Earticle

From the time of the industrial revolution, fossil fuel has been the main source of energy, acting as a stimulant for many modernized industries. Despite the positive changes fossil fuel has brought to the mankind, it has produced carbon emission, facilitating the rising temperature of Earth resulting in global warming. Limited supply of fossil fuel has also hastened the search for alternative sources of energy. Biofuel from microalgae is recently gaining attention for its environmental friendliness, for example CO2 fixation during cultivation and high lipid content. Two strains of microalgae are used, Botryococcus braunii and Nannochloropsis oceanica, for their high potential as biofuel sources. Different colored settings of LED light, Green, Red, White, Blue, Red: Blue = 5:1, Red: Blue 3:1, Red: Blue = 1:1 were controlled to investigate the effects of mixture of colors on growth and lipid content of microalgae. Spectrophotometry and fluorescence spectrophotometry were used to measure the growth and lipid content of each microalgae strain. The experiment was conducted over the period of eight days, with measurements done on day 0,2,4,6, and 8. The optimum color of light differed slightly between strains, with B. braunii Red: Blue = 5:1 and N. oceanica red. The mixture of red and blue LED light had the better growth and lipid content than the single colored lights, red and blue mixed light with 18% more lipid content than white light in Botryococcus braunii. The ultimate light conditions for the cultivation of microalgae vary among species, but the best outcomes can be expected from using a mixture of red and blue lights. To find the optimum light ratio for each microalgae strain, further research and experiments using various ratio mixtures of red and blue lights are essential.

최근 환경 문제로 대두되고 있는 것 중 하나는 대기 중 CO2의 증가로 인한 기후변화이다. 이에 대한 영향으로 생태계가 변화하고 있으며, 다양한 환경문제가 발생되고 있다. 이로 인해 전 세계적으로 CO2 저감을 위한 다양한 연구들이 수행 중이며, 이 중 미세조류를 이용한 CO2 저감 방안은 환경 친화적인 방법이라 할 수 있다. 그러나 미세조류를 이용한 CO2 저감 방안은 대부분 단일 종을 대상으로 하고 있으며, 자연 하천을 대상으로 한 미세조류의 CO2 고정 효율에 대한 연구는 전무한 실정이다. 그러므로 본 연구는 우리나라 하천 내 존재하는 미세조류들을 파악하고, 미세조류의 생장특성을 분석하여 최적의 배양조건을 도출 하였다. 그리고 CO2 농도와 주입 속도에 따른 미세조류의 biomass와 클로로필 a의 변화를 분석하여 자연 하천 내 존재하는 미세조류의 CO2 고정효율에 대해 연구하고자 하였다. 섬강 내 존재하는 미세조류를 배양하여 동정한 결과 6종의 우점종(Ankistrodesmus falcatus, Scenedesmus intermedius, Selenodictyum sp., Xanthidium apiculatum var. laeve, Cosmarium pseudoquinarium, Dictyosphaerium pulchellum)이 관찰되었으며, 이 종들은 모두 녹조류에 해당하였다. 한편 이산화탄소 농도 구배(5% CO2, 10% CO2, 15%CO2, 대기조건의 가스 0.038% CO2)와 유속(0.25, 0.5LPM)이 다른 가스를 주입하여 미세조류의 biomass와 클로로필 a의 변화를 살펴본 결과 이산화탄소의 농도가 증가 할수록 biomass와 클로로필 a가 증가하였으며, 같은 이산화탄소 농도에서는 유속이 더 빠른 곳에서 미세조류의 biomass와 클로로필 a의 양이 더 증가하였다. 또한 미세조류에 고정화된 이산화탄소의 양은 주입되는 가스의 유속이 빠를수록 고정 되는 이산화탄소의 양이 더 높아지는 경향을 보였다. 본 연구는 기존의 단일 종에서 행해지는 연구가 아닌 하천 전체의 미세조류를 대상으로 수행한 연구이며, 하천 내 존재하는 미세조류의 이산화탄소 고정을 위한 최적의 조건을 도출하고, 하천 내 존재하는 미세조류로부터 고정화된 이산화탄소의 양을 정량화하여 향후 이산화탄소 감축을 위한 정책을 위한 기초자료에 이용할 수 있다는 것에 큰 의의가 있다.

