Conventional pretreatment of surface seawater for reverse osmosis application, state of the art

Desalination, 74 (1989) 3-36 Elsevier Science Publishers B.V.. Amsterdam

CONVENTIONAL

-

Printed in The Netherlands

PRETREATMENT

OF SURFACE

SEAWATER FOR REVERSE OSMOSIS APPLICATION, STATE OF THE, ART

A.Y. AL-BORN0

AND

M. ABDEL-JAWAD

Water Desalination Department, Kuwait Institute for Scientific Research,

P.O.Box 24885, 13109 &fat, Kuwait.

ABSTRACT Conventional methods have been used to pretreat surface seawater prior to desalination by reverse osmosis membrane technology. The successful pretreatment should remove most matters that give rise to fouling due to biological activities, scale products and materials in suspension. The extent of seawater pretreatment is site dependent with regard to water quality, in general, and suspended materials in particular. This paper reviews the present technologies, capacities, efficiencies, and problems of various pretreatment system currently used to treat surface seawater for reverse osmosis application. Potential improvements in process steps and chemical consumption is also discussed. Special emphasis is given to currently used pretreatment systems in Kuwait and the Arabian Gulf region.

4

INTRODUCTION

The commercial

application

desalination

of seawater

construction

of large RO plants

which

can stand

usually

contains

matters

which

major

biological

has increased

high pressure

which

(ref.

rapidly

since 1978 with of new

1). The feed seawater of inorganic

membrane

the membranes

to RO plant

salts, and foreign

and decrease its productivity.

are associated with

slime formation,

osmosis (RO) process for

and the development

high concentration can foul

foulants

of reverse

suspended

the feed seawater

solids, colloids, metal

The

are due to oxide and

scale formation. The pretreatment

requirement

used in conventional pretreatment

water

membrane

suspended

solids; to adjust

to inhibit

or control

which

when

membrane;

precipitated

will

The importance temperature,

and source prior

overemphasized

system

should

usually

such as disinfection, dechlorination

feed water

includes

many

of feed; salts,

and to prevent any emulsified

composition,

and

a RO system that

to avoid

variability,

cannot

pretreatment

interdependent

coagulation/flocculation,

be

a costly

be designed for the worst

seawater

or

.3).

to designing

5). The conventional

application

(ref

(ref. 4). It was suggested

pretreatment

turbidity

passages or coat the

and to remove

of knowing

to achieve

such as inorganic

slime growth

organ&

necessary

the pH and temperature

plug the water

those

of

to remove

of compounds

and prevent

oil and similar

conditions

is practiced

and control

of the equipment;

unemulsified

case (ref.

the feed water

the formation

are essentially

(ref. 2). The purpose

life. Pretreatment

to disinfect

contamination

failure,

treatment

is to provide

maximum

for RO installation

system possible

process for RO

pretreatment

stages

sedimentation/filtration,

and scale control.

Di.sirifeuioTl Disinfection and bacteria

within

of seawater

is needed to prevent

the membrane

modules

the growth

and other

parts

of marine

of the RO

life

5

desalination

process from

of potenti&J

tiecti~~e

using conventional flocculation, extent have

the intake objec+;b!e

water

rates are tco slow achieved

of

iron

Chlorination

and to a less

and flocculaticn whenever

molecrriar

5 apphed

their

ciarificaticn.

?fflUeIlr:

of chemicah

salts, acci high

(CuSOd)

Seawater

in water

to provide

by addition

‘Jy

disinfection.

F-n

solids icolloids)

removal

processes such as coagulation/

(UV> light, ozon and copper sulphate

Tae process of coagulation suspended

Partial

can >e aamphhed

and filtration.

been used for seawater

Coagui&ion and

orgum

pretreatment

sedimentation

ultraviolet

to the discharge.

and appj7jng

weight

aaturai

su’csidence

T2.5 :s usua2y I . .._ _--..A_, > =*0-7-.-. --b-J_

-0

poiymers

to separate

.are ccmmcn

.ccagulanx

and flccculants.

In sedimentation, gravitational their

settling.

particulate

matters

and crushed

sand, depends

very

Due to high nation

much

6).

as well

(ref.

rate of particles

as the density

pretreatment

3). The most common

on the required

quality

by

addition

on Filtration

fouiing

media filters

The selection

achieved

depends

to reduce membrane

of polyamide

are removed

of the water.

coal (anthracite).

sensitivity

is usually

solids in the seawater

Tne settiing

size and density

is the most common

(ref.

suspended

of filter

3y

are silica design

of the effluent.

membranes of sodium

to chlorine, bisulfite

dechlori(SaHS03)

‘oy

6

S&

Gmtrd

Scaling

potential

(CaCOS>, calcium and strontium trolled

sulfate

sulfate

by addition

Sodium

salts

encountered

(CaSOd,

(SrSO4).

scale (ref.

the recovery

ratio

difficult of the

or by chemical

brackish

for

water

and

(ref.

and

into the reverse

to some

Each

contains

seawater and

of a particular

after passing

application

are

proven

well

pretreatment to

due to the high

AND

be a

turbidity

which

SELECTING

potential

method

depends very

in

addition

to the

can

enter

was

the turbidity

pretreatment.

was considered

or silt

feed water

index

as a stand

pretreatment

process.

(treated

in

method. much

different

The

choice

on the seawa-

of

for evaluating

seawater

measurement

the

of the feed

process which

successful.

of the pretreated

density

foulant

understanding

Pretreatment

predictor

OF

contractor

plant.

the used measure

by DuPont

any

11).

RO have

pretreatment

ly used accepted

developed

inhibit

by decreasing

the

pretreatment

the feed turbidity

ging factor

7 - 9).

to

however,

different

Traditionally,

the

RO

(ref.

either

micro-organism,

different

and the users of the intended

and after

can be con-

used

(ref.

requires

characteristic

process

by

is mainly

EVALUATING PROCESS

ment

for

water,

marine

PXETXEATMENT

ter

commonly

controlled

desalination

12) which

scaling

(CaF2)

osmosis system.

