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Pilot investigation on the treatment of fertilizer manufacturing process effluent using lime and electrodialysis reversal
Desalination,70 (1988)407-429 Elsevier Science PublishersB.V.,Amsterdam-Printedin The Netherlands
407
PILOT INVESTIGATION ON THE TREATMENT OF FERTILIZER MANUFACTURING PROCESS EFFLUENT USING LIME AND ELECTRODIALYSIS REVERSAL J.J. SCHOEMAN, I.J.M. BUYS, I.B. SCHUTTE and H. MACLEOD DWT., CSIR, P.O.Box 395, Pretoria 0001, South Africa SUMMARY The treatment of a fertilizer company's effluent was evaluated using lime and electrodialysis reversal (EDR) for phosphate removal, water and chemical recovery, and effluent Phosphate could be reduced from 3 800 to less volume reduction. than 50 mg/l at pH 8.5 with lime: however, phosphate removal from the lime treated effluent using EDR was poor (75% removal). The EDR product water complied with the requirements for cooling tower make-up except for TDS and phosphates. However, the required specifications should be met using 10 stage EDR. In addition, plant nutrients
(NH4+ ,N03-) may be recovered
from
the brine, which comprised 20% of the initial effluent volume. A full scale EDR plant Membrane scaling was virtually absent. should run well with electrical adjustments and/or frequent acid cleaning. Electrical energy consumption for EDR treatment was found to be
4.5 kWh/m3 feed
(pumping costs excluded).
capital cost for a 30 ml/h EDR plant and clariflocculator removal) was estimated at US $750 000.
The (PO4
INTRODUCTION A fertilizer company in South Africa
produces
a wide
range of N:P:K fertilizers from phosphate rock, nitric acid, limestone
and
ammonium
nitrate.
The
resulting
manufacturing
process effluents comprise a concentrated waste process effluent (CWPE; 5 500 mS/m, 4m'/h) and a more dilute waste effluent (DWE; + 500 mS/m, 143/h) rich in plant nutrients (NO3-, NH4 ,PC,3-), which are disposed of in costly evaporation ponds, constituting an environmental pollution hazard. Electrodialysis
(ED), reverse
osmosis,
evaporation are desalination/concentration OOll-9164/88/$03.50
0 1988Elsevier Science Publishers B.V.
ion-exchange
and
processes potentially
suitable
for treatment of the DWE
(refs. l-2).
Of these, ED
appears most suitable when large volumes have to be treated, high brine
concentrations
(small volumes)
are
required,
and
waters
with membrane fouling characteristics are encountered. Numerous examples are given in the literature to demonstrate how ED can be used for desalination/concentration of model waters and industrial effluents (refs. 3-9). to
evaluate
the
treatability
It was therefore decided
of
electradialysis reversal (EDR) for water
the
effluents
using
(cooling tower make-up)
and chemical recovery, and effluent volume
reduction.
Preliminary batch ED tests conducted in the laboratory on
a
sample
of
the
CWPE
(7 000 mS/m)
effluent could be desalinated
showed
concentration
of 15 500 mS/m was
tests on a more dilute sample
the
in stages to less than 1 000
Effluent volume was reduced by 50%
mS/m.
that
and a maximum brine
obtained.
(ref. 10). Further
(3 100 mS/m) with other membranes
showed that the effluent could be desalinated to 200 mS/m.
The
effluent volume was reduced to 20% of its original volume in this case
and
obtained.
a maximum
brine
concentration
of
16
300
mS/m
was
No scale was detected on the membranes after the tests
despite very high concentrations of calcium (3 800 mg/l) and phosphate
(700 mg/l), sulphate
(25 000 mg/l) encountered in the feed
water. Phosphate and TDS, however, should be reduced to less than 5 and 230 mg/l to make the ED product water cooling tower make-up.
suitable for
Since phosphate concentrations in the DWE
as high as 3 000 mg/l were encountered, significant
phosphate
reduction was required. Preliminary tests with lime for phosphate removal showed that phosphate could be reduced from approximately 5 000 to
less than
20 mg/l
(ref. 11).
Lime
treatment
was
409
therefore considered for phosphate removal. The
objectives
following:
a)
of our
lime
treatment for water
investigation
treatment
were
to
for phosphate
evaluate
removal,
b)
(cooling tower make-up) and chemical
the EDR
(plant
nutrient) recovery and effluent volume reduction, c) the fouling potential of the effluent for the EDR membranes: and to determine process design criteria and costs for a full scale (30 m'/h) EDR plant.
This
paper
describes
some
of the
results
of
our
investigation (ref. 12). COOLING TOWER BAKE-UP WATER SPECIFICATIONS These specifications are shown in Table 1. TABLE 1 Required maximum specifications for cooling tower make-up Concentration
Constituent
(mg/l)
230 25 25 35 120 45 5 8,5
TDS Total hardness Calcium hardness Silica Sulphate Chloride Phosphate Iron
GENERAL PROCESS DESCRIPTION AND EDR TEST APPARATUS Dilute
waste
effluent
was
simulated
by
mixing
14
parts
flocculated raw water (FRW) with 4 parts CWPE in an 8 m' tanker. This water capacity)
was and
approximately
pumped lime
8.5.
into a stainless
was
added
until
Polyelectrolyte
steel the
was
clarifier
pH
then
was added
(2 m3
raised to
to
enhance
sludge settling. The clarified
sludge water
was
withdrawn
sand
filtered
after and
proper
settling
collected
in
a
and 4
m
the 3
410 glass fibre tank.
The pH of the sand filtered water was adjusted
to 7 with 60% nitric acid.
This water was again sand filtered to
ensure a low turbidity feed water (<2 NTU) and stored in two 4 m3 glass fibre tanks before EDR treatment. The process flow diagram is shown in Fig. 1.
r ,-
-Lime FRW CWPE
la-n Neutralization tank
Fig. 1. Process flow diagram An Aguamite I EDR unit from Ionics Inc., USA, was used for the
desalination/concentration
tests.
The
membrane
stack
contained two electrical and eight hydraulic stages with a total of 120 cell pairs.
The first, second, third and fourth hydraulic
stages (of each electric stage) contained 21, 17, 13 and 9 cell pairs, respectively.
Ionics anion (A.402 UZL 386) and cation
(C.62 LMP 401) membranes were used. per membrane was 230 cm2.
The effective membrane area
411 EXPERIMENTAL Lime dosaaes for vhosvhate removal as a function of nH The pH of DNE samples (500 ml) was adjusted to approximately 6; 7; 8; 8,5; and 9 with lime while the suspensions were stirred at 100 revolutions accurately.
Polyelectrolyte
lime addition minutes.
per minute
and the
and the
lime dosages
determined
(4 mg/l) was added 10 minutes after
suspensions
were
stirred
for another
2
The suspensions were then allowed to flocculate slowly
for 5 minutes
at 40 revolutions
allowed to clarify.
per minute
and the water
Phosphate was determined
was
on the clarified
samples.
EDR overation and measurements Pretreated DWE feed water was passed at a flow rate of 1,51 l/min through the EDR unit. of approximately initially
set
Brine was circulated at a flow rate
1,14 l/min.
at
0,38
l/min
The brine make-up (80% water
flow rate was
recovery),
and
later
voltages
were
adjusted to give a water recovery of 90%. The
first
and
second
electrical
stage
initially set at 50 and 40 volts, respectively.
These voltages
were later increased to 70 and 50 volts, respectively.
