8)
Pergamon
War. Sci. Tech. Vol. 32, No. II, pp. 4S-54, 1995.
Copyright C> 1996IAWQ. Published by ElsevierScienceLtd.
Printed in GreatBritain. Allrights reserved.
0273-1223195 $9'50 + 0-00
Pll:S0273-l223(96)00117-5
MANAGEMENT OF WASTEWATER FROM
THE FERTILIZER INDUSTRY
S. I. Abou-Elela*, E. M. EI-Kamah*, H. I. Aly** and
E. Abou-Taleb*
• WaterPollution Control Department, National Research Centre, Cairo, Egypt
•• CivilEngineering Department, Ain ShamsUniversity, Cairo, Egypt
ABSTRACT
Two schemes of treatment were applied to wastewaterproduced from a superphosphatemanufacturing mit
In the flrst scheme the fmal effluent, comprising washing water from the scrubbing towers in combination
with cooling water, was subjected to chemical coagulation-sedimentation using lime. In the second scheme
the washing water from the scrubbing towers was chemically treated with recycling of a percentage of the
treated effluent The two treatment schemes were carried out using a continuous flow compact unit The
results obtained revealed that chemical treatment of washing water from the scrubbing towers including
recycling treated effluent waste (with a ratio of 1:2) was recommended.The treatment process proved to be
very efficient in removing fluoride, phosphate, silicate and suspended solids. Also. the optimum conditions
required for drying the sludge using sludge drying beds were determined. Analysis of the dry sludge
indicated that it can be reused with the initial raw material in the plant A process design of the proposed
treatment plant was also included. Copyright 0 1996IAWQ. Publisbedby Elsevier Science Ltd.
KEYWORDS
Superphosphate; industrial wastewater; chemical coagulation; fluoride removal.
INTRODUCTION
In Rosetta branch of the Nile River in Egypt there are many manufacturing plants discharging wastewater
without treatment Among these plants is the El-Maliya company, which produces single superphosphate
fertilizer and sulfuric acid as main products, and ferrous sulfate and sodium fluorosilicate as byproducts. The
wastewater discharged to the Nile River (16,000 m 3/d) is highly acidic and contaminated with high
concentrations of inorganic pollutants such as fluoride and phosphate. Fluoride becomes toxic to animals
and human beings when present at >1 mg/l in drinking water and injurious to some crops when present at
>10 mg/l in soil solution (Helaly and Abou-Elela 1990). Also, untreated industrial effluents have highly
toxic effects on the growth of various microorganisms and especially algae (Kozioroski and Kuchaski 1972).
The killing of algae in an aquatic habitat polluted with industrial wastes leads to disturbances in the primary
food chain and ultimately the ecosystem.
There are several treatment techniques which can be applied for the treatment of superphosphate wastewater.
Electrodialysis. reverse osmosis. ion exchange. evaporation and desalination concentration processes are
potentially suitable for the treatment of more dilute effluent However. for wastewater produced from the
45
S. I. ABOU-ELELA et aL
46
scrubbing towers, chemical coagulation-sedimentation using lime and lime aided with polyelectrolyte
provedto be successful techniques(Schoeman et a11988).
In this study segregationand treatmentof wastewaterfrom the superphosphate unit was investigated.
MATERIALAND METHODS
Sourcesof Wastewaterin the Company
As a result of a plant survey it was found that the main source of pollution is the wastewater from the
superphosphate production unit. Other wastewater in the plant, cooling water from the sulfuric acid
production unit, is relatively clean (6000 m3/day). In the superphosphate production unit there are two
sources of wastewater, namely cooling water from the sulfuric acid dilution unit (3600 m3/day) and the
wastes produced from the washing of the scrubbing towers (1200 m3/day). The wastewater from the three
scrubbing towers (50 m3/hr) is discharged to the drainage system in open circuit operation (Fig. lA). When
sodium fluorosilicic acid (NaZSiF&> is to be produced, a closed system is employed (Fig. lB). Accordingly,
only IS m3/batehld is producedand dischargedto the drainage system as a shock load.