FOR

concentration

is

carbonate

floride

acid (H2S04)

pretreatment

river

calcium

carbonate

methods

seawater

problem

CRITE3YA

&IMP)

pretreatment

for

requirements

Calcium

10). Silica is usually

Although established

silica (SiO$,

of acid such as sulfuric

hexametaphosphate

CaS04

in RO are calcium

Currently water

fouling The

water

the most wideis the plug-

factor

test of feed water test

and untreated)

is usually through

0.45

before

used to lower

quality

(SDI). The plugging

pretreat-

test

was

before

and

carried

out

Millipore

by fil-

ter

at

time

The

30 psi.

required

ti, followed t-f, after

drop

to collect

in flow

an initial

(5 ruin)

by

measuring

500 ml (100 ml> of filtered

by the time required

15 min

is determined

to collect

of flowing.

a final

Flow

the

water,

500 ml (100 ml>,

decline

is defined

as a

percentage. Percentage SD1 is determined

Plugging

Factor

by dividing

= 100 (1 - t#f)

the plugging

factor

by

the

total

time

of the test. The high

SD1 of

value

brane

the

of the feed

manufacturer.

while

spiral

Therefore,

wound

feed water

water

membrane objective

the only measure

to determine

it with

an actual

seawater. could

be reduced

tered

are related

feed

can shorten

and efficiency

membrane

process, is to

process conditions.

life when,

three

under

or more this

1). Major

membrane

problems

of the pretreatment change

good

years

are associated

life and adversely

to

treated

of the process

actual

which

6).

for life

encounwith

the

process.

its salt rejec-

characterstic.

Salt rejection

that

water

fouling

the

pretreatment

conditions, (ref.

(ref.

in order

SD1 of

of any

can be about

5.0

SD1 value

the

under

SD1 ~3.0,

process is to provide

have a finite

months

than

efficiency

unfavourable

to membrane

Fouling

to reject

the actual

to several

of the

although

a

ty_pe of mem-

requires

SD1 less

the specified

Infact,

life

under

quality

tion or flux

with

usually

membrane

However

accept

membrane

The RO membranes the

membrane

of the efficiency

way

conditions,

fiber

is considered

by any

of any pretreatment

fouling.

is a good measure

6 which

to be accepted fine

to RO membranes

membrane

is usually

quality

Hollow

the main

prevent

seawater

dissolved

(a factor

solids), and membrane

can pass through control

expressing

time)

are

reflect

on the efficiency

a given

measures

the ability flux

(the

area of membrane of

any

of RO membranes

membrane

of the used pretreatment.

quantity

in a specific performance

of water unit

of

which

8

This paper treatment

process

RO plants.

REVERSE

seawater include

OSMOSIS

ment

methods

which

membrane

A pilot coagulation,

1972

(ref.

detention tration than

Vista

capaci-

systems

carried

investigated

be used in conjunction

the effect

manganese

earth

out by

the

Vista,

Wrights-

seawater

pretreat-

with

RO desalina-

of chlorination,

- zeolite,

pressure

13). The

study

granular

filters

sand

showed

pressure

sufficient

to

obtain

1 JTU

turbidity

at

all

that

commercial

technology,

1970’s at Chuta

studies

were

found

was

was

Test site over the period July

(40 min),

and

pre-

effectiveness.

sand,

diatomaceous

pilot

pretreatment

RO work

test to determine

settling,

OSW Chula ary

plant

by

of the present

during

Their

could

of conventional

PLANTS

(OSW)

Beach and elsewhere.

and

review

seawater

ville

tion to prolong

desalination

PILOT

water

experiences

of the various

experimental

of saline

bon

operating

and problems

of the

office

for

This will

ty, efficiency

Mast

deals with

activated

carbon

In 1972, four

different

that

the

times

was

performed

during

their

effective

the

Febru-

(10

activated

water

car-

at

1971 through

and

desired

very

activated

chlorination

filtration,

aium

mg/l),

carbon

quality

tests.

It

fil-

of

less

was

also

in removing

residual

chlorine. pretreatment

possible use at OSW Wrightsville 1) chlorination

Beach (ref.

(5 -10 mg/l>, detention filtration,

and activated

tion,

and

filtration;

filtration,

and

sand filtration, cated that turbidity chlorine

sand

manganese

and activated

system

0.35 JTU

zero in system

evaluated

Their

systems

carbon

filtration;

3) chlorination,

filtration;

carbon

1 and 2 were

of less than was

zeolite

14).

were

(40 min>, sand filtration,

ganese - zeolite detention,

systems

Results

capable of producing and

1.0 JTU,

1 and less than

were man-

2) chlorina-

detention,

4) chlorination,

filtration.

for

detention,

obtained effluent

respectively.

one in system

sand

indiwith

a

Residual 2. Acti-

9

vated

carbon

materials.

filter

The

manganese

was

study

three

pretreatment

was

the

lowed

by

filter;

coagulation

cartridge called tem

pretreatment

base line 2 and

3 provided

filter;

water

Facility) first

filtrations,

system fol-

and

carbon

by a polishing

filter,

obtained

acceptable

of and

filtration

coagulation

Results

with

systems.

included

followed

in-line

system.

as

coagulation

15). The

cartridge

system

carbon

pretreated

Chemical

(ref.

which

filtration,

pretreatment and

as effective

Beach Test

evaluated system

organic

in 1976 ( at the Office

Wrightsville

were

manganese-zeolite

filter

dissolved

was

removal.

was conducted

systems

of

any of the above mentioned

and Technology

base-line

most

chlorination

in iron

with

test program

Research

remove

that

filtration

was also recommended

Water

to

revealed

- zeolite

A field

able

before

indicated

SD1 factor

the that

for

so sys-

feeding

RO systems. In 1979 a pilot West

Africa

(ref.

establishing ment

the

optimum

(ref.

tion and/or

sludge

filtration

NaHS03

months

of less than rant

two

which

45% was

achieved

seawater

(ref.

17).

Hetden

and

Brother

(W/Oxidant>

process

They

found

that

days

under

ultraviolet

improving

the

treatability

the

seawater

mainly

reported

they

heavily

system

in

developed chlorinated

or

sunlight of the

(to approx-

gravity

media, and

gave

results

Index

(PI1zo)

rich

recalcit-

(ref.

17) on the

southwest

Africa

seawater was southwest

when

found

stored to

Africa

fikra-

dechlorination

due to nutrient

for

air

pH adjust-

satisfactory

plugging

1980

and non-

dissolved

rapid

of SHMP (10 mg/l),

pretreatment

after

or

to

pretreat-

(25mg/l)

using Celite 455 as filter

using

three

systems,

given

tested

pH adjustment

clarification,

parallel

in South

was

The

using alum

blanket

(5.5 to 6.01, in addition The

emphasis

conditions.

