Structural Conversion and Biodegradability Improvement of Refractory Pollutants by Hydrothermal Reaction

다국어 초록 (Multilingual Abstract)

The feasibility of improving biodegradability induced from the structural conversion of refractory pollutants by hydrothermal reaction was investigated in order to develop a new pretreatment method for the following conventional biological treatment methods. Besides, the application of hydrothermal reaction was mainly considered on the viewpoint of treatment of refractory pollutants, treated reactant reuse and enhancing biological treatment process.
At first, the feasibility of improving biodegradability of polyvinyl alcohol (PVA) representing for high-molecular-weight refractory pollutants was evaluated under various hydrothermal conditions (Chapter 2). The structural conversion of PVA was obtained from hydrothermal reaction without much reduction of carbon contents. The change of molecular weight distribution and ultraviolet (UV) absorbance collected by gel-permeation chromatography (GPC) system was corresponding to the biodegradability improvement of PVA. Biodegradable low-molecular-weight products from high-molecular-weight refractory pollutants such as PVA could be secured by using hydrothermal reaction.
Then, the reaction mechanism of biodegradability improvement induced from the structural conversion of chloroacetic acids (CAAs) by hydrothermal reaction was investigated (Chapter 3). CAAs were used as test materials for linear hydrocarbon structured refractory pollutants involving recalcitrant parts. The production of biodegradable products followed by the elimination of recalcitrant chlorine atoms from CAAs was obtained at the beginning of hydrothermal reaction. Hydrothermal reaction might be possibly applied to the pretreatment of refractory pollutants prior to conventional biological treatment method, due to very simple apparatus, easy control and extremely short reaction time with exception of the heat-up time of reactor.
Finally, hydrothermal reaction was applied to excess sludge in order to verify its applicability on the viewpoint of treatment of refractory pollutants and reuse of treated reactant for enhancing biological treatment methods (Chapter 4). The readily biodegradable substrate was produced from the content change of excess sludge by hydrothermal reaction. The usability of treated excess sludge as a carbon source in biological phosphorus removal (BPR) process was demonstrated in Chapter 4. During hydrothermal reaction, the control of content change of excess sludge was the most important factor on the viewpoint of excess sludge reuse. Recycling of excess sludge treated by hydrothermal reaction indicates not only a decrease of excess sludge amount discharged but also an improvement of conventional biological treatment methods including BPR process.

다국어 초록 (Multilingual Abstract)

本論文は、旣存の廢水處理施設に高溫高壓水反應技術を導入し、新たな廢水處理システムの構築を目指して硏究を行った。この廢水處理システムは、難分解性有機物の生物分解性を改善し、生物處理の前處理としての利用を考えたものである。それに加えて、水熱反應の應用として、主に難分解性有機物の制御、處理した物質の再利用および生物分解能性の向上といった觀点から檢討を行った。
まず初めに近年、難分解性高分子量化學物質として問題視されてきているポリビニルアルコ一ル(PVA)に對して、高溫高壓水を用いた生物分解性の改善を檢討した(Chapter 2)。PVAの構造變換は炭素含有量の減少無しに水熱反應より得られた。 Gel permeation chromatography(GPC)による分子量分布、及び紫外線吸光度の結果から、PVAは無機化が起こらずに、低分子化が起こることによって生物分解性が向上していることが判明した。
次に、ハロ酢酸類の一種であるクロロ酢酸(CAAs)を對象に、高溫高壓狀態における反應經路や反應速度を解析し、生物分解性改善のメカニズムを解明した(Chapter 3)。クロロ酢酸は、扱い難い部分を含む直鎖狀の炭化水素構造難分解性汚染物質の試驗材料として用いた。その結果、高溫高壓とする有機酸に轉じた。これにより、反應後のクロロ酢酸が生物による分解が可能なレベルにまで達することが明らかとなった。水熱反應は、簡易な反應裝置、制御方法で實現可能であり、反應時間が短時間でよいことから、上記の結果により難分解性物質の前處理として有效であることが判明した。
最後に、水熱反應の應用として難分解性物質の生物分解性向上、リサイクルの促進、處理プロセスの改善という觀点から生物學的廢水處理の過程で發生する余剩汚泥に對して檢討を行った(Chapter 4)。その結果、發生した余剩汚泥を水熱反應により可溶化することにより、微生物が容易に分解可能である易分解性有機物の生成が認められた。水熱反應により余剩汚泥から易生物分解性基質の生成と生物學的リン除去(BPR)過程での炭素源としての處理した余剩汚泥の有用性をこの硏究より?明した。このことより余剩汚泥發生量の削減とリン除去性能の向上が可能であることが判明した。

목차 (Table of Contents)

• Abstract
• ndex = ⅰ
• Chapter 1. Introduction = 1
• 1.1 Overview of this research = 1
• 1.2 Theoretical background = 2
• 1.2.1 History of hydrothermal reaction = 2
• 1.2.2 Characteristics of water under hydrothermal conditions = 3
• 1.2.3 Application field of hydrothermal reaction = 6
• 1.2.4 Dilemma of refractory pollutants in environment and advanced treatment methods = 8
• 1.2.5 A new trend in hydrothermal reaction = 10
• 1.3 Objectives and construction of this thesis = 11
• 1.4 References = 14
• Chapter 2. Biodegradability improvement and structural conversion of poly vinyl alcohol (PVA) by hydrothermal reaction = 16
• 2.1 Summary = 16
• 2.2 Introduction = 17
• 2.3 Materials and methods = 19
• 2.3.1 Reagent = 19
• 2.3.2 Batch reactor apparatus = 19
• 2.3.3 Experimental methodologies = 20
• 2.3.4 Analytical methods = 21
• 2.4 Results and conclusions = 22
• 2.4.1 Change of water quality indexes under various conditions = 22
• 2.4.2 Trend of BOD improvement at each reaction condition = 23
• 2.4.3 Structural conversion and improvement of water quality = 25
• 2.4.4 Biodegradability improvement based on TOC reduction = 30
• 2.4.5 Dependence of biodegradability on reaction conditions = 32
• 2.5 Conclusions = 34
• 2.6 References = 35
• Chapter 3. Production of biodegradable substances from Chloroacetic acids (CAAs) under hydrothermal conditions = 37
• 3.1 Summary = 37
• 3.2 Introduction = 39
• 3.3 Materials and methods = 41
• 3.3.1 Reagent = 41
• 3.3.2 Batch reactor apparatus = 41
• 3.3.3 Experimental methodologies = 42
• 3.3.4 Analytical methods = 42
• 3.4 Results and discussion = 44
• 3.4.1 Biodegradable products from monochloroacetic acid (MCAA) = 44
• 3.4.1.1 Change of water qualities after hydrothermal reaction = 44
• 3.4.1.2 Evaluation of products = 46
• 3.4.1.3 Reaction pathway of MCAA under hydrothermal conditions = 48
• 3.4.1.4 Relationship between BOD improvement and the yield of glycolic acid = 50
• 3.4.1.5 Relationship between biodegradability improvement and reaction conditions = 51
• 3.4.1.6 Suitable TOC reduction range for BOD improvement = 53
• 3.4.2 Structural Conversion of Di- and Trichloroacetic Acid to Biodegradable products = 55
• 3.4.2.1 Identification of products = 55
• 3.4.2.1 Reaction mechanism of CAAs under hydrothermal conditions = 58
• 3.4.2.3 Change of water quality indexes by hydrothermal reaction = 61
• 3.4.2.4 Relationship between TOC reduction and BOD improvement = 62
• 3.4.2.5 Effect of reaction time on biodegradability improvement = 64
• 3.5 conclusions = 66
• 3.6 References = 68
• Chapter 4. Application of hydrothermal reaction for excess sludge reuse as carbon sources in biological phosphorus removal = 70
• 4.1 Summary = 70
• 4.2 Introduction = 71
• 4.3 Materials and methods = 73
• 4.3.1 Materials = 73
• 4.3.2 Batch reactor apparatus = 73
• 4.3.3 Experimental methodologies = 73
• 4.3.4 Phosphorus release test = 74
• 4.3.5 Analytical methods = 76
• 4.4 Results and conclusion = 78
• 4.4.1 Relationship between improving biodegradation of excess sludge and TOC reduction = 78
• 4.4.2 Effect of TOC reduction on the improvement of biodegradation of excess sludge = 80
• 4.4.3 Fraction of organic contents in treated excess sludge based on respirometric test = 83
• 4.4.4 Effect of readily biodegradable substrate on biological phosphorus removal process = 86
• 4.5 Conclusions = 90
• 4.6 References = 91
• Chapter 5. General conclusions = 94
• Acknowledgements = 97
• List of publication = 99
• List of presentation (International) = 100
• List of presentation (Domestic) = 101
• List of patent = 102
• List of award = 103