IJERD – International Journal of Environmental and Rural Development (2020) 11-2

Research article
erdTreatment of Wastewater from Dyeing Process of Weaving
Workshop in Inle Lake by Using Lotus Stalk and Coconut
Shell Charcoal
CHAW SU HLAING*
Department of Chemistry, Taunggyi University, Taunggyi, Myanmar
Email: chaw88@gmail.com

NAN NOE NOE OO
Department of Chemistry, Taunggyi University, Taunggyi, Myanmar

AH MAR YI
Department of Chemistry, Taunggyi University, Taunggyi, Myanmar
Received 30 January 2020

Accepted 12 November 2020(*Corresponding Author)

Abstract Inle Lake is the second largest natural lake in Myanmar. It has a population of some
150,000 people, many of whom live on floating islands of vegetation. About half of thepeople who live in Inle Lake work the traditional hand weaving business. It is now facing theenvironmental degradation of its area due to human activities. Direct discharging ofwastewater containing contaminants (especially azo dyes and heavy metals) from dyeing
process into its environment impairs the soil and water qualities and causes a series ofproblems in living beings. In this research, the treatment of wastewater of dyeing processfrom silk, lotus and cotton hand weaving workshops in Inle lake was performed by sorption
technique using local available waste, lotus stalk and coconut shell charcoal as the major
sorbent materials. The results obtained from dyed wastewater treatment using activatedcoconut shell charcoal (5 g), activated lotus stalk (5 g), and a combination effect of activatedlotus stalk and activated coconut shell charcoal at a 4:1 ratio for appropriate time taken
treatment indicated that the highest color removal efficiency (94%, 95%, 100%) respectively.
Therefore, a combination of sorbent materials (4:1) might be the best choice for the dyed
wastewater treatment. The resultant data of before and after treatment of wastewater werecompared with WEPA standard for public health. Some tested heavy metals andphysicochemical properties of treated water were within the WEPA standard. However, longterm disposing of wastewater without proper treatment causes a serious problem. Therefore,
treatment of wastewater before discharging into its environment is necessary for theconservation and sustainability of Inle Lake.
Keywords coconut shell charcoal, cotton, dyeing wastewater, Inle Lake, lotus stalk, silk

INTRODUCTION
Water pollution has become one of the most dangerous threats to the environment in today’s world.
The negative effects of water pollution are not just limited to human beings, but it is fatal for theentire ecosystem. Water comes from many sources like ground water, surface water such as lakewater, pond water, river water, etc., which is why the causes of its pollution are different dependingon the source. Chemical, textiles, tannery industries etc. cause high rate of pollution (Vijaya, 2014).
The effluent containing heavy metals, chemicals, such dyes, oils and many other harmful materials
are discharged by the industries into the water bodies without proper treatment, thus leading tocontamination of said water bodies. All the wastes of the colorant category produced from various
types of industries might have injurious impacts on microbial flora and fauna and may be unhealthyand sometimes even fatal to mammals. At low concentrations, dyes have an adverse effect on the lifeof marine animals and therefore, the food cycle. As per their design, dyes are relatively very steadyⒸ ISERD

62

IJERD – International Journal of Environmental and Rural Development (2020) 11-2

molecules, created to fight against the deterioration by light, biological, chemical and other naturalmodes of degradation (Qada, 2008).
The most widely methods for removing dyes from wastewater systems include physicochemical,
and biological methods, such as flocculation, coagulation, precipitation, adsorption, membrane
filtration, electrochemical techniques, ozonation and fungal decolorization (Sotelo et al., 2002).
Amongst the numerous techniques of removal of dye, adsorption is an effective and useful process.
Adsorption is considered to be superior in comparison with the other techniques of dyeing
wastewater treatment due to low cost, easy availability, simplicity of design, high efficiency, ease ofoperation, biodegradability and the ability to treat dyes in more concentrated form which can mix thewastewater and the porous material powder or granules, such as activated carbon and clay, or let thewastewater through its filter bed composed of granular materials (Zongping, 2011).
But the use of one individual process may often not be sufficient to achieve complete
decolorization. The present study is to explore the feasibility of natural waste materials, lotus stalkand coconut shell charcoal as a low cost and local available sorbent materials in Inle Lake,
Nyaungshwe Township, Taunggyi District of Southern Shan State in Myanmar. The lake has 22 kmlong and 10 km across. It is famous for its scenic beauty and the unique leg-rowing of the Inthas, thenative lake dwellers. It is one of the main tourist attractions in Myanmar. Moreover, the hand weavingwith lotus fiber is also a well-established part of the tourist trail. But, the dyeing wastewater and fiber
extracted lotus stalks which discharged from these hand weaving workshops were adverse effectfrom ecosystem of Inle Lake. Therefore, through this research the potential of treatment of indigo
color dyeing wastewater by the use of new waste matter (lotus stalk) which is handily available inabundance of Inle area has been explored. The used indigo color dye powder is the Bayer trademark.
The chemical formula of indigo is C16H10N2O2 (Wouten, 1991) and its molecular structure is asshown in fig. 1.