One of the recent environmental problems is climate change due to the increase of atmospheric CO2, which causes ecological changes and various environmental problems. Therefore, various studies are being carried out to reduce CO2 in the world in order to solve various environmental problems caused by increase of CO2. The CO2 reduction using microalgae is an environmentally friendly method by using photosynthesis reaction of microalgae. However, most studies using single species. There is no study on the CO2 fixing efficiency of microalgae in natural rivers. Therefore, this study was to identify the microalgae in the Sum river and to analyze the growth characteristics of microalgae in the river to obtain optimal culture conditions. And the changes of biomass and chlorophyll-a of microalgae were analyzed according to CO2 concentration and injection rate. The purpose of this study was to investigate the fixing efficiency of carbon dioxide in microalgae in natural rivers. Six kinds of dominant species were observed as a result of the identification of microalgae in Sum river(Ankistrodesmus falcatus, Scenedesmus intermedius, Selenodictyum sp., Xanthidium apiculatum var. laeve, Cosmarium pseudoquinarium, Dictyosphaerium pulchellum ). All of these species were green algae. Biomass and chlorophyll-a increased with the increase of CO2 concentration and biomass and chlorophyll-a increased faster flow rate at the same CO2 concentration. Also, the quantity of CO2 fixation on the microalgae tended to be higher when the flow rate of injected gas was faster. This study can be referred as being significant in the micro-algae in river. In addition, the optimal conditions for CO2 fixation of microalgae in rivers and the quantification of the quantity of CO2 fixation from microalgae in rivers can be used as basic data for future policy of CO2 reduction.

본 연구는 역삼투 농축수의 생물복원 과정에서 Scenedesmus quadricauda 미세조류가 난분해성 유기물질의 분해와 이 용에 어떻게 관여하는지에 대하여 조사하였다. 조류를 이용하여 역삼투 농축수를 처리한 결과, 염도 500 및 8000 mg Cl- /L, 연속폭기(10% CO2), 그리고 간헐조명(L/D=16/8) 조건에서 용존유기물질의 생분해도 향상과 무기영양염류의 높은 제 거율을 확인할 수 있었다. 본 연구에서는 조류 처리수로부터 과산화수소 농도를 측정하여 조류에 기인하는 난분해성 유 기물질의 분해 메커니즘을 평가하였다. 세포 성장과정에서 유기탄소원의 이용이 가능한 조류를 농축수와 같은 난분해성 폐수처리에 적용하는 경우 영양염류의 동시 제거가 가능하다는 점에서 일반적으로 사용되는 전기화학적 산화기술보다 지속가능성과 비용효율 면에서 상대적으로 그 적용성이 높다고 평가 할 수 있다.

This study explored how Scenedesmus quadricauda microalga is involved in the degradation and subsequent assimilation of refractory organic matter during remediation of reverse osmosis concentrate. The algal cells were cultivated in the reverse osmosis concentrate with low to high salinities under the given conditions, which resulted in a remarkable increase in the biodegradability of dissolved organic matter, along with robust removal of nutrients (N and P). In this study, hydrogen peroxide from algal-treated wastewater was measured to investigate the mechanism of organic deformation which was associated with algal growth. The degradation of refractory organic matter with microalgae can be considered as more sustainable and cost-effective when compared to commonly used electrochemical oxidation techniques.

Recently, microalgae have been focused on potential biomass for bio-diesel and biorefinery process. The aim of this paper is to review the biorefinery process including biodesel using microalgae as a microreactor. The state-of-the-art of biodiesel and biorefinery research such as extraction and reaction process as well as byproducts utilization is described. In addition, we suggest possibility for develop bioactive substances and their industrial products from byproducts of microalgae massively obtained after bio-diesel extraction.

