ARSENIC REMOVAL FROM DRINKING WATER BY FIXED BED ADSORPTION

Transcription

1 ARSENIC REMOVAL FROM DRINKING WATER BY FIXED BED ADSORPTION by TONY SARVINDER SINGH DEPARTMENT OF CHEMICAL ENGINEERING Submitted In fulfillment of the requirements of the degree of DOCTOR OF PHILOSOPHY to the INDIAN INSTITUTE OF TECHNOLOGY, DELHI May, 2004

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3 CERTIFICATE This is to certify that the thesis entitled, "ARSENIC REMOVAL FROM DRINKING WATER BY FIXED BED ADSORPTION" being submitted by Mr. Tony Sarvinder Singh to the Indian Institute of Technology, Delhi for award of Doctor of Philosophy is a record of bonafide research work carried out by him under my guidance and supervision in conformity with the rules and regulations of Indian Institute of Technology, Delhi. The research report and results presented in this thesis have not been submitted, in part or full, to any other university or institute for the award of any degree or diploma. (Dr. K.K Pant) Assistant Professor Department of Chemical Engineering Indian Institute of Technology, Delhi New Delhi

4 DEDICATED TO MY PARENTS (SARDARNI & S. SHER SINGH)

5 ACKNOWLEDGMENT At this moment, available word seem to be inadequate to express my deep sense of gratitude to Dr K. K. Pant Department of Chemical Engineering, by whose inspiration, keen interest and kind of support, I had the opportunity to conduct this study. I shall be indebted to him forever for inculcating within me the qualities of confidence, perseverance and a sense of commitment towards one's work. He is a teacher parexcellence. Without his support, this task couldn't have been so easy for me. I specially thank him for being kind and considerate toward me throughout the course work. It was a fortunate and unforgettable experience to work under his reflective and revered guidance. His endless kindness and incomparable support cannot be thanked adequately here. I am profoundly thankful to Prof A K Gupta Head Chemical Engg. Department, for his concern about my work and clarifying certain doubts about adsorption in fixed bed columns and for providing me with all the necessary laboratory facilities. Encouragement and constant support given by Prof K.D.P Nigam, Prof V.K. Srivastava, Prof B. K. Guha and Dr. S. C. Dhingra throughout my research work is greatly acknowledged. I wish to thank the faculty members and laboratory and office staff of the Department. I am especially grateful to Mr. N.K. Gupta, Mr. Bishamber Dayal and Mr Krishna for their encouragement and help and assistance in laboratory, which enabled me complete this research work. I am thankful to Rekha (Guddu) Singh for her constant inspiration and unstinted support without which I wouldn't have been in position to complete the PhD, as she is a cook, colleague, my best friend, and my greatest critic. Hard to find people like you Guddu. When one owes so many, it is almost impossible and invidious to single out names. However I acknowledge my friends Ms. V Padmavathy, Shugi, Sandeep (Ganju), Zaidi, Nandini, Sanjay Patel, Mr Sarin, Azad & Renu bhabhi, Subhuasini, Dr Surekha, Shubha,

6 Buzz, Ankit Jain, Tej and all GJUians for their love, concern and help during my PhD. Special thanks to Dr. Vimal for final formatting (setting) of my thesis. And when it comes to personal support, I want to express my heartfelt thanks to my dear parents for their support and advice throughout my work. I also remember the valuable words of encouragement from my brothers Dr Prince, Bhabhiji, Jr. Prince and my jaan, Dimple. I also have to thank those people I got became friends at IIT Rahul Sanga, Ashok, Rakesh, Jani, Bamboo, Gullu, Gunja Singh and Munmun, you almost made me feel like at home. I greatly acknowledged University Grants Commission for awarding me Senior Research Fellowship. Herewith I would like to thank for all of those, who have directly or indirectly contributed to the realisation of this thesis. c-t-7,gat, (TONY SARVINDER SINGH) ii

