本研究採用鋁和鐵電極作為犧牲陽極之電混凝法處理包括人工合成的含硼廢水和燃煤火力發電廠中煙道脫硫所產生的實廠含硼廢水。實驗中探討了不同參數，如:電流密度、pH值、溫度和電導度對除硼效率的影響。並同時比較化學混凝法與電混凝法之除硼效率。除了以批次系統探討上述影響因子外，本研究中也建構了連續式處理系統，由三座反應槽組成，針對實廠廢水施做了固定鋁硼莫爾比，無pH值及溫度控制之去除程序，探討連續系統用於處理實廠廢水的除硼效率。

在使用鋁電極的部分，電流密度、電導率和固定溶液 pH 值對硼去除效率的影響可以忽略不計，最高去除率約為 80%，而溶液溫度顯著影響硼的去除效率，在 20 oC 和 50 oC 的溫度下，除硼效率分別為 65% 和 50%。在鐵電極的部分，pH值對於硼的去除效率有著顯著地影響，pH為7、8和9的去除效率分別為15%、35和30%。另一方面，連續系統在第一反應器、第二反應器和第三反應器中的去除率分別達到約 70、85 和 90%。

整體來說，化混法的除硼效率在本研究中較優於電凝法。使用化混法在鋁硼莫爾比為 15:1 時，硼的去除效率為 70%。而使用電凝法時，鋁硼的莫爾比需要約為 35:1，才能達到約 80% 的除硼效率。對於鐵電極，化混法在鐵硼莫爾比為 5:1 時達到了約 67%的去除率，而使用電凝法在鐵硼莫爾比為 20:1 時僅去除了 31% 的硼，這是因為電生成的二價鐵離子主要以氫氧化亞鐵的形式沉澱，可能對硼酸鹽的結合能力較低。所以在經過一系列的實驗及探討之後，在批次實驗的部分使用三價鐵混凝劑的化學混凝法對於除硼效率有著最適合用且最具經濟性的效果，而電混凝法則可使用鋁犧牲電極之連續式系統來處理實廠的含硼廢水。

In this study, electrocoagulation process using aluminum and iron plates as sacrificial anodes was employed to treat synthetic boron-containing wastewater and actual wastewater collected from a flue-gas desulfurization process at a coal-fired power plant. The effects of different parameters such as current density, pH value, temperature, and electrical conductivity on boron removal efficiency were investigated. Both batch and continuous systems were constructed. For Al plate as an anode, the effect of current density, conductivity and fixed solution pH on boron removal were negligible with the highest removal of around 73%. The solution temperature significantly affects the removal of B with the efficiency of 65% and 50% for the temperature of 20 oC and 50 oC, respectively. For iron anode, pH value significantly affects the removal efficiency of B with the efficiency of 15%, 35 and 30%, respectively for the pH of 7, 8 and 9. 

A continuous EC system with three reactors connected in series for the removal of B from FGD wastewater was investigated. The overall B removal efficiency reached around 70, 85 and 90% for the first reactor, second reactor and third reactor, respectively.

In general, the B removal efficiency using CC process was better than that of EC process. The B removal efficiency was 70% at Al:B molar ratio of 15:1 using CC process. The Al:B molar ratio around 35:1 was required to obtain the B removal efficiency around 72% using EC process. For iron system, CC process obtained around 67% of B removal at Fe(III):B molar ratio of 5:1, while only 31% of B was removed at Fe:B molar ratio of 20:1 using EC process because the electrogenerated Fe(II) ions mainly precipitate as Fe(OH)2 which might have a low adsorption ability toward of borate.


After a series of experiments, it was concluded that chemical coagulation method of batch system using Fe(III) coagulant to remove B-containing wastewater is the most applicable and economical method.  Electrocoagulation using an aluminum sacrificial electrode is applicable for the continuous system.

中文摘要 i
Abstract iii
Acknowledgments v
Contents  vi
List of Tables  ix
List of Figures  x
1 Introduction  1
1.1 Background  1
1.2 Objectives  3
1.3 Research scope 4
2 Literature reviews 5
2.1 Boron chemistry  5
2.2 Processes for boron removal  7
2.2.1 Membrane  filtration 7
2.2.2 Liquid-liquid extraction  9
2.2.3 Layered double hydroxides (LDHs)  10
2.2.4 Coagulation  11
2.3 Electrocoagulation for boron removal  11
2.3.1 Effect of anode material  11
2.3.2 Effect of current density  12
2.3.3 Effects of pH  14
2.3.4 Effects of temperature  16
2.4 Boron removal mechanisms  17
3 Materials and Methods  19
3.1 Chemicals and wastewater  19
3.2 Experimental setup  20
3.2.1 Batch system  20
3.2.2 Continuous system  21
3.3 Experimental procedure  22
3.3.1 Batch experiments  22
3.3.2 Continuous system  24
3.3.3 Chemical coagulation process  25
3.3.4 Layered Double Hydroxides process  25
3.4 Analytical methods 26
4 Results and Discussion  27
4.1 Effect of current density  27
4.2 Effect of  fixed pH  33
4.3 Effect of temperature  35
4.4 Effect of conductivity or ionic strength  37
4.5 Effect of anode materials  39
4.6 Effect of Layered Double Hydroxides  41
4.7 Boron removal using chemical coagulation  42
4.7.1 Effect of aluminum dosage 42
4.7.2 Effect of ferric dosage  44
4.8 Continuous EC system for the removal of B from FGD wastewater 47
5 Conclusions and Recommendations  50
5.1 Conclusions  50
References 52

