See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/322701601
Optimization of Coagulants and Polyelectrolyte Dose for the treatment of
Industrial Dyeing Wastewater
Conference Paper · February 2017
CITATION
READS
1
1,353
3 authors, including:
Bappi Chowdhury
Md. Shahinoor Islam
University of Alberta
Bangladesh University of Engineering and Technology
8 PUBLICATIONS 116 CITATIONS
93 PUBLICATIONS 2,564 CITATIONS
SEE PROFILE
All content following this page was uploaded by Md. Shahinoor Islam on 16 May 2023.
The user has requested enhancement of the downloaded file.
SEE PROFILE
Fifth International Conference on Chemical Engineering (ICChE 2017)
Energy, Environment and Sustainability
OPTIMIZATION OF COAGULANTS AND POLYELECTROLYTE DOSE FOR THE
TREATMENT OF INDUSTRIAL DYEING WASTEWATER
Syed Mohammad Maskur Hossain, Bappi Chowdhury, Md. Shahinoor Islam*
Department of Chemical Engineering, Bangladesh University of Engineering and Technology, Dhaka,
Bangladesh
(*Corresponding author: shahinoorislam@che.buet.ac.bd)
ABSTRACT
Coagulation flocculation has received considerable attention for yielding high pollutant removal
efficiency, which can remove color, toxicity and recalcitrant compounds from the textile wastewater.
Thus, the objective of the current study was to treat the real textile wastewater using coagulationflocculation (CF) method by applying two different coagulants like Magnesium chloride (MgCl2) and
Ferric chloride (FeCl3) w/o anionic polymer. The study was carried out at different doses of the
coagulants for optimization of the coagulants and polymer doses. Color, chemical oxygen demand
(COD), and total suspended solids (TSS) were measured from raw and treated wastewater to fulfill the
objective. The removals of color, COD and TSS at optimum dose of MgCl2 (800 mg/L) were 94%, 75%,
and 57%, respectively. Whereas, the removals of color, COD, and TSS at optimum dose of FeCl3 (600
mg/L) were 88%, 84%, and 65%, respectively. The results showed that the MgCl2 has greater removal
efficiency than FeCl3 for color and at higher doses, but in case of COD and TSS FeCl3 has better removal
efficiency than MgCl2 at lower dose and thus indicated the better choice of coagulant for the treatment of
textile wastewater.
KEYWORDS: Magnesium Chloride, Anionic Polymer, Coagulation, Ferric Chloride, Textile
wastewater
1
INTRODUCTION
Wastewater is the major environmental issue of textile industries in Bangladesh besides other minor
issues like solid waste, resource wastage and occupational health and safety. Textile and dyeing industries
use many kinds of artificial composite dyes and discharged large amount of highly colored wastewater.
The characteristic feature of this sector is high water consumption, and generally100- 200 L of water is
required to produce 1 kg of fabric [1]. The Department of Environment (DoE), Bangladesh has
categorized the textile industries
as a heavily
polluting sector [2]. During the dyeing processes, a portion of the applied dyes to the fabrics remains
unfixed and gets washed out.
Therefore, the wastewater produced from the textile industries is highly colored because of dye
content and also contains several other organic and inorganic constituents which are used at several stages
of production of fabrics. These include sizing agents, wetting chemicals, pigments, softening agents,
surfactants, oils, and other additives [3]. Due to the presence of the above chemicals, the textile
wastewater has high pH, total suspended solids (TSS), chemical oxygen demand (COD) and color. The
wastewater is not suitable for the treatment by using direct biological/advanced oxidation processes due to
its intense color and the presence of recalcitrant compounds. It has been reported that the
(CF) is one of the widely used processes for the removal of color and
recalcitrant compounds from the dyeing wastewaters. The CF process has several advantages over other
processes such as easy operation, relatively simple design and low energy consumption. Usually, the
process has three distinct stages: (i) rapid mixing of dispersed coagulant into water/wastewater to be
treated via violent agitation; (ii) flocculation for agglomeration of small particles into well-defined flocs
via gentle agitation; and (iii) separation of flocs under settling of the treated wastewater. The settled
405
Fifth International Conference on Chemical Engineering (ICChE 2017)
Energy, Environment and Sustainability
sludge is removed and the treated water/wastewater (supernatant) is transferred into subsequent treatment
processor discharge into the surface water body [4].