The 'off
The treatment
cycle was
spec' period was set at 140 seconds.
initially set at 20 minutes and later increased to 30 minutes. The
following
readings
were
taken
daily:
a)EDR
running
hours: b) pressure drop across the cartridge filters; c) feed and brine inlet pressures; d) feed, product and brine flow rates; e) voltage
and
current
across
the
two
electrical
stages:
f)
electrode and membrane voltages (stack probings). Daily water samples were taken of the EDR feed, product and brine for the following analyses: a) conductivity: b) TDS; c) pH;
412
d) turbidity
(NTU); f) temperature: and g) chemical composition.
Salt rejection,
water
recovery,
stack resistance,
electrical
energy consumption and current efficiency were calculated
from
the above data. (NOTE: all chemical analyses were automated). Membrane
resistance,
ion-exchanoe
canacitv,
nercentaae
water
content, and weiaht chancre These
membrane
properties
were
determined
according
to
PB 181575 (ref. 13). Enerav disnersive X-rav analvsis IEDXA) Membrane
samples
(membrane
edges
and
examined under a scanning electron microscope
flow
paths)
were
(SEM) equipped with
an energy dispersive X-ray analyzer to determine the presence of foulants
after
use.
The
samples
were
mounted
on
double-sided
adhesive tape and carbon coated to make them conductive before analysis. RESULTS AND DISCUSSION Lime dosaaes and ohosohate concentrations as a function of oH Lime
dosages
for
phosphate
removal
and
phosphate
concentration as a function of pH are shown in Fig. 2. the
phosphate
3 g/l. 8.5.
(99%) was removed at pH 8,5 at a
lime
Most of dosage of
Phosphate was reduced from 3800 to less than 50 mg/l at pH The settled sludge volume at pH 8.5 comprised approximately
20% of the treated water volume.
413
6
I 5:
5-
:
4-
-2000
1500 .i
5 " a,
3-
E
2-
a
l-
::
-
ar I/x
o*
6
I
9
,q
I
I
10
12
PH
2.
Lime dosages for concentration as
phosphate of
removal and phosphate mg/l polyelectrolyte)
of DWE before and after of the water quality after
and
is shown in
2.
TABLE 2: and after
PH
5.3
Conductivity 2+ Mg 4 Alkalinity 2+ Mn
(mS/m)
8.8
2 048 140
850 10
244 (CaC03)
447 1.8
< 0.025
414
Excellent However, levels
better (>
introduced be
9)
increasing The
phosphate with
the
with
a
the scaling
and
addition.
the
Most
acid before
can
disadvantage Better of
was
obtained more
phosphate and
at
pH
at higher
calcium
removals ferric
8.8. pH
will
should
chloride
be also
without
of the water.
slightly
alkalinity
of this
be
that
lime
potential
obtained
decreased
increased
alkalinity,
as
due a
however,
to
phosphate
result
was
of
lime
destroyed
with
EDR treatment.
Conductivitv The
was
removals
mixture
conductivity
removal
removal
into the water.
obtained
shown
phosphate
of the EDR feed, product
conductivity
in Fig.
of
the
EDR
and brine
feed,
product
and
brine
are
3.
10 000
-
Brine
. . . . . .._ Feed Product
8000 E \ v) 5 6000 2 ._ .z z
4000
5 0 2000
0
100
200
300
400
500 Time
Fig.
3.
Conductivity eendastiv&$~
of a&e
600
700
000
900
1000
(h)
feed, product and en sn;tsrqad rsa&e)
brine
(Note:
Product
415
The conductivity of the feed water varied between 1 500 and Product water with a conductivity between 100 and 200
1 900 mS/m.
mS/m was obtained when 50 and 40 volts were applied across the first and second electrical stages, respectively.
However, when
the voltage was increased to 70 and 50 volts, respectively, after 460 hours of operation, product water conductivity decreased to between
50 and
slightly
after
Product water
100 mS/m. 680 hours
increased to 90%.
conductivity
of operation when
However,
increase
water
increased
recovery
in conductivity
was
was
more
000
mS/m
pronounced towards the end of the run. Brine
conductivity
varied
between
5
000
and
6
before voltage adjustment and between 6 000 and 8 000 mS/m after voltage
A
adjustment.
maximum
brine
conductivity
of
approximately 10 000 mS/m was obtained at 90% water recovery. Excellent
conductivity
rejection
was
obtained;
92%
before
voltage adjustment and 97% after voltage adjustment.
Pressure dron across cartridse filters This pressure drop is shown in Pig. 4. The turbidity of the feed water varied between 1 and 2 NTU. Two cartridge
filters
(10 micron) were used in series.
The
firs
filter was replaced with the second one when the pressure drop increased inserted
to in
69 kPa
(10 psi)
its place.
and
Cartridge
a new filter
necessary approximately every 200 hours.
cartridge
filter
replacement
was
appears
416
00
00
........
Filtei Filter
inlet outlet
75
60
55 50
---
Feed inlet
----
Brine inlet 1,111,
0
100
200
300
I 500
1,
400
Time
I
I I I 600 700
feed
nutrients. and
the
replaced,
water
contains
600
I”‘40 900
t 000
(hl
Fig. 4.Pressure drop across cartridge inlet pressures The
I(
filters and feed and brine
high
concentrations
of
plant
Therefore, biological growth was expected to occur
cartridge
filter
had
a
showing that biological
greenish
colour
growth had taken
when
it
was
place.
biological growth, however, was detected on the membranes.
No This
may be ascribed to the low pH of the brine.
Feed and brine inlet Pressures These pressures are also shown in Fig. 4.
The pressures
remained more or less constant during the test period, showing that there was no significant membrane scaling and/or fouling.
417
Product water flow rate EDR product water flow rate is shown in Fig. 5. decrease
in
pronounced recovery
flow
during
was
rate
was
detected
last
the
increased
to
300
hours
90%.
with of
time, the
(This may
run
be
A slight
being
more
when
water
indicative
of
membrane fouling.) Stack resistance The Fig. 6.
first
electrical
stage
stack
resistance
is
shown
in
Stack resistance remained reasonably constant over the
test period,
showing that there was no severe membrane
scaling
and/or fouling. Electrical enerqv consumntion The stack electrical energy consumption
0
100
200
300
400
500 Time
Fig. 5.
Product water flow rate
(h)
600
is
700
800
900
1000
418
60 ----
0
100
200
kWh/m3
Product
kWh/m3
Feed
300
400
Fig.
6.
8 ’\
500
Time
9,
600
700
(h)
First electrical stage stack resistance stack electrical energy consumption
also shown in Fig. 6.
was
3.5 kWh/m3 product, respectively. increased,
approximately
the 4.5
total
The electrical energy consumption for the
first 460 hours of operation was approximately or
and
electrical kWh/m3
feed
Thereafter, when voltage
energy
feed
2.5 kWh/m'
or
6.0
consumptions kWh/m3
were
product,
respectively. Electrical energy requirements for pumping are not included in
the
above
figures.
approximately 1.1 km/m3
Pumping
energy
will
contribute
feed on a large scale commercial plant.
Current efficiencv The current efficiency varied between 80 and 90% at a water recovery
of approximately
80%.
However,
current
efficiency
419
decreased
to
70%
when
water
recovery
was
increased
to
approximately 90%. Stack nrobinq No hot spots were encountered during the first 460 hours of operation (before voltage adjustment). there
was
a definite
increase
However, it appeared that
in potential
drop
across
the
membranes of the fourth hydraulic stages towards the end of the test run. Turbiditv of EDR feed, nroduct and brine The turbidity of the lime clarified water varied between 3 and 8 NTU.
The turbidity of this water was reduced to less than
2 NTU with sand filtration.
The EDR feed water had a turbidity
of approximately 1.0 NTU most of the time.
