Indian Journal of Chemical Technology Vo l. 10. November 2003, pp. 670-679

Articles

Treatment of wastewater from dyes manufacture using adsorption

A K A Rathi"* & S A Puranikh

''Technica l Adv iser (C hemical ), Government of Gujarat, Industries Commi ssionerate, Udyog Bhavan. Gandhi nagar 382 01 7. Indi a

byyp Engi neering College, Rajkot 360 005, India

Received 2 April 2002; revised received 17 April 2003; accepted 4 July 2003

In a typical wastewater treatment flow sheet used by several industrial units in India, various stages of treatment include the primary treatment-oiUgrease removal and neutralization, followed by the secondary treatment-chemicaUbiological oxidation and clarification, and the tertiary treatment-adsorption onto activated carbon. The neutralization of the wastewater with acidlmilk of lime increases the concentration of total dissolved solids, which adversely affects the activity of microorganisms during biological oxidation process. To overcome this limitation, adsorption is proposed in the first stage of treatment and other stages could follow depending on the quality of the wastewater. Experiments were carried out on wastewater samples from different plants manufacturing dyes using adsorbents-activated carbon, fly ash, bentonite and lignite. The effectiveness of adsorbents in reducing chemical oxygen demand (COD) and colour was evaluated. The results of COD reduction are fitted into difl'erent models available in the literature. A model for predicting COD equilibrium values is proposed. Sorption kinetics and rate of reduction of COD over time are also discussed.

The dyes and dye intermediates sector of chemical industry in Indi a is dominated by small and medium en terpri ses. More than 750 units are engaged in the manufac ture of a wide range of products in Gujarat, contributing to more than 60% of Indian exports of dyes and dye intermediates. The structure of small ­scale uni ts is revealed by a survey 1 indicating that these units, on an average, employed 2 1 persons, $100.000 (approx) of capital, had annual sa les turnover of $300,000 (approx) and used 14,000 Llday wa ter. The wastewater from such industri es is characteri zed by high chemical oxygen demand and co lour. Consideri ng limited resources available with such units, it is essenti al that simple and cost-effective wastewater treatment solutions be evolved.

A wide range of adsorbents including ac tivated carbon, c lays, bentonite, fl y ash , a lumina, magnesium oxide, ferric oxide, silica, saw dust, zeolites and activated anthracite vo lcanic ash soils are used in wastewater treatment for the removal of metal io ns like chrom ium, copper, arsenic , cad mium, mercury , z inc, molybdenum. uranium, manganese, iron , lead, nicke l and tin , and removal of dissolved organic compou nds which results in the reduction of COD, BOD and colour. Granulated adsorbents are used in vertical columns through which wastewater is passed

*For correspondence (E-mail : icenv@ ic.guj. nic.i n; Fax: 079 3252672)

ti ll the breakthrough occurs . The adsorbent bed is th en regenerated or replaced. The f inely powdered adsorbents are mixed with wastewater in ba tch/stirred tanks and spent adsorbents are removed by filtration. Activated carbons are also reported to have been used in combination w ith activated sl udge processes and with oxidation processes.

Wastewater, contai ning non-biodegradable organic contaminants in varying compos iti on and concentration from multi-product chem ical plants. was treated with act ivated carbon. The adsorption process, in combination with other processesc is considered very effective in reducing COD and colour.

The effectiveness of powdered activated carbon in the removal of COD and colour of disperse dye ' was inves tigated . The investi gations o n effecti veness of molecular sieves, activated a lu mina, granular activated carbon, di atomite, saw dust and powdered activated carbon were carried out on the laboratory scale for di sperse dyes and it was conc luded that powdered activated carbon4 was most effective in removing COD. Activated a lumina, molecular sieves and powdered activated carbo n were found to be comparable in their effecti veness for colour removal. While studying different dyes at va rying dye concentrations and quantiti es, it was observed in most of the cases that better results were obtained for d ilut e sample as compared to a concentrated dye solut io n

Rathi & Puranik: Treatment of wastewater from dye manufacture using adsorption Articles

when fly ash5 was used as adsorbent. Contact time experiments6 were conducted in a completely mixed bed reactor with activated clay as adsorbent for basic blue 69 and direct red 227 dyes. Mass transfer coefficients and dilution rates were determined and it was concluded that diffusion inside the void of the clay pore was the rate-controlling factor. The adsorption of basic cationic dye yellow X-8 GL from water onto brown coal7 has been reported. Batch adsorption studies8 were carried out for colour removal from synthetic reactive red dye aqueous solution and encouraging results were obtained.

