Defouling on demand — a new strategy for potable water production

Defoding on demand a new strategy for potable wafer production New approaches

to the application

water are constantly impact of fouling researchers

for the production

application

on the economic

viability of membrane

enzymes for defouling

of dynamic

immobilised

layer fdtration

on demand.

processes.

University

Now,

of

immobilised

immobilised

“activatable”

“activatable”

refers during

activated. factor

explains.

or

the drive towards of

enzymes

membranes due

to

has the

conditions

for

greener the

found

cechnoiogy,

cleaning

of

widespread

efficiency

and

application

mild

of these bioiogic‘al catalysts.

the cost of enzymes

the

fouled

that the fouling

layer is degraded

of attachment,

obviating

on demand.

whole

layer. The disadvantage

foulanr

However,

means such processes

to this problem

onto the active filtration

membrane,

so they

periods.

The added

be used

advantage

depicted

of using

in Fig.

term

are

not

operation

of the

are dormant

until

occurs when a chemical 1s Introduced For example

to

when

the ultrafiltration baxd

on

as follows

and

cothe

fouling process.

this

technology

is schematically

1

lmmobilisation of the inactive enzyme

‘the fouling

layer is degradedfiom the point of attachment”

are not

these

layer of the

IMMOBILISED

INACTIVE

IMMOBILISED

LAYER

the

retained

: PROCESS

ENZYMES

2. FOULANT

immobilised

degrade

for extended

of such a system is

I. ENZYMES

very

enzymes

is that

macromolecules

that

The enzyme

may are

by filtration.

3. INDUCER

ADDED

: ENZYMES

CATALYSE

is a manganese

by

white

the

1: ‘; -

: FLUX

MEMBRANE

DECLINES

ACTWE

CHEMICAL

LAYER

ACTIVATOR

DEGRADATION

OF FOULANT

LA YER : FLLX

DEVELOPS

SOLUTION

ENZYME

4. ENZYMES

chosen for application

treatment

BEGINS

-

DEVELOPS

they

I FOULANT

ADDED

ACTIVATED

RESTORED

DISRUPTION

OF FOULANT

LAYER

Membrane Technology No. 102

process

proceed

The

that

is to immobilise

the enzymes

can

would

the

use of

operating

yet cost effective. A solution

affxting

water

rhe

enzymes. enzymes

They

to the

cleaning

during involves

the normal

process.

A typical

from the point

the need to digest

to

co-substrate

is adversely

use

system

Activation

at Rhodes

for

membranes

ultrafiltration

when fouling occurs.

enzymes

This

functional

in the presence of

scientists

a new approach

purification.

enzyme With

this problem,

have developed

ultrafiltration

to this problem

with the use of

only functioning

that can be added to the feed solution

Leukes of Rhodes

use

process for river water clarification.

the enzymes remain dormant,

a co-substrate

To combat University

This process involves the

in conjunction

enzymes in an ultrafiltration

Interestingly,

of potable

This is especially true with regard to the

in South Africa may have come up with a solution

using “activatable”

Winston

of membranes

being sought.

rot

to river water

peroxidase filamentous

produced fungus,

/%itnerochn~t~chrysosporirrnr. I-his enzyme chosen

because

polyphenolic

tannins

to the fouling

in ultrafiltration

requires

Without

rhese

research

carried

found

this

for

out

African

enzyme

can

immobilisation

he

However,

could

and

activity.

is inactive.

in steady

batch

ultrafiltration

after

enzyme

So far,

and significant

major

component

river warer ultrafiltration.

acids,

of

African

context.

colour in upland

The water purification

the Southern

UF membrane

substances

originate

vegetation

such

problem

or cross-flow retains

make

microbes humic

filtration

substances

aromatic

forms

over the layer of immobilised

enzymes,

aiding

the filtration

and

macromolecules A cake layer

entrapment the

increases

by adsorption

molecules.

resistance

to

decline,

process

of smaller

hydraulic

(mostly

an

of

extent

resulting

where

cake

layer

it causes

in unacceptably

flux

Activation of the defouling enzymes (Defouling on demand) a state

of low be

trans-membrane activated

enzymes

can

demand)

by addition

containing

the

achieved

by addition

as

amount

Only

of this

restoration

was shown

to the catalytic ‘The

solution

flux

transformation

occurs

of the tannins

and

returns

and

of other

and

the

for

foulanr

rhe

has several ccrrain

act on the upstream

layer is obviated. efficiency

Also, enzymes

chemical

cleaning

washing

is required

methods,

filtration

and chemical

system

could

required

occasionally

cell. Flat sheet membranes

minimisation

of backflushing

the product

wafer is needed

0

with a

were used. that

the defouling

and that an approximately

to

layer.

action

permeate

is

20 %

adsorbent quality

1~0 systems,

rhereby

chemical

improving

rhe process.

cleaning that

for

srill be

productivity relevance

rcquiremcnts

the rhar of

arc much

applicarions

include

of

this

portable/compact of

potable

communities.

Ar

purification

water

number

South

Africa.

