Membrane distillation for radioactive waste treatment

Membrane distillation for radioactive wate treatment At the Institute method

of Nuclear

and Technology,

for low level liquid radioactive

distillation

has been developed.

advantageous,

Warsaw (INCT),

waste treatment

The researchers

of the apparatus

factors,

Chemical

but also due

solution

of’ rhis

radionuclides

finely

Radionuclides

liquid

radioactive

wasrrs.

artracrivc

in

decontamination

Traditional methods of low and intermediate level radioactive liquid waste treatment

Ion exchange Ion exchange proces\e\

industry.

nuclear

research

from orher (Isers of radioacrive medical

cenrres,

in other

scienrik

wide

range

liquid

from rhe and

such as

rhat

a

of liquid

Since the volume proceAses from

is generally

separare

the

non-radioacrive

radioactiviry

as

and

decontamination radioisoropes

J permeate

Tl

T>

asphalt

are employed radionuclides

‘I‘he

elimination

process

sewage

or

warer on

regenerated purificarion

precipirarion,

standards

water of

can methods

is

employed.

-I‘hc

(narurally

use

exchangers

of

ulrlafil~rx~on

01

small

materials

in

proved

a

ihs pr
is an c\rahlished

method

in

industry

for to

which he

including ion

rrcarmenr

of

provides

good

chosen

of

for communal

he accomplished

sedimentation,

on with

feldspars,

decotl[,lnllll.trioII

evaporation

wafer to the levels

purpose

sorthents

vcI-y effective

concentrarion.

processes

rhe concenrrarion

urilised

Iresins based formaldehyde

wirh

of

in glass,

and mulristagc

the

of

In ion

conjunction

of

reduction

and rhen fossilisation

ro reduce

To

:and rhc treatment

clays, /eoliles,

of inorganic ion

from

reprocessing.

phenol

J

6.~~1

operations

or Inorganic

are

in

of llranium

mining

fuel

material\:

synthetic)

other

the nuclear

cxrhanI;e

.lnd

Evaporarion

for suhsequenr

disposal.

by sanitary

number

Membrane Technology No. 103

concentrate

in regenerated

permirred

‘rhe

wasre and/or

includes

methods

depending Tl >T2 hydrophobic porous membrane

substances

or concrete.

Different

horn

from

groups

low

to

Evaporation

low the treatment

radioactive

from the waste, volume

of rhe concentrate

is economically

waste is quire large

inro small voIumcs

conditioning

acrivc

or

exchange,

I-clarively

extraction

organic

polysryrenc

amounts

conrain

dnd even derergcnrs.

well as radioisotopes. and the acriviry

exchange,

streams

.HL’ employed

of acrinideb

arlsing

occurring

users produce

wastes

emulsions.

wasres

and developmcnr

fields. l‘hese

initial

rhe separation

cenlres

(ion

of smges throughout from

hy onro

C. g. evaporation.

leach I’lquors coming

marerials

and research

of

parricularcs,

cycle,

waste

f.1cror.s compared

method,,

number

die il(lc

achieves

trearmenr

ICadioacrive liquid waste’s are generated

sed

hut

ionic form.

nuclear

i

in the

solurion sorprion

crc,) ‘l‘he process

in

rnainly

remove materidl.

from

d carrier,

present onto

chcmisorption, low-level

is m solid

lemtrvrd

wirh

particulares sorprion rhar arc present

ground

are

co-precipitarion

of radionuclides

process

from liquid waste by the use of an

inaoluhle

can have,

treatment.

scpararion

mcmbranc

.lIlJ

precipitation

‘Ike object&c

In this article Dr Grazyna Zakrzewskadistillation

cvap,r,trl,,n

permeation.

say this novel process is

discusses the benefits membrane

when applied to radioactive

rhermal

and its ability to utilise waste heat from

sources such as nuclear reactors.

Trznadel from INCT

a new

based on membrane

not only because of high decontamination

to the simplicity power

Chemistry

the

liquid

radioacrivc

deconraminarion~ Ikspirc

is at

when

high

(>I()‘)

discharge

is necessary

discharge

requirements.