Adsorption for effluents9 is reviewed including mechanism of adsorption process, types and characteri stics of adsorbents, solute properties, adsorption process design, regeneration and disposal of spent adsorbents. The use of activated carbon as adsorbent in wastewater treatment, water purification and soi l reclamation has been reviewed 10

. The kinetics and dynamics of adsorption of anionic dyes 11 , e.g. direct blue, cango red and methyl orange containing wastewater by a coal-attapulgite sorbent were studied and the results obtained were used for the optimization of adsorption treatment of dye contai ning effluents from synthetic leather manufacture. Commercially available activated carbons were evaluated in removing the dye colour 12

from the wastewater from dye utilization and manufacturing industries . The removal of dyes and selected intermediates from wastewater using carbon is reviewed 13 with respect to applications (disperse and cationic dyes , anionic dyes and dye intermediates), properties of carbon adsorbents and alternate adsorbents . The concentrated wastewater from the plants manufacturing Direct Black NBR, Direct Red 3 BL and Direct Black BF dyes were treated with inexpensive adsorbents like fly ash, bentonite and lignite14 before the conventional primary treatment step to reduce COD and colour.

The scope of the present study is restricted to the adsorption process.

Approach The conventional flow-sheets of industrial

wastewater treatment include the primary treatment -oil and grease removal , pH adjustment and clarification, the secondary treatment which may consis t of biological/chemical oxidation and clarification, and depending on the quality of the wastewater and the statutory discharge standards, tertiary treatment/polishing with activated carbon. During pH adjustment, the total dissolved solid

content of the wastewater gets increased because of the formation of inorganic salts (by neutralizat ion of acids/alkalis). The increased total dissolved sol ids content has inhibiting effect on the metabolic activity of microorganisms 15 whereby the biological as well as chemical degradation does not proceed to the desired extent. To address this constraint, it was decided to reduce COD of the wastewater discharged from the process plant as it is i.e. when the stream is concentrated with all kind of pollutants.

It was decided to consider COD as the measure of organic solutes in the wastewater samples. The colour of the wastewater was also measured. These parameters (COD and colour) reflect the practical aspects of wastewater treatment on the industri al scale. Thus, such a study should be of much relevance to the industry in selecting cost-effective wastewater treatment technique to comply with the statutory regulations. The approach followed for the evaluation of adsorption performance of different adsorbents vi ::. . activated carbon, fly ash, bentonite and lign ite in the treatment of wastewater from dyes manufacturing plants belonging to small as well as large-scale sectors is based on detection of COD and colour (optical density) in the treated water with vary 1ng degree of treatment.

Experimental Procedure Initial exploratory experiments were conducted for

2 h on wastewater streams from some dyes manufacturing plants (Table I ). Elaborate contact time experiments were planned for wastewater samples from twenty plants manufacturing different dyes (Table 2). These samples were taken direct ly from the process plants, before these had any chance of getting mixed with any other streams. In most of the case·s these were concentrated streams, often referred to as mother liquor. 500 mL of sample was taken from the respective carboy in a cylindrical jar. 2.5 g activated carbon (AC) was added into the flask

Table 1- Initial exploratory ex periments

Dye in wastewater

Viscous orange-A dye

Acid black 10-BX dye

Chlorantine fast 5GLL

Acid black GTS

Direct green NBB

Direct black EP

COD reduction, %

AC BP

73 .91 82.6 1

8 1.63 67 .35

47 .62 57.14

91.31 89. 13

28.58 33.35

95.00 70.00

Colour reducti on. 'it AC BP

92 .78 78.89

40.85 44.27

54.59 35.7:\

67 1

Articles

Table 2-Effluent stream samples

Sample Dye

Fast Red B Base 2 Reactive Black-5 3 Reactive Yellow FG 4 Reactive Red-HE5B 5 Reactive Red RB 6 Azo 7 Direct Black-22 8 Direct Black-BT 9 Direct Blue 79 10 Direct Black NBR II Direct Red 3BL 12 Direct Black BF 13 Auramine 0 14 Rhodamine B 15 Vat Green FFB 16 Disperse Yellow-7GL 17 Disperse Golden Yellow GG 18 Acid Black lOBX 19 Acid Black SB 20 Phthalogen Blue

