매립지 침출수를 이용한 미세조류 배양과 레이저 조사를 통한 지질 추출 = A Study on the Cultivation of Microalgae in landfill leachate for Biodiesel Production and Lipid Extraction from Microalgae using laser eradiation

다국어 초록 (Multilingual Abstract)

In this study, the possibility of culturing microalgae in landfill leachate and elimination capacities of nutrients such as total phosphorus and total nitrogen in leachate according to growth of microalgae was identified. Because Scenedesmus sp. has several advantages such as being less contaminated by other microorganisms and having a potential of propagation in the water containing high concentration of organic materials and heavy metals, it was selected as target microalgae.
For identifying the production possibility of biodiesel using biomass obtained from Scenedesmus sp. cultured in landfill leachate, lipid extraction method with laser and absorbent was developed and its optimum operation control was also sought. In addition, this study compared lipid extraction efficiency between laser extraction method under the optimum condition as derived from the experiment and existing extraction method, and also analyzed FAME content according to reaction temperature and input of catalyst for optimizing trans-esterification reaction of extracted lipid. The following results were obtained.

1. In order to test Scenedesmus sp. cultivation ability in various concentrations of landfill leachate, the microalgae's growth rate was observed. Without any alteration to the pH, the microalgae required a lag phase of about four days, and after 8∼10 days, the growth rate began to decline. When the pH was maintained at 7, the microalgae were able to grow for more than 8 days. The reason for this being, when the pH exceeded 9.3, ionized ammonia was converted into NH3, and the ammonia acts as toxic material. This showed that Scenedesmus sp. does have the potential to grow in landfill leachate, as long as the pH is maintained under 9.3.
When analyzing the removal rate of TP in concentrations of landfill leachate of 10%, 30%, 50% and 100%, the results were 69.2%, 63.3%, 58.1% and 24.1% respectively. The removal rates for T-N for the same concentrations of landfill leachate were 81.7%, 71.5%, 67.3% and 26.7% respectively.

2. Scenedesmus sp. used as a target microalgae in this study showed lower total lipid content(13.2±0.73%(w/w, d.b.)) than the result(23% average lipid content of green algae) reported by literatures on the lipid content of microalgae. Research proves that lipid content in microalgae tends to increase when microalgae is faced with high stress environments such as the lack of nutrients in culture medium. Thus, it is considered that low lipid content of Scenedesmus sp. in this study is because microalgae store less fat due to an abundance of nutrient in landfill leachate.
As a result of GC analysis for fatty acid composition, it showed that Scenedesmus sp. in this study has suitable composition of fatty acid(C14∼C20) which is necessary for the biodiesel production, and the order of main fatty acids was C 18:2 > C16:2 > C16:0. As unsaturated fatty acid content(68%) was higher than that of saturated fatty acid(23%), it seems that biodiesel made of lipid extracted from Scenedesmus sp. in this study has the characteristics of a good flow property at low temperature and a poor oxidation stability.

3. As a result of experiments for optimizing lipid extraction method using laser and label, 75 Wh/ℓ of consumption energy showed maximum extraction efficiency(81.8%) in the case of laser extraction method. When conducting microwave treatment for ten minutes as pre-treatment, extraction efficiency was improved up to 90.8%. In the case of laser and label extraction method, 50 Wh/ℓ of consumption energy with activated carbon showed maximum extraction efficiency (93.8%) which is higher than that of the soxhlet method (79.6%).

4. When compared to fatty acid content of extracted lipid and fatty acid extraction efficiency by each lipid extraction method to identify the possibility of transforming extracted lipid into FAME, total fatty acid contents of extracted lipid by each extraction method were respectively laser and label extraction method 853.7 mg/g oil, soxhlet extraction method 825.4 mg/g oil and laser extraction method 811.4 mg/g oil. Laser and label extraction method had also the highest value (80.1%) in extraction efficiency of fatty acid, and laser extraction method(73.7%) was more efficient than soxhlet extraction method (65.7%). It means that laser and label extraction method might have a higher production rate of biodiesel than soxhlet method as there are more unnecessary fatty acids contents(34.3%) which is not able to transform into biodiesel in lipid extracted by soxhlet extraction method.