This

benefit

here because

energy

[requirement,

rhc rural

municipal

wareI available

ofsuch communities rechnology

would

of irs good arc

requiring

(no

~scrl)

a low

in

be

efficiency,

safeery

chemicals

operarion,

for small.

are not currently

to a significant

cleaning

to

present,

faciliries

rechnology

units

aggrcssivc

and

lcvrl

ot low

c.tse

of

of technical

proficiency. In addition,

wirh

rhe drive

rechnologies,

rhis “dcfouling

on demand”

suitable

dn

for

rowardb strategy

inct-easing

In hct,

in rhe tood industl-y.

be applied

to any form of filtration

on

rhe

fouling -

the

by

future on

die

of

fouling

01‘

applicarion arc

would

activatable

major

be

I[ c:,n

complexes

applicarions

provision

a

depend enzymes

componen’

in the system. major

limitations

through

to dlc .~pplication

are the cost

used. However,

production

already

organic

that

might

numbcl

apphcatlons where

greener

it ih anticipated

and

and

concurrent stabilisation

immobilisarion

in place to address

arability

of

of the.

programs

on

of rhc Mnl’ techniques

arc

this p~mblcm.

For Further information contact: Winston Leukes, Department of Biochemistry & Microbiology, Rhodes

for this procedure,

the inherent

to match

The

means that less of

This is of particular

Alrhough

is nor expected

the energy

Anticipated

enzyme

extended

in some applicarions.

prop&es.

Conclusion

enzyme

back-

it will

rhc hrlmic

l0wc.r using this approach.

The

Although

without

laycl

acids have

very good

problem

sufficient

less frequent

cleaning.

operate

ultrafiltration

the

from

quite easily. dynamic

by enzyme

and aa mentioned,

this technology

results

and toxic heavy mcrals

action.

Efficient

operation

of

small unwanted

since the cake layer is easily detached

occurring

ultrafiltration

showed

where

al-c

rctcnrion

this procesh

Clean, effective operation

and

Results

solution

as opposed

ro remove the foulant

it is anticipated

instantaneous

have a

Ease of operation fouling,

However.

wafer

wirh

on their

One only has m add a slug of acrivaror

and

can be encouraged

production

flushing

NMWCO

side of

rhe whole

and act rapidly

periods,

30,000

ic are

substrate.

rhis in

making ‘I‘hcsc

layer, the need to digest

backflushing proven

by

criteria.

batch

was

solure rejecrion strengths

of raw river water feed with batch stirred in a laboratory

concept

rhis than

applications.

removal

like pesticides

formation

effective

Pilot results ultrafiltration

.l‘hus, quality

enzyme

process can begin again.

This

impurities

rourincly

of brown

can find their way in Co rhe permeate

provision

Co the system to alleviate

at its

l&red off. Once

state

system

membranes

be RO

alone.

high catalytic

action,

the

through

can

pressure

due

(and certain

is exhausted,

to irs inactive

of flux

because

layer to be removed

metals

sorbents.

the foulant

the foulant

to

also make

warer of a higher

in

enzyme

srrongly

properties

Because the enzymes

allowing

solution

river

be

by

of attachment

m pollute

can

polymers)

poinr

and

Speed of action

organic

activator

the

as pcsticidcs

solution

(on

of the enzyme.

restoration

layer

bind

additional

cleaning membranes

IJnhkc several other IJF proceshcs,

of metal ions. ‘l‘his could

based on rhe following

to be instantaneous

efficiency

substances

the

(micromolar)

is required

or

produces

This

from the outside

a minuscule

In

unwanted

attractive

of a slug of this solution

the feed or by back flushing rhe membrane.

This

Capt.

other

rhe membrane

required

co-substrare.

and viruses.

a

such

heavy

uhrafiltrarion

microbes

the use of high

aggressive

Co damage

to rhe clarification

constitutes

in rhar ir could bind (:a’*. On the

without

costs.

rhereforc

Benefits of the dynamic layer filtration ar colour

be deleterious hand,

chemical would

their pl-opertics.

efficient

dynamic

found

and change

with soil and

humic

overall

since

making

~nvironmenraily

life expectancy

are known

applied

they

ion exchange

what can be achieved

flux,

of the activator

since

reducing

extended

Ar present,

humic

is in rhe range

for

rypically

water. Their

process

At

candidates

water

These

This

as Pr. The

aids

systems

productivity.

is

Colour

for potable

and Western

compounds

retained

low process

surface waters.

from conract

them strong adsorbents

Eventually

the

ro

as Fynbos.

mg/ml

phycoroxins,

and

in

Cape water colour

ideal

of humic

large

substances).

present

in the Southern

of 1000

in the South

consumption.

more

humic

give rise Co a yellow

requirement

for human

layer

cleaning

of- rhesc chemicals

into the envirc,nment, safer,

and

be

chemical

large quantities

process

als

ot water- arc to bc

frequent

The membrane

are

cake

substances

waters

quality

the

interest

Humic

soil and surface

Operation of the UF process can be operated

of

is of considerable

brown

The

improvemenrs

the

friendly

however,

during

supply

filtration.

is,

‘l’hc

by

by dead-end

thar

chemicals

a primary

either

in

immediately

This

formed

immobilised

here.

as required

of river water

acrivation.

unoptimised

has

also be used, but are not

process

state flux is atrained

expected.

University other methods

small batches Less

are nor released improvement

used

peroxide

at Rhodes

adsorption.

disclosed

means

significant

its catalytic

the enzyme

clarified.

which

of membranes

hydrogen

as co-factors

compararively

‘2efouZing action is instantaneous”

of this water.

‘This enzyme

physical

are

was

degrade

of some South

?‘hese

contriburors

or

such as tannins,

componenr

waters.

Mn(Il)

rransform

complexes,

are a major river

ir can

of when

University, Grahamstown 6140, South Africa. Tel: +27 461 318 262 441;Fax: +27 461 24377.

Membrane Technology No. 102