Fresh H20
~
Chimney
-.
SiF4
C02
3
HF
Storage Tank
I!==::..-+ Waste
Figure IA. Open circuit technique in the superphosphate unit.
TreatabilityStudies
Two schemes of treatmentwere investigatedas follows.
Scheme I. In this scheme the final effluent from the superphosphate unit was subjected to chemical
coagulation-sedimentation using lime as a coagulant.Lime is added mainly to raise the pH of the wastewater
to 9.3 ± 0.2. The optimum pH value which gave the best removal of fluoride and phosphate was determined
using ajar test procedure (Cohen 1957).
Scheme II. In this scheme treatment of washing water from the scrubbing towers mixed at different recycling
ratios with the treated effluent was carried out. The recyclingratio was varied between0.5 and 4.0 Q.
47
Management of wastewaterfrom fertilizerindustry
Fresh
~O
+
Chimney
l!===-.Waste
Pump
Figure lB. Closed circuit technique in thesuperphosphate unit
Treatment Unit
A schematic diagram and specification of the treatment unit are given in Fig. 2 and Table 1. The unit was
operated at a hydraulic load of 18.89 m3tm3tday.
Table 1. Specificationof the treatment unit
Dimensions
Volume
Flow rate
Detention time
Flasb mwn&
tank
IOx7xS em depth
3S0 em 3
Flocculation
tank
ISxlOX30 em depth
4S00 em 3
Sedimentation
tank
4OXlSx2S em deoth
ISOOOem3
SUb
4.2 min
SUb
S4min
SUb
180 min .
Slud!:e DO'in!: Beds
A laboratory-scale unit simulating sludge drying beds was designed and manufactured to determine the
optimum conditions for drying the sludge. The unit consisted of three PVC columns fixed in a wooden rack.
A schematic diagram of the unit used is shown in Fig. 3. The volume of the sludge applied to the bed was
calculated according to the followingequation:
volume of sludge applied = surface area of column x depth of sludge.
To obtain the optimum conditions required to get 60% moisture content, different sand depths (12-20 em)
were used at a fixed sludge volume of one litre. Another experiment was carried out by changing the sludge
volume from 1 to 2 litres while the sand zone was fixed at 17 em depth. The experiments were repeated four
times with different quantities of the sludge. In each run the sludge moisture content was determined daily
and for a duration of 8 days.
S. I. ABOU·ELELA et aL
48
40
5
lI'I
Outlet
I--=~.-'
o
N
Sec. Elevation
f-t
I~~i
! ----------[r~t
40
~-f
. - u.:
I
I
Plan
Figure 2. Aschematic diagram of thetreatment unit
Analysis
The physico-ehemical parameters includedthe following: electric conductivity (BC), total dissolved solids at
105°C(TSS), total residue at 105°C (fR), total dissolved solids at 105°C (IDS), turbidity (NTIJ), 'total
phosphate (TP), soluble silicate (Si02) fluoride (F-) sulfate (S04-)' chloride (CI-), total Kjeldahl nitrogen
(TKN) and calcium (Ca++). Also, sludge analysis was performed. The physico-chemical characterizations
werecarried out accordingto StandardMethods(American Public Health Association 1991).
RESULTS
Characterization of Wastewater
Analysis of wastewater from the different sources of pollution in the company is shown in Table 2.
Physico-ehemical analysisof wastewater produced from the scrubbing towersshowed a wide variation in the
wastewater characteristics. The data indicated that the wastewater is highly acidic. The pH varied from 0.7
to 2.06. It also contains a high concentration of phosphate: values reached as high as 308 mg/l with an
averagevalue of 107mg/l. It was found that the majorpollutantis fluoride. Its concentration ranged between
49
Management of wastewater fromfertilizer industry
80 and 13500 mg/l according to the daily operation. Suspended solids content was as high as 1227 mg/l.
Moreover, the waste contains a considerable concentration of dissolved solids which represents71.4% of the
total residue,calculatedon an average basis.
I
d
0
o
I
;; E
~
....
"ON
CII""
.g'1
::>..n
lilo
"ON
§
I
Vl~
E
....
~1i'\,~J;:~i
..n
e-,
Figure 3. Aschematic diagram of thedrying sand bed.
Althoughwashing water from the scrubbing towers represents only 3.6% of the total wastewaterdischarged
from the plant, its influencecan be seen clearly in the quality of the end-of-pipe effluent The average values
of the total suspendedsolids.silicate and phosphate were 100 mg/l, 154 mg/l and 36.5 mg/l, respectively.
Table 2. Characterization of wastewater from differentsources in the company
WasteWllter
ParamClcn
Coolinc watar froID
lulCurie odd unit
CooUnc Wllter from
luporpholphote unit
Waste'MIter from
Krubblnc to_n
W.ste. .ter from
IUpOrphOlphote unit
Average
Rang.
Average
Rmg.
AVcrBge
".3
339-1114
33$-1026
23-63
0.$-2.0
H·17.$
1$.0-$2.8
408
31H
486
37.3
1.116
10.21
31.1
0.7-2.1
4200-38000
1891-4460
917-3674
182-1227
2$-308
120-8000
28-2200
1492$
3117
2226
70$
107
3480
$28
2.8
1900-3300
872-1364
723-11"
31-24$
108-90
g$-363.6
N.D-420
2$48
1088
988
100
36$
1$4.2
108
N.D
N.D-\.6
0.3
80-13$00
32$7
.
.
Rang.
Average
Rang.
70-8 I
480-2000
336-1$73
20$·1209
1$.$-610
0.3-6.4
6.$049.1
31.1-66 00
1231
108J
861
178.$
2.3$
U3
zoo-soo
N.D
moIL
DH
EC
TR
TOS
TSS
TP
S'02
SO 2·
4
F'
69·7
Cooling water from the superphosphate unit was relatively clean. The pH is around 7, while the electrical
conductivity values were in the range between 200 and 600 mho/em. The average values of total solids,
so
S. I. ABOU-ELELA et aL
chloride, silicate and phosphate were 514, 260, 10.0 and 1.2 mgll, respectively. These results are in the
normal ranges of boiling blowdown contaminants (Sittig Marchal 1979).
Analysis of cooling water from the sulfuric acid manufacturing process indicated that the only contaminants
are the inorganic salts which are represented by the EC value. It ranged between 480 and 2000 mho/em with
an average value of 1231 mho/em. This value may be attributed to the use of groundwater in combination
with Nile water as a source of cooling water in this department. Average concentrations of chloride, silicate
and sulfate were 271, 25 and 55 mgll, respectively.
Treatment of Wastewater from the Superphosphate Department
Batch scale treatment. A jar test procedure was applied to obtain the optimum pH and coagulant dose which
produced the best removal of both fluoride and phosphate. Chemical treatment of the final effluent of the
superphosphate unit using a dose of lime of 2.5 gil at a pH of 9.0 gave satisfactory results (Table 3).
Moreover, the results obtained in Table 4 indicated that the treatment of washing water of the scrubbing
towers required a dose of lime equivalent to 12.1 gil.
Table 3. Chemical treatment of the final effluent from the superphosphate department using lime
Parameters, mgIL
Samole
Dose or
lime
pH
NTU TR
TDS
TSS
II'"
SiOl
TP
Ca l +
l!'1L
-
R.W.W·
crs«
1.9
9.2
2.5
61
1.S
1010
879
849
854
115
24
2925
28.5
250
35
22
1.3
248
320
*R. W. W: Raw Wastewater
** erE: Chemically Treated EjJ1uenl
Table 4. Chemical treatment of washing water of scrubbing towers using lime (Q =50 m 3/h )
Parameten mgIL Dose or
lime gIL pH
Samole
R.W.W
crs
.