Fig. 1 Molecular structure of indigo dye
OBJECTIVES
The aim of this research is to reduce the adverse effect of wastewater from dyeing process on Inle
Lake area by using the treatment with local available waste sorbent materials such as lotus stalks andcoconut shell charcoal, and to protect the environmental deterioration of the lake caused by dye
pollution.
METHODOLOGY
An experimental process of this research was done to evaluate the removal capacity of lotus stalkand coconut shell charcoal with respect to various parameters such as color adsorbent capacity ofmaterial with initial concentration at different doses, time and pH on indigo color dyeing-wastewater.
In all the investigations, the methods and techniques involved both conventional and modern
methods. All observations and measurements except scanning electron microscope (SEM) analysis
were performed in laboratory of Chemistry Department, Taunggyi University, Southern Shan State,
Myanmar. SEM analysis was performed in laboratory of Chemistry Department, Western University
of Yangon.
Collection of samples: The fiber extracted residual lotus stalks, coconut shells and indigo color
dyeing wastewater were collected from one of the silk, lotus and cotton hand weaving workshop in
Inle area in December, 2018. The chemicals used in the experimental work were purchased fromlocal chemical store. All chemicals were of reagent grade.
Ⓒ ISERD

63

IJERD – International Journal of Environmental and Rural Development (2020) 11-2

Preparation of sorbent materials (non-activated and activated lotus stalk): The fiber extracted
residual lotus stalks were cleaned with tap water and distilled water to remove dust particles andwater-soluble impurities. After that, these were cut into small pieces, dried in sunlight for 2 days
until the stalks became crisp. Then using a mortar the stalks were crushed until uniform size particle
was obtained and sieved to desired particle size in order to produce the non-activated lotus stalks.
In the preparation of activated sorbent material, non-activated lotus stalk powder was washedthoroughly with distilled water to remove the dust particles, then soaked overnight in 0.1 M NaOH
solutions and again washed with double distilled water. Then they were soaked in 0.1 M CH3COOH
for a period of 2-3 hours to remove the traces of NaOH. It was thoroughly washed again with double
distilled water till the wash water became colorless and then filtered, air dried, powdered and sieved
before use.
Preparation of non-activated and activated coconut shell charcoal: The coconut shells wereseparated and cleaned from other materials, such as coconut fiber or soil and then dried in sunlight.
The dried coconut shells were burned at burning sink or drum at 200 to 550C for 3-5 hours to getcharcoal. Some charcoal was soaked in chemical solution (25% H3PO4) for 24 hours to become
activated charcoal. The obtained activated charcoal was washed with distilled or clean water andspread on tray at room temperature to be drained. Then, it was dried in oven at temperature 110Cfor 3 hours. These non-activated and activated charcoal were ground and sieved to get the size rangeof 50-100 mesh. The prepared sorbent materials are shown in Fig. 2 (a) and (b).
Characterization of the surface function of prepared sorbent materials: The prepared sorbent
materials were examined by Fourier-transform infrared spectroscopy (FTIR) analysis and scanningelectron microscope (SEM) for a visual inspection of surface morphology.
Determination of maximum wavelength absorbed by indigo dyeing wastewater: The maximum
wavelength, max is the wavelength at which the highest absorbance of the solution has. At thiswavelength, the solution is most sensitive to concentration changes. To determine the λmax ofcollected dyeing wastewater sample, the absorbance versus wavelength graph was constructed byexamining the absorbance of a certain concentration of collected dye sample using UltravioletVisible (UV-VIS) spectrophotometer. The resulted graph was showed in Fig. 6 (a).
Determination of molar absorptivity of indigo dyeing wastewater: The four indigo dyeing
wastewater with the various concentrations of 0.25%, 0.5%, 1%, and 1.25% were prepared and theirabsorbance were examined by UV-VIS spectrophotometer at 530 nm (λmax of collected dye sample).
Then the calibration curve of absorbance versus concentration was constructed and the molar
absorptivity () of indigo dyeing wastewater was determined from the slope of the trend line. The
resulting data are described in Fig. 6 (b).
Treatment of indigo dyeing wastewater: In each twenty separate flasks, 100 mL of 1% originaldyeing wastewater was mixed with the varying masses of 1-5 g of non-activated lotus stalk, activatedlotus stalk, non-activated coconut shell charcoal, and activated coconut shell charcoal respectively
and allowed to stand for 1 day at room temperature. Moreover, the varying amount of 1-5 g of nonactivated coconut shell charcoal, and activated coconut shell charcoal were added in five separate
flasks and allowed to stand for 2 hours. Then the mixtures were separately filtered through filter
paper Whatmann No.1 and the absorbance of each filtrate was determined by UV-VIS
spectrophotometer at 530 nm.
Furthermore, the 100 mL of 1% original dyeing wastewater was mixed with prepared sorbent
materials (non-activated and activated lotus stalk) of various masses ranging from 1 g to 5 g wereadded to this solution in each separate flasks and the mixtures were allowed to stand for 1 day. After
that, the mixtures were separately filtered through filter paper Whatmann No.1. To the filtrates, thedesired amount of various masses (1-4 g) of non-activated coconut shell charcoal and activatedcoconut shell charcoal were separately added and allowed to stand for 2 hours. After sufficient time,the mixtures were filtered again and the pH of each filtrate was adjusted to 7 using 0.1 M citric acid.
Finally, the absorbance of dye solutions before and after treatment were determined by UltravioletVisible (UV-VIS) spectrophotometer at 530 nm. From the observed absorbance of each dye solution,Ⓒ ISERD