There is no single process which can be applied for the treatment of wastewater effectively and
always a combination of different processes is used to treat the wastewater. Usually, the CF process is
used as a pretreatment process before applying other processes such as physical (filtration), biological and
advanced oxidation process. Thus, the performance of the effluent treatment process exclusively depends
on the pretreatment of wastewater i.e. on the performance of CF process. However, it is reported that the
coagulant/flocculent dose plays an important role in determining the CF process efficiency [5].
Insufficient or overdosing dose yields a poor performance of the CF process. Thus, it is crucial to
determine the optimum dose in order to minimize the cost and maximize the performance of the treatment
process. Therefore, the main objective of the study was to optimize of coagulants doses using MgCl2 and
FeCl3 w/o addition of polymer for the treatment of real dyeing wastewater. The coagulant doses were
optimized based on the removal of different parameters such as color, COD, and TSS from wastewater.
2
MATERIALS AND METHODS
2.1
Coagulants
There are various inorganic salts which can be used as coagulants such as alum, PAC, ferric
sulfate, ferric chloride, lime, magnesium chloride and inorganic polymer flocculers. In this study, two
different coagulants MgCl2 and FeCl3 were applied to select the suitable ones for textile wastewater
treatment with optimum removal efficiency. Besides, organic coagulants such as poly electrolytes,
synthetic polymers are used for coagulation process as coagulant aid. Polymers (containing
amino/carboxylic group) are large molecules with a high molecular weight and have high ionization
power [6]. It produces a large amount of ions in water and shows the properties of both polymer and
electrolytes. Polyamhotypes, anionic and cationic poly electrolytes are some types of poly electrolytes.
The most practical benefit of poly electrolytes is the formation of massive flocs. These massive flocs
speed up the flocs settling velocity, reduce the expenses of decolorization and also decrease the settled
sludge volume.
2.2
Experimental
Dyeing wastewater from wastewater collection pit (before applying any treatment) was collected
from Alema Textile, Gazipur, Bangladesh. The characterization of wastewater was performed after
collection and the Table 1 shows the results. The collected wastewater has higher color, COD, and TSS,
treatment of this wastewater is necessary before discharge into the surface water intake body. The
wastewater was stored at 40 C until the experiment conduction completed.
Table 1. Characteristics of raw dyeing wastewater received from Alema textile, Gazipur and comparison
with ECR 1997, Bangladesh
Parameters
pH
COD, mg/L
TSS, mg/L
Color, Pt-Co
Results
9.5 ~ 11
1385
210
4600
DoE guidelines [7]
6-9
200
150
-
During coagulation studies, the coagulants and coagulant aids (flocculants) were added as
solution. The salts of MgCl2 and FeCl3were dissolved to prepare 5 g/L solution of both salts in separate
volumetric flask and stored. Similarly, the flocculent solution with a concentration of 500 ppm was
prepared and stored. Then the concentrated solutions were diluted according to their requirement for a
406
Fifth International Conference on Chemical Engineering (ICChE 2017)
Energy, Environment and Sustainability
specific dose. All the experiments were carried out at room temperature. The volume of studied
wastewater was 250 mL.