The objective of this paper is to investigate into the design of photbioreactor for mass production of microalgae. Characteristics of previously developed photobioreactors were examined to obtain design factors, including light transfer, fluid dynamics and metabolic reactions, of the photobioreactor. Design technology of components related to the design factors, such as light sources, photobioreactor cases, spargers, mixer, etc., was discussed to improve the viability and the growth rate of microalgal and productivity of the photobioreactor. Finally a principle direction of the design for an airlift flat plane photobiorectors was investigated.

This paper describes current status and future prospects of the mass production of microalgae biomass. Microalgae have attracted considerable attention since they not only effectively fix $CO_2$ gas during their metabolic process but also have the great potential to be utilized for producing valuable substances as a kind of efficient light-harvesting cell factories. In this review, we outline various types of photobioreactors employed for mass production of biomass by culturing microalgae in a well controlled way and give an overview about the present state of affairs, both domestic and international, in the field of the microalgal culturing technologies.

Microalgae are aquatic microorganisms capable of photosynthetic growth using water, carbon dioxide and sunlight, and can replace petroleum for transportation. It is receiving great attention as a potential next-generation biological resource. The microalgae biodiesel production process is largely based on the development of highly efficient strains and mass production. It consists of cultivation, harvesting, oil extraction, fuel conversion and by-product utilization. Currently, microalgae diesel is 3-5 times more expensive than petroleum diesel. However, with the optimization of each element technology and the development of integrated systems, not only biofuels, but also industrial materials, wastewater treatment, and greenhouse gases As application expands to various fields such as abatement, the timing of commercialization may be brought forward. Oil prices have recently fallen due to the influence of sail gas. Although there has been a significant drop, global warming is an urgent challenge for current and future generations. In particular, Korea, which does not have oil resources, We must always prepare for political environmental changes, high oil prices, and energy crises. In this paper, the need for eco-friendly biofuel for carbon dioxide conversion. In addition to research trends, domestic and international research trends, and economic prospects, the concept of microalgae and the element technologies of the biodiesel production process are briefly discussed introduced.

본 연구에서는 방사성 폐액내 포함된 방사성 핵종인 세슘-137(Cs-137) 및 스트론튬-90(Sr-90)의 친환경적인 제염을 위해 미세조류의적용 가능성을 평가하였다. Cs-137 및 Sr-90이 각각 함유된 일원계 표준 방사성 용액과 3차 증류수를 희석하여 1.5 Bq/mL Cs-137, 1.0 Bq/mL Sr-90 농도로 제조한 뒤 실험에 사용하였다. 미세조류는 2종을 사용했으며, Sr-90 제염에는 Chlorella Vulgaris를 사용하였고, Cs-137 제염에는 Hematococcus pluvialis를 사용하여 실험을 수행하였다. 실험 방법은 2주 간 배양된 미세조류를 반투과막이 부착된 병에 투입한 뒤, 미세조류가 투입된 병을 제조된 방사성 용액에 투입하여, 반투과막을 통해 미세조류와 방사성 용액이 48 시간 동안 반응하도록 하였다. 각 시료에 대한 방사능 농도 분석은 γ선 동위원소인 Cs-137은 감마선 핵종 분석기를 사용하였고, β선 동위원소인 Sr-90은액체섬광계수기(LSC: Liquid Scintillation Count)를 사용하였다. 실험 결과, Cs-137은 약 88.0 %, Sr-90은 약 89.7 % 제염이 가능함을 확인하였으며, Sr-90은 2단 제염 방법에 의해 최종적으로 약 98.6 % 제염이 가능하였다.

In this study, the applicability of microalgae was evaluated for eco-friendly decontamination of cesium-137 (Cs-137) and strontium-90 (Sr-90), which are radioactive nuclides contained in radioactive waste. The monolithic radioactive solution used in the experiment was manufactured at a concentration of 1.5 Bq/mL Cs-137 and 1.0 Bq/mL Sr-90 by diluting a standