REMOVAL OF CHROMIUM FROM A LOCAL CHROME-TANNERY WASTEWATER BY SODIUM SULFITE REDUCTION COUPLED
WITH ALKALI PRECIPITATION
MA. IVY SABLAON DELA CRUZ
SUBMITTED TO THE FACULTY OF THE COLLEGE OF ENGINEERING AND AGRO-INDUSTRIAL TECHNOLOGY,
UNIVERSITY OF THE PHILIPPINES LOS BAÑOS IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
BACHELOR OF SCIENCE IN CHEMICAL ENGINEERING
OCTOBER 2009
Table of Contents
vii
TABLE OF CONTENTS
Page
TITLE PAGE i
APPROVAL PAGE ii
ACKNOWLEDGEMENT iii
TABLE OF CONTENTS vii
LIST OF TABLES xi
LIST OF FIGURES xii
LITS OF APPENDICES xv
ABSTRACT xvi
1. INTRODUCTION 1
1.1. Significance of the Study 1
1.2. Objectives of the Study 4
1.3. Date and Place of Study 5
1.4. Scope and Limitations of the Study 5
2. REVIEW OF LITERATURE 6
2.1. The Tanning and Leather Finishing Process 6
2.2. Waste Generation Profiles in the Leather Tanning Industry 7 2.2.1. Source, Quantity and Characteristics of the Chrome-tannery
Wastewater
7 2.2.2. Chromium and Other Pollutants in Chrome-Tannery
Wastewater
8 2.3. Waste Management Options for the Leather Tanning Industry 8
2.3.1. Wastewater Segregation 8
2.3.2. Chromium Recovery and Reuse 9
2.3.3. Wastewater Reuse 9
2.3.4. Conventional Metal Removal/ Recovery Methods 9
Table of Contents
viii
2.3.4.1. Electrochemical Treatment 9
2.3.4.2. Chemical Coagulation 10
2.3.4.3. Ion Exchange 10
2.3.4.4. Combined Reduction-Precipitation Process 11 2.3.4.4.1. Principle of Chemical Reduction 11 2.3.4.4.2. Sodium Sulfite as Reductant 14 2.3.4.4.3. Principle of Chemical Precipitation 15 2.3.4.4.4. Hydroxide Precipitation 15
3. METHODOLOGY 17
3.1. Evaluation of the Combined Reduction-Precipitation Process using Synthetic Chrome-containing Solution
17 3.1.1. Preparation of Synthetic Chrome-containing Solution 18 3.1.2. Sulfite Reduction using Synthetic Chrome-containing
Solution
19 3.1.2.1. Experimental Set-up for Sulfite Reduction 19 3.1.2.2. Determination of Reaction Time to attain
maximum Cr(VI) Reduction Efficiency
21 3.1.2.3. Determination of the Effect of Sulfite Dose on
Reduction Efficiency
22 3.1.2.4. Determination of the Effect of pH on Reduction
Efficiency
22 3.1.2.5. Optimization of pH, Sulfite dose, Reaction time
for Cr(VI) Reduction in Synthetic Solution
23 3.1.3. Alkali Precipitation Experiment using Reduced Synthetic
Solution
25 3.2. Evaluation of Combined Reduction-Precipitation Process using
Actual Chrome Tannery Wastewater
26 3.2.1. Preparation and Characterization of Actual Chrome
Tannery Wastewater
28 3.2.2. Optimization of pH and Sulfite Dose for Cr(VI) Reduction
for Actual Wastewater
28
Table of Contents
ix
3.2.3. Alkali Precipitation Experiment for Actual Wastewater 30 3.2.3.1. Alkali Precipitation Experiment using Raw
Actual Wastewater
30 3.2.3.2. Alkali Precipitation Experiment using Reduced
Actual Wastewater
30
3.3. Preliminary Cost Analysis 31
4. RESULTS AND DISCUSSION 32
4.1. Evaluation of the Combined Reduction-Precipitation Process using Synthetic Chrome-containing Solution
32 4.1.1. Characteristics of the Synthetic Chrome-containing
Solution
32 4.1.2. Sodium Sulfite Reduction using Synthetic Solution 32
4.1.2.1. Reaction time that allows Maximum Cr(VI) Reduction Efficiency
32 4.1.2.2. Effect of Sulfite Dose on Cr(VI) Reduction
Efficiency
33 4.1.2.3. Effect of pH on Reduction Efficiency 36 4.1.3.4. Optimum Operating Conditions (pH, Sulfite dose,
Reaction time) for Sulfite Reduction using Synthetic Solution
39
4.1.3. Alkali Precipitation using Synthetic Solution 44 4.2. Evaluation of the Combined Reduction-Precipitation Process using
Actual Chrome-tannery Wastewater
