This presentation summarizes a study on the efficiency of different alkalis in removing pollutants from chrome tanning liquor waste in tannery industries in Bangladesh. The study characterized waste from two tanneries and tested the removal efficiency of chromium, COD, color, and turbidity using various alkalis including sodium hydroxide, lime, and magnesium oxide. Sodium hydroxide was found to have the fastest settling time but lime achieved the highest color removal. Magnesium oxide produced the least amount of sludge. The study concluded that chemical treatment alone was not sufficient and effluent should undergo further biological treatment. It also found that using mixtures of alkalis could increase cost efficiency for treatment.

1. Presentation on
Efficiency of Different Alkalis in Removing Pollutants
of Chrome Tanning Liquor Waste in Tannery
Industries of Bangladesh
Presented by-
Arnob Barua
(1204181)
Billal Hossain
(1204172)
Supervised by-
Prof .Dr. Md. Delwar Hossain
Dept. of Civil Engineering, BUET, Dhaka-1000

2. Back Ground of the Study
 The Tannery industries are one of the major polluting industries in
Bangladesh
 Chrome tanning is the widely used tanning process in Bangladesh
because of low cost and soft leather product
 Chrome liquor from tanning process contains high BOD, COD and
compounds of trivalent Chromium
 Chromium has carcinogenic effects on human health
 From the tanning units of Hazaribagh area, roughly 5000 m3 of untreated
wastes containing various chemicals go to the Buriganga river
 Thus the Government of Bangladesh has decided to move the whole
tannery industries to Savar Central Effluent Treatment Plant (CETP)

3. Scope of The Study
 Chrome tanning liquor contains various types of
toxic chemicals .
 High concentration of pollutants has already taken
considerable dimension to threaten public Health
and environment .This situation creates necessity
to study the pollution problems and to find out
appropriate removal technique for removal of such
pollutants

4. Objectives of the Study
 To characterize the Chrome liquor of Apex & Reliance Tannery from Savar
CETP area
 To determine the optimum pH for chromium removal
 To determine removal efficiency of Cr, COD, turbidity, and color of different
alkalis as precipitating agent
 To determine cost effectiveness of different combination of alkalis by cost
analysis.
 To Recover Chromium from sludge produced by the Chemical precipitation
 Removal of Chromium from Laboratory Stock Solution of Chromium

5. Conventional Treatment Methods for pollutants
removal
Chemical Treatment Option
 Ion exchange
 Reverse osmosis
 Adsorption
 Chemical precipitation
Biological Treatment Option
 Aerobic Treatment
 Anaerobic treatment

6. Chemical precipitation method
 The Chemical precipitation is carried out in
tanneries to remove pollutants from chrome
liquor.
 Main precipitating agents used are: calcium
hydroxide, sodium hydroxide, magnesium oxide
 Addition of the alkaline substance to the liquid
effluent with stirring at required pH is necessary.
With this methodology, a supernatant with less
pollutants can be obtained.

7. Methodology
 Collection of chrome liquor from Apex and Reliance
Tannery
 Test procedure for chrome liqor characterization for Cr,
COD ,pH,DO,Color)
 Preparation of Laboratory Chromium stock
solution(potassium Dichromate)
 Performing Jar test
 Determination of Chromium
 Determination of color
 Determination of COD
 Recovery of Chromium from Chromium sludge by adding
Conc.Sulphuric acid

8. Devices We Used

9. Devices We Used
AAS Machine Setup Flocculation Chamber

10. Chrome Liquor Characterization

11. 99.70
99.75
99.80
99.85
99.90
99.95
100.00
100.05
0 2000 4000 6000 8000 10000 12000
%Crremoval
Dose
NaoH
lime
MgO

12. Data Analysis
0
50
100
150
200
250
300
350
400
0 50 100
sludgevolm(mL)
TIME(min)
NaOH
MgO
Lime
0
50
100
150
200
250
300
NaOH MgO Lime
SludgeVolume(ml)
vv

13. Removal of Cr from Laboratory Stock Solution
of Potassium Di Chromate
1100
1422
693
973
0
200
400
600
800
1000
1200
1400
1600
5000 10000
RemovalofCr(ppm)
concentration
(mg/l)
MgO
NaOH