and agitated with magnetic stirrer. 5-10 mL sample was drawn from this mass every 15 min, fil tered on filter paper and the filtrate analyzed for pH, colour and COD. At the end of 2 h, the stirrer was stopped. The experiments were repeated with 5 g lignite (BP) and with 5 g bentonite (WP) . For wastewater samples 10, ll and 12, the adsorbent AC was replaced with fly ash (FA). All the experiments were carried out at room temperature 32°C. The characteristics of adsorbents used are listed in Table 3.

Results and Discussion

Performance of adsorbents It may be observed from Figs 1(a-d) that the COD

reduction in the range 9.7-88.1, 20.1-34.4, 13.2-83.1 , and 3.2-90% was obtained for different wastewater samples from dyes manufacturing plants using adsorbents AC, FA, WP, and BP respectively.

For the purpose of comparison, the performance with respect to COD/colour reduction is put in the graded scale as follows:

Reduction, %

> 70 45-70 30-45 20-30 < 20

672

Performance

Very effective Effective Moderately effective Marginally effective Not effective

Indian J. Chern. Techno!. , November ~om

Table 3-Characteristics of adsorbents

Activated carbon (AC) Appearance Fine black powder. free from

gritty matter Acidity/alkalinity 3g boiled in 60 mL water

should give a neutral and colourless fi It rate

Moisture by oven at 100°C 5% Chloride as Cl 0.2% max Sulphate as S04 0.2% max Iron 0.1 % max Alcohol soluble matter 0.2% max Ash content 2-3% Decolouri zing capacity 40% Particle size 10-100 micron Mesh size

- BS 100 90%

White powder (WP) pH 8.76 Moisture 10.2% Adsorption on kerosene 28 mL per 100 g Porosity 19.5% Melting point 1550°C Speci fie surface 220 sq m per g Refractive index 1.502 Particle size 10-100 mi cron Mesh size

+ BS 100 0.45% -BS 100 + BS 200 27.22%

-BS 200 + BS 300 11.77%

- BS 300 60.56%

Fly ash (FA) Silica 7-20% Mixed oxides 55-60% Iron oxide as Fe20 3 2.7-3.7% Alumina as AI20 3 50-55% Calcium oxide as CaO 5-8% Loss on ignition 6-8% Particle size 5-10 micron

Black powder (BP) Volatile matter 30-35% Fixed carbon 20-22% Ash 12-20% Moi sture 10-20% Particle size I 0-100 micron Mesh size

-BS 72 100% (The particle size of the adsorbents was determined with the help of Scanning Electron Microscope)

COD reduction It may be observed that for COD reduction, AC is

very effective for wastewater from the plants manufacturing Acid black 10 BX and Acid black SB dyes, and effective for Fast red B base, Reactive red HE 5B, Azo, Direct black BT, Direct blue 79. Basic auramine 0 dyes and SO rhodamine B. It is

Rathi & Puranik: Treatment of wastewater from dye manufacture using adsorption Articles

100 -·------ ------------- ---- -- - --

90

80

70 -+- 1 AC

;oft --- 1 WP

z 60 -a- 1 BP 0 ---*-2 AC 1-

----+--- 2 WP (J :::) 50 c -+- 2 BP w ~ -+-3AC c 40

- -3\f\/P 0 (J

- 3 BP 30 -+-- 4 AC

--4 VVP

20 -a- 4 BP

-5 .A.C

10 --swP

-+- 5 BP

0 0 0.25 0.5 0.75 1.25 1.5 1.75 2 2.25 2.5

TIME, h

Fig. I a-COD reduction over time

100 ----------

90

80

70 -+- 6AC

~ ~6WP

--.-- 6 BP z 60 0 ---*-7 AC i= u --- 7 WP ;:) 50

-+- 7 BP 0 w

-+- 8 AC 0:: 0 40 - BWP 0 u - SBP

30 -+- 9AC

--9WP

20 -a- 9 BP

---*-10 FA

10 -- 10WP

-+- 10 BP

0 0 0.25 0.5 0.75 1.25 1.5 175 2 2.25 2.5

TIME, h

Fig. lb-COD reduction over time

67:.