(5 mg/l),

16) as independent

DE

at Swakopmund

special

pretreatment

ment

for

and

and flocculation

polyelectrolyte,

flotation

17)

chlorination

71, coagulation

ionic

was established

16 and

process included

imately

plant

be

WOX

seawater. for several

effective

seawater,

in

to the

10

extent

that

only

eliminated

the

clarification

sand and/or need for

DE filtration

chemical

coagulation

acetate-cellulose

membrane

Bargas region some main

(ref.

of Black

ment

systems

Chlorination,

filters

line coagulation

not

ensured

processes,

obtain

were

only

was

found

The

necessary were

found

were

used sand

amounts

during

results

obtained

indicated

method

for Black seawater In

1980,

a seawater

one year

under

tropic

non-acid

pretreatment

tem consisted tration, tion

by

dechlorination several

that

methods:

(ref.

UF can

pretreatment desalination

methods

with

season

18). The

chloride and

second

system

the

third

system

filtration

speed.

FeC13 (3 - 10

higher same

concentrapilot

(ref.

as an

plant

19) and

alternative

process. pilot

plant

was

operated

(St. Croix, U.S. V.I.> to study

coagulation

excess NaHS03 conventional

pH

with

adjustment

sys-

iron sulfate,

and alkaline

for

various

(ref. 20 and 21). The pretreatment in-line

for

the fourth

method

be applied

in

filter

and and

down-

down-flow

at higher

(UF) pretreatment

conditions

of chlorination,

by

automn

ultrafiltration

ferric

while

the

(3 - 6 mg/l)

to be changeable

required and

of chlorine

3)

sand filtration

the

speed.

requirements

on

coagulation

and

fil-

sedimentation,

requirements

at low filtrate

pretreat-

filter,

filtration

but

sys-

on downflow

disinfection,

water

RO feed

tested

(NaOCl),

requirements

10-15 hours

four

polishing

first

near

to determine

multi-media

filter

The

tubular

pretreatment

4) Chlorination,

used for

water

to ensure

done in order

hypochloride

feed

seashore

Black

coagulation,

respectively.

RO

RO feed

runs

tions

the

the

RO. The

multi-media

were

with

on up-flow

in-line

Sodium

NaHS03

the

mg/l>

expensive

RO system

and filtration

and dechlorination,

dechlorination. and

by

and filtration

on up-flow

dechlorination did

The process

relatively

and the required

desalination

sedimentation,

sand

at

19). This was

1) Sedimentation

ter; 2) Sedimentation

(FeC13),

and

Pilot

installed

parameters

seawater were

with

was

18 and

technological

tem

and

required.

systems.

In 1980, a unit-experiment

flow

was

fil-

scale prevenwith

H2SO4,

11

polyacrylate, were

citric

acid, and

also reported

by Winles

polyacrylate

and

tan&

acid pretreatment The

tration

system

in-line

coagulation

was

Bay near

23). Their

which

that

both

as alternative

filtrate

due

was

indicated

to

filter

to pretreat

studied

by Kawaa

that

mean for seawater

this

type

of fil-

pretreatment

when

out using FeC13 at dosage levels

winter quality

to tidal

sand

(Japan)

results

was carried

and summer, which

variation

was

and

respectively.

observed

was

The dete-

during

overcome

of 0.9

by

summer deep

pipe

system.

COMMERCIAL The plants low

22) indicated

the continuous

was an effective

of the

intake

obtained

some promise

Hiroshima

as Fe+3 during

mainly

et.al. 1983 (ref.

of using

et. al in 1987 (ref.

rioration

results

and chlorination.

at Kure

- 4.5 mg/l

acid. The

acid exhibited

application

seawater

tannic

SEAWATER

increasing

is primarily cost. The

tion plants

m3/day).

for

Malta

20,000

However

the

with

capacity

plants

RO

experience

of these plants

m3/day

Jarj-

and Jeddah RO plant

of of 56,500 Saudi

at

desalina-

such as Ra’a Abu

largest

in Jubail,

desalination

RO seawater

by large plants

m3/day),

of two

Arabia,

in

in the m3/day

and

now

(ref. 24).

present

some seawater

commercial

capacity

to be constructed

tendering The

of increasing

(12,000

each, is planned

large

due to good operating

(46,000

consisting

under

for

can be exemplified

Arabia

world,

interest

trend

our in Bahrain Saudi

RO PLANTS

technologies,

pretreatment

capacities,

systems

plants

along with

plant

capacity

en in

Table

show

that

1.

whereby

7 of these located

ing that

the operating

efficiency

currently

and type

were

region.

expenses of Venezula

problems

used in commercial

of membrane

12 RO plants in the Gulf

and

cited

of RO

used are givin

literature

It is worth

mention-

RO plant

is not included.

12

Doha

Revwse The

capacity

Osmosis

plant of

was

5,000

with

different

plate

and

Plunt

inaugurated

m3/day.

types

frame)

(DROP)

in December

It comprises

of

modules

as shown

common pretreatment

(CP> system

for

which

has been used in W. Germany

and

colloidal

tion, and gravity rinated

surface

from

filtration seawater

to the CP system

from

ed if the chlorine

content

destabilization

tank,

polyelectrolyte

are added

The

seawater

From

the

water

in this

water

from

lected

by

before the

the

(Table

treatment

The flow.

tank,

storage

tank

each

line

transfer

further

receives pump

treatment

3) to obtain

filtered

water

is col-

to main

storage

filtered

water

manufacturer.

the

to

the

fouling

required

carried

control.

the out

of feed water

As we can see in Table

parallel

quantity

38). Before

is being

the quality

the treated four

biological

(ref.