64

IJERD – International Journal of Environmental and Rural Development (2020) 11-2

the concentrations and removal percent were calculated using Beer- Lambert’s law and the equation(1) respectively. The resulting data are presented in Tables 2, 3 and 4.
Assessments of quality of dye treated water: The parameters analysed to assess the treated water
qualities were pH, chemical oxygen demand (COD), biochemical oxygen demand (BOD), dissolved
oxygen (DO), total hardness, total alkalinity and some heavy metals. BOD, COD and total hardness
were determined by titration methods. pH, DO and total alkalinity were examined by pH meter, DO
probe (AMT-07) and alkalinity test kit, respectively. Arsenic and heavy metal contents were analysed
by Palintest arsenator and atomic absorption spectrophotometer (SHIMADZU AA-7000). The
resulting data are presented in Table 5.
RESULTS AND DISCUSSION
Fig. 2 (a) and (b) show the prepared lotus stalks and coconut shell charcoal.

Fig. 2 (a) Lotus stalk (b) Coconut shell charcoal
FTIR Analysis
Fourier transform infrared (FTIR) was used to provide structural and compositional information on
the functional groups presented in the solid sorbent materials. Figure 3 shows the infrared spectrumof prepared lotus stalk. The band assignments are tabulated in Table 1.

Fig. 3 FTIR spectrum of lotus stalk
The characteristic peaks of O-H stretching and C-H stretching bands were observed at 3396.64
cm and 2922.16 cm-1. The band at about 875.68 cm-1 shows the characteristic of the deformation of
the glycosidic linkage in cellulose. Furthermore, some peaks in the 600 to 900 cm-1 region associatedwith the aromatic ring C–H out of plane bending vibration were found in the spectrum, corresponding
to the aromatic skeletal vibration in lignin. A dominant absorption bands at 1629.85 and 1431.18 cm1, representing the stretching of symmetric and asymmetric C=O groups of hemicelluloses which
present in the lotus stalk. The band at 1035.77 cm-1 corresponded to C-OH represents the stretchingof alcoholic group-1Ⓒ ISERD

65

IJERD – International Journal of Environmental and Rural Development (2020) 11-2

Table 1 FTIR spectrum assignments for lotus stalkExperimental
Frequency (cm-1)
3396.642922.16
1629.85
1431.181035.77875.640*Literature
Frequency (cm-1)
3200-3600
2800-3000
1600-1950
1400-1470
1000-1200
450-1000*Band assignments
(OH) stretching
(C-H) aliphatic, CH2 , CH3
 asy (C=O) (carbonyl) sym (C=O) (carbonyl)(C-O) (alcohol)(C-H) aromatic*Silverstein (1981)