Articles

100

90

80

70

;;F.

z 60 0

6 :;:) 50 0 U..l c: 0 40 0 u

30

20

10

0 0 0.25 0.5

100 - -- --------

90

80

70

;;F.

z 60 0

6 :;:)

0 50

U..l c: 0 40 0 u

30

20

10

0 0 0.25 0.5

674

Indian J. Chern . Techno!. , November :!Oo:l

·----- -- -

=== _____.

0.75 125 1.5 175

TIME, h

Fig. lc-COD reduction over time

-------- -- ··- -- -·- - -

0.75 1.25

TIME, h

1.5

Fig. ld- COD reduction over time

175

2

--+-- 11 FA

_.... 11 WP

-- 11 BP

---'*-- 12 FA

--1 21/VP

-+- 12 BP

-+-13 AC

- 131/VP

- - 13 BP

-+-14 .A.C

- 14 1/VP

--.-14 BP

--15AC

--151/VP

--15 BP

2.25

--+-- 16 AC

_.... 16 1/VP

--16 BP

---1 7 AC

--17 VVP

-- 17 BP

-+-1 8 .A.C

-18 1/VP

- 188P

-+- 19AC

- 191/VP

--.- 19 BP

---'*--20 AC

--20 \NP

-+- 20 BP

2.5

--Poly. (16 .A.C)

- - Poly. (16 /l.C')

2.25 2 5

Rathi & Puran ik: Treatment of wastewater from dye manufacture using adsorption Articles

Table 4---Colour reduction

Adsorbent AC WP BP Sample no. Colour redn, % Time, h Colour redn, % Time, h Colour redn , % Time, h

2 77.7 2 3 23.5 1.5 4 58.8 2 5 13.6 2 7 28.8 1.5 8 64.3 2 9 52.9 2 10 59.9 2 11 14.9 2 12 17.4 2 13 99.9 1.5 14 26.3 2 15 67.7 2 18 42 .2 2 19 98.3 2

moderately effective for wastewater from the plants manufacturing Reactive red RB and Vat green FFB dyes, and marginally effective for Direct black 22, Disperse yellow 7 GL, Phthalogene blue dyes and Vat dyes. AC is not effective for wastewater from Reactive black 5, Reactive yellow FG and Disperse golden yellow GG dyes.

WP is very effective for wastewater from Acid black SB dye, and effective for Fast red B base, Reactive red HE 5B, Direct black BT and Acid black I OBX dyes. lt is moderately effective for Reactive black 5, Reactive yellow FG, Reactive red RB, Direct black 22, Direct blue 79, Direct red 3BL, Direct black BF, Basic auramine 0 and Vat green FFB dyes, and marginally effective for Direct black NBR and Disperse yellow 7GL dyes. WP is not effective for wastewater from Azo, SO rhodamine B, Disperse golden yellow GG and Phthalogene blue dyes.

BP is very effective for wastewater from Acid black IOBX and Acid black SB dyes, and effective for Fast red B base, Reactive red HE 5B, Azo, Direct black BT, Direct blue 79, Direct black BF and Basic auramine 0 dyes. It is moderately effective for Reactive red RB , Direct red 3BL, SO rhodamine B and Vat green FFB dyes , and marginally effective for Direct black 22, Disperse yellow 7GL and Phthalogene blue dyes. BP is not effective for Reactive black 5, Reactive yellow FG, Direct black NBR and Disperse golden yellow GG dyes.

FA is moderately effective in COD reduction of wastewater from Direct red 3BL and marginally effective for Direct black NBR and Direct black BF dyes.

83.4 74.4 2 20.6 2 19 0.5 36.1 2 53.8 2 8.8 2 12.2 2

36.9 1.5 31.5 2 49 2 54.9 2

33.9 2 51.5 2 66.9 2 52 2 14.8 2 17.9 2 11.5 2 58.4 2 90.7 2 98.7 0.5 21 2 23.6 2

13.8 2 21.5 2 30.6 2 44.5 2 21.6 85 .8 0.5

It may thus be observed that all the three adsorbents viz. AC, WP and BP are very effective in reducing COD from wastewater from the plant manufacturing Acid black SB dye. These are also effective in reducing COD from wastewater from the plants manufacturing Fast red B base, Reactive red HE 58 and Direct black BT dyes. None of these adsorbents are effective in reducing COD from wastewater fro m the plant manufacturing Disperse golden yellow GG dye. It may also be observed that the performance of AC and BP is comparable in reducing COD from wastewater from the plants manufacturing Fast red B base, Reactive black 5, Reactive red HE 58. Reacti ve red RB, Azo, Direct black 22, Direct black BT. Direc t blue 79, Basic auramine 0, SO rhodamine B. Vat green FFB, Disperse golden yel low GG, Acid black 10 BX, Acid black SB, Disperse golden yellow GG. Disperse yellow 7GL and Phthalogene blue dyes.