7 ABSTRACT Contamination of drinking water by arsenic has become a key environmental problem of 21 St Century. Millions of peoples are suffering from ill effects of arsenic contaminated drinking water in various parts of the world. Effects are being made to provide arsenic free drinking water in rural areas using low cost adsorbents. In the present study removal of arsenic ions [As(III) and As(V) ions] from water using activated alumina and iron oxide impregnated activated alumina were investigated. The experiments were carried out in batch and fixed bed mode. Preliminary experiments were carried out with a series of sorbents in order to find out a suitable adsorbent for the effective removal of arsenic ions. Five different sorbents were chosen out of which two were different grades of activated alumina (AA). Other sorbents activated carbon prepared from rice husk, Mn02 impregnated AA and iron oxide impregnated AA were used. Based on preliminary experiments AA (AD 101, IPCL grade) and IOIAA had shown maximum percent arsenic removal and highest sorption capacity. Further investigations were made with these two sorbents on As (III) and As (V) removal. The effect of ph, initial sorbate concentration and amount of sorbent in batch mode was studied. ph has shown to be a decisive factor on arsenic removal. Equilibrium, Kinetics and Thermodynamics studies were carried in order to evaluate sorption parameters. The adsorption isotherms were well fitted by Langmuir and Freundlch isotherm. First order kinetics parameters were fitted by Lagergren kinetics and pseudo second order kinetics. Diffusion effect in a solid pellet was also investigated to understand the mechanism of adsorption. Presences of other ions such as P043-, S042-, Cl- and F-, which are generally present in ground water iii

8 sources, were also investigated on the arsenic removal efficiency. It was observed that removal was strongly affected because of presence of these ions and P043- and F were the most interfering ions. Exhausted AA was regenerated by using NaOH solution and regeneration efficiency was tested for repeated regeneration cycles. Both weight loss of activated alumina during subsequent regeneration cycles and the effects of acid concentration on reactivation were studied. The performance of the sorbent for arsenic removal was also studied in a continuous operation, as batch adsorption data do not predict the breakthrough behavior. The effect of inlet flow rate, initial arsenic concentration and bed height has been studied in a fixed bed of sorbent (25 mm ID column) based on the parameters of batch experiments. Experiments were carried out to evaluate the As (III) and As(V) removal efficiency on AA and IOIAA. Percent arsenic removal as a function of run time and uptake capacity related to flow volume was determined by evaluating the breakthrough curves at different flow rate, bed height and initial concentration. Data revealed that an early saturation and lower arsenic concentration in the effluent was observed at higher flow rate and higher arsenic concentration. The column experiments data were analysed by Bohart Adam model. This model satisfactorily explained the behavior during the initial period of breakthrough, but not in the final tailing zone. Therefore another onedimensional model for non-isothermal, non-equilibrum and non-adiabatic, axial dispersed fixed bed adsorption was developed and solved numerically. The model includes the fluid velocity gradient across the axial direction of the bed. Predicted simulations based on the assumption of pore diffusion rate control condition matched the experimental data. The model results revealed that specific interaction between the iv

9 solute and the sorbents increases the ion removal and adsorption equilibrium seems to become decisive factor, as the column tends to saturate. The results of this investigations suggested that activated alumina (AA) and iron oxide impregnated activated alumina (IOIAA) can be effectively used for the treatment of arsenic contaminated groundwater. The treatment of waste is not complete until there is a suitable method available for the disposal of solid waste generated. ANSI standards test methods are available for the safe disposal to various kinds of waste generated during treatment. In the present study investigation were also carried out for the safe disposal of arsenic sludge. The technique was employed to reduce the mobility of arsenic ions so as not to present any environmental hazard. Various matrices were prepared by adding cement, flyash, lime, polystyrene and poly-methyl-methaacrylate (PMMA). These matrices were prepared as per ANSI/ANS standards. The leaching experiments were carried out as per TCLP test method. Semi dynamic leachabilty test were also carried out to determine the leachability of contaminants from monolithic solidified waste forms. Based on results of solidifcation/stablisation studies, an efficient method for disposal of arsenic waste has been proposed. v