However, turbidities
of 2 NTU were obtained for short periods towards the end of the test run. Product water turbidity varied between
0.5 and
1.0 NTU.
The turbidity of the brine was usually less than 2 NTU.
However,
brine turbidity as high as 5 NTU were experienced at times. pH of EDR feed, nroduct and brine The pH of the feed water was adjusted to approximately 7 with 60% nitric before
EDR
acid to
reduce
treatment.
manufactured
at the
the
Nitric
fertilizer
scaling acid plant.
potential
was
used
The
of the water because
product
it
water
is was
slightly alkaline (pH between 8 and 9.5) and the brine acidic (pH between 2 and 5). EDR product water was used for electrode rinsing.
The rinse
water was collected in the EDR degassing tank as product water. The
electrode
product water.
reactions
could
The brine was
have
increased
acidic
because
the
pH
of the
ammonium
nitrate
420
solutions have an acidic nature.
cCalcium
sul
ate
ammonium
of the EDR feed. vroduct and brine These concentrations are shown in Figs. 7 to 12. The calcium and sulphate concentrations of the product water varied between 2 and 17 mg/l and 20 and 180 mg/l, respectively. Therefore, excellent calcium and sulphate removals were obtained
1800 I ; 1600 \ z 1400
Brine
.......... Feed Product
5 1200 .-
:
i
..:* ‘-*.. .* . . . . . . . . . . . . . . . . . . . . . . ....’ 200 -. . . ‘* -.. . . . . . . . . . . . . ... . . . . . _*...... -*-**-.- . . . . ..* o-’ 0
100
200
300
400
500 Time
600
700
800
(h)
Fig. 7.Calcium concentration of feed, product and brine.
900
1000
421
7000 T E”
6000
. . . . . . . . . ..
Feed
-
Product
0 100
0
200
300
400
500
Time
8.
Fig.
Sulphate
concentration
600
700
of feed, product
18 000
t-
_
16000
-
v ‘,
Brine . . . . . . . . . Feed
14000
-
-
800
900
1000
(h)
and brine
Product
E -12000 .-s
-
~lOOO0
-
E 2
0 000
-
ii u
6000
-
E .z
4000
-
2ooo
. . . . . . . . . . . .. ..f . . . . . . . . ...***.. -. . . . . . 3. . . . .f O.....
z
_..* . . . .
. . . . . . . . . . . . . . . . . . . ......_.‘...,
E
0
100
200
300
400
500
Time
Fig.
9. Ammonium
concentration
600
700
800
(h)
of feed,
product
and brine
900
1000
422
F
55
000
50
000
45000 40
000
c .e
35
000
G ,’
30000
;
25000
z
20000
100
0
200
300
500
400
Time
Fig.
10.
0
Nitrate
100
concentration
200
300
400
11.
Phosphate
concentration
700
500
800
900
1000
(h)
of feed, product
Time
Fig.
600
600
700
and brine
800
900
(h)
of feed, product
and brine
1000
423
Time
(h)
Fig. 12. Phosphate concentration of product water scale - see Fig.11).
(Note: Enlarged
and the calcium concentration of the product water complied with the requirement for cooling tower make-up. The
calcium
concentration
increased after the voltage were increased.
of
the
brine
was
(460 h) and water
recovery
The sulphate concentration
of the brine varied between 3 000 and 7 000 mg/l. indicative
sodium
of
a
calcium
hexametaphosphate
However,
SHMP
(680 h)
A maximum calcium concentration of approximately
1 700 mg/l was obtained in the brine.
are
significantly
dosing
sulphate
(SHMP) was
should
be
These results
scaling dosed
potential.
during
considered
in
a
the full
No
tests. scale
application for scale control. The ammonia and nitrate concentrations of the product water varied
between
100
and
300
mg/l
and
100
and
750
mg/l,
respectively. The ammonia and nitrate concentrations of the brine
424 v a r i e d b e t w e e n 9 000 and respectively.
Therefore,
concentrated product.
17 000 mg/l
and
these
ammonia
chemicals
Alternatively
the
20% of the t r e a t e d water,
and 25 000 and
and
nitrate
can
be
brine,
are
significantly
recovered
which
55 000 mg/l
as
comprise
a
useful
approximately
can be d i s p o s e d of in e v a p o r a t i o n ponds
for further concentration.
This
will
increase
effective
use
of
the p r e s e n t e v a p o r a t i o n ponds. No
specifications
ammonium cooling
and
nitrate
tower
industrial
and
ion
make-up.
expert
concentration problems
could
in
the
that
EDR
however,
concentration
the
can be r e d u c e d to v e r y
necessary
of
low
to
be
ammonium
product
levels
literature
water
the
EDR
an
nitrate not
give
The a m m o n i a
product
levels w i t h
for
with
and
would
is used.
for
used
communication
in a c o o l i n g t o w e r if an a l g i c i d e
nitrate
the
levels
personal
indicated of
found
concentration
However,
has
levels
be
water,
ion-exchange
if
(ref. 12).
P h o s p h a t e removal was p o o r w h e n the pH of the DWE was raised to only 8 w i t h lime
(first 300 h, Figs.ll and 12).
pH
8.5,
was
raised
obtained product
to
much
(PO 4 < 50 mg/l). was
reduced
to
the
ferric
requirement
approximately
chloride)
adsorption
(ref.
of
or
phosphate
removal
w h e n the was
The p h o s p h a t e c o n c e n t r a t i o n of the EDR
i n c r e a s e d across the stages. than
better
However,
i0
mg/l
when
This c o n c e n t r a t i o n
5 mg/l.
Better
phosphate
voltage
is still h i g h e r
pretreatment
removal
by
(lime
activated
14) or even 10-stage EDR should
was
and
alumina
reduce p h o s p h a t e
to less than 5 mg/l. Poor obtained
phosphate with
EDR
The m o s t p r o b a b l e
rejection
relative reason
to
(approximately some
for this
of
the
is that
50%,
other
Fig. ions
ii) (>
90%).
ammonium phosphate
p r o b a b l y less d i s s o c i a t e d than some of the o t h e r compounds.
was
is
425
Chemical
comoosition
A feed,
typical product
TABLE
of EDR
example
of
and brine
feed, wroduct the
is shown
chemical
and brine composition
in Table
of
the
EDR
after
512
3.
3:
Chemical hours
composition
of
EDR
feed,
product
and
brine
of operation
Constituent
Feed
Product
Brine
PH
6.9
8.9
2.5
1 777
64
6 501
96.4
67
4
269
94.0
94
7
426
92.6
141
9
1 000
93.6
Conductivity
(mS/m)
Na+(w/l) K+(w/l) Ca2+ (w/l) 2+
% Rejection
Mg
(mg/l)
33
2
146
93.9
NH 4-
(mg/l)
2 575
100
11 839
96.1
NO - (mg/l)
8 292
177
36 326
97.9
13.2
12.1
14.0
(mg/l)
1 000
20
4 200
98.0
(mg/l)
32
8
107
75.0
135
31
575
77.0
27
68
23
16
37
30.4
12 415
452
54 905
$+ (mg/l) so PO
24 34
cl-
(w/l)
Alkal. (as COD
CaC03)mg/l
(mg/l)
TDS(calculated)
*
Current
Very
(mg/l)
efficiency
good
ion
nitrate
showed
However,
phosphate,
was
78.8%
rejections
rejections chloride
of
were
obtained.
Ammonium
96.1
and
respectively.
97.8%,
and COD rejections
were
and
not as good.