Although

or when

conventional

costs,

invariably factors

arc

very low radioactivity

may he considered

rhat

chemical

in rhe treatment

high

in order to mcer regularory

evaporarion

operation,

and

with optracing

almoqr

deconrarnination

required

simple

high

present

for the

waste

is \utcesbtully mdustries.

of radioactive

a very used

in

its application

waste may give rise

to various

problems

such corrosion,

scaling

and

used.

foaming.

Corrosion

is a !;cvere

problem

in

by a

evaporators,

chemical exchange,

temperarure addition,

mainly of scaling

rhe

because of the relatively high heat

is caused

tl-ansfer

surface.

In

by the t&rmation

ot A W

the

overriding

factors

considerations. costs

of

streams

In short,

the

plant

are

capital

cleaning

improvement

cost has led to new and

specific for liquid

on methods

treatment.

considered

Membrane

For the selection the

secondly

the

a very

process

purity

method

describe

purification

process:

The volume

effluent the

the

ought

volume of the

rhe bulk of the radioacriviry

total activity in feed

_ a/v/ a,v,

a, are the specific

ur and

are the volumes

and

on

the

inner

surface

reducing

the heat transfer

it

expensive

making

Evaporation

more

may also enhance

of

the

There

efficiency

processes

operate.

radioactive

to

are

many

used

advantages

for

waste

the

of

membrane

concentration

(radwaste),

these

specific of

reasons

include:

corrosion.

respectively,

of feed and effluent.

Membrane

processes processes

established

methods,

can

Generally,

clean-up

of laundry

plants,

mixed

clean-up

wastes

laboratory

industry.

working

successfully

For example,

a mixed

processing

plant

Laboratory

of the Atomic

The

consists

plant

wound

tubular

is operated

the

Enhanced

Power Plant, cleaning

is also used in two stages

at

system

Removal

The contaminated polysulphone

volume

plant

volume

reduction

achieved.

decontamination (about

200)

problems

is one factor,

economically it is often used Other

processes

either

as bed

or the high costs of resin in

the case of ion exchange.

In addition,

intermediate

in

products

possible

biotechnological

processes

are a problem,

secondary

wastes,

accompanies

most other separation

can be very easily combined

with

Extensive

and the formation sludge,

feasibility

operations

etc.,

studies

have showed

processes

including

biotechnological,

or electroflotation

extraction

are

also

processes currently

and

under

as membrane

of

which

processes

membrane

can

have to be treated.

have

been

A variety particular

of factors purification

affect method,

the

choice

of any

but most notably

It

higher

seems

disadvantages

the

that

energy

that

all

production

operate

high-pressure

such regular

and

that

pressure

high

processes, requires

wastes

associated

and

which

operations

and

plant in the

secondary

45

Advantages of membrane distillation over other membrane techniques

pilot

cleaning

installations

examination.

and

some limitations

fouling,

involve

floe and

not

shortcomings,

pressure

used to separate

has been

many

complex

pilot

Good

also

give

of 10 -

is

waste treatment.

that

is treated

in the range

it

use of pressure-driven Other

electrochemical

acid

UK site an ultrafiltration

plant

easy to link in series,

at

100. At the Harwell liquid.

conditions,

other methods

solvent

of

operating

factor

with other processes,

for radioactive

are

(Table 1). A characteristic

though

competitive

that

disadvantages.

cause trouble.

boric

solution factor

factors

by other

have

Simple apparatus,

is used for

membranes

reduction

decontamination

Plant

at the Paks Nuclear

contaminated

solutions.

are several

Low energy consumption,

Processes

system.

an ultrafiltration

and recycling

that obtained

Ltd. a

by using a

River

of Canada

a

Actinide

those

methods, Moderate

and

UK. In Hungary,

factors

than

waste

units,

osmosis

reduction greater

those

many

is a high decontamination

even

blockage

in the nuclear aqueous

of microfiltration

reverse osmosis

Sellafield,

In

times

of membrane

at the Chalk

Energy

reverse

Ultrafiltration

for the

even

have

a low decontamination

of evaporation and

Volume

power

and

for recycling.

applications

factors,

to the

in nuclear

are many

technology

applied

wastes,

of boric acid solutions

fact, there

spiral

High decontamination

have been

T h e same of DFs for

radionuclides.