12.1
0.97
9.2
NTU TR
450
2.8
3435
2259
TDS
2614
2247
TSS
821
12
II'"
3750
35.5
SiOl
5000
100
TP
caJ+
80
N.D
1
710
However, recycling of the treated wastewater with pH around 9.0 is expected to raise the pH of the raw
wastewater; accordingly it will reduce the dose of lime required for the mixture. Recycling with 50-75% of
treated effluent (Fig. 4) was satisfactory to obtain a significant reduction (50 %) in the total lime dose
required per hour.
Continuous flow chemical treatment. Based on the results obtained from batch scale treatment, a continuousflow chemical treatment was carried out using a recycling ratio of treated waste of 200% of the influent
waste. The obtained data showed that the treatment process is very efficient in removing fluoride, phosphate,
silicate and suspended solids (Table 5). Average percentage removal values of phosphate and suspended
solids were 97.3% and 90.3%, respectively. Although the fluoride percentage removal value reached 99.7%,
the average residual value was 52.6 mgll. This problem was solved by mixing the treated effluent with
cooling water from both the superphosphate and the sulfuric acid units.
Managementof wastewaterfran fertilizerindustry
...
s:
<,
C7'
CIo
1Il
0
'0
x
0
51
Run 1
Run 2
800
600
CIo
.~
-
X
a
,2
200
0k----t---+---+---+-.......
4
Fraction of recycled treated waste. Q
Figure4. Determination of optimum recycled treatedwater.
Table S. Results of chemicaltreatment of washing waterfrom scrubbing towerswitha recycling ratio of 1:2
(Doseof lime 1.7 gil).
Parameters m&fL
Minimum
Maximum
Averaze-
Samples
Raw
W.W.
Final
effluent
Raw
W.W.
Final
effluent
Raw
W.W.
Final
effluent
pH
1.2
4200
130
2101
1618
182
28
1680
760
91
800
2.1
23400
200
3737
2917
820
160
13500
6500
9.3
2000
12
2958
2883
75
1.7
67.5
105
1.6
11600
159.5
2707
2198
509.3
55.8
5120
3340
9.1
137
4.3
222
218
45
1.4
52.6
83
E.e.
eOD
TR
TOS
TSS
TP
F'
Si02
N.D
1757
1745
11.5
0.8
37
53
·Ave7'ag' of 4 runs
The concentration of fluoride after dilution with cooling water was almost nil (Table 6). The fluoride
concentration specified in the National Regulatory Standards Act 48 (1982) for wastewater disposal into the
River Nile is 0.5 mg/l. Arora and Chattopadhya (1974) found that for industrial effluent discharged into
inland surface water a threshold limit of 2.0 mgll is recommended. Also, it has been found that industrial
effluents containing fluoride up to 10 mgll have no detrimental effect whatsoever on soil and plants when
usedfor irrigation purposes. A general layoutof the proposed treatment plant is shownin Fig. 5.
52
S. I. ABOU-ELELA tt al.
Sludge Drying
t 5.1.5
1~;-:·~·11
wa~ewa~rr1~~~
Cooling Water From Different
3/hrl
Departments (400 m
1.5.1.5
~1
From Scrubbln
Towers 3
H
Q= 30 m IIY'
10
Clari- FIoc:c:ulator
RIC)'Cled Treated Waste
I
2Q
Dim. in: m
Table 6. Characterization of treated effluent after mixing with cooling water from different departments
Parameters, m&fL
Samnles
1
2
Slud~e DO'in~
pH
TR
TDS
TSS
TP
Sial
F"
73
7.02
831
562
825
529
5.6
33
N.D
N.D
11.8
15.0
N.D
N.D
Beds
The optimum design parameters for sand drying beds were determined. The results obtained in Figs 6 and 7
showed that increasing the depth of the sand layer up to 20 em improved the filterability of the sludge. The
corresponding maximum depth of sludge on drying beds was 32 cm. Also it was found that a 6 day drying
period was sufficient to reduce the sludge moisture content to 60%. However, increasing the drying period
from 6 days to 8 days did not improve the sludge dewaterability. Therefore, a 6 day drying period was
considered optimum to achieve the maximum dewaterability. Air temperature is considered one of the main
design criteria governing the efficiency of drying beds (Eckenfelder 1989). Air temperature during the
drying period varied between 24.8°C and 36°C. The results obtained indicated that there is no dramatic
effect of the temperature on the efficiency of the drying beds. This may be attributed to the fact that air
temperature during this period of the study (September-OCtober) was changing within a narrow range. This
cannot be the case in wintertime as the drying period must be increased.