From

of

water for

enters

each

specified 2 and

feed

to remove

residual

chloride

line

by the

3 the pre-

for RO Line 1 consists of :

dosing system

of

through

is added

for

time

passed

it is pumped

the

3).

flocculation

Finally,

where

Chlorine

the

(Table

dwelling

tank

pump.

cationic

aid, respectively.

to

intermediate

system

NaHS03

passes

of the

a

of H2SO4

2). The

stage,

RO system’s

coagulant

pipe

gas is add-

and

(Table

a booster

2 and

is

floccula-

At the inlet

filters

by a separate first

stage

suspended

fiberglass

Chlorine

level.

tanks.

riv-

2. At DROP, the chlo-

gravity

it enters

water

water

35 - 371,

coagulation,

addition

cascaded

flocculation

open

storage

the

a

cur-

of Rhine

(FeClSOd)

and

to 6 by

of three

(ref.

an inforced

stage is 10 min at maximum the

in an

tank

as coagulant

fiber,

2). The

of removing by

required

fine

(Table

Station.

sulfate

tank

hollow

system

in Table

through

is below

ferrochloro

consists

water

Doha East Power

pH is adjusted

stage, which

raw

is pumped

is equipped

and

for the treatment

as shown

destabilization

multi-layer

the

lines

each line

uses the basic principle

particles

it has total

25 - 27). DROP has

is based on Wahnbach

system

i9S-4 and

wound,

1 (ref.

in Table

used CP system

This

three

(spiral

rently

er water.

Kuwait

in the feed

13

two

parallel

removal

activated

of residual

carbon

chlorine,

the NaHS03

reaction

anti-sealant

dosing

with

filters and

to

ensure

the

complete

to act as a holding

tank

r^or

chlorine

system

to prevent

sulfate

scaling

(phosphate

scaling

(H2SO4>

based inhibitor) acid dosing system two

cartridge

than

5pm.

pressure

to prevent

filters These

carbonate

(micron two

filters)

filters

are

to filter located

out particles just

before

larger

the

high

pumps.

The pretreatment

system

acid dosing system polyelectrolyte three

in-line

feed,

since

water

with

NaHS03

for RO Line II consists of:

to prevent

carbonate

scaling

dosing system coagulation the

filters

membranes

SD1 greater

dosing

reduce

RO Line

2 do

of

than

system

to further

the SD1 of the not

accept

feed

3.0

to remove

any

residual

chlorine

in

the

feed three

cartridge

filters

filters

are always

The pretreatment

to remove

in operation

system

while

larger

the third

than

5pm.

Two

is on stand-by.

for RO Line 3 consists of:

acid dosing system

to prevent

anti-s&ant

system

dosing

particles

carbonate

to prevent

scaling

(H2SO4)

sulfate

scaling

(phosphate

based inhibitor) NaHS04 two

dosing system

cartridge

Since

filters

to filter

the beginning

satisfactorily

time,

it has been successfully

some

cases

it

has

residual

out particles

of the plant’s

ning

in

with

to remove

availability

failed

to

produce

larger

operation,

of more

controlled

chlorine.

than

than

25,um.

CP has been run96%.

Most of the

to give SD1 less than acceptable

quality

4, but and

the

in

some

cases

required

it

quantity

can be related failure of

has

mainly

destabilizer

seawater.

to the clogging

mixer,

and

system

mg/l,

climatic

polyelectrolyte

of dual

and

of these

media

filters

of FeClSO4,

conditions

pretreatment

has

the

failuz (ref.

391,

break-down

(i.e., temperature,

The

obtained

SD1 value

1 and

3 With

the

SD1 of less than general, managed

to give

the membrane in reducing

dust

feed

pH

operated

4 especially

to 4.0 - 5.0

in-line

to

6.0, the

to achieve during

1986

value

coagulation

most (ref.

by RO

system,

for RO Line 2 has been maintained. systems

feed

water

frequencies,

the In

of all RO lines have been quality

requirements.

in accordance

This achievement maintaining

with

resulted

design recover-

(ref. 25 - 27).

at Ra’s Abu

1) was started

Jarjur

with

up in October

groundwater,

containing

is at present

the largest

28 and 29).

The groundwater,

pumped

a capacity 1984.

The

dissolved

of

46,000

raw

water

hydrogen

sul-

hydrocarbons.

solids TDS 12000 mg/l),

to the following

the

rate

FeClS04

RO Plant, Bahrain

fide (H2S) and miscible

is

dosing

the

(4.0) is the acceptable

RO availability

RO plant

(ref.

than

of the

cleaning

source is high salinity

membranes

aid

manufacturer’s

Abu Jarjour

The plant

Fe+3

reducing

pretreatment

membrane

(Table

less

satisfactory

ies and increasing

The

of

3.0 required

the individual

minimizing

been successfuily

25-27). Lines

SD1 value

the

and

time

lutants

quality

causes

sequence,

adjusting

the

solved

The

overdosing

the backwash

failures,

adding

common

m3/day

acceptable

wind).

dosing

R&s

produce

dosing system.

By modifying

of

to

of filtered

of FeClSO4

storms,

failed

containing

and transferred

pretreatment

stages:

in the world high

with saline

seawater (total

H2S and hydrocarbons

by submersible

well

intake

dispol-

pumps

15

Protection ~ressurc In-line

water

against

hammer

in an anti-surge coagulation

(Table

Filtration

dual

using

using

vessel (to IXe-~-cnt

with

or to filtration

by

a polyelectrolyte

Nitrogen

flccculation

media

filters

(sand

and anthracite)

3.

Activated

for

the

removal

H2S04

for

pH-adjustment

Spent carbon Chemical

filtration

with

carbonate

scale contrcij,

XaHSOm 2 Gntermittant The

oxygen

of

methcd

from

H2S after

shcck

deahg

the

air

in

pH-adjustment

upstream

of the RO stacks.

coupled

requires

pretreated any

a

water

HzS has ken,

to energy

to colloidal

pretreatment,

pressuried,

suspended

recovery

turbines

Z;st1y,

sulphur

and,

6 and

(Telton

by dissoivtd to

by aeration

to

remove

in stripping

pretreatment

through

solids,

prevent

tc

secondly,

closed

is transferred

remaining

to about

for disi.&ecticn:‘.

to the RO permeate

This

removing

treatment

with

the

towers.

Tne

hydrocarbons.

SI-IU? :CLSC~ scale control>

of H23 and hjjdro-sulphide

oxidation

of

in order

is regenerated.

treatment

(calcium

?ri-

2 and 3).

to decrease the SD1 to below carbon

under

of I-=25>.

XZCLitiOil

causing

gas

system

micro-guard

high

turbines)

filters,

pressure

pumps

and further

into

the permeators.