Colour reduction For colour reduction, it may be observed from

Table 4 that AC is very effective for wastewater of Reactive black 5, Basic auramine 0 and Acid black SB dyes , and effective for Rective red HE 58. Direc t black BT, Direct blue 79 and Vat green FFB dyes. It is moderately effective for Acid black I 0 BX dye. and marginally effective for Reactive yellow FG. Direc t black 22 and SO rhodamine B dyes. AC is not effective for Reactive red RB dyes.

WP is very effective for wastewater of Reacti ve black 5 and Basic auramine 0 dyes, and effecti ve for Direct black BT, Direct black NBR dye. It is moderately effective for Reactive red HE 5B. Direc t

675

Articles

black 22, Direct blue 79 and Acid black 10 BX dyes, and marginally effective for Reactive yellow FG, SO rhodamine and Acid black SB dyes. WP is not effective for wastewater from Reactive red RB, Direct red 3 BL, Direct black BF, Vat green FFB and Acid black SB dyes.

BP is very effective for wastewater from Reactive black 5, Basic auramine 0 and Acid black SB, and effective for Reactive red HE SB, Direct black BT, Direct blue 79, Direct black NBR and Direct black BF dyes. It is moderately effective for Direct black 22 and Acid black lOBX dyes, and marginally effective for SO rhodamin B and Vat green FFB dyes. BP is not effective for Reactive yellow FG, Reactive red RB and Direct red 3 BL dyes.

FA is effective for wastewater from Direct black NBR dyes and not effective for Direct red 3BL and Direct black BF.

It may thus be observed that all the three adsorbents viz. AC, WP and BP are very effective in reducing colour from wastewater from the plants manufacturing Reactive black 5 and Basic auramine 0 dyes. These are also effective in reducing colour from wastewater from the plant manufacturing Direct black BT dye. None of these adsorbents are effective in reducing COD from wastewater from the plants manufacturing Reactive red RB dye. It may also be observed that the performance of AC and BP is comparable in reducing colour of wastewater from the plants manufacturing Reactive black 5, Reactive yellow FG, Reactive red HE SB, Reactive red RB, Direct black 22, Direct black BT, Direct blue 79, Basic auramine 0 , SO rhodamine B, Acid black 10 BX and Acid black SB dyes. However, AC is observed to perform better than BP for wastewater from Vat green FFB dye plant.

Comparing the cost of adsorbents used in the experiments, it is found that activated carbon is about ten times expensive than either bentonite or lignite, and fly ash being a waste product, may be available almost free. The spent activated carbon or lignite could be di sposed easily and gainfully alongwith solid fuel in boilers. The adsorbate organic matter from wastewater would also contribute to calorific value to some ex tent. At high temperatures in the boilers, large molecules of organic adsorbate would get disintegrated into harmless non-toxic small molecules like carbon dioxide and water. Thus, spent activated carbon as well as lignite have the advantage of easy and safe disposal. Lignite, moreover, has cost advantage over activated carbon .

676

Indian J. Chern. Techno!., Nove mbc:r 2003

Experimental data and models The COD values at different time interval s we re

predicted using the following models available in literature:

l. Weber and Morri 's equation

(C-C)/C; = m, t0·5 + c1

2. Lagergren equation

log( C-Ceq) = m2 t + c2

3. Rathi Puranik equation 16

log(CODRT) = m t + c

The values of COD predicted from these mode ls are plotted against the experimental COD values in Figs 2(a, b) for different ranges. The lines of ±151ft deviation are also drawn. It may be observed that the Rathi Puranik equation predicts the COD with least errors as compared to the other two models.