426
It appeared that the product water, with the exception of TDS
and phosphate,
complied
with
the
quality
requirements
for
cooling tower make-up (see Table 1). Ten stage EDR should reduce TDS and phosphate to within the limits for cooling tower make-up. MEMBRANE ANALYSIS Resistance,
ion exchanae
caoacitv.
oercentaae
water
content,
and
weiaht chanae The membrane stack was opened at the end of the 1 000 hour test run and a membrane inspection showed that there was a slight whitish scale on the anionic membrane surfaces of both the fourth hydraulic
stages of the two electrical stages.
Membranes
from
the other hydraulic stages showed no visual scale formation and the membranes appeared to be in very good condition. properties
of the membrane
edges
Membrane
(ME) and membrane
flow paths
(MFP) are shown in Table 4. TABLE 4: Anion membrane properties flow paths (MFP) Stage(l)
of membrane
Resistance(') 2 (ohm.cm ) Before After
E:H
edges
Capacity
(ME) and membrane
% Weight
% H20
change
(me/W)
ME
MFP
ME
MFP
ME
MFP
ME
MFP
MFP
1:1(3)
9.8
9.6
9.6
9.6
2.69
2.69
37.6
37.8
+0,8
1:3(3)
9.6
9.8
9.7
9.8
-
-
-
-
-
2:1(3)
10.1
9.8
9.8
9.5
-
-
2:2(3)
9.6
9.7
9.3
9.5
-
-
1
1
1
1:4(3)
10.0
20.9
9.8
16.2
2.64
2.10
38.2
34.6
+6.6
2:4(3)
9.8
20.9
9.3
14.8
2.66
2.15
38.5
36.3
+5.4
1:4(4)
10.0
20.9
9.8
17.2
2.64
1.95
38.2
32.5
1:4(5)
10.0
20.9
9.8
11.1
2.64
2.40
38.2
37.0
+2.8
427 1)
lE.lH: 1st electrical.lst hydraulic, etc.
2)
Resistance before and after conditioning.
3)
Soaked in 0,l N NaCl.
4)
Soaked for 1 hour in 1 000 mg/l NaOCl.
5)
Soaked for 1 hour in 4 N HCl.
The anionic membranes from the first three hydraulic stages were
as good as new except
hydraulic
stages.
These
for the membranes membranes
causing an increase in weight
were
scaled
effected
fourth
internally,
and resistance and a decrease
ion exchange capacity and gel water content. (4 N HCl)
from the
in
Strong acid
removal of the scale and improved
capacity
with a close return to the membranes original properties.
(Note:
no change in cationic membrane properties was noticed.) The same current density was applied across all stages of each electrical stage during the tests.
hydraulic
Therefore,
too high current density could have caused polarization fourth hydraulic stages.
However,
a
in the
in a full scale application,
each hydraulic stage will have its own electrical stage which can be controlled independantly thus preventing polarization.
It is
expected that a full scale plant should run well with electrical adjustments and/or frequent acid cleanings.
Energy dispersive X-ray analvsis The scale on the anion membrane surfaces mainly of calcium phosphate. and nickel were also present. most of the scale.
(lE.4H) consisted
Traces of sulphate, manganese, iron Acid treatment
(5% HCl) removed
428 EDR vrocess desian criteria and costs Process design criteria for a full-scale EDR plant can be derived
from the EDR pilot results. 3 indicated that a 30 m /h EDR plant
Preliminary estimates had and
clariflocculator
for
phosphate removal would cost approximately US $750 000 (ref. 12). CONCLUSIONS Lime treatment is effective for phosphate
removal.
However,
better phosphate removals should be obtained with lime and ferric chloride. EDR treatment of the effluent should be successful for water and chemical recovery and effluent volume reduction. Membrane
scaling and/or fouling was virtually
absent.
A
full scale plant should run well with electrical adjustments and/or frequent acid cleanings. With the exception of phosphate and TDS, the EDR product water
complies
tower
make-up.
sufficiently chloride).
with
the
quality
Phosphate, with
Both
requirements
however,
should
improved pretreatment
for
cooling
be
reduced
(lime and
ferric
TDS and phosphate should be reduced to the
required
specifications with 10 stage EDR. + Plant nutrients (NH4 ,N03-) may be recovered successfully and
effluent
volume
reduced
significantly
(by
80%)
to
increase service time of the evaporation ponds. Total electrical energy consumption for EDR treatment of the effluent was determined at approximately 5,5 kWh/m3 feed. Process design criteria for a full scale EDR plant
(30m3/h)
can be derived from the pilot plant results. The
cost
of
a
full
scale
EDR
plant
(30 m3/h)
and
clariflocculator for treatment of the effluent was estimated at US $750 000.
429
ACKNOWLEDGEMENT Appreciation is expressed to Sasol Fertilizers (Pty) Ltd for their financial support of this investigation. Acknowledgement is also given to Mr R Jones from Process Plant (Pty) Ltd for his valuable advice during the execution of the project. REFERENCES 1 2
3
4
5 6
7
8
9 10 11 12 13 14
U.S.A.I.D. Desalination Manual, CHZM Hill International Corporation, 7201 N.W., 11th Place, Gainesville, Florida, U.S.A., 32601, 1980. Concentration of electrolytes prior to T. Nishiwaki, evaporation with an electro membrane process, in: R.E. (Ed),Industrial Processing with Lacey and S. Loeb Membranes, Wiley Inter-science, New York, 1972. w. G. Millman and R.J. Heller, Some successful applications of electrodialysis, 4th Conference on Advanced Pollution Control for the Metal Finishing Industry, Lake Buena Vista,Jan.l8 to 20,1982, EPA-600/9-82-022, pp.70-74. N. M. Smirnova, B. N. Laskorin, J.S. Mishukova and A.V. Borisov, The Application of electrodialysis with ionexchange membranes for treatment of sodium sulphate solutions, Desalination (Amsterdam) - 9th World Congress on Desalination and Water Re-use, 3, Membrane Processes, Florence 23-27 May, 46 (1983) 197-201. J.J. Schoeman, The Status of electrodialysis technology for brackish and industrial water treatment, Water S-A., ll(2) (1985) 79-86. V.N. Smagin and V.A. Chukhin, Concentration of brines of desalination plants with electrodialysis, 5th International Symposium on Fresh Water from the Sea, 3 (1975) 139-148. s. P. Vysotskii, V.S. Parykin and S.A. Ulasova, Use of the series - manufactured UEO-50-4/12-5 electrodialysis plants for concentrating the waste waters from demineralization plants, Thermal Engineering, 30(9)(1983) 540-542. J. R. Wirth and G. Westbrook, Cooling water salinity and brine disposal optimized with electrodialysis water recovery/brine concentration systems, Combustion, May (1977) 33-37. D. R. Jordan, M.D. Bearden and W.F. McIIhenny, Blowdown concentration by electrodialysis, Chemical Engineering Progress, 71 (7)(1975) 77-82. J.J. Schoeman, I.B. Schutte and H. MacLeod, Lime treatment of an ammonium nitrate effluent from a fertilizer company followed by electrodialysis treatment, Unpublished report. J.J. Schoeman, I.B. Schutte and H. MacLeod, Concentration of an ammonium nitrate effluent from a fertilizer company with electrodialysis, Unpublished Report. J.J. Schoeman and I.B. Schutte, A pilot investigation of the treatment of a fertilizer company waste effluent with lime and electrodialysis reversal, Unpublished report. Test Manual for Penn Selective Membranes, Office of Saline Water Research and Development Progress Report No 77 (1964). PB 181575. J. J. Schoeman and H. MacLeod, The effect of particle removal by size and interfering ions on fluoride activated alumna, Water S-A., 14(4) (1987) 229-234.