All treatment

of these disadvantages Membrane

activities

and z, and v<,

can be used for calculation

expression

residues

(OF) defined as

factor

total activity in efjuent

deposits

before

containing

Where

rhe

(VRF), which

factor waste

volume

of feed and effluent,

Two of

to

Decontamination

be and

to be of

treatment

DF=

solid

to

volume,

performance

of the

two First

safe discharge.

reduction

ratio

have

small

to allow

parameters

is the

evaporator,

can be

into account.

compounds to

sufficient

Table 2. Comparison of membrane distillation and reverse osmosis processes

and

radioactive

of a purification

radioactive

l

research

distillation

have to be taken

concentrated

l

the at low

as a one such new method.

assumptions

processes

radioactive

Subsequently,

development waste

Table 1. Different treatment

the

have to be minimised.

need for deconraminarion

economical

and operational

at increased

pumps

and

be

run

the

above

can be avoided

decontamination

under and

the

requirement. mentioned

by the use of MD.

This process does not require high pressures, can

of Also,

moderate

conditions

temperature. factors

were

expected

and of High with

Membrane Technology No. 103

Table 3. Preliminary cost evaluation of membrane distillation in comparison with reverse osmosis (in German DM)

,\~l)

IOI non-vola~ilc

lnostlv

low

.~nd

radioactive \hown

solutions.

which

intermediate

wastes.

I’ilot

level

tests

at

,111hll)

plani

other methods

liquid

INCYI

such high decontamination

energy sources, the process can compete

form

factor\

whcl-c only one filtration

proccsves:

of

whtch

I<0

introdllccd illu\trared

two

h.15

to rhc nuclear

.~nti Ml 1 whtch

advantage

stage is

in~lustry, stage

IS shown

capital

cost\

of membrane

is

module

110 units ofthc I&oratory

distillati~~n

i> generally

experiments

showed

effluents

f.~ctor~ could

only bc c)bt.lined

similar

cnerb7

comumptton .md

the

be

than

inlprovcments.

and careful

plant

design

heat of condensation

Hut.

with

it is possible to minimise

economic

‘l‘he study plant

INCT

reactor

makes

of the MD

experiments

process,

discharged

stainless

and minimising

all radioisotopes

or

factor

is

stream Such

not

are

that can in

utilised

processes.

many accurate

to recover heat

MD

more

beneficial.

The

reached

two

a

of

MI1

of the following

.

‘The capability

the process

concentrations

of waste of

the

to produce required

radwaste

high

for

the

in concrete

Membrane

l

concentration

of liquid

can bc applied

Achieving

this high concentration

in a one-

l

Elimination

of high

reverse osmosis

pressures

and expensive

required

by

high-pressure

pumps Because of such advantages moderate apparatus,

process

.md the possibility

Membrane Technology No. 103

simple

of using cheap

radioactive

the

as tritium.

need

that

home

are often

waste:S. purification

of

Waste in one stage and does

additional puritv

prcccsses

of water

to

ensure

discharged

to

the

Barriers to the commercialisation of membrane distillation ‘rhc

main

barriers

implementation

unit

area,

along

energy consumption

the case of nuclear power

commercial distillation

low fluxes which are ohtained

membrane

thermal

to

of membrane

stations

there

heat, so the nuclear

with

are from high

in the process, ‘l‘he

by efficient sources

research

heat recovery

or waste heat. In centres

or nuclear

ate rich sources industry

of waste

:seems I-Obe one of

the better areaS for MI) implementation.

as high retention,

conditions,

at

‘aso decreases

the complete

or by use of low-energv

wastes. .

in radioactive

latter can be overcome

to the

low level radioactive

temperatures

steel. even at Operation

environment.

the

have led researcht%rs at

distillation

of srainless

\uch

two

temperature

concentrations.

of nuclide\

the generally

(25% of solute)

stage process .

acid

drops

separates

of iodines and ruthenium

liquid

using

points:

by

conclusions:

the corrosion

nitric

such as

and

operational

MD also allows

high

processes:

advantage

over RO is the consequence

and a very followed

(membl-ant

inhibits

volatility

foaming

MD and RO show that in some case5 MD can bc

fossilisation

process

the

of

problems

evaporation

or

Lower

forms

z~vo~d:; various

scaling

streams).

present

other a

losses. svstem

MI1

entrainment

not between

of the

sorption

minimisation

with convcnrlonal

sufftctent

proposition.

to the fJlowing

enable the

evaporation.