5. In esterification reaction to reduce high acid value of lipid extracted from microalgae, optimum input of catalyst was 1.0%(w/w) which showed the highest removal rate of free fatty acid. Removal rate was lower, as input of catalyst was increased. It is likely that oil and fat content was burned because of excessive catalyst input.

6. In order to optimize trans-esterification reaction, FAME content by reaction temperature and catalytic amount was analyzed. It was identified that FAME content generally increased by increase of reaction temperature and catalytic amount. However, FAME content decreased with reaction temperature of 75℃. It indicates that transformation rate of FAME is decreased because methanol is vaporized if heating temperature is more than 65℃ in transesterification reaction when methanol reacts to extracted lipid with fixed ratio under base catalyst(KOH).
In input amount of catalyst, it was identified that FAME content increases as input amount increases. Although FAME content was the highest (94.2%) at 1.5(%, w/w) of input amount, the difference when compared with 1(%, w/w) of input amount, was imperceptible.

목차 (Table of Contents)

• I. 서론 1
• 1. 연구 배경 1
• 2. 연구 목적 5
• 3. 연구 내용 및 범위 7
• II. 이론적 배경 8
• 1. 국내 매립지 침출수 발생 현황 및 처리 기술 8
• 1.1 국내 침출수 배출허용 기준 8
• 1.2 국내 매립지내 침출수 발생량 및 처리 현황 12
• 1.3 매립지 침출수 처리 공법 14
• 1.4 국내 매립지 침출수 처리 기술적용 및 운영현황 22
• 2. 바이오 디젤 24
• 2.1 바이오디젤의 개요 24
• 2.2 국내·외 바이오디젤 보급 현황 및 정책 29
• 2.3 미세조류로부터 바이오디젤 생산 37
• 3. 레이저 53
• 3.1 레이저의 특성 53
• 3.2 레이저의 발생 원리 56
• 3.3 레이저의 종류 59
• 3.4 레이저의 수중에서의 이동 특성 61
• 4. 레이블링(Labeling) 63
• 4.1 레이블의 정의 63
• Ⅲ. 실험재료 및 방법 67
• 1. 실험 재료 67
• 1.1. 침출수(Leachate) 67
• 1.2. 바이오디젤용 조류 68
• 1.3. 레이블 70
• 2. 실험장치 및 기기 71
• 2.1 레이저 지질추출장치 71
• 2.2 UV 분광광도계(UV spectrophotometer) 73
• 2.3 가스 크로마토그래피 분석(Gas Chromatography) 75
• 2.4 속실렛 추출장치 77
• 3. 실험 방법 79
• 3.1 미세조류를 이용한 침출수 처리 79
• 3.2 미세조류로부터 지질 추출 82
• 3.3 레이저 및 레이블을 이용한 지질 추출 최적화 설계 86
• 3.4 지방산 분석 89
• 3.5 회수된 지질의 전처리 에스테르화 반응 90
• 3.6 추출 지질의 바이오디젤 전환반응 92
• Ⅳ. 실험 결과 및 고찰 94
• 1. 미세조류의 침출수의 질소 및 인 제거능 평가 94
• 1.1 배양시간 별 pH 및 개체수 변화 94
• 1.2 ph 고정 후 배양시간에 따른 개체수 변화 97
• 1.3 개체수 증가에 따른 침출수 내 질소 및 인 제거능 99
• 2. 미세조류를 이용한 바이오 디젤 생산 105
• 2.1 대상미세조류(Scenedesmus sp.)의 총 지질 함량 및 조성 분석 105
• 2.2 레이저를 이용한 지질 추출 최적화 111
• 2.3 레이저 및 레이블링을 이용한 지질 추출 최적화 115
• 2.4 추출방법 별 지질 추출 효율 비교 119
• 2.5 추출 방법별 지방산 분석 120
• 2.6 에스테르화 반응 121
• 2.7 전이 에스테르 반응에 미치는 운전조건의 영향 123
• 2.8 추출 방법 별 FAME 함량 비교 125
• Ⅴ. 결론 127
• Ⅵ. 참고 문헌 131