LIST OF TABLES
2.1 Boron removal effciency using chemical coagulation from various studies 12
2.2 Boron removal efficiency from various studies  13
3.1 Major ions in the FGD wastewater collected from a coal-fired power plant 19
4.1 Estimation of Al:B molar ratio and energy consumption under different
electric current intensity conditions  29
4.2 B removal efficiency and estimation operating cost using various treatment
methods 43
4.3 B removal efficiency using Fe as a coagulant under EC and CC 44

LIST OF FIGURES
2.1 Effect of temperature on B(OH)−4 species  at  pH  8  for  ionic  strength ranging from 0.001 to 0.1 M. Modeled by Mineql+ 6
2.2    Effect  of  temperature  on  B(OH)−4species  at  0.01  M  ions  strength  for various pH. Modeled by Mineql+ 7
2.3    The  schematic  of  the  PVA-Borax  crosslink  reaction  (di-diol)  [17]. n represents the number of monomers in the polymer chain 8
2.4    The effect of pH on the total dissolved metal concentration using modeling (Mineql+ version 4.6).  Metal concentration = 1 mM 15
3.1    Schematic of the electrocoagulation setup 21
3.2    Schematic of the 3-stage electrocoagulation setup for the treatment of the real FGD wastewater 22
4.1    The effect of different current density on boron removal efficiency withfixed  temperature  of  20oC.  Experimental  condition:  B  concentration= 100 mg/L; Conductivity:  4 mS/cm; Mechanical mixing = 100 rpm;Fixed temperature = 20oC, Anode area = 75.7 cm2 28
4.2    The effect of different current density on boron removal efficiency withfixed  temperature  of  20oC.  Experimental  condition:  B  concentration= 100 mg/L; Conductivity:  4 mS/cm; Mechanical mixing = 100 rpm;Fixed temperature = 20oC, Anode area = 757 cm2 29
4.3    The  effect  of  Al:B  molar  ratio  on  boron  removal  efficiency  under  in-termittent current supply.  Experimental condition:  B concentration =100 mg/L; Current intensity = 3 A; pH = 8; Conductivity:  4 mS/cm;Mechanical mixing = 100 rpm 31
4.4    The effect of time on boron removal efficiency under intermittent currentsupply.  Experimental condition:  B concentration = 100 mg/L; Currentintensity = 3 A; pH = 8; Conductivity:  4 mS/cm; Mechanical mixing= 100 rpm 32
4.5    The effect of different anode area on boron removal efficiency w/Temp.control.  Experimental condition:  B concentration = 100 mg/L; pH =8; Current intensity = 3 A; Conductivity:  4 mS/cm; Mechanical mixing= 100 rpm; Fixed temperature = 20oC 33
4.6    The effect of Al:B molar ratio on boron removal efficiency under variousfixed pH values.  Experimental condition:  B concentration = 100 mg/L;Current intensity = 1.5 A; Conductivity:  4 mS/cm; Mechanical mixing= 100 rpm 35
4.7    The  effect  of  temperature  on  boron  removal  efficiency.   Experimentalcondition:  B concentration = 100 mg/L; Current intensity = 3 A; pH= 8; Conductivity:  4 mS/cm; Mechanical mixing = 100 rpm 37
4.8    The effect of conductivity on boron removal efficiency without tempera-ture controlling.  Experimental condition:  B concentration = 100 mg/L;Current intensity = 3 A; pH = 8; Mechanical mixing = 100 rpm 38
4.9    Temperature under different conductivity.  Experimental condition:  Bconcentration = 100 mg/L; pH = 8; Conductivity: 4 mS/cm; Mechanicalmixing = 100 rpm 39
4.10  The effect of Fe:B molar ratio on boron removal efficiency under variousfixed  pH  values  with  aeration.   Experimental  condition:  B  concentra-tion = 100 mg/L; Current intensity = 1.5 A; Conductivity:  4 mS/cm;Mechanical mixing = 100 rpm 40
4.11  The effect of LDH on boron removal efficiency compared with EC. Ex-perimental condition:  B concentration = 100 mg/L; Mg(II) added = 18g/L; Current intensity = 3 A; pH = 8.  Mechanical mixing = 100 rpm 41
4.12  The  effect  of  Al/B  using  chemical  coagulation  on  boron  removal  effi-ciency.   Experimental  condition:  B  concentration  =  100  mg/L;  pH  =8.5; Rapid mixing (200 rpm) = 5 mins; Slow mixing (50 rpm) = 20 mins 43
4.13  The  effects  of  Fe(III)/B  molar  ratio  on  boron  removal  efficiency.   Ex-perimental condition:  B concentration = 220 mg/L; pH = 8.5;  Rapidmixing (200 rpm) = 5 mins; Slow mixing (50 rpm) = 20 mins 45
4.14  The effects of Fe(II)/B molar ratio on boron removal efficiency.  Experi-mental condition: B concentration = 220 mg/L; pH = 8.5; Rapid mixing(200 rpm) = 5 mins; Slow mixing (50 rpm) = 20 mins 46
4.15  Comparison of B removal efficiency for CC process with Al and Fe(III)coagulant under the same molar ratio.  Experimental condition:  pH =8.5; Rapid mixing (200 rpm) = 5 mins; Slow mixing (50 rpm) = 20 mins 47
4.16  The sludge showing in the continuous system 48
4.17  The effects of operation time on boron removal efficiency.  Experimen-tal condition:  B concentration = 400 mg/L; pH = 8;  Flow rate = 1.2ml/min; HRT = 4.2 hrs 49

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