All the experiments were conducted using the jar test method to determine the optimum dose of
coagulants. Five beakers (500 mL capacity) positioned on magnetic stirrers with a 250 mL of sample
wastewater. A specified dosage of coagulant was added into each beaker with wastewater. The samples
were stirred rapidly for 90 seconds at 200 rpm. Literature showed that most of the inorganic coagulants
work in the pH ranging from 5 to 11 [4]. The optimum pH range for MgCl2 is 9~11 [6] and that for FeCl3
is 5~6.5 [8]. Therefore, the pH was adjusted in different trials by using concentrated sulfuric acid and
sodium hydroxide so that a favorable condition for CF process is maintained. Following that a specified
amount of coagulant aid (60 mg/L) was added and mixed slowly at 10 rpm for 15 minutes for
flocculation. The flocs were visible and were allowed to settle for 30 min before withdrawing samples for
analysis. These procedures are performed for several times so that the optimum dose of coagulants can be
obtained. All the stages have been summarized and shown by the Figure 1.
2.3
Analysis
The wastewater parameters such as color, COD and TSS were determined by following the
standard methods. COD concentration of the samples was measured after digestion of samples by using
potassium dichromate oxidant in acidic environment and by using HACH spectrophotometer. Color was
determined by comparative methods using HACH spectrophotometer DR 2000. The color measurement
unit is Pt-Co. TSS was determined by following standard methods (gravimetric analysis method) using
filter and goose crucible. pH was measured by digital SCHOTT pH meter.
Figure 1. Steps involved during CF treatment of dyeing wastewater used in the laboratory.
3
RESULTS AND DISCUSSIONS
The dyeing wastewater sample collected from the industry was characterized and the Table 1 shows
the results. The wastewater has very high values of color, COD, and TSS as compared ECR 1997 (Table
1). Thus, the wastewater can be discharged into the surface water intake body after a proper treatment. CF
process was applied for the treatment of wastewater as the process is reliable and promising for the
treatment of organics and color from dyeing wastewater. Table 2 shows the treated wastewater
characteristics for color, COD and TSS removal for different doses of MgCl2 and FeCl3. The removals of
407
Fifth International Conference on Chemical Engineering (ICChE 2017)
Energy, Environment and Sustainability
color, COD, and TSS at optimum dose of MgCl2 (800 mg/L) were 94%, 75%, 57% and respectively.
However, the removals of color, COD, and TSS at optimum dose of FeCl3 (600 mg/L) were 88%, 84%,
and 65% respectively (Table 2). The concentrations of COD, and TSS in treated wastewater at optimum
coagulants dose (Table 2) were almost within the range of DoE guidelines as suggested by ECR, 1997
(Table 1). The results for the removals of color, COD, TDS and TSS are discussed in the following
paragraphs below.
3.1
Color removal
The performance of coagulants MgCl2 and FeCl3for color removal is shown in Figure 2. Based on
the removals of color from different doses of MgCl2 and anionic polymer, the optimum dose was 800 mg
MgCl2/L wastewater. The color removal at MgCl2 dose of 400 mg/L wastewater was 82% which was
increased to 85% at MgCl2 dose of 600 mg/L wastewater; then the highest removal efficiency attained at
800 mg MgCl2/L wastewater and then the removal was decreased (88%) even at the highest MgCl2 dose
(1000 mg/L wastewater). However, in the case of FeCl3 as coagulant with anionic polymer, the optimum
dose was 600 mg/L wastewater, at which the highest removal of color (88%) was observed. There was a
drastic increase in color removal from 64% to 88% when the dose of coagulant increased from 200 mg to
600 mg FeCl3/L wastewater. It was also behold that always higher removal of color was observed for
MgCl2 coagulant as compared to FeCl3 coagulant for each dose. From the above two profiles (Figure 2), it
can be concluded that a drastic change of color removal was observed for a short range of FeCl3 (200-600
mg/L wastewater); however, in the case of MgCl2, there was no such drastic increase of color removal
was observed for a long range of coagulant dose (400-1000 mg/L wastewater). The explanation of
achieving highest color removal can be stated as: when the dose of coagulants reached the optimum
amount in the suspension, it caused larger amount of dye particles to aggregate and settle. However,
overdosing of the coagulant in the suspension would cause the aggregated particle to re-disperse and
would also disturb particle settling [9].