50 4.2.1. Characteristics of Actual Chrome Tannery Wastewater 50 4.2.2. Optimum Operating Condition (pH and Sulfite dose) for
Sulfite Reduction using Actual Chrome-tannery Wastewater
51
4.2.3. Alkali Precipitation for Actual Chrome Tannery Wastewater
55
4.3. Preliminary Cost Estimate 62
Table of Contents
x
5. SUMMARY AND CONCLUSION 63
6. RECOMMENDATIONS 68
7. REFERENCES 69
APPENDICES 74
List of Tables
xi
LIST OF TABLES
Table Title Page
1 Advantages and Disadvantages of Commonly used Reductants
13 2 Design selection guide for using Response Surface
Methodology
24
3 Experimental Box-Behnken Design for the Optimization Experiment for Sulfite Reduction using Synthetic
Solution
25
4 Experimental Face-Centered Central Composite Design for the Optimization Experiment for Sulfite Reduction using Actual Chrome-tannery Wastewater
29
5 Summary of the results for the combined reduction- precipitation process for treating synthetic solution containing 350ppm Cr(VI)
49
6 Characteristics of Actual Chrome-Tannery Wastewater 50
List of Figures
xii
LIST OF FIGURES
Figure Title Page
1 Basic Flow Diagram for Leather Tanning 6
2 Theoretical Solubility of Chromium(III) Hydroxide as a function of pH
16 3 Overview of the experimental process for the evaluation
of combined reduction-precipitation using synthetic solution
17
4 Actual experimental set-up for pH adjustment of synthetic solution
19
5 PR2003 Delta Range Analytical Balance 20
6 Shaker orMixer 20
7 DR 2800 Portable Spectrophotometer 21
8 Overview of the experimental process for the evaluation of combined reduction-precipitation using actual
chrome-tannery wastewater
27
9 Sample of Synthetic solution containing 350ppm Cr(VI) 32 10 Reaction Time that allows Maximum Cr(VI) Reduction
Efficiency
33 11 Effect of Sulfite Dose on Reduction Efficiency at 1.5
solution pH and 2 hours reaction time.
34 12 Theoretical effect of pH on cell potential for reduction
of Cr(VI), oxidation of sulfite, and the overall reaction
37 13 Effect of pH on Reduction Efficiency at 1.270g/L sulfite
dose and2 hours reaction time
38 14 Cr(VI) Reduction Efficiency with respect to Sulfite
Dose and pH at reaction time of 1.5 hours
40 15 Cr(VI) Reduction Efficiency (%) with respect to pH
and reaction time at a fixed sulfite dose of 0.127g/L.
41
List of Figures
xiii
16 Maximum Cr(VI) reduction efficiency (in %) with respect to pH at reaction time equal to 1.5 hours (red area in the plane)
42
17 Minimum Residual Cr(VI) concentration (ppm) with respect to pH at reaction time equal to 1.5 hours (blue area in the plane)
42
18 Numerical optimization plot for a reduction of Cr(VI) to Cr(III) at different sulfite dose (in g/L) and pH
43 19 Residual Total Chromium Concentration with respect to
pH for the Alkali Precipitation of Total Chromium using Reduced Synthetic Solution
45
20.a Samples undergoing precipitation reaction at pH1 to pH7
46 20.b Samples undergoing precipitation reaction at pH8 to
pH14
46 21 Residual Cr(VI) Concentration with respect to pH for
the Alkali Precipitation of Total Chromium using Reduced Synthetic Solution
47
22 Total suspended solids (in grams) per liter of synthetic solution with respect to pH for the Alkali Precipitation of Total Chromium using Reduced Synthetic Solution.
48
23 Synthetic Solution of Pure Cr(VI) (a) Before Reduction (b) After Reduction and (c) After Precipitation
50
24 Actual Chrome Tannery Effluent 51
25 Residual Cr(VI) with respect to Sulfite Dose and pH at reaction time of 1.5 hours
52 26 Cr(VI) Reduction Efficiency with respect to Sulfite
Dose and pH at reaction time of 1.5 hours
54 27 Cr(VI) Reduction efficiency (%) with respect to sulfite
dose (mg/L) at pH 1.0 and reaction time of 1.5 hours.
55 28 Residual Total Chromium Concentration with respect to
pH for the Alkali Precipitation of Total Chromium using Reduced Actual Chrome-tannery Wastewater
57
List of Figures
xiv
29 Residual Total Chromium Concentration with respect to pH for the Alkali Precipitation of Total Chromium using Raw Actual Chrome-tannery Wastewater
57
30 Residual Cr(VI) Concentration with respect to pH for the Alkali Precipitation of Total Chromium using Reduced Actual Chrome-tannery Wastewater
59
31 Residual Cr(VI) Concentration with respect to pH for the Alkali Precipitation of Total Chromium using Raw Actual Chrome-tannery Wastewater
59
32 Total suspended solids (in grams) per liter of raw actual chrome-tannery wastewater with respect to pH for the Alkali Precipitation of Total Chromium using Reduced Actual Chrome-tannery Wastewater
60
33 Total suspended solids (in grams) per liter of raw actual chrome-tannery wastewater with respect to pH for the Alkali Precipitation of Total Chromium using Raw Actual Chrome-tannery Wastewater
61
34 Samples of (a) Actual Chrome-tannery wastewater before treatment, (b) after the reduction process and (c) after the precipitation process
62
List of Appendices
xv
LIST OF APPENDICES
Appendix Title Page
A Theoretical Considerations for Sulfite Reduction 74 B Theoretical Considerations for Alkali Precipitation 81 C Calculation of Reduction Efficiency and
Precipitation Efficiency
82 D Calculations For Preliminary Cost Estimation 83 E Statistical Data Analyses for the Combined Reduction-
Precipitation Treatment Using Synthetic Solution of Pure Hexavalent Chromium
84
F Statistical Data Analyses for the Combined Reduction- Precipitation Treatment Using Actual Chrome-tannery Wastewater
111
G Method 8013 of Hach Handbook 131
H Material Safety Data Sheet for Potassium Dichromate 133 I Material Safety Data Sheet for Sodium Sulfite 140 J Material Safety Data Sheet for Sodium Hydroxide 146
Abstract
xvi
Ma. Ivy S. Dela Cruz. College of Engineering and Agro-Industrial Technology, University of the Philippines Los Baños, October 2009. Removal of Chromium from a Local Chrome-tannery Wastewater by Sodium Sulfite Reduction coupled with Alkali Precipitation.
Adviser: Dr. Catalino G. Alfafara and Prof. Monet Concepcion C. Maguyon Co-Adviser: Dr. Veronica P. Migo
ABSTRACT
The technical feasibility of sodium sulfite reduction coupled with alkali precipitation for the removal of chromium for a local chrome-tannery effluent was evaluated. Initially, the combined reduction-precipitation process was tried using a synthetic solution of pure hexavalent chromium. Independent effects of operating variables (reaction time, pH and sulfite dose) for chromium removal were explored.
Results showed that 20 minute-reaction time was needed to attain maximum reduction efficiency. In addition, Cr(VI) reduction efficiency increases with sulfite dose but decreases with pH. Maximum Cr(VI) reduction efficiency (100% Cr(VI) reduction) was attained at pH 1.0 and 2g/L sulfite dose. For alkali precipitation, minimum residual total chromium (1.6 ppm) and minimum residual Cr(VI) (0.023 ppm) concentrations were attained at a pH range of 8 to 12. The treated synthetic solution complied with the DAO 35 limit of 0.1ppm for Cr(VI), however, the total chromium concentration was still above the 0.5ppm standard.
Using actual chrome-tannery effluent, results of sulfite reduction experiments showed that a maximum of 50% Cr(VI) reduction efficiency was attained at pH 0.5 and sulfite dose of 15mg/L. Alkali precipitation results showed that 100% removal of Cr(VI) (or 0ppm residual Cr(VI)) can be attained at pH 8 whether the actual chrome wastewater underwent sulfite reduction prior to alkali precipitation or not. Respective residual total chromium of 12ppm and 14 ppm were attained for combined reduction-precipitation process and for alkali precipitation process only . The treated actual chrome wastewater complied with the DAO 35 limit of 0.1ppm for Cr(VI), however, the total chromium concentration was still above the 0.5ppm standard. The treatment cost per cubic meter of wastewater was estimated at Php36.50 and Php334.50 for sulfite reduction and alkali precipitation, respectively.