COD equilibrium prediction It may be seen that Lagergren equation requ1res

data on the equilibrium value of the COD for the prediction of COD at a given time, necess itating experiments for each system. The Rathi Puranik equation does not require equilibrium value of COD for predicting COD of a given system at any time. In fact Rathi Puranik model can predi ct equilibrium value of COD using the following equation:

Ceq= C; + a (1/m In 10) I o·"'" 10

COD equilibrium values so predicted are compared with the experimental values in Fig. 3. It may be observed that the predicted values are within ± 15 % of the experimental values. Rathi Puranik model is thus considered superior to the other two models available in the literature.

Sorption kinetics The most simplified equation of rate of

disappearance17 of COD, with the assumption of elementary reaction may be written as,

-rate = k(COD)"

Sorption constants viz. order of reaction and rate constant are evaluated, Table 5. It may be ob~erved

Rat hi & Puranik: Treatment of wastewater from dye manufacture using adsorption Articles

100000

90000

70000

~60010

" Jll u soo:xJ '6 Q)

a_

8 40000

0

30000

10000

2600000

2100000

-~1600))0

" Q)

u '6 (" a.

8 1100000

0

• •

• COD WM 4 COD L + COD RP

10000 20000 30000 4txXXl 50000 60010 70000 80000 90000 100000

COD experimental , mg/lit

Fig. 2a- COD predicted and experimental

•

•CODWM .;. COD L + COD RP

600000 1 100000 1 60000J 21 ()()()()() 2600000 COD experimental , mg/l1t

Fig. 2b-COD predicted and experimental

from this table th at when order of reaction is highest for a given sample, the rate constant is the least and vice-versa.

The siope of the Weber and Morri equation gives the rate constants of intraparticle diffusion 18

• It is observed that the straight lines do not pass through origin, indicating that the intraparticle diffusion is not the only rate-controlling step except in case of the following samples where the intraparticle diffusion appears to be the rate-controlling step:

900000

800000

...J

t 700000

E ·E sooooo g '5 ~ 500000

0

8 400000

~ ¥ 300000 a.

200000

100000

100000 200000 300000 o400000 500000 600000 700000 800000 900000 1000000

Experimental COD equilibrium, mg/ l

Fig. 3-COD equilibrium values

AC 2, 3, 5, 9, 11 , 16, 17

WP 1, 5, 6, 14, 15, 17

BP2,3, 9, 10, 11 , 15, 17

The rate of sorption which predicts the contact time of sorption system is given by the slope of Lagergren equation 19

. It appears that Lagergren equation is applicable in case of the following samples:

AC 1

WP 2, 3, 8, 10

BP19

The slope indicates the effectiveness of the adsorbents and the initial rate of reduction of COD is indicated by the constant of the Rathi Purani k equation .

Conclusion Adsorption could be used as the first step of

wastewater treatment. COD could be considered a~ a measure of the organic pollutants in complex wastewater streams. The Rathi Puranik model can be used to predict COD at any time in a given system in which adsorbent is used in wastewater treatment for reducing COD. In addition to the initial value or COD, all this model requires, is an experiment on the given system to get just one value of COD at a known time. The other equations require detailed experimentation on a given system. Thus, Rathi Puranik equation can be used to predict COD value<>

677

Articles Indian J. Chern. Techno!. , November :200:1

Table 5-Sorption kinetics constants

Order of reaction Sample AC WP BP

I 2.68 3.04 2.08

2 13.63 10.53 21.22

3 52.57 14.76 1.20

4 4.61 6.22 8.26

5 3.63 6.61 6.04

6 7.75 22.06 7.65

7 8.48 14.12 12.90

8 4.40 6.53 2.60

9 3.96 7.74 3.61

10 29.39 22.49 23.58

II 6.72 6.90 5.93

12 36.08 25.72 35.46

13 4.18 14.73 7.91

14 14.01 11.93 9.80

15 6.90 5.79 5.92

16 12.85 18.80 10.94

17 11.98 14.57 12.02

18 3.19 6.86 4.10

19 2.74 1.40 1.02

20 24.87 37.02 22.65

of a sample in a given system at any time with least experimentation . Moreover, it can also predict equilibrium COD values. The prediction of COD and COD equilibrium values should be useful in the design of adsorption systems.