15 higher

This IIX of waste heat from the cooling of the nuclear

inherent

from J 2.3 stage

demands

the

high

from the distillate

retention

decontamination

in Ml>

and

and

waste cenerntion.

In addition,

(e.g.

reactors)

of expensive

corrosion

technological

that in the case

process

~,perati~,nal

pilot

instead

(Iomparison

111 RO

.tttractivc

uye of plastics

removed

Ii0 plam. ‘fh~

process conditions

cycles because

for low heat

system of nuclear

The moderate

In a one-stage

are

the, price

higher

fouling

low evaporation

same cffectivc area. Additionally,

of radioactive

than

waste

total costs of installation

of the

even though

of

secondary

the

in 1’:thlc 3. It can 1,~ seen

Iowcr (for one unit plant), of .I rtm-‘Ml)

distillation

utilising

steel, eliminating evaluation

washing

corrosion,

in I:tblc J..

two methods

indicated

.i Iready

been

technolog

economic

has

of membrane plants

from the cooling

membrane

I\ still .u rhe testing

‘I’ll? prelimlnal-y that

analysis

Economic capacity

compuison

133s frequent elimination phenomena

have using

acquired. A general

.

with

used for LI.LW treatment.

l

Avoidance l”7Cs’,

of sorption

‘j4Cs+

of such ions as j°Co2*,

inside the membrane

pores

Another consumption

possible

way

is to use the

to spiral

minimise

energy

wound

module

0

increase

of

permeate

energy

consumption

warm

streams

tlux,

but

the

for additional makes

rise

of

heating

of

operation

the

uneconomic. Experiments process

showed

conditions

temperatures range This

the

optimum

higher

inlet

feed

energy

consumption

per

unit

of

is lower than that at lower temperatures.

illustrates

the importance

the unit. This design

wdistillatg

at

(70 - 80 ‘C). In this temperature

the

product

that

are

re-use

of the design

should

a significant

of

aim to recover and

amount

of conducted

heat

and latent heat of condensation. For this study, tests were performed

L

active solutions or original activity

with

integrated

heat

the GORE-TEX

now

under

integrated

energy is equal -600

interest

present. along

temperature

polarisation the

distillation A study showed

that

economically In some

nuclear

pilot

do not

of

purification

by other

It is also possible

MD

cycle methods

clean-up

processes.

One

final cleaning condensate

pass to the distillate opportunity

to

with

factor of the evaporator a hydrophobic,

comprised

the

an

with PTFE

in Japan

and was used for cleaning

At present implementation

of

which is also a barrier some new applications cost of commercial lack of commercially

0

membranes

through

modules. available

and the required

that

the heat filters

module.

The

from

through

the heater

the

the heat

and then through

Both

streams

(tetentate)

-

permeate

to

stream to

is obtained.

for speedy

(7).

cooled

temperature

down

was

Under

these

on

is the high is a

The at

highest higher

rates

distillate in

water

the

to

the

temperatures flow

radioactive

compounds

retentate.

in

Retention

retentate

was

of

complete

$=I).

Concluding remarks Membrane

processes

alternative

for nuclear

they can provide relatively

low

volume

energy

competitive membrane

combined

with

can

separation

or replace

existing

be

In easily

processes ‘Ihey

can

and also

techniques

such

extraction.

ion

etc. distillation

concentration

radioactive

justifiable

solutions

therefore

for liquid is extremely

can

treated be

replacement

for

combination

of MD with

with

of

lower

methods.

additives.

adsorption,

high

costs much

methods

other

It is economically and

and

often

require

distillation,

effluent

are

as

factors,

operating

separation

addition,

supplement

operations

consumption The

separations

do not

to be an attractive

clean-up

high decontamination

reductions.

membrane

seem

RO units with

the

reverse operated

when

radioactive interesting. volumes

of

ate not too large,

considered osmosis.

a good Finally,

evaporation

the

or even

in the nanofilttation

subsequent

lower

prove to be a very advantageous

pressures, option.

stream For further information please contact:

were obtained and resulted

the

coefficient

could

high

flow rates. The increase rate

of

in

(retention

dm’/hr.

permeate

volumes

was

ions

range,

1500

During and

radioactive

feed and

(180 - 300 dmj/m2day).