Slud~e
Reuse
The sludge produced from the chemical unit was analyzed for the possibility of its reuse with raw material in
the plant. Analysis of the chemical sludge indicated that the constituents are almost inorganic in nature. It
contains 62.5% CaF2. 3% CaCI2, 6.6% Si02 and 19.4% Ca5(OH)(PO~3' Therefore the dried sludge can be
reused with the phosphate rock by the company.
Management of wastewater from fertilizerindustry
S3
80
C
~
c
75
0
u
"QI
70
(;
::;:
~
55
Depth of Sand
• IS em
x 17 em
o 20 em
60
3
4
S
Time. days
Figure 6. Sludgedewaterability at differentlayersof sand and fixeddepth of sludge.
7S
c
c
~
70
C'
u
"~
5S
« 50
~
Depth of Sludge
• lS.7 em
x 23.5 em
o 31.S em
Time •days
Figure7. Sludgedewaterability at differentdepthof sludgeand fixed depth of sand.
CONCLUSION
It was found that the main source of pollution from the plant was washing water from the scrubbing towers.
Therefore segregation and treatment of this wastewater is carried out via chemical
coagulation-sedimentation using lime. To minimize the dose of lime, recycling of a part of the treated
effluent was recommended: the recycling ratio was I :2. The treated effluent can be discharged safely into
the public sewerage network. However, for other purposes the treated effluent should be mixed with cooling
water from other departments in the plant. Also, the sludge produced after treatment can be dried and reused
with the raw material in the plant.
ACKNOWLEDGMENT
The authors would like to acknowledge the Science and Technology Cooperation (STC) board for offering
the grant under which this work was carried out. This grant was part of the STC program grant number
263.0016 between the Government of the Arab Republic of Egypt and the United States of America.
S. I. ABOU-ELELA et al;
54
REFERENCES
American Public Health Association (1991). Standard Methods/or The Examination o/Water and Wastewater. 17th edn, APHA,
Washington.
Arora, H. C. and Chattopadhya, S. N. (1974). A study on the effluent disposal of superphosphate fertilizer factory. Indian J.
Environ. Health, 16 (2) 140-150
Coheo,J. M. (1957). ImprovedjartesL J. Amer. Waf. WksAss., 491427-1431.
Eckenfelder, V. W. lt (1989). Industrial Water Pollution Control. 2nd edn, McGraw-Hill International, Civil Engineering Series.
Helaly, A. and Abou-E1ela, S. I. (1990). Protection of surface water from eutrophication via controlled release of phosphate
fertilizer. J. Controlled Release 11 39-44.
Koziorosld. B. and Kuchaski, I. (1972). Industrial Waste Disposal; English Translation Edition, published by Wydawnietwa
Naukowo-Techniczue.
Schoeman, J. J.. Buys, I. J. M.. Schutte, I. B. and Macleod, H. (1988). Pilot investigation on the treatment of ferlilizer
manufacturing process effluent using lime and electrodialysis reversal Desalination V70. Nl-3, P407 (23).
Sittig Marchal (1979). Fertilizer Industry Processes Pollution, Control and Energy Conservation. Mayes-Data Corporation
Chemical