10 TABLE OF CONTENTS Page No. Certificate Acknowledgements Abstracts List of Figures List of Tables Nomenclature CHAPTER 1: INTRODUCTION 1.1 Background 1.2 Arsenic Chemistry 1.3 Mobility Mechanism 1.4 Arsenic affected areas 1.5 Health Effects 1.6 Permissible limits 1.7 Mode of action 1.8 Treatment Methods 1.9 Scope of the present research work 1.10 Objectives of the present study CHAPTER 2: LITERATURE REVIEW 2.1 Arsenic Removal Methods Precipitation Coagulation

11 2.1.3 Floatation methods Ion exchange Membrane processes Oxidation Air oxidation Chemical oxidation Biological oxidation Adsorption Activated Carbon Activated Alumina Zeolites Ferric Compounds Biological Processes Other Technologies 2.2 Fixed bed Adsorption Breakthrough Curves Modeling of fixed bed adsorbers Mass transfer Models 2.3 Solid Waste Disposal of Arsenic Rich Waste Material Permissible Limit and TCLP Disposal Methods Observations from Literature Survey 70

12 CHAPTER 3: MATERIALS AND METHODS 3 1 Introduction 3.2 Materials Arsenic stock solution Adsorbent materials Preparation of Activated Rice Husk Carbon (ARHC) Preparation of MnO2 Impregnated Activated Alumina (MDIAA) Preparation of Iron Oxide Coated Activated Alumina (IOIAA) Characterization of Adsorbents 3.3 Experimental Methods Determination of Arsenic concentration Effectiveness of sorbents for arsenic removal 3.4 Batch Experiments Effect of ph Equilibrium Studies Kinetics study Thermodynamic Study Effect of competing/ coexisting ions Regeneration Studies on Activated Alumina 3.5 Fixed Bed Adsorption Studies 3.6 Solidification/ Stablisation (S/S) Studies

13 3.6.1 Materials for solidified/stablised monolithic matrices Monolithic matrix composition Monolithic matrices Formation Toxicity Characteristic Leaching Procedure (TCLP) Semi dynamic leachability test CHAPTER 4: RESULTS AND DISCUSSION 4.1 Introduction 4.2 Characterisation of adsorbents 4.3 Performance of sorbents for arsenic removal 4.4 Effect of ph Effect of ph on As(III) removal Effect of ph on As(V) removal 4.5 Equilibrium Studies Adsorption Isotherms Freundlich Adsorption Isotherm Langmuir adsorption isotherm 4.6 Thermodynamics Study Adsorption of arsenic on AA Adsorption of arsenic on IOIAA 4.7 Kinetics Study Lagergern kinetics model Intraparticle and Mass transfer steps Mass transfer analysis

14 4.8 Effect of competing ions (C1", S042-, P043", F ') on arsenic removal Effect of Phosphate ion Effect of Chloride ions Effect of Fluoride ions on arsenic removal Effect of Sulfate ions 4.9 Regeneration Studies Mechanism of arsenic regeneration CHAPTER 5: FIXED BED ADSORPTION STUDIES ON ARSENIC REMOVAL 5.1 Introduction Effect of operating parameters Effect of bed height on the performance of breakthrough Effect of flow rate on the performance of breakthrough curves Effect of initial arsenic concentration on breakthrough curve 5.3 Modeling of Breakthrough curves Adam Bohart modelm Pore diffusion model Model equations Numerical Solution Analysis of breakthrough curves

15 CHAPTER 6: SOLIDIFICATION AND STABLISATION OF ARSENIC WASTE 6.1 Introduction 6.2 Toxicity Characteristic Leaching Procedure (TCLP) 6.3 Semi-dynamic Leaching 6.4 Leachability Index CHAPTER 7: CONCLUSIONS REFERENCES Appendices