From the information which found in FTIR analysis, it may be confirmed that lotus stalkprincipally consists of cellulose, pectin, hemicellulose, lignin and chlorophyll pigments.
SEM Analysis

(b)

(a)

Fig. 4 SEM photograph of non-activated coconut shell charcoal
and activated coconut shell charcoal
Fig. 4 (a) and (b) show the surface morphology of non-activated coconut shell charcoal and activatedcoconut shell charcoal. Since micro and meso pores are observed on the surface of the sorbent
materials, significant adsorption is likely to occur. SEM image of the activated coconut shell charcoal
revealed that a more cluster form of aggregate with cavitated pores than the non-activated one.
Therefore, the activated charcoal may be responsible for the more enhanced specific sorption
properties than non-activated one.
Lotus stalk has spongy like and porous structure. Fig. 5 (a) and (b) show surface morphology
of lotus stalk before and after treatment of indigo dyeing-wastewater. After treatment of indigo dye
is very different from surface morphology of before treatment. The significant changes of foam likeand porous structure of the lotus stalk before treatment of indigo dye waste were observed in surface
morphology of the lotus stalk after treatment of dye waste materials. It is one way to explain thenature of images that sorption of dye waste materials on the surface of lotus stalk may take place.

Fig. 5 SEM photographs of lotus stalk before treatment andafter treatment of indigo dyeing-wastewaterⒸ ISERD

66

IJERD – International Journal of Environmental and Rural Development (2020) 11-2

Determination of  max and Molar Absorptivity of Indigo Dyeing Wastewater
Fig. 6 (a) shows absorbance versus wavelength plot of indigo dyeing wastewater to determine  max.
It is found that the max is at 530 nm. Fig. 6 (b) shows the calibration curve of absorbance versus
concentration of indigo dyeing wastewater. The molar absorptivity, ε, was determined from the slopeof the line. The observed value of molar absorptivity, ε, of indigo dyeing wastewater was found tobe 0.5054 cm-1mol-1L by Beer-Lambert’s Law, A = ε c l, A = absorbance of the sample,c = concentration of the sample, l = optical path length.
0.45

AbsorbanceAbsorbance

0.40
0.35
0.30
0.25
0.20

0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0

y = 0.5054x
R² = 0.9823

0400420440460480500520540560580600

0.25

0.5

0.75

1

1.25

1.5

Concentration (%)

Wavelength (nm)

(b)

(a)

Fig. 6 (a) Absorbance versus wavelength plot of indigo dyeing wastewater and(b) Absorbance versus concentration plot of indigo dyeing wastewater
Effect of Prepared Sorbent Materials on Treatment of Dyeing Waste Water
In this research, dye color in collected sample was not completely removed by using only one
prepared sorbent material at fairly time and dosage. Only if the combination effects of prepared twosorbent materials, discharge of dye color was found to be high activity.
Table 2 shows the removal efficiency of indigo dye color by each of the prepared four types ofmaterials. It is found that the removal efficiency of the use of non-activated lotus stalk and nonactivated coconut shell charcoal were not so good on indigo dye color by the use of increase dose of
non-activated lotus stalk and decrease dose of non-activated coconut shell charcoal. Although theoriginal indigo dye color is discharged, the pale yellow color which produced from lotus stalk was
remained. But, the removal efficiency of activated lotus stalk and activated coconut shell charcoal
were found to be fairly high.
Table 2 Removal activity of indigo dye’s color by four types of sorbent materials
Time
taken
Materials (hour)

