Application of Nano-Silica and Bentonite to Paper Mill Sludge Dewatering Dinh Thi Luyen、彭元興
E-mail: [email protected]
ABSTRACT
Nano-silica and bentonite have successfully been used in a papermaking dualretention system to help increase the retention of fines and fillers. Nanomontmorillonite although has not been widely applied like nano-silica or bentonite but it owns a similar property to nano-silica and bentonite: the main composition is silica oxide (SiO2) and aluminum oxide (Al2O3). There are a few studies on their application to sludge dewatering purposes,however. Fly ash also is mainly composed of silica oxide and aluminum oxide and it is known that fly ash could be used as an agent to enhance dewatering efficiency but none of works mentioned dewatering mechanism of dewatering system using fly ash clearly. We enlisted the help of a paper mill in central Taiwan which produces cultural and industrial paper products and which applies sedimentation and a single-stage activated sludge (AC) process to treat its mill effluent.The primary sludge and the wasted activated sludge (bio-sludge) were collected for the experiment. In stage 1, a
conventional cationic polymer and a nano-silica (a bentonite) preparation were respectively used as a dewatering agent and co-agent to see whether the dewatering efficiency could be enhanced. Sludge dewatering efficiencies were quantified using the specific resistance to filtration (SRF), capillary suction time (CST) and colloidally dissolved (particles) charge (PCD) methods. A 23 factorial experimental design was used to delineate the effects and interactions of the sequence of polymer addition and the dosage. Analyses of the factorial design on the CST, SRF and PCD tests showed that for the primary sludge all 3 variables under investigation were significant, but none showed interactions with each other; for bio-sludge test results demonstrated stably significant effect of polymer but nano- silica (bentonite) and addition sequence. Besides, tests with bio- sludge also revealed interactions between variables were negligible. We determined that the cationic polymer should be vadded first, followed by the anionic nano-silica (bentonite). The reverse sequence of addition was largely deleterious to the dewatering of the primary sludge. In stage 2,experiments were conducted to compare dewaterability of sludge using single-conditioner system (polymer only) and co-conditioners system (polymer together with nano-silica, bentonite, nano-montmorillonite, fly ash). Based on results from stage 1, we assessed and selected conditions (dosage of conditioners and the sequence of addition) that were able to result in the best dewaterability for each dewatering system and then compare dewaterability of systems at such best conditions. The experimental esults indicated that the co-conditioners system dewatered more effectively than single-conditioner system. Besides, a dewatering mechanism was proposed to illustrate the role of nano-silica, bentonite, nano-montmorillonite and fly ash that helped improve dewaterability of the co-conditioners system.
Keywords : nano-silica, bentonite, nano-montmorillonite, fly ash, primary sludge, biological sludge, capillary suction time (CST), specific resistance to filtration (SRF), PCD.
Table of Contents
授權書 ... iii ABSTRACT ... iv 中文摘要 ... vi ACKNOWLEGMENTS ... viii TABLE OF CONTENTS ... ix LIST OF FIGURES ... xii LIST OF TABLES ... xvi ABBREVIATION ... xviii CHAPTER I.
INTRODUCTION ... 1 CHAPTER II. BACKGROUND ... 4 2.1. Sludge dewatering ...
4 2.1.1. Water distribution in sludge ... 4 2.1.2. Sludge conditioning methods ... 7 2.1.3. Aggregation mechanisms of particles in sludge conditioning systems ... 16 2.1.4. Methods to evaluate the properties of sludge dewaterability ... 20 2.2.
Nanosilica, bentonite and polymer background ... 26 2.2.1. Nano-silica ... 26 2.2.2. Bentonite ... 28 2.2.3. Polymer ... 39 2.3. Factorial design ... 42 CHAPTER III. LITERATURE REVIEW ... 47 3.1. Components affect sludge dewaterability . 47 3.1.1. Cations ... 47 3.1.2. Mixing ... 48 3.1.3. ECP (extracellular polymers) ... 49 3.1.4. Effect of type, dosage and addition sequence of conditioners .... 49 3.2. Conditioning systems ... 52 3.3. Nanosilica and bentonite applications to sludge dewatering ... 58 3.3.1. Nano-silica ... 58 3.3.2. Bentonite ... 59 CHAPTER IV. EXPERIMENTAL MATERIALS AND APPARATUS ... 61 4.1. Materials ... 62 4.1.1. Sludge ... 62 4.1.2. Conditioners-Polymer;Nano-silica, Bentonite, Nano-montmorillonite and Fly ash ... 62 4.2. Conducted
experiments and apparatus ... 66 4.2.1. Specific resistance to filter (SRF) test ... 66 4.2.2. Capillary suction time (CST) test .... 68 4.2.3. Colloidally dissolved (particles) (PCD) test ... 71 4.3. Experimental stages ... 75 CHAPTER V.
EXPERIMENTAL RESULTS ... 77 AND DISCUSSION ... 77 5.1. Properties of primary sludge
... 77 5.2. Factorial design ... 78 5.2.1. Primary sludge ... 78 Polymer/Nano-silica ... 78
Polymer/Bentonite ... 84 5.2.2. Bio-sludge ... 89 Polymer/Nano-silica ... 89
Polymer/Bentonite ... 95 5.3. Dewaterability of co-conditioners system 101 5.3.1. Primary sludge ... 101
Single-Polymer system ... 101 Polymer/Nano-silica ... 103 Polymer/Bentonite ... 112
Polymer/Nano-montmorillonite... 121 Polymer/Fly ash ... 131 5.3.2. Bio-sludge ... 136
Single-Polymer system ... 137 Polymer/Nano-silica ... 139 Polymer/Bentonite ... 148
Polymer/Nano-montmorillonite... 158 Polymer/Fly ash ... 165 CHAPTER VI. PROPOSED DEWATERING MECHANISM OF .. 171 THE CO-CONDITIONERS SYSTEM ... 171 6.1. Co-conditioners system used polymer and nano-silica (bentonite, nanomontmorillonite) ... 171 6.2. Co-conditioners system used polymer and fly ash ... 175 CHAPTER VII. CONCLUSIONS AND SUGGESTIONS ... 178 7.1. Conclusions ... 178 7.2. Suggestions ... 179 REFERENCES ... 181 APPENDIX ... 188
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