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Novel applications of forward osmosis process for industrial wastewater treatment

  • Songbok Lee (이성복, 대학원 건축사회환경공학과 환경공학전공)

초록/요약

Nowadays, water shortage is one of the biggest problems in global. Therefore, the importance of reusing wastewater is emphasized in terms of the discovery for new potential water resources. In order to achieve efficient wastewater reuse, FO process as advanced membrane based technology is applied for various fields due to its low energy consumption, high rejection, and high fouling reversibility. In this study, based on these advantages, the FO process is evaluated with various wastewater as shown high TDS, high contaminants and high fouling potential. Firstly, membrane-based desalting processes including reverse osmosis (RO), forward osmosis (FO), and membrane distillation (MD) were systematically evaluated for concentrating RO brine to verify its fundamental porformance. Basic characteristics of membrane processes were first examined. Commercial polyamide RO exhibited higher water and lower salt permeability coefficients than cellulose FO membrane. However, salt rejection by FO seemed to be higher than RO primarily due to the hindrance of reverse draw solute flux. The water flux of MD comparable to RO was obtained when temperature gradient was more than 20˚C. The applicability of RO, FO, and MD was further tested with real RO brine obtained from full-scale RO plant processing brackish water. Results demonstrated that water flux was not significantly reduced in MD, while severe flux decline was observed in both RO and FO at high recovery. To elucidate major causes of different flux behaviors, the fouled membrane surfaces were analyzed by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Foulant analysis suggested that CaCO3 scaling occurred particularly at high water recovery, which was in good agreement with water quality simulation. CaCO3 scaling, however, had only small impact on performance of MD. From these findings, MD could be suggested as the best option for concentrating industrial RO brine if low-grade heat form the plant such as power plant and steel mill (below 60˚C) is available. Secondly, the feasibility of forward osmosis (FO) hybridized with membrane distillation (MD) was systematically investigated for treating flue gas desulfurization (FGD) wastewater. FO experiments were conducted using raw FGD wastewater obtained from a coal-fired power plant in Korea for its treatment. Severe membrane fouling in FO was observed since FGD wastewater contained various components (i.e., particles, colloids, organics, and ions). To elucidate fouling mechanism of FO, the combined fouling layer by particulates and scales was identified via SEM, EDX and XRD. Microfiltration (MF) pre-treatment was effective in removing particulates and mitigating the initial fouling. Antiscalant-blended draw solution (DS) could inhibit the formation of membrane scaling by reverse draw solute flux. With such fouling control schemes, FO achieved the highest recovery rate compared to other desalting processes (i.e., RO and MD), suggesting that FO is suitable for treating wastewater with high fouling potential and high TDS. Finally, the diluted DS was recovered by MD. MD could re-concentrate the diluted DS up to 50% recovery rate with no significant flux decline. Rapid flux decline was then observed due to membrane scaling. Thus, appropriate antiscalants in DS should be considered to inhibit scaling formation in FO and MD simultaneously. Lastly, the use of forward osmosis (FO) for concentrating radioactive liquid waste from radiation therapy rooms in hospitals was investigated systematically. The removal of natural and radioactive iodine using FO was first investigated with varying pHs and draw solutions (DSs) to identify the optimal conditions for FO concentration. Results showed that FO had a successful rejection rate for both natural and radioactive iodine (125I) of up to 99.3%. This high rejection rate was achieved at a high pH, mainly due to electric repulsion between iodine and membrane. Higher iodine removal by FO was also attained with a DS that exhibits a reverse salt flux (RSF) adequate to hinder iodine transport. Following this, actual radioactive medical liquid waste was collected and concentrated using FO under these optimal conditions. The radionuclides in the medical waste (131I) were removed effectively, but the water recovery rate was limited due to severe membrane fouling. To enhance the recovery rate, hydraulic washing was applied, but this had only limited success due to combined organic-inorganic fouling of the FO membrane. Finally, the effect of FO concentration on the reduction of septic tank volume was simulated as a function of recovery rate. To our knowledge, this study is the first attempt to explore the potential of FO technology for concentraing radioactive waste, and thus could be expanded to the dewatering of the radioactive liquid wastes from a variety of sources, such as nuclear power plants. FO could succefully concentrate various wastewater compared to other membrane-based desalting processes. However, the efficient operation still suffered from membrane fouling due to low efficiency of physical washing. Therefore, a further study is required to develop more effective cleaning methods for harsh wastewater treatment. Furthermore, the accumulated contaminants in DS should be considered for the continuously stable operations in FO process and the production of reusable permeate due to the negative impacts on the efficient recovery of DS and the reuse/discharge of the produced water.

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목차

Abstract I
TABLE OF CONTENTS IV
LIST OF TABLES VII
LIST OF FIGURES IX
Chapter 1. Introduction 1
Chapter 2. Literature review 7
2.1 FO Applications for Industrial Process: Its challenge and future 7
2.1.1 Introduction 7
2.1.2 Application of forward osmosis for industrial process 9
2.1.3 Conclusions and Future prospects 19
2.2 Liquid radioactive waste treatment using membrane based technologies 21
2.2.1 Introduction 21
2.2.2 Hybrid microfiltration system 27
2.2.3 Hybrid ultrafiltration system 30
2.2.4 Reverse osmosis system 32
2.2.5 Membrane distillation system 34
2.2.6 Conclusions 35
Chapter 3. Evaluation of membrane based desalting processes for RO brine treatment 38
3.1 Introduction 38
3.2 Materials and Methods 40
3.2.1 RO brine 40
3.2.2 RO experiments 41
3.2.3 FO experiments 42
3.2.4 MD experiments 44
3.2.5 Surface analysis of fouled membrane by SEM-EDX and XRD 44
3.3 Results and discussion 45
3.3.1 Basic performance evaluation of RO, FO, and MD membrane processes 45
3.3.2 Application of RO, FO, and MD processes for RO brine treatment 48
3.3.3 Foulant analysis for the verification of scale formation 52
3.4 Conclusions 54
Chapter 4. Treatment of industrial wastewater produced by desulfurization process in a coal-fired power plant via FO-MD hybrid process 56
4.1 Introduction 56
4.2 Materials and methods 59
4.2.1 FO membrane and draw solutions 59
4.2.2 FGD wastewater 60
4.2.3 FO experiments 61
4.2.4 MD experiments 62
4.2.5 RO experiments 63
4.2.6 Membrane surface analysis 63
4.3 Results and discussion 64
4.3.1 Evaluation of FO performance for the treatment of raw FGD wastewater 64
4.3.2 Strategies for fouling control in FO 69
4.3.3 Comparison of the performance with RO and MD 77
4.3.4 DS recovery using MD 79
4.4 Conclusion 88
Chapter 5. Concentration of Medical Radioactive Liquid Waste Using Forward Osmosis (FO) Membrane Process 90
5.1 Introduction 90
5.2 Materials and methods 94
5.2.1 FO membrane and draw solutions 94
5.2.2 Radioactive feed solutions 95
5.2.3 FO experiments 97
5.2.4 Membrane surface characterization 99
5.2.5 Analytical methods for natural and radioactive iodine 101
5.2.6 Simulation of radioactive liquid waste management 102
5.3 Results and discussion 105
5.3.1 Basic FO performance: Water flux and rejection of natural iodine 105
5.3.2 FO performance with radioisotopes 109
5.3.3 Concentration of real radioactive liquid waste from radioactive therapy 115
5.3.4 Simulation of radioactive liquid waste management 122
5.4 Conclusion 129
Chapter 6. Summary 131
Chapter 7. References 134

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