14. 0
20
40
60
80
100
120
140
160
0 5000 10000 15000
ResidualColor(pt-counit)
concentration
(mg/l)
NaOH
lime
mgo
0
2000
4000
6000
8000
10000
12000
2000 5000 10000
CODRemoval(ppm)
Concentration
(mg/l)
Lime
MgO
NaOH

15. 0
5
10
15
20
25
30
35
40
45
0 2000 4000 6000 8000 10000 12000 14000 16000
Turbidity(NTU)
concentration (mg/l)
NaOH
Lime
MgO

16. Comparison of Cr Recovery Efficiencies of
MgO and NaOH
3164
2800
2600
2700
2800
2900
3000
3100
3200
MgO NaOH
recoveredCr(ppm)
Recovered Cr(ppm)

17. Cost Analysis
1800
3650
30.34
0
500
1000
1500
2000
2500
3000
3500
4000
NaOH Mgo Lime
cost(Tk.)/m3
Cost

18. Comparison of color between different ratios of
Lime and MgO and Lime and NaOH
3930
3946
4019
3974 3972
3999
3880
3900
3920
3940
3960
3980
4000
4020
4040
5:1 6:1 7:1
Residualcolor(pt-counit)
ratios of alkali mixture
Lime:MgO
LIME:NaOH

19. Comparison of COD between different ratios of
Lime and MgO and Lime and NaOH
55.15
52.68
34.948
50.23
48.36
31.66
0
10
20
30
40
50
60
5:1 6:1 7:1
%CODremoval
ratio
Lime:MgO
Lime:NaOH

20. Comparison of final concentration of Cr between different
ratios of Lime with MgO and Lime with NaOH
0.517
0.65
0.72
0.337
0.517
0.539
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
5:1 6:1 7:1
ResidualCr(ppm)
Lime:NaOH
Lime:MgO

21. Comparison of recovery efficiencies between
different ratios of Lime with MgO and
Lime with NaOH
2370.7
1836.9
1625
3564.8
3110.4
2841
0
500
1000
1500
2000
2500
3000
3500
4000
5:1 6:1 7:1
RecoveredCr(ppm)
Lime:NaOH
Lime:MgO

22. 391
464
362
657
597
572
0
100
200
300
400
500
600
700
5:1 6:1 7:1
cost(Tk.)/m3
Lime:NaOH
Lime:MgO

23. Cost analysis of 5000 mg/l solution of
different ratios of Lime and MgO and Lime
and NaOH
391
464
362
657
597
572
0
100
200
300
400
500
600
700
5:1 6:1 7:1
cost(Tk.)/m3
Lime:NaOH
Lime:MgO

24. Conclusion
 COD removal was insignificant by the chemical treatment
process. There was still a significant amount of biodegradable
waste was present. Therefore effluent should be taken to CETP
for further treatment.
 Color efficiency decreases with the greater concentration of
doses. Among these alkalis, color removal efficiency in lime
was found greater.
 pH is the dominant factor in treating the chrome liquor.
 NaOH is found a better alkaline agent than Ca(OH)2 in shorter
settling time in precipitation process. The performance of the
two alkalis becomes almost same after 24 hour settling.

25. Conclusion (cont.)
 MgO is the best precipitating agent as its sludge
accumulation rate was found much less than NaOH and
Ca(OH)2. So recovery is easier than other precipitating
agent. NaOH is easily soluble but its settling rate is too
slow that, greater retention time will be needed for the
treatment of waste.
 In this study, cost analysis was done and it was found
that using MgO and NaOH was not cost effective.
Therefore, they can’t be used in large scale in developing
countries. Combination was done for increasing cost
efficiency.
 An attempt was made to see the turbidity removal
characteristics. The turbidity removal characteristics
curves were irregular.
 An attempt was made to remove Cr from laboratory stock
solution potassium di chromate. Removal of chromium
was not effective.

26. Recommendation
 The samples were taken from two different locations. Analysis
should be done with different sampling locations with a wide
range of chromium concentration and other contaminants in
the wastewater.
 The use of MgO, NaOH is not cost effective, so a relative
economic analysis was performed to see the cost
effectiveness of the different options. But it was limited. We
should try using more ratios to find the optimum doses that are
cost effective and removal efficiency is also good.
 Variation of mixing time can be done to find the effects of
mixing rate of various alkalis on pollutant removal. In this
investigation, same mixing time was used in the expriment for
all the alkalis.
 Alternative methods can be investigated for the removal of
pollutants of chrome liquor. Here nano particle can be used for
the removal of pollutants.