Considering the rate of reduction of COD obtained for different adsorbents, effectiveness and cost of the adsorbents , and ease of disposal of spent adsorbents, . uitable adsorbent or a combination of adsorbents could be selected for optimizing the cost of wastewater treatment. The performance of lignite is observed to be comparable with that of the activated carbon . Lignite is, therefore, considered to be very cost-effective adsorbent in reducing COD as well as colour from wastewater generated during the manufacturing of a number of reactive, azo, vat, direct and acid dyes and bases . This study should be very useful to the manufacturers of dyes in the developing countries in tackling water pollution problems.

Nomenclature a =constant AC =activated carbon BOD =Biological Oxygen Demand BP =lignite

678

Log (rate constant) AC WP BP

-7.37 -9.21 -4.44

-65.52 -47.72 - 104. 11

-283.04 -73.59 -1.94

-17.52 -25.62 -35 .47

-14.15 -29.84 -26.48

-27.07 -89.58 -27.24

-30.89 -53.8 1 -49.22

-19.19 - 29.82 -9.44

-16.80 -37.67 -14.91

-160.73 - 120.87 - 128.23

-28.74 -29.06 -24.56

-201.57 - 139.24 -194.13

-13.69 -63.37 -30.15

-80.51 -70. 13 -54.92

-26.62 -21.86 -22.34

-49.04 - 72.70 -40.93

-49.72 - 61.21 -50.02

-9.25 - 27.38 -13.55

-5 .1 6 -0.87 - 0.81

-141.27 -215.58 - 128.83

c, c ~o c2 =constant c =COD, mg/L at time 1

=COD, mg!L at time 1=0 =COD at equilibrium =Chemical Oxygen Demand =(C;-C)/t

Ci C eq

COD CODRT FA =fly ash

n I

WP

=slope of straight lines =reaction rate constant =order of reaction =time, h =bentonite

References I Rathi AKA & Puranik S, Indian Che111 Eng. 40 ( ILJ9X) 17, '. 2 Gerhartz W, Elvers B, Ravenscroft M, Roun savill a J F &

Schulz G, Ull111ann 's Encyclopaedia of Industrial Chelni,tn· (VCH Verlag, Basel, Switzerland), 1988. B3. 9.49.

3 Lin Sheng H. J Chem Techno! Biotech no!. 57 ( 199:1) :IX7. 4 Lin Sheng H, J Chern Teclwol Biotechnol. 58 ( 199]) l:'ilJ. 5 Malik A & Taneja U, A111 Dyest Rep, 83 ( 1994) 20. 6 Wa F C. Hsu Y C & Tseng R L, Zhongvuo Huoniing

Gongcheng Xuekan , 4 (1994) 207. 7 Ding D & Gu J, Huax ue Shijie, 35 ( 1994) 322. 8 Geeta K, Murthy D V S & Shastry C A. J Ins! E11g ( 11/(/io ).

Chem Eng Div, 73 (1992) 12. 9 Gordan M K, Bushra A D, Stephen A & Thornpson A. l111cgr

Pol!ut Control Clean Techno!. 3 ( 1992) 17.1. 10 Helmet K & Harald M, U111welt Techno/ Aktue/1 . I ( 1990) 46.

Rathi & Puranik: Treatment o f wastewater from dye manufacture using adsorption Articles

II Rudenko V M. Tarasevich Y I & Ivanova Z G, Khim Techno/ \lody. IS ( 1993) 715.

12 Rao K C, Narayan L, Krishnaiah K & Ashutosh, Indian J Chem Techno/. l (1994) 13.

13 Abraham R & Horad S F. Environmental Chemistry of Dyes and Pigments (Wiley, New York) , 1996.

14 Rathi AKA & Puranik SA, Am Dyest Rep, 88 (1999) 42. 15 Wesley E Jr. Principles of Water Quality Management (CBI

Publishing Company Inc, Boston, USA), 1980.

16 Rathi A K A, Chemical Industry: A Cri tical Anal ys i-, nr Technology Adoption and Upgradation. Ph.D. Thesis. ~ S University of Baroda, Yadodara, 2000.

17 Octave Levenspiel, Chemical Reaction Engineeri11g ( Wi ky Eastern Private Limited, New Delhi , India). 1962.

18 Gupta G S, Prasad G, Panday K K & Singh V N. Wmer. Air Soil Pollut, 37 (1988) 13.

19 Keerthinarayana S, Yijayashankar Y N, Shivalingaiah 8 & Yisweswariah K, J Environ Sci Health , B25 ( 1990) 493.

679