407
PILOT INVESTIGATION ON THE TREATMENT OF FERTILIZER MANUFACTURING PROCESS EFFLUENT USING LIME AND ELECTRODIALYSIS REVERSAL J.J. SCHOEMAN, I.J.M. BUYS, I.B. SCHUTTE and H. MACLEOD DWT., CSIR, P.O.Box 395, Pretoria 0001, South Africa SUMMARY The treatment of a fertilizer company's effluent was evaluated using lime and electrodialysis reversal (EDR) for phosphate removal, water and chemical recovery, and effluent Phosphate could be reduced from 3 800 to less volume reduction. than 50 mg/l at pH 8.5 with lime: however, phosphate removal from the lime treated effluent using EDR was poor (75% removal). The EDR product water complied with the requirements for cooling tower make-up except for TDS and phosphates. However, the required specifications should be met using 10 stage EDR. In addition, plant nutrients
(NH4+ ,N03-) may be recovered
from
the brine, which comprised 20% of the initial effluent volume. A full scale EDR plant Membrane scaling was virtually absent. should run well with electrical adjustments and/or frequent acid cleaning. Electrical energy consumption for EDR treatment was found to be
4.5 kWh/m3 feed
(pumping costs excluded).
capital cost for a 30 ml/h EDR plant and clariflocculator removal) was estimated at US $750 000.
The (PO4
INTRODUCTION A fertilizer company in South Africa
produces
a wide
range of N:P:K fertilizers from phosphate rock, nitric acid, limestone
and
ammonium
nitrate.
The
resulting
manufacturing
process effluents comprise a concentrated waste process effluent (CWPE; 5 500 mS/m, 4m'/h) and a more dilute waste effluent (DWE; + 500 mS/m, 143/h) rich in plant nutrients (NO3-, NH4 ,PC,3-), which are disposed of in costly evaporation ponds, constituting an environmental pollution hazard. Electrodialysis
(ED), reverse
osmosis,
evaporation are desalination/concentration OOll-9164/88/$03.50
0 1988Elsevier Science Publishers B.V.
ion-exchange
and
processes potentially
suitable
for treatment of the DWE
(refs. l-2).
Of these, ED
appears most suitable when large volumes have to be treated, high brine
concentrations
(small volumes)
are
required,
and
waters
with membrane fouling characteristics are encountered. Numerous examples are given in the literature to demonstrate how ED can be used for desalination/concentration of model waters and industrial effluents (refs. 3-9). to
evaluate
the
treatability
It was therefore decided
of
electradialysis reversal (EDR) for water
the
effluents
using
(cooling tower make-up)
and chemical recovery, and effluent volume
reduction.
Preliminary batch ED tests conducted in the laboratory on
a
sample
of
the
CWPE
(7 000 mS/m)
effluent could be desalinated
showed
concentration
of 15 500 mS/m was
tests on a more dilute sample
the
in stages to less than 1 000
Effluent volume was reduced by 50%
mS/m.
that
and a maximum brine
obtained.
(ref. 10). Further
(3 100 mS/m) with other membranes
showed that the effluent could be desalinated to 200 mS/m.
The
effluent volume was reduced to 20% of its original volume in this case
and
obtained.
a maximum
brine
concentration
of
16
300
mS/m
was
No scale was detected on the membranes after the tests
despite very high concentrations of calcium (3 800 mg/l) and phosphate
(700 mg/l), sulphate
(25 000 mg/l) encountered in the feed
water. Phosphate and TDS, however, should be reduced to less than 5 and 230 mg/l to make the ED product water cooling tower make-up.
suitable for
Since phosphate concentrations in the DWE
as high as 3 000 mg/l were encountered, significant
phosphate
reduction was required. Preliminary tests with lime for phosphate removal showed that phosphate could be reduced from approximately 5 000 to
less than
20 mg/l
(ref. 11).
Lime
treatment
was
409
therefore considered for phosphate removal. The
objectives
following:
a)
of our
lime
treatment for water
investigation
treatment
were
to
for phosphate
evaluate
removal,
b)
(cooling tower make-up) and chemical
the EDR
(plant
nutrient) recovery and effluent volume reduction, c) the fouling potential of the effluent for the EDR membranes: and to determine process design criteria and costs for a full scale (30 m'/h) EDR plant.
This
paper
describes
some
of the
results
of
our
investigation (ref. 12). COOLING TOWER BAKE-UP WATER SPECIFICATIONS These specifications are shown in Table 1. TABLE 1 Required maximum specifications for cooling tower make-up Concentration
Constituent
(mg/l)
230 25 25 35 120 45 5 8,5
TDS Total hardness Calcium hardness Silica Sulphate Chloride Phosphate Iron
GENERAL PROCESS DESCRIPTION AND EDR TEST APPARATUS Dilute
waste
effluent
was
simulated
by
mixing
14
parts
flocculated raw water (FRW) with 4 parts CWPE in an 8 m' tanker. This water capacity)
was and
approximately
pumped lime
8.5.
into a stainless
was
added
until
Polyelectrolyte
steel the
was
clarifier
pH
then
was added
(2 m3
raised to
to
enhance
sludge settling. The clarified
sludge water
was
withdrawn
sand
filtered
after and
proper
settling
collected
in
a
and 4
m
the 3
410 glass fibre tank.
The pH of the sand filtered water was adjusted
to 7 with 60% nitric acid.
This water was again sand filtered to
ensure a low turbidity feed water (<2 NTU) and stored in two 4 m3 glass fibre tanks before EDR treatment. The process flow diagram is shown in Fig. 1.
r ,-
-Lime FRW CWPE
la-n Neutralization tank
Fig. 1. Process flow diagram An Aguamite I EDR unit from Ionics Inc., USA, was used for the
desalination/concentration
tests.
The
membrane
stack
contained two electrical and eight hydraulic stages with a total of 120 cell pairs.
The first, second, third and fourth hydraulic
stages (of each electric stage) contained 21, 17, 13 and 9 cell pairs, respectively.
Ionics anion (A.402 UZL 386) and cation
(C.62 LMP 401) membranes were used. per membrane was 230 cm2.
The effective membrane area
411 EXPERIMENTAL Lime dosaaes for vhosvhate removal as a function of nH The pH of DNE samples (500 ml) was adjusted to approximately 6; 7; 8; 8,5; and 9 with lime while the suspensions were stirred at 100 revolutions accurately.
Polyelectrolyte
lime addition minutes.
per minute
and the
and the
lime dosages
determined
(4 mg/l) was added 10 minutes after
suspensions
were
stirred
for another
2
The suspensions were then allowed to flocculate slowly
for 5 minutes
at 40 revolutions
allowed to clarify.
per minute
and the water
Phosphate was determined
was
on the clarified
samples.
EDR overation and measurements Pretreated DWE feed water was passed at a flow rate of 1,51 l/min through the EDR unit. of approximately initially
set
Brine was circulated at a flow rate
1,14 l/min.
at
0,38
l/min
The brine make-up (80% water
flow rate was
recovery),
and
later
voltages
were
adjusted to give a water recovery of 90%. The
first
and
second
electrical
stage
initially set at 50 and 40 volts, respectively.
These voltages
were later increased to 70 and 50 volts, respectively.