Concentration of 1% original dyeing
Removal percent (%)
wastewater (mol L-1)
Pr
BeforeAfter treatment (ce)valuetreatment
1g
2g
3g
4g
5g
1g 2g 3g 4g 5g
(co)
NALS
24
0.084 0.048 0.040 0.056 0.078 0.081 43 52 33
740.906*
0.034
ALS
24
0.084 0.034 0.032 0.017 0.005 0.004 59 62 80 94 95
0.963** 0.008
NACSC
20.084 0.049 0.044 0.041 0.038 0.039 42 48 51 55 54
0.935*
0.020
ACSC
20.084 0.037 0.024 0.020 0.013 0.005 56 71 76 85 94
0.988** 0.002
NALS = Non-activated lotus stalk, ALS = Activated lotus stalk, NACSC = Non-activated coconut shell charcoal,
ACSC = Activated coconut shell charcoal, Volume of 1% original dyeing wastewater = 100 mL, Wavelength = 530 nm
r = Pearson correlation coefficient, P-value = probability of obtaining result, * = significant correlation𝑐 𝑐Percent removal of dye = 𝑜− 𝑒 × 100(1)
𝑐𝑜

Where, co = initial concentration (mol L-1),
ce = equilibrium concentration (mol L-1)

Ⓒ ISERD

67

IJERD – International Journal of Environmental and Rural Development (2020) 11-2

Table 3 shows the removal efficiency on indigo dyeing wastewater by the combination effectof non-activated lotus stalks with non-activated and activated coconut shell charcoal. From theseresults, it is found that the dye removal efficiencies of activated coconut shell charcoal is superior to
the non-activated coconut shell charcoal. Activation of prepared sorbent materials has more effectover non activation. Therefore, the treatment of dyeing wastewater was continually performed by
activated sorbent materials to achieve high efficacy.
Table 3 Comparison of removal efficiency on the indigo dyeing wastewater by the
combination effect of non-activated lotus stalk with non-activated and activatedcoconut shell charcoal
Absorbance of 1% original
Concentration of dyeing
Removaldyeing wastewater
wastewater (mol L-1)
Materials
Percentr
P-value
BeforeAfter
BeforeAfter(%)
Treatment
Treatment Treatment
Treatment
NALS (1g) and NACSC (1g)
0.424
0.242
0.084
0.048
42.9
NALS (2g) and NACSC (1g)
0.084
0.424
0.323
0.064
23.8
-0.998*0.04
NALS (3g) and NACSC (1g)
0.084
0.424
0.436
0.086
0
NALS (1g) and ACSC (1g)
0.424
0.235
0.084
0.050
44.6
NALS (2g) and ACSC (1g)
0.424
0.261
0.084
0.052
33.4
-1.000** 0.005
NALS (3g) and ACSC (1g)
0.424
0.331
0.084
0.065
21.9
NALS = Non-activated lotus stalk, NACSC = Non-activated coconut shell charcoal,
ACSC = Activated coconut shell charcoal, Volume of 1% original dyeing solution = 100 mL, Wavelength = 530 nm
r = Pearson correlation coefficient, P-value = probability of obtaining result, * = significant correlation

Table 4 shows the removal activity of the combination effect of activated coconut shell charcoal
and activated lotus stalk. It was found to be more effective on the discharge of indigo dye color. The
combination effects of various masses (1 g, 2 g, 3 g, 4 g) of activated lotus stalk and activated coconut
shell charcoal were found to be (68.9, 80.7, 91.3 %, 94.1% ) removal efficiency respectively. The
dye removal efficiency increases with increasing usage of the amount of activated sorbent materials.
But the combination effect of 4 g of activated lotus stalk and 4 g of activated coconut shell charcoal
was found just a little high efficacy than 3 g combination of each type of sorbent material. This isdue to the 4 g of each type of activated sorbent material only has high efficiency. The combination
effect was seemed to be need to fix amount of one sorbent material and another with variable dose.
Thus, the investigation was continually performed by the use of reduced mass of one of the activatedsorbent materials. In this study, the main attention is to explore the effect of lotus stalk materials on
the discharge of color of dyeing wastewater. Therefore, the observation was performed by the use of
lotus stalk as major sorbent material. The optimum condition was found to be the combination effectof 4 g of activated lotus stalk with 1 g of activated coconut shell charcoal (100%).
Table 4 Removal efficiency on the indigo dyeing wastewater by the combination effect ofactivated lotus stalk and activated coconut shell charcoal
Materials