The operation quality

was

formance quality

found

was

tion

to be better

has been successful, than

guaranteed.

better

than

projected,

of the pretreatment

raw

water.

The main is related

also

of the plant

problem to

algae

encountered and

media

and activated

carbon

tivelv

cnnttnlld

nlant

hv

during

excessive

filter

(ref.

sterili7Atinn

which

29). and

The

This rwular

membrane

explained

the first

bacteria

and the product

the

6 months

growth problem

in

maintenance

gcod

opera-

the was

per-

dual effec-

work.

16

A-2%-.~ 2?0 Plaz’ The plant ing

to

the

m3/day

Sam&: h&h

)

is located

Red

Sea.

The

of drinking

water

salinity

seawater

at Al-Birk plant

water

is 39,000

which

was

commenced

fiber,

Dunont

B10 membranes

in the bay during ment

in

be seen

chlorination level

of

tridge

and

Al-Brik pericd

1987

had

designed 6 and

tables

these

NaHSG3.

RO piant

steadily]

1983

declined,

The

uses

The

RO plant

Umm

in Tabies

hollow

is achieved of

10

fine

6 and

~i?tXat-

carried

3.

_A2

cur

b:?

-using high

mg/'i)

dcsage and

flcccalaticn

followed

30).

brought

2 and

is being

by micrcnic

satisfactory

to April

of membranes

Sdi

and

respectivelg.

is usuaily

performance The

1984. salt

was due to microbiological

Lujj I20 Rant,

(car-

passage fouling

using

during

performance was

till

higher

than

of membranes

(ref.

500 mg/l

NaHS03

was

performance.

Lujj

Arabia

of city

of Yanbu.

of drinking

water

200 mg/l

ide membranes

feed

silt

lead

(feed

for

1 (ref.

filters

membrane

Umm

exceeding

500 mg/l

in Table

disce&cn

demonstrated

to improve

m3/day

is 2,275

allowable

19S3,

open-

filters.

of September

25). Sterilization

north

design

are given

dosage

found

km

heavy

and medium

pressure

which

exceeding

The

Coaguiation (max.

course

5 micron)

capacity

rides and the Eeeci -water SDI is T-1. Tl;e

from

using

not

as shown

or‘ the plant,

polyelectrolyte

filtration

estimated

Sentember

Rrccess stages and chemicals

can

the

TDS).

has a narrow

is ~3.0 and 0.5 - 1.0 mg/l,

plant

Due to the iccation

design

of salinity mg/l

SD1 and chlori

Bay which

(ref.

is located Design

(Table

zero, respectively.

capacity

1) with

6 and 28). Spiral

are used and the plant The pretreatment

on the Red .Sea Coast of the

total

dissolved

wound

design process

plant

TFC

SD1 and for

154

is 4,4CO solids

not

1501 polyamchlorine

Umm

Lujj

is ~5 plants

17

includes nation

chlorination, system.

Chlorination

shock treatment a

coagulant

gravity

and

which

while

filter

ter (Table

However,

After

by CuSO4

achieved

using

(cartridge

were

was

when

CuSO4 (25

no information

was

on the

medium fil-

production

Membrane

was

is a

pressure

the plant

halogen

mg/l)

given

and

20 micron)

by

dechlori-

FeC13 is used as

coarse

declining.

attacked

and

using chlorine

28 days of operation,

quality

membrane

was solved

is

filtration,

achieved

replaced

by micronic

water

that

was initially

filtration

2 and 3).

revealed,

flocculation,

was then

followed

product

problem

coagulation,

autopsy

compound.

The

used as disinfectant.

environmental

effect

of

cuso4 Jeddah RO #ant The plant

m3/day TFC

- Saudi Arabia

was placed on-line

of drinking

membrane

element

of coarse filtration, a deep seawater fish

and

anthracite). well

well

filled

The

filtered

approximately

2.0 mg/l

to each RO stream

micron

cartridge

system

it was

coagulant

filter. found

aid polymer

It was hrs acceptance

reported

dual

water

A solution

system

filtration.

has cleanable

The

screens

supply

media

is then

consists plant

has

to prevent

pumps.

is then

gravity

collected

to the water

The

pumped

the initial

coagulation

were

not required.

the

plant

test since the performance

in

feed

(sand

and clear

the pH from

8 to

feed ‘mainfold

in

added at dosage level

is then testing

using

1.0

a concrete

to the

and the water

that

filters

to lower

of SHMR is usually

During

that

on spiral-wound

pretreatment

gravity

12,000

the algaeside CuSO4 at dosage level

through

6. The water

the RO building.

and

1979 to supply

is based

the seawater

with

and H2SO4 is added

and

It’s

which

entering

is treated

then

31).

disinfection,

from

Red Sea water

to Jeddah

(ref.

pump

or thrash

mg/l

water

in January

filled

through

25

of the pretreatment

Alum

successfully of all plant

(10 mg/l)

completed units

and

its were

a

120 very

18

lU*s

The RO plant water

to

Ra’s

two-stage wound

region

osmosis plant

RO modules

ROGA

(Table

chlorine

and

The

80 mg/l

introduced

The

supernatant

then

through

H2SO4

into

the

The

32).

and

water

4160

feed

the polishing

and chlorine

operation

line

and

produced

salinity

of about

C&bra

RO

The seawater

ppm

and

it

plant

initially

TDS from

mg/l

at

Culebra,

a design

operated

capacity

coagulation

using

The plant

failed

in

two

achieving

adequate

of this

RO system

of organic the

fouling. feed

Puerto

of

on a pretreatment

and dechlorination

Analysis

is

and

is stored

stage RO unit. seawater.

months

The

performance

seawater

with

Rico and

TDS) as its feed source.

filtration,

for

the

filter

seawater

added to the filled eight

water

sedimentation.

sent to the first

its

mg/l

Fe+3 for coagu-

media

The filtered

during

2

dos-

a high

Rico

is located

has

in-line

with

and

dual

pre-

45,000 ppm TDS.

plant

B-10

rination,

2-300

the

spiral

chemical

treated

flocculation

and then

successful

appropriate

The

a

media filtra-

is injected

through

employs

1). The

dual

control.

for

is then

Piunt, Puerto

(37,000

pH

potable

using

I-IR (Table

FeC13 (1 mg/l)

sand filter.

tank

was

for

is filled

Scale inhibitor plant

system

in capacity

along with

clarifier

storage

acid

6085

seawater

in the interim

hrs

(ref.

of 40 m3/day

sand filtration

2).

then

media

1977 to provide

using NaOCL for disinfection,

lation,

test

in January

process consists of coagulation/clarification,

tion, and polishing ages

was operated

Al-Khafji

reverse

treatment

- Saudi Arabia

RO Plant

Al-Khafji

Results water.

with

was

However,

polymer,

(Table

out

to study

this

problem

chlo-

by dual

2 and 3).

test period

salt

the

included

followed

and

indicated

1). The

(Table

which

performance

carried

obtained

m3/day

NaHS03

productivity

coastal

It is based on DuPont

system

cationic

acceptance

575

uses

rejection

of 600

(ref.