Figure 2.Percentage removal of color for different dose of coagulants MgCl2and FeCl3.
408
Fifth International Conference on Chemical Engineering (ICChE 2017)
Energy, Environment and Sustainability
Table 2.Coagulant dose and percentage removal of color, COD and TSS with MgCl2 and FeCl3
Color removal
COD removal
TSS removal
Coagulant & coagulant aid
Dose (ppm)
Raw wastewater
------
4600
-----
1385
-----
210
-----
400
828
82
651
53
147
30
600
690
85
512
63
119
43
800
276
94
346
75
90
57
1000
552
88
484
65
107
49
200
1656
64
872
37
130
38
400
1104
76
637
54
113
46
600
552
88
221
84
73
65
800
782
83
443
68
86
59
Treated wastewater with
MgCl2 & anionic polymer
(60 ppm)
Treated wastewater with
FeCl3& anionic polymer (60
ppm)
3.2
Color
%
(Pt-Co) removal
COD
(mg/L)
%
TSS
%
removal (mg/L) removal
COD removal
Figure 3 shows a comparative removal trend of COD for different doses of coagulants for MgCl2
& FeCl3. A similar trend of removal of COD was observed for color removal with MgCl2 and FeCl3
doses. The highest COD removal was observed at 800 mg MgCl2/L wastewater; however, the highest
removal of COD was observed at 600 mg of FeCl3/L wastewater. Coagulants dose greater than 800 mg of
MgCl2/L wastewater and 600 mg of FeCl3/L wastewater provided a negative trend of removal of COD.
This could be explained by the charge density of both polymers. Any dose higher than the optimum dose
restabilizes the colloidal particles and thus increased the COD in the suspension, which reported earlier
[5].
Figure 3. Percentage removals of COD for different doses of coagulants MgCl2 and FeCl3
409
Fifth International Conference on Chemical Engineering (ICChE 2017)
Energy, Environment and Sustainability
3.3
Solids removal
A similar trend of TSS removal with coagulant doses was observed and the Figure 4 shows the
results. The solid TSS removals were increased until optimum doses of MgCl2 and FeCl3, and then the
removals of solid were decreased at any dose after optimum dose. The maximum TSS removal was 57%
at optimum MgCl2 dose of 800 mg/L wastewater; whereas the maximum removal of TSS for FeCl3 was
65% at optimum FeCl3 dose of 600 mg/L (Figure 4). From the Figure it is clear that the optimum doses
for TSS removals for MgCl2 and FeCl3 were 600 mg/L and 800 mg/L wastewater. After optimum dose of
coagulants, the percentage removal of TSS was decreased slightly.
It is reported that the colloidal particles in wastewater have very little weight (size 10-3 to 10-6)
and the charges present on the colloid surfaces result into repulsion and do not allow them to agglomerate
and form flocs [6]. Unlike polymeric flocculants which are unfazed by pH changes, most coagulants and
flocculants require pH adjustment for effective treatment. It has been widely known that the efficiency of
most conventional coagulants is highly sensitive to the pH of effluents. In general, optimum pH in the
coagulation process is proven to be specific to the type of coagulant used in the treatment. A specific pH
range is usually determined by the type of wastewater and coagulant used during the coagulation process
in order to achieve higher coagulation efficiency. Coagulation performance is inclined to decrease
significantly mainly due to the restabilization of colloids during the treatment at pH outside the effective
pH range. The destabilization of colloidal particles are made possible through the addition of chemicals,
such as acid or alkali, which promoted electrostatic attraction due to the elimination of interparticle forces
by reducing surface charges during pH alteration.