permeate

and tetentate

cooling

inlet, with

of up

conditions

inlet

in

of 45 - 80 IJC at feed inlet,

and 5 - 20 CC at distillate flow

is

process

conducted

in experiments

solutions.

the

Membrane

due

distillate the

range

the

temperature

(8).

factor.

were obtained

radioactivity

exchange,

to

was 30 - 50 dm3/hr

distillation,

The

the retention

on the level of natural

through

in the heat exchanger process

distillate

(BWR).

did and

results

after

of distillate

as

of waste heat is possible

exchanger

The

a

The outlet

at the

activity

coefficients

is lower than that of the cold

and recovery

heat

are set in such a

transport

pS/cm

flow rate significantly

permeate

place

than

cold

are returned

heat-transfer

of the warm stream

is an

In fact, there

PTFE

filters.

appropriate

membrane

This which

MD units because

the reservoir

is circulated

200

in concentration

concentration

took

The conducrivity

from

and

for pte-

through

The flow rates in the module

liquid wastes

of the process,

from

the

ions

all of them

40 hr. An increase

experiment

they

is the

working

the stream)

and warm

way

additionally

membrane

(9,lO);

with ceramic

pumping

other

temperature

for researchers

filters

(6);

X-6150

the membrane.

radioactive

stable

the reservoirs.

stages

with

barrier

(JAD

and is pte-treated

contacting

In fact, a new

reactor

(I), equipped

(sodium that

to a 10 pS/cm

with the

(3); PRI 505M

Ebara pump,

exchanger,

and

installation

Omegu supplier

(7.8);

is pumped

the pre-treatment

was developed

water

an additional

distillate

by

There

at a

salts

showed

of experiment

Similar

(V = 80 dm3) (2); a

heat

and ceramic

reservoir

factors

evaporator

demister

from a boiling

6/50)

for

decontamination

membrane. of

JAD

(4,5);

exchangers

(warm

by using a demisrer

porous

Ebara pumps

traditionally

droplets.

improve

inorganic

chloride)

decreased

not affect

of effective surface area

(V = 80 dmj)

reservoir

centre,

module

retentate heat

approx.

of specific

Bq/dmj.

in the retentate.

of distillate

low-level

The

reservoir

before

radionuclides,

m’/ht.

(4 m2); a distillate

two

were retained beginning

at the

clean

a nuclear

with a PTFE membrane

tetentate

after evaporation.

contains

from

of spiral-wound

most

several

contact

and Technology

can

-0.05

The

such possibility

of distillate often

consists

shown of

(distillate)

and

Chemistry

wastes

exchangers

any additional

that

with

potassium

did not change

plant

radioactive used

direct

2).

Cold

methods.

many

nitrate,

with non-

salts and simulated

waste samples

to 4.7.104

Experiments

for

was constructed

of Nuclear

by the PRI 505M

waste,

to use MD in specific

purification

designed

employing

distillation

radioactive

units.

decontamination

combines

modules

treatment.

produce

of

justified.

is plants

separation

for liquid

seems

is high

tests and

distillation

in a single unit without

generated

will

experiments

volumes

of MD

purpose

with

that

advantage

obtained

system

of

membrane

plant

numerous

treatment

plant

throughput

control

for low capacity

centres

large

important

a

by the

operational

of

membrane

implementation

of

The

the careful

favourable

extremely

this

(Figure

coupled

after

that do not involve

wastes

of MD

phenomena

of literature

at INCT

pilot

Institute

in the future.

analysis

A

one of the reasons

productivity

use

operations.

Results of pilot plant tests

the

sticking

in MD shown

with

researchers

membrane

However,

developments increase

recovery

implementation

This is probably

for only moderate

as

while for

are a crucial

point as far as industrial

at

is estimated

heat

most

microfiltration

radioactive

2.10’

did not pass through

kWhl,,/m3.

low fluxes

is concerned.

are

energy

per I rnj of distillate,

without

As stated,

is based on modules

Thermal

in such a module

150 - 280 kWh,,

industry

that

These

development.

consumption modules

recovery,

principle.

of inorganic

in

the

Dr Grazyna Zakrzewska-Trznadel,

Institute of Nuclear

Chemistry and Technology, Dorodna 16, 03-195 Warsaw, Poland. Tel: +48 22 811 09 16; fax: +48 22 811 15 32. E-mail: [email protected]

Membrane Technology No. 103