The 'off
The treatment
cycle was
spec' period was set at 140 seconds.
initially set at 20 minutes and later increased to 30 minutes. The
following
readings
were
taken
daily:
a)EDR
running
hours: b) pressure drop across the cartridge filters; c) feed and brine inlet pressures; d) feed, product and brine flow rates; e) voltage
and
current
across
the
two
electrical
stages:
f)
electrode and membrane voltages (stack probings). Daily water samples were taken of the EDR feed, product and brine for the following analyses: a) conductivity: b) TDS; c) pH;
412
d) turbidity
(NTU); f) temperature: and g) chemical composition.
Salt rejection,
water
recovery,
stack resistance,
electrical
energy consumption and current efficiency were calculated
from
the above data. (NOTE: all chemical analyses were automated). Membrane
resistance,
ion-exchanoe
canacitv,
nercentaae
water
content, and weiaht chancre These
membrane
properties
were
determined
according
to
PB 181575 (ref. 13). Enerav disnersive X-rav analvsis IEDXA) Membrane
samples
(membrane
edges
and
examined under a scanning electron microscope
flow
paths)
were
(SEM) equipped with
an energy dispersive X-ray analyzer to determine the presence of foulants
after
use.
The
samples
were
mounted
on
double-sided
adhesive tape and carbon coated to make them conductive before analysis. RESULTS AND DISCUSSION Lime dosaaes and ohosohate concentrations as a function of oH Lime
dosages
for
phosphate
removal
and
phosphate
concentration as a function of pH are shown in Fig. 2. the
phosphate
3 g/l. 8.5.
(99%) was removed at pH 8,5 at a
lime
Most of dosage of
Phosphate was reduced from 3800 to less than 50 mg/l at pH The settled sludge volume at pH 8.5 comprised approximately
20% of the treated water volume.
413
6
I 5:
5-
:
4-
-2000
1500 .i
5 " a,
3-
E
2-
a
l-
::
-
ar I/x
o*
6
I
9
,q
I
I
10
12
PH
2.
Lime dosages for concentration as
phosphate of
removal and phosphate mg/l polyelectrolyte)
of DWE before and after of the water quality after
and
is shown in
2.
TABLE 2: and after
PH
5.3
Conductivity 2+ Mg 4 Alkalinity 2+ Mn
(mS/m)
8.8
2 048 140
850 10
244 (CaC03)
447 1.8
< 0.025
414
Excellent However, levels
better (>
introduced be
9)
increasing The
phosphate with
the
with
a
the scaling
and
addition.
the
Most
acid before
can
disadvantage Better of
was
obtained more
phosphate and
at
pH
at higher
calcium
removals ferric
8.8. pH
will
should
chloride
be also
without
of the water.
slightly
alkalinity
of this
be
that
lime
potential
obtained
decreased
increased
alkalinity,
as
due a
however,
to
phosphate
result
was
of
lime
destroyed
with
EDR treatment.
Conductivitv The
was
removals
mixture
conductivity
removal
removal
into the water.
obtained
shown
phosphate
of the EDR feed, product
conductivity
in Fig.
of
the
EDR
and brine
feed,
product
and
brine
are
3.
10 000
-
Brine
. . . . . .._ Feed Product
8000 E \ v) 5 6000 2 ._ .z z
4000
5 0 2000
0
100
200
300
400
500 Time
Fig.
3.
Conductivity eendastiv&$~
of a&e
600
700
000
900
1000
(h)
feed, product and en sn;tsrqad rsa&e)
brine
(Note:
Product
415
The conductivity of the feed water varied between 1 500 and Product water with a conductivity between 100 and 200
1 900 mS/m.
mS/m was obtained when 50 and 40 volts were applied across the first and second electrical stages, respectively.
However, when
the voltage was increased to 70 and 50 volts, respectively, after 460 hours of operation, product water conductivity decreased to between
50 and
slightly
after
Product water
100 mS/m. 680 hours
increased to 90%.
conductivity
of operation when
However,
increase
water
increased
recovery
in conductivity
was
was
more
000
mS/m
pronounced towards the end of the run. Brine
conductivity
varied
between
5
000
and
6
before voltage adjustment and between 6 000 and 8 000 mS/m after voltage
A
adjustment.
maximum
brine
conductivity
of
approximately 10 000 mS/m was obtained at 90% water recovery. Excellent
conductivity
rejection
was
obtained;
92%
before
voltage adjustment and 97% after voltage adjustment.
Pressure dron across cartridse filters This pressure drop is shown in Pig. 4. The turbidity of the feed water varied between 1 and 2 NTU. Two cartridge
filters
(10 micron) were used in series.
The
firs
filter was replaced with the second one when the pressure drop increased inserted
to in
69 kPa
(10 psi)
its place.
and
Cartridge
a new filter
necessary approximately every 200 hours.
cartridge
filter
replacement
was
appears
416
00
00
........
Filtei Filter
inlet outlet
75
60
55 50
---
Feed inlet
----
Brine inlet 1,111,
0
100
200
300
I 500
1,
400
Time
I
I I I 600 700
feed
nutrients. and
the
replaced,
water
contains
600
I”‘40 900
t 000
(hl
Fig. 4.Pressure drop across cartridge inlet pressures The
I(
filters and feed and brine
high
concentrations
of
plant
Therefore, biological growth was expected to occur
cartridge
filter
had
a
showing that biological
greenish
colour
growth had taken
when
it
was
place.
biological growth, however, was detected on the membranes.
No This
may be ascribed to the low pH of the brine.
Feed and brine inlet Pressures These pressures are also shown in Fig. 4.
The pressures
remained more or less constant during the test period, showing that there was no significant membrane scaling and/or fouling.
417
Product water flow rate EDR product water flow rate is shown in Fig. 5. decrease
in
pronounced recovery
flow
during
was
rate
was
detected
last
the
increased
to
300
hours
90%.
with of
time, the
(This may
run
be
A slight
being
more
when
water
indicative
of
membrane fouling.) Stack resistance The Fig. 6.
first
electrical
stage
stack
resistance
is
shown
in
Stack resistance remained reasonably constant over the
test period,
showing that there was no severe membrane
scaling
and/or fouling. Electrical enerqv consumntion The stack electrical energy consumption
0
100
200
300
400
500 Time
Fig. 5.
Product water flow rate
(h)
600
is
700
800
900
1000
418
60 ----
0
100
200
kWh/m3
Product
kWh/m3
Feed
300
400
Fig.
6.
8 ’\
500
Time
9,
600
700
(h)
First electrical stage stack resistance stack electrical energy consumption
also shown in Fig. 6.
was
3.5 kWh/m3 product, respectively. increased,
approximately
the 4.5
total
The electrical energy consumption for the
first 460 hours of operation was approximately or
and
electrical kWh/m3
feed
Thereafter, when voltage
energy
feed
2.5 kWh/m'
or
6.0
consumptions kWh/m3
were
product,
respectively. Electrical energy requirements for pumping are not included in
the
above
figures.
approximately 1.1 km/m3
Pumping
energy
will
contribute
feed on a large scale commercial plant.
Current efficiencv The current efficiency varied between 80 and 90% at a water recovery
of approximately
80%.
However,
current
efficiency
419
decreased
to
70%
when
water
recovery
was
increased
to
approximately 90%. Stack nrobinq No hot spots were encountered during the first 460 hours of operation (before voltage adjustment). there
was
a definite
increase
However, it appeared that
in potential
drop
across
the
membranes of the fourth hydraulic stages towards the end of the test run. Turbiditv of EDR feed, nroduct and brine The turbidity of the lime clarified water varied between 3 and 8 NTU.
The turbidity of this water was reduced to less than
2 NTU with sand filtration.
The EDR feed water had a turbidity
of approximately 1.0 NTU most of the time.