Absorbance of 1% originaldyeing wastewater
BeforeAfter
Treatment
Treatment

Concentration of dyeing
wastewater (mol L-1)
BeforeAfter
Treatment
Treatment

RemovalPercent (%)

r

ALS (1g) and
0.424
0.132
0.084
0.026
68.9
ACSC (1g)
ALS (2 g) and
0.424
0.082
0.084
0.016
80.7
ACSC (2g)
ALS (3g) and
0.424
0.037
0.084
0.007
91.3
0.976**ACSC (3g)
ALS (4g) and
0.424
0.025
0.084
0.004
94.1
ACSC (4g)
ALS (4g) and
0.424
0.000
0.084
0
100
ACSC (1g)
ALS = Activated lotus stalk, ACSC = Activated coconut shell charcoal
Volume of 1% original dyeing solution = 100 mL, Wavelength = 530 nm
r = Pearson correlation coefficient, P-value = probability of obtaining result, * = significant correlationⒸ ISERD

68

P-value

0.004

IJERD – International Journal of Environmental and Rural Development (2020) 11-2

Statistical analysis of observed results were performed with Pearson correlation analysis. The
results were significant correlated for non-activated sorbent materials and highly significant
correlated for activated sorbent materials.
Table 5 shows the assessments of quality of dyed wastewater before and after treatment process.
By comparing the resulted data with the WEPA wastewater discharge standards for public area, thetested parameters of dye treated water were within the desirable range for ecosystem of Inle Lake.
Table 5 Assessments of Quality of Dye Treated Water
Parameters(ppm, except pH)

1 % original
dyed wastewater

Treated water

pH
BOD
COD
DO
Total alkalinity (as CaCO3)
As
Cd
Cu
Fe
Pb

8.2
13.8
54
3.97
300
ND
0.06180.14502.81850.0307

7
10.0
22
3.04
70
ND
0.01800.04570.42990.0154

Wastewater discharge standards for
public area
(WEPA, 2013)
6-9.5
30
120
600
0.25
0.03
0.5
2.0
0.2

CONCLUSION
From this study, it may be concluded that the removal of dyeing wastewater from Silk and Lotus
Hand Weaving Workshop in Inle Lake area by activated lotus stalk and activated coconut shellcharcoal has been found to be useful for controlling water pollution caused by dyes. From thisexperiment, it is clear that the removal of color of dyes is influenced by the amount of adsorbents
and contact time. The completely destruction of dye color, the highest removal (100%) was favorable
for the combination effect of activated lotus stalk (4g) and activated coconut shell charcoal (1g) in
100 mL of 1% original indigo dyeing wastewater. Thus, with the experimental data obtained in thisstudy, it is possible to design and optimize an economical treatment process by recycling local wastematerials for the dye removal from Silk, Lotus and Cotton Hand Weaving Workshop effluents in Inle
area.
ACKNOWLEDGEMENTS
The authors would like to express special gratitude to Rector Dr Mu Mu Myint, Taunggyi University
and our Ministry of Education for giving us the opportunity to present this research paper. I also
thanks to Professor and Head, Dr Ah Mar Yi, Department of Chemistry, Taunggyi University, ourco-workers and friends for their guidance, helpful and encouragements during this field. We wish to
express our grateful thanks to Shan State Young Entrepreneurs Association (SSYEA) in Taunggyi
City for their kind help and financial support throughout this research paper. Moreover, we also thankthe reviewers of IJERD for their help in improving the quality of our research paper and their criticalreviews.
REFERENCES
Qada, E.A. 2008. Adsorption of basic dyes from aqueous solution onto activated carbons. Chemical
Engineering Journal, 135, 174-184
Silverstein, R.M. 1981. 4th Edition, Jhon Wiley & Sons, Inc. N.Y. 306-311.
Sotelo, J.L., Ovejero, G., Deiado, M.J.A. 2002. Adsorption of lindane from water on GAC: Effect of carbon
loading on kinetic behavior. Chemical Engineering Journal, 87 (1), 113-120.
Vijaya, L. 2014. Removal of malachite green dye from water using orange peel as an adsorbent. 4-34
http://ethesis.nitrkl.ac.in/6030/1/E-178.pdfⒸ ISERD

69

IJERD – International Journal of Environmental and Rural Development (2020) 11-2

WEPA (Water Environment Partnership in Asia). 2013. Environmental quality standards for water and effluent
standards.
Wouten, J.V.A. 1991. High-performance liquid chromatography of blue and purple indigoid natural dyes.
Journal of the Society of Dyers and Colorists’, 107, 266-269.
Zongping, W. 2011. Textile dyeing wastewater treatment, advances in treating textile effluent. 100. derived
from https://en.wikipedia.org/wiki/Beer Lambert lawⒸ ISERD70