33).

the

possibility

presence

of humic

was

overcome

by

Location

Total

High salinity

ground water

Hollow

3000

purta

*

Hollow

Hollow

Hollow

fiber,

fiber,

fins

fiber,

El0

El0

Du Pont

610

810

and now under

60408

k Schuellt

tendering

89

810

of 56.000m3/doy

and ROGA 4160HR

(6”)

a capacity

fibers

flu Pant

Du Pont

DuPont

DuPont

EnrotScheiclw

fiber.

6600

1501

wound. Hydronautlcs

Polyamide

to be constructed.

Du Pont

fiber,

Spiral

Film Tee.

610

fine

fine fiber.

wound, UOP-PA

k frame.

hollow plate

Osmosis Plants

wound. UOP-PA

Permeator

with

wound and hollow

fine

fine

each Is planned

Spiral hollow

-

-

-

Spiral

Reverse

ROGA6085

plants

wound TFC,

wound TFC

-

DuPont

6640

-

-

Stags

stage

stage

stage

stage

stage

(TFCl501)

fiber.

wound.

fine

E-10

Second

Two separate

Spiral

Spiral

Spiral

Hollow

“Permasep”

20,000

Moron

Second RO line 3: First

Malta

400

575

Second

1: First

RO line 2: First

RO line

Spiral

West Indianas

40 56,500

Seawater

Membrane Used k Remarks

1. Commercial

Japan

British

Rico Island

Puerto

Grand Caymon

Culebra

5. Jubail

4. RA’s Al-Khafjl

12,000

4,400

3. Jeddo

2,275

1. Al-Birk

46,000

3000

m3/day

Capcacity

2. Umm Lujj

Saudi Arabia

RA’s Abu Jorjur*

Bahrain

3 RO Plants

(DROP)

Kuwait-Doho

Plant

Table

1 k 43

34

33

33

24

32

31

6 k 30

6 k 3%

29

26

25-27

Reference

(DROP)

Doha RO Plant

Location

Additional

RO Line III

no Line II

RO Line I

Pretreatment

ND

t40

NO

J&ail

ND

used

used

Ros’Al-Khofji

not

not

not

used

not used

“ot

used

Jeddoh

used

used

used

used

not used

not

Sedimentation

used

used

used

used

used

not

Umm Lujj

used

not used

used

shock

used

FlOCCUlotiO”

used

Arabia

Intermittent treatment

used

Destabilization

used

Saudia

Abu.Jorjur

Soperate

used

---

RO Plants

Components

Seawater

System

Components

Commercial

System

for

2. Pretreatment

Al-Birk

-

Rh’s

Bahrain

2)

1) Common Prelreotment

Kuwait

Plant

Plant

Table

three

+ anthracite

ND

polishing

Presserized

sand filter.

dual media filter+

and 25 filter.

filter.

micron cartridge

pressure

sand filter

filter.

Dual media filter

+micronic

Gravity

pressure

+ anthracite

+ micro-guard

filter

filters

and

+ activated

filters

filters.

sand filter

filter

+ micronic

Gravity

carbon

filter

coogulotlon

filters.

Dual medlo filter

Two cartridge

in-line cartridge

Three

two cartridge

carbon

filters

Two porollel

multi-layer

Four parallel open gravity

Filtration

k

k 29

24

32

31

6

k 30

6 & 30

26

25-27

Reference

__

NA

NA

Venezuala

Puntouoron

not used

not used

Malta

coagulation

Coagulation

In-line

In-line

NA

not

not

not

used

used

used

used

not

in-line

coagulation

Flocculation

Components

Destabilization

used

West Indies -

used

used

Dislnfectlon

Jopon

British

Caymem Island

Grand

Rico

Pureto

Locat’on

Culebra

Plallt

System

Components

used

used

NA

not used

not used

not

not

Sedimentation

RO Plants(...continued)

System

Seawater

2. Pretreatment Commercial

Plant

for

lobls

filter

filter.

NA

Cartridge

filters

Dual media filters

Cartridge

Dual media filter+

+ cartridge

Dual media filter

Filtration

1

1 k 43

34

33

33

Reference

Pursto

purto

VelVd0

British

Island

Moron

West Indians

Grand Caymon

Rico

--___ Culebra

Juboil

Type

and

Location

of Pretrootment

Plant

PH Control

used

NA

Used

NA

Not

‘lot used

H2S04

NA

Acid

:I2

qot used

:I*

NA

Disinfectant

NA

Not

F&l3

F&l3

used

NA

Coagulonts

Chemicals

3. Chemicals

F&l3

Table

Aids

used

used

NA

Not used

Not

Not used

Not

used

used

used

used

NA

Not

Not

Not

Not

NA

Flocculants

(mg/l)

(continued....)

Pretreatment

----I

Coagulants

NA

Seawater

Components

Seawater

System

to Pretreat

Used for

Plant

Used

used

NA

Used

Not

H2S04

H2S04

NA

Antiscolants

NA

Not used

NaHS03

NoHS03

NA

Dschlorlnotlon

1

1 k 43

34

33

33

24

Reference!

I

24

eliminating

the use of cationic

_polyelectrolyte.

Cn*rvd *“*AL to cause the formation were

not removed

by pretreatment.

coagulation

of the seawater

in-line

After exactly now

of insoluble

the

600 hrs

as predicted

rarely

ernment

for

as its feed

is lccated m3iday

source

operation.

and

at Grand

(ref.

