d (1989)

Duba (SWCC)- 4,400m3/d (1989)

Yanbu (SWCC)- 128,000m3/d (1998)

Yanbu (MARAFIQ)- 50,400m3/d (2006) Bahrain (MEW)

- 45,500m3/d (2005)

Al Jubail (SWCC)- 85,000m3/day (2007)(90,000m3/day)

Ras Al Khair (SWCC)- 345,000m3/d (2013)

Manifa (Aramco)- 27,000m3/d (2012)

Shuqaiq (SqWEC)- 240,000m3/d (2010)

Rabigh (RAWEC)- 218,000m3/d (2008)- 109,000m3/d (2015)

Al Birk (SWCC)- 2,200m3/d (2001)

Jeddah (SWCC) (RO1) 56,800m3/d (1989)(RO2) 56,800m3/d (1994)(RO3) 260,000m3/d (2012)

TOYOBO RO Membrane for Seawater Desalination

(16/17)

SWRO plant that applies ICI

Conclusions

1. It was demonstrated that ICI (Intermittent chlorine

Injection) was an effective method for preventing

biological fouling and it has already been proved

practically in the regions of both Red Sea and Arabian

Gulf.

2. CTA based RO membranes and ICI is a good

combination for a long-term operation of SWRO

desalination plant.

3. Even with the seawater of the Middle East, ICI can

ensure the stable operation of RO modules by

adjusting its condition to the followings.

- Concentration: 0.2 to 0.4 mg/l as residual chlorine

- Injection time: 1 to 3 hour per 24 hours

(17/17)

Thank you for your kind attention.

successful long-term operation results of seawater ro plant by using hollow fiber...

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