However, turbidities
of 2 NTU were obtained for short periods towards the end of the test run. Product water turbidity varied between
0.5 and
1.0 NTU.
The turbidity of the brine was usually less than 2 NTU.
However,
brine turbidity as high as 5 NTU were experienced at times. pH of EDR feed, nroduct and brine The pH of the feed water was adjusted to approximately 7 with 60% nitric before
EDR
acid to
reduce
treatment.
manufactured
at the
the
Nitric
fertilizer
scaling acid plant.
potential
was
used
The
of the water because
product
it
water
is was
slightly alkaline (pH between 8 and 9.5) and the brine acidic (pH between 2 and 5). EDR product water was used for electrode rinsing.
The rinse
water was collected in the EDR degassing tank as product water. The
electrode
product water.
reactions
could
The brine was
have
increased
acidic
because
the
pH
of the
ammonium
nitrate
420
solutions have an acidic nature.
cCalcium
sul
ate
ammonium
of the EDR feed. vroduct and brine These concentrations are shown in Figs. 7 to 12. The calcium and sulphate concentrations of the product water varied between 2 and 17 mg/l and 20 and 180 mg/l, respectively. Therefore, excellent calcium and sulphate removals were obtained
1800 I ; 1600 \ z 1400
Brine
.......... Feed Product
5 1200 .-
:
i
..:* ‘-*.. .* . . . . . . . . . . . . . . . . . . . . . . ....’ 200 -. . . ‘* -.. . . . . . . . . . . . . ... . . . . . _*...... -*-**-.- . . . . ..* o-’ 0
100
200
300
400
500 Time
600
700
800
(h)
Fig. 7.Calcium concentration of feed, product and brine.
900
1000
421
7000 T E”
6000
. . . . . . . . . ..
Feed
-
Product
0 100
0
200
300
400
500
Time
8.
Fig.
Sulphate
concentration
600
700
of feed, product
18 000
t-
_
16000
-
v ‘,
Brine . . . . . . . . . Feed
14000
-
-
800
900
1000
(h)
and brine
Product
E -12000 .-s
-
~lOOO0
-
E 2
0 000
-
ii u
6000
-
E .z
4000
-
2ooo
. . . . . . . . . . . .. ..f . . . . . . . . ...***.. -. . . . . . 3. . . . .f O.....
z
_..* . . . .
. . . . . . . . . . . . . . . . . . . ......_.‘...,
E
0
100
200
300
400
500
Time
Fig.
9. Ammonium
concentration
600
700
800
(h)
of feed,
product
and brine
900
1000
422
F
55
000
50
000
45000 40
000
c .e
35
000
G ,’
30000
;
25000
z
20000
100
0
200
300
500
400
Time
Fig.
10.
0
Nitrate
100
concentration
200
300
400
11.
Phosphate
concentration
700
500
800
900
1000
(h)
of feed, product
Time
Fig.
600
600
700
and brine
800
900
(h)
of feed, product
and brine
1000
423
Time
(h)
Fig. 12. Phosphate concentration of product water scale - see Fig.11).
(Note: Enlarged
and the calcium concentration of the product water complied with the requirement for cooling tower make-up. The
calcium
concentration
increased after the voltage were increased.
of
the
brine
was
(460 h) and water
recovery
The sulphate concentration
of the brine varied between 3 000 and 7 000 mg/l. indicative
sodium
of
a
calcium
hexametaphosphate
However,
SHMP
(680 h)
A maximum calcium concentration of approximately
1 700 mg/l was obtained in the brine.
are
significantly
dosing
sulphate
(SHMP) was
should
be
These results
scaling dosed
potential.
during
considered
in
a
the full
No
tests. scale
application for scale control. The ammonia and nitrate concentrations of the product water varied
between
100
and
300
mg/l
and
100
and
750
mg/l,
respectively. The ammonia and nitrate concentrations of the brine
424 v a r i e d b e t w e e n 9 000 and respectively.
Therefore,
concentrated product.
17 000 mg/l
and
these
ammonia
chemicals
Alternatively
the
20% of the t r e a t e d water,
and 25 000 and
and
nitrate
can
be
brine,
are
significantly
recovered
which
55 000 mg/l
as
comprise
a
useful
approximately
can be d i s p o s e d of in e v a p o r a t i o n ponds
for further concentration.
This
will
increase
effective
use
of
the p r e s e n t e v a p o r a t i o n ponds. No
specifications
ammonium cooling
and
nitrate
tower
industrial
and
ion
make-up.
expert
concentration problems
could
in
the
that
EDR
however,
concentration
the
can be r e d u c e d to v e r y
necessary
of
low
to
be
ammonium
product
levels
literature
water
the
EDR
an
nitrate not
give
The a m m o n i a
product
levels w i t h
for
with
and
would
is used.
for
used
communication
in a c o o l i n g t o w e r if an a l g i c i d e
nitrate
the
levels
personal
indicated of
found
concentration
However,
has
levels
be
water,
ion-exchange
if
(ref. 12).
P h o s p h a t e removal was p o o r w h e n the pH of the DWE was raised to only 8 w i t h lime
(first 300 h, Figs.ll and 12).
pH
8.5,
was
raised
obtained product
to
much
(PO 4 < 50 mg/l). was
reduced
to
the
ferric
requirement
approximately
chloride)
adsorption
(ref.
of
or
phosphate
removal
w h e n the was
The p h o s p h a t e c o n c e n t r a t i o n of the EDR
i n c r e a s e d across the stages. than
better
However,
i0
mg/l
when
This c o n c e n t r a t i o n
5 mg/l.
Better
phosphate
voltage
is still h i g h e r
pretreatment
removal
by
(lime
activated
14) or even 10-stage EDR should
was
and
alumina
reduce p h o s p h a t e
to less than 5 mg/l. Poor obtained
phosphate with
EDR
The m o s t p r o b a b l e
rejection
relative reason
to
(approximately some
for this
of
the
is that
50%,
other
Fig. ions
ii) (>
90%).
ammonium phosphate
p r o b a b l y less d i s s o c i a t e d than some of the o t h e r compounds.
was
is
425
Chemical
comoosition
A feed,
typical product
TABLE
of EDR
example
of
and brine
feed, wroduct the
is shown
chemical
and brine composition
in Table
of
the
EDR
after
512
3.
3:
Chemical hours
composition
of
EDR
feed,
product
and
brine
of operation
Constituent
Feed
Product
Brine
PH
6.9
8.9
2.5
1 777
64
6 501
96.4
67
4
269
94.0
94
7
426
92.6
141
9
1 000
93.6
Conductivity
(mS/m)
Na+(w/l) K+(w/l) Ca2+ (w/l) 2+
% Rejection
Mg
(mg/l)
33
2
146
93.9
NH 4-
(mg/l)
2 575
100
11 839
96.1
NO - (mg/l)
8 292
177
36 326
97.9
13.2
12.1
14.0
(mg/l)
1 000
20
4 200
98.0
(mg/l)
32
8
107
75.0
135
31
575
77.0
27
68
23
16
37
30.4
12 415
452
54 905
$+ (mg/l) so PO
24 34
cl-
(w/l)
Alkal. (as COD
CaC03)mg/l
(mg/l)
TDS(calculated)
*
Current
Very
(mg/l)
efficiency
good
ion
nitrate
showed
However,
phosphate,
was
78.8%
rejections
rejections chloride
of
were
obtained.
Ammonium
96.1
and
respectively.
97.8%,
and COD rejections
were
and
not as good.