TX

system

2 and

3) which

followed

by dual

(Table

polymer,

antiscaiant.

after paper

problem

chemicals

expanded

was found

1,000 hours revealed was

were

achieved

Japan

by the gov-

w&s

Titer

and it contains

plant

operated

includes media

is not

and has a

seawater

I3iO hoLlow

filtration

used

mema hum-

with

in-line

a pre-

coagulation and organic

as the

to be performing

operation.

the presence

solved

when

eliminated excellent

The infra

feed

water

the polymic

with

humic

coagulant

acid to keep so that

the additional

in an unacceptabie

red analysis

of coagulated

performance,

to 750 m3 with

of the SD1

acid. However, and

antiscalant

pH to 6.5. Tae the

third

site

has

RO skid (ref.

system

been

now

33).

RO Plant A 800 m3/day

since

were

H2S.

manner

has

The

Chlorination

The RO system

the

rejection

Indies

It uses

is 37,CCO mg/l

treatment

filter

salt

British

33).

is based on DuPont

of 40.2 mgil.

contains

for

The SD1 of the feed water

Cayman,

concentration

polyacrylic

and

has been accepted

ic acid

cationic

t&i

feed.


branes. Tlae feed seawater

using

acid complexes

FeC13 was adopted

productivity

normal

was

Rico.

This piant of 300

h~mic

Therefore,

exceeds 3.0 and the system

of Puerto

capacity

period,

The used polymer

RO seawater

1979 at Chigasaki

PEC 1,000, and hollow

(ref. fiber

desalination

plant

has been running

34 and 40) using

spiral-wound

modules,

modules,

Pretreatments

used are

hollosep.

25

in-line

coagulation

’ the ?11

pretreatment

adjusting

agent,

followed prccess

is used to reduce

reduce

dissolved

time

are

the

oxygen.

1981 indicated

tion

media

EC13

amount

The results

that

there

(MF)

value

of

organism

growth

from

April

value

the

of

dual

pretreated

raw

of

through

with

MF of seawater.

The highest

was

obtained

m

spry

as $1

Febru-

in the membrane

filtra-

June. found

?I value when

operation

the

season

The

fouling

to

vary

value

of

of

micro-

:mdex @I)

in

3f pretreated

MT

to

till

during

was

E2SC4

used

NaHSG3 dosage in order

of the plant

water

Chemical

For PEC 1,COO a dearation

was an increase

seawater

mainly

filtration.

as ccag~lant,

and NaGCL as disinfec*mnt.

tower

ary

by

correlation water

ra7v

> 1.0

seawater

became high. An attempt centration found

was made to lower

for the long term

was

started

DuPont water ter

RG plant up

BlO with

term

of this plant.

Gllar

Lapsi

with

1982

and

December The

TDS of less than

coarse filtration

(Table

performance

permeators.

containing

ing,

at

in

followed

38,900

mg/l

of increasmg

ccn-

information

was

piant

TDS.

based

is

5CO mg/l

capacity

of

on

designed for raw

by

cartridge

to

performance

no further

to

remove

information

of this plant

fiber,

prcduce

potable

Mediterranean

seawa-

It’s pretreatment

filters

20,CO m3/day

hollow-fine

system

by the use of 18 weUs, acid injection

2 and 3). However, operational

by means

Gef. 40). Howevzr, no further

of coagulant

Tie

FI value

consists

to prevent

particulate was

(ref. 41).

found

of

scal-

materials on long

26

DISWSSION Pretreatment of the surface seawater feed for RO application is a very important step acknowledged by both users and manufacturer. Inspite of the great effort still

not

fully

manufacturers

by the OSW the pretreatment process is

developed and established. Although accept the fact

RO membranes

that the pretreatment plays

important role in the success of this process, none

a very

gave enough atten-

tion to conduct research and development (R&D) work to improve and The Available citation clearly indi-

develop this part of technology. cate the need for

further

R&D work

in this area. However,

the

reviewed citation high lighted some of the drawback of adopted conventional pretreatment components. tlhttd

of

Actbit-1

Bidow

The degree of biological activity present in the feed seawater to RO usually determine the extent of the pretreatment process required for biological control. The concentration and types of micro-organism usually

depend

on the source of the seawater. Infact, water from

deep wells has low

level of biological activity and does not require

pretreatment. In addition, deep surface seawater usually has less activity than shallow shoreline. The biological activity varies from one site to another and also at single site from season to season since seawater temperature significantly growth

and

reproduction

affect

the type of micro-organism and the

rate (ref.

42).

The

most

cost effective

means of disinfection is by chlorination either continuous or intermittant. Other means of disinfection such as W,

ozon, other halogen, and

CuSO4 are also available depending on the membrane type and on the type of pollution in the seawater. The summary of the currently used pretreatment systems and chemicals in ten commercial RO plants shown in Table 2 and 4 indicates that 80 percent of the commercial RO plants use disinfectant either for the feed water or as intermittent shock treatment. Chlorina-

27

tion

to 0.5 - 1.0 mg/l

residual

plants

located

Japan

and

Culebra

Puerto

Abu

Jarjour)

and

seawater

contains

(Ras

since their NaHS03

at Kuwait,

RO plant

the algacide fectant

Saudi

the

plant

NaHS03

Removal of lion and

Kuwait,

is not

used

at

Bahrain

(Grand

Cayman

Island)

of 1 mg/l.

used to react

in Table

by

at Bahrain

uses

Jadda (Saudi

Furthermore, from

with

no disin-

deep wells

is used

RO

1.0 mg/l

membranes

towards

with

residual

chlorine

after

residual

chlorine

requires

2 1.5

Arabia,

3. No other

Japan

and

chlorine

Puerto

scavanger

Rico

use

was cited.

by Coa~n,

parkdutes

own.

organism).

can cause mechanical

caught

type

for pretreatment of

the

in the

particles

The coagulation,

carried

removal

usually

being

The colloidal

by their

membrane

do not usually

flocculation

Ftocudu-

achieved

(quartz,

fouling

or on its

coagulate

or settle

in order

clay

processes

are

to accelerate

minerals,

by the addition

in RO

fibers

and settling

of the seawater

particulates

This is usually

and

micro-

of chemical

coagu-

and flocculants. Table

for

Kafji),

but is being treated

commercial

Saudi

matter

units

surface.

lants

the

Settling

membrane

the

of

Ra’s Al

for disinfection.

seawater

of

solid and cdlddal

Particulate

usually

and

the plant

since seawater

process. Nearly

as shown

60 percent

(ref. 41).