Figure 4.Percentage removal of TSS for different doses of coagulants MgCl2 and FeCl3
From the study it was observed that the optimum dose of MgCl2 was 800 mg/L wastewater; whereas
the optimum dose of FeCl3 was 600 mg/L wastewater. Thus, the MgCl2 has higher removal efficiency as
compared with FeCl3. The improvement of coagulation efficiency at increasing pH with MgCl2 can be
explained by the facts that, a) metal ions are easily hydrolysed in alkaline conditions and form
precipitable hydroxide; b) the aggregation of dyes takes place at specific alkaline pH and hence, reduction
in the solubility. Thus, the MgCl2 has relatively higher removal efficiency than FeCl3.. Again with the
enhanced surface activity and improved charge neutralizing capacity of FeCl3 may influence them more
effective at TSS and COD removal comparatively at lower dose than MgCl2 dose. However, MgCl2 in
presence of colloidal particles has rapid aggregation velocity and thus, forms the larger and heavier flocs;
resulting in higher removal efficiency in case of color.
410
Fifth International Conference on Chemical Engineering (ICChE 2017)
Energy, Environment and Sustainability
4
CONCLUSION
Present experimental studies of dyeing wastewater treatment by MgCl2 and FeCl3 indicated that
both coagulants have higher performance for the removal of color, COD and TSS. Observing all the data
it can be reported that MgCl2 has higher removal efficiency than the FeCl3 at higher doses for color
removal and COD. Maximum removals of color and COD were 94% and 75% for MgCl2, respectively, at
optimum dose of 800 mg/L; and 88% and 84% for FeCl3, respectively, at optimum dose of 600 mg/L of
wastewater. However, for the TSS removal FeCl3 act as a better coagulant than MgCl2 with 8% higher
removal efficiency. The treated wastewater quality almost followed the DoE guidelines as provided by
ECR, 1997. Finally, the study suggested that the use of MgCl2 is a promising coagulant for the color
removal of real textile wastewater and for COD and TSS removal FeCl3 can be considered as a better
coagulant.
5
ACKNOWLEDGEMENTS
We would like to express our gratitude to Bangladesh University of Engineering Technology
(BUET) for providing fund for the research, Department of Chemical Engineering, BUET for providing
laboratory facility, and Alema Textile, Gazipur, Bangladesh for providing us dyeing wastewater.
REFERENCES
[1] Yadav, A., Mukherji, S., and Garg, A., 2013, Removal of Chemical Oxygen Demand and Color
from Simulated Textile Wastewater Using a Combination of Chemical/Physicochemical Processes ,
Industrial and Engineering Chemistry Research, 52, pp.
[2] Dey, S., and Islam, S., 2015, A Review on Textile Wastewater Characterization in Bangladesh,
Resources and Environment , 5(1), pp. 15-44
[3] Holkar, C., R., Jadhav, A., J., Pinjari, D., V., Mahamuni, N., M., and Pandit, A. B., 2016, A critical
review on textile wastewater treatments: Possible approaches Journal of Environmental Management,
182, pp.351-366
[4] Teh, C. Y., Budiman, P., M., Shak, K., P., Y., and Wu, T., Y., 2016, Recent Advancement of
Coagul
, Industrial and Engineering
Chemistry Research, 55, pp.
[5] Can O., T., Kobya, M., Demirbas, E, and Bayramoglu, M., 2006, Treatment of the textile wastewater
by combined electrocoagulation Chemosphere, 62, pp. 181 187.
[6] NabiBidhendi, G. R., Torabian, A., Ehsani, H., and Razmkhah, N., 2007 Evaluation of industrial
dyeing wastewater Treatment with Coagulant and Polyelectrolyte as a Coagulant Aid , Iranian Journal of
Environment Health Science and Engineering, 4(1), pp. 29-36.
[7] Environmental conservative rules (ECR), 1997, Department of environment, Bangladesh.
http://faolex.fao.org/docs/pdf/bgd19918.pdf
[8] Metcalf, L. and Eddy, H., 2003, Wastewater engineering treatment disposal and reuse , McGraw-Hill
Companies, Inc., New York. Pp. 393-500.
[9] Gibbie, P., 2001, Using Polyaluminium Coagulants in Water Treatment , 64th annual water industry
engineers and operaters conference, pp. 39-47
411
View publication stats