426
It appeared that the product water, with the exception of TDS
and phosphate,
complied
with
the
quality
requirements
for
cooling tower make-up (see Table 1). Ten stage EDR should reduce TDS and phosphate to within the limits for cooling tower make-up. MEMBRANE ANALYSIS Resistance,
ion exchanae
caoacitv.
oercentaae
water
content,
and
weiaht chanae The membrane stack was opened at the end of the 1 000 hour test run and a membrane inspection showed that there was a slight whitish scale on the anionic membrane surfaces of both the fourth hydraulic
stages of the two electrical stages.
Membranes
from
the other hydraulic stages showed no visual scale formation and the membranes appeared to be in very good condition. properties
of the membrane
edges
Membrane
(ME) and membrane
flow paths
(MFP) are shown in Table 4. TABLE 4: Anion membrane properties flow paths (MFP) Stage(l)
of membrane
Resistance(') 2 (ohm.cm ) Before After
E:H
edges
Capacity
(ME) and membrane
% Weight
% H20
change
(me/W)
ME
MFP
ME
MFP
ME
MFP
ME
MFP
MFP
1:1(3)
9.8
9.6
9.6
9.6
2.69
2.69
37.6
37.8
+0,8
1:3(3)
9.6
9.8
9.7
9.8
-
-
-
-
-
2:1(3)
10.1
9.8
9.8
9.5
-
-
2:2(3)
9.6
9.7
9.3
9.5
-
-
1
1
1
1:4(3)
10.0
20.9
9.8
16.2
2.64
2.10
38.2
34.6
+6.6
2:4(3)
9.8
20.9
9.3
14.8
2.66
2.15
38.5
36.3
+5.4
1:4(4)
10.0
20.9
9.8
17.2
2.64
1.95
38.2
32.5
1:4(5)
10.0
20.9
9.8
11.1
2.64
2.40
38.2
37.0
+2.8
427 1)
lE.lH: 1st electrical.lst hydraulic, etc.
2)
Resistance before and after conditioning.
3)
Soaked in 0,l N NaCl.
4)
Soaked for 1 hour in 1 000 mg/l NaOCl.
5)
Soaked for 1 hour in 4 N HCl.
The anionic membranes from the first three hydraulic stages were
as good as new except
hydraulic
stages.
These
for the membranes membranes
causing an increase in weight
were
scaled
effected
fourth
internally,
and resistance and a decrease
ion exchange capacity and gel water content. (4 N HCl)
from the
in
Strong acid
removal of the scale and improved
capacity
with a close return to the membranes original properties.
(Note:
no change in cationic membrane properties was noticed.) The same current density was applied across all stages of each electrical stage during the tests.
hydraulic
Therefore,
too high current density could have caused polarization fourth hydraulic stages.
However,
a
in the
in a full scale application,
each hydraulic stage will have its own electrical stage which can be controlled independantly thus preventing polarization.
It is
expected that a full scale plant should run well with electrical adjustments and/or frequent acid cleanings.
Energy dispersive X-ray analvsis The scale on the anion membrane surfaces mainly of calcium phosphate. and nickel were also present. most of the scale.
(lE.4H) consisted
Traces of sulphate, manganese, iron Acid treatment
(5% HCl) removed
428 EDR vrocess desian criteria and costs Process design criteria for a full-scale EDR plant can be derived
from the EDR pilot results. 3 indicated that a 30 m /h EDR plant
Preliminary estimates had and
clariflocculator
for
phosphate removal would cost approximately US $750 000 (ref. 12). CONCLUSIONS Lime treatment is effective for phosphate
removal.
However,
better phosphate removals should be obtained with lime and ferric chloride. EDR treatment of the effluent should be successful for water and chemical recovery and effluent volume reduction. Membrane
scaling and/or fouling was virtually
absent.
A
full scale plant should run well with electrical adjustments and/or frequent acid cleanings. With the exception of phosphate and TDS, the EDR product water
complies
tower
make-up.
sufficiently chloride).
with
the
quality
Phosphate, with
Both
requirements
however,
should
improved pretreatment
for
cooling
be
reduced
(lime and
ferric
TDS and phosphate should be reduced to the
required
specifications with 10 stage EDR. + Plant nutrients (NH4 ,N03-) may be recovered successfully and
effluent
volume
reduced
significantly
(by
80%)
to
increase service time of the evaporation ponds. Total electrical energy consumption for EDR treatment of the effluent was determined at approximately 5,5 kWh/m3 feed. Process design criteria for a full scale EDR plant
(30m3/h)
can be derived from the pilot plant results. The
cost
of
a
full
scale
EDR
plant
(30 m3/h)
and
clariflocculator for treatment of the effluent was estimated at US $750 000.
429
ACKNOWLEDGEMENT Appreciation is expressed to Sasol Fertilizers (Pty) Ltd for their financial support of this investigation. Acknowledgement is also given to Mr R Jones from Process Plant (Pty) Ltd for his valuable advice during the execution of the project. REFERENCES 1 2
3
4
5 6
7
8
9 10 11 12 13 14
U.S.A.I.D. Desalination Manual, CHZM Hill International Corporation, 7201 N.W., 11th Place, Gainesville, Florida, U.S.A., 32601, 1980. Concentration of electrolytes prior to T. Nishiwaki, evaporation with an electro membrane process, in: R.E. (Ed),Industrial Processing with Lacey and S. Loeb Membranes, Wiley Inter-science, New York, 1972. w. G. Millman and R.J. Heller, Some successful applications of electrodialysis, 4th Conference on Advanced Pollution Control for the Metal Finishing Industry, Lake Buena Vista,Jan.l8 to 20,1982, EPA-600/9-82-022, pp.70-74. N. M. Smirnova, B. N. Laskorin, J.S. Mishukova and A.V. Borisov, The Application of electrodialysis with ionexchange membranes for treatment of sodium sulphate solutions, Desalination (Amsterdam) - 9th World Congress on Desalination and Water Re-use, 3, Membrane Processes, Florence 23-27 May, 46 (1983) 197-201. J.J. Schoeman, The Status of electrodialysis technology for brackish and industrial water treatment, Water S-A., ll(2) (1985) 79-86. V.N. Smagin and V.A. Chukhin, Concentration of brines of desalination plants with electrodialysis, 5th International Symposium on Fresh Water from the Sea, 3 (1975) 139-148. s. P. Vysotskii, V.S. Parykin and S.A. Ulasova, Use of the series - manufactured UEO-50-4/12-5 electrodialysis plants for concentrating the waste waters from demineralization plants, Thermal Engineering, 30(9)(1983) 540-542. J. R. Wirth and G. Westbrook, Cooling water salinity and brine disposal optimized with electrodialysis water recovery/brine concentration systems, Combustion, May (1977) 33-37. D. R. Jordan, M.D. Bearden and W.F. McIIhenny, Blowdown concentration by electrodialysis, Chemical Engineering Progress, 71 (7)(1975) 77-82. J.J. Schoeman, I.B. Schutte and H. MacLeod, Lime treatment of an ammonium nitrate effluent from a fertilizer company followed by electrodialysis treatment, Unpublished report. J.J. Schoeman, I.B. Schutte and H. MacLeod, Concentration of an ammonium nitrate effluent from a fertilizer company with electrodialysis, Unpublished Report. J.J. Schoeman and I.B. Schutte, A pilot investigation of the treatment of a fertilizer company waste effluent with lime and electrodialysis reversal, Unpublished report. Test Manual for Penn Selective Membranes, Office of Saline Water Research and Development Progress Report No 77 (1964). PB 181575. J. J. Schoeman and H. MacLeod, The effect of particle removal by size and interfering ions on fluoride activated alumna, Water S-A., 14(4) (1987) 229-234.