is being

NaHS03

Indies

H2S. However,

sensitivity

NaHS03

the filtration mg/l

West

uses deep surface

as feed to the RO system

to

(Al-Birk

Rico. Chlorination

CuSO4 at dosage level

Due

used by

shock treatment

is used at Malta

chlorine

Arabia

British

as intermittent

Arabia)

is being

2 and

particulate

60 percent

3 show

removal

of these

located

at Kuwait

Japan,

Culebra

the

currently

in commercial

plants

which

Rico, and

pretreatment

RO plants.

use ferric

(DROP), Saudi Arabia

Puerto

used

British

West

As can be seen, the

(Fe+3)

(Urn Luji

methods

as coagulant

are

and Ras Al Kafji),

Indies

(Grand

Cayman

28

Island). The used concentration of iron as Fe+3 is usually 3ppm PeC3) rl0V-J ,,,,ading

low

(2

on the type of feed water. Kuwait and X-

Birk Plant (Saudi Arabia) use polyelectrolytes

in their pretreatment

process. This is being used as a coagulant aid in Kuwait while it !s used as coagulant in Al-Birk

plant.

As can be seen from Table 3,

the RO plants at Bahrain (Ra’s Abu Jarjour), Saudi Arabia (Jadda) and Maita do not use any pretreatment chemicals since the source of their feed water is from the underground deep wells.

The components of the pretreatment prccess used tc yemove ticniate in each slant is shown in Tabiz V. ? _is can be seam “Y any piants ‘use the conventionai prccess (DROP, Al-&k,

method of

and

Plant. Grand

Kuwait

three

coaguiation and ilccculatxa

and Urn Luji). Seciimentaticn -,vhich h asuaZy

Iused after coagulation and flocculation Kafj

par-

is being used omy at Ras’ _i-:

Tne pretreatment process at Japan, Cu!ebra Puerto Eco Cayman

Island utilize

in-line

coagulation

oniy,

uses this as a secondary pretreatment process for

while

their RO

line 2.

Tine result of reviewing

different

case reports of piiot plants

(ref. 13 - 23) and commercial RO plants (ref. 24 - 4) indicates that most of them utilize either in-line coagulation or conventional clarification as a destabilization means prior to the filtration step.

Sand and anthracite are the most commonly

used filter media

in conventional pretreatment method in order to remove soluble organits and the residual chlorine from the water. Filtration is usually carried out for the feed water to the RO plant after coagulation, flocculation and settling process.

29

Table 2, shows the kind of filtration system used in commercial RO plants. It is clear from Table 2, dual media filters are the most commonly used filters in Kuwait, Bahrain, Saudi Arabia, Japan, Puerto Rico and British West Indies. This type of filtration is usually followed by carbon filters and/or cartridge filter to further improve the quality of the feed water and/or to protect the RO membrane. Carbon filter prove, in the case of Kuwait (DROP) that this additional precaution is very successful in protecting the sensitive thin film composite (polyamide RO membrane) from chlorine attack. Only cartridge filters are being used in Malta, assuming that the feed water has less solid suspended particles and colloids after being filtered through the deep wells.

Deposition of inorganic salts on RO membranes surfaces retards the rate of water permeation as the result of membrane fouling damage.

and

The scaling tendency of any feed water usually depends on

the concentration of the inorganic salts in the feed and the plant percentage of recovery. Good operation of the RO plant balances between the concentration of salts in the feed and the amount of water recovery. This balance can be altered where the recovery can be increased while

scale potential is reduced. Scale control is applied to achieve

this objective by reducing

the concentration of potential sealant (addi-

tion of acid to control carbonate scale) or addition of threshold antiscalant chemicals &IMP

and other polymers) to keep the potential sca-

lant in solution.

The commonly

used and cost effective

antiscalant additives to

control carbonate and sulfate scale problems are H2SO4 and SHMP, respectively. tion. However,

Polyelectrolyte antiscalant is also used for RO applicatheir application for seawater RO still needs further

investigation since it has been reported to act as nutrient for microorganism in seawater (ref. 20 - 21).

30

As can be seen in Table 3, nearly all commercial RO p1ant.s use H2SO4 and/or SHMP as scale control additives.

WNCWSION The review shows clearly that the extent of pretreatment has a direct effect on the performance of RO membranes. As it was clearly demonstrated, the better the quality of the feed, the less problems and steady flux and salt rekction were encountered. Also, it is clear that conventional pretreatment varies from one place to another depending on the understanding of

the contractor and the end users of

the

intended plant.

Conventional pretreatment still has unsolved problems related to certain time of the year. During these periods conventional ment methods are ineffective

pretreat-

and consequently the plant has to be

shut down or otherwise the membrane will be fouled.

In conclusion, conventional pretreatment process is a very effective mean to treat surface seawater and render it suitable for application during most of the year. However, further work required to identify

the most effective

RO

is still

chemical, and their optimum

dosages at lowest cost. Further more, different

methods and processes

are still required to provide suitable seawater feed for RO system at all times.

The pretreatment processes, till today, is not well identified and each RO process contractor tries to minimize his capital charge by reducing component for his system if end users allow him to do that.

31

Most trouble

was

the feed and high operation

before

backwash putting

membrane

improvement RG requires

quality

the

of the

time.

steps

in membrane

by sufficient will

i.e. enough, major fcr

Yrequently,

zeal-

fouling.

infiltration

definitely foulants

criteria

seawater

of

for

result to foul potential

desalination

by

Gualifieti

of the prccess

including

ident%cadon

of the

characteristic.

Clear and simpie and

operating

experienced

manuai. operators

the efficiency

of the adopted

in the system

if any.

is

funded

ences to identify as alternative

results

disinfection

:

feed water

Research

feed

Therefore,

pretreatment

Clean understanding

Work

often

of fculm-t&

if it is not followed

with of

system

of complete

the bed back into operation

in an unacceptable the

due to lack

degree of ehm&ticn

of the filtration

For example, time

faced

under

process

by Kuwait the

chemicals

system

at

best pretreatment applied

and idem?? ” 3::

Kuwait

Foundation

322 _; mprove

abie to mcciify

for

Institute the

chemicais

to process adopted

deficiencies

for

Advancement which

Scientific of Sci-

can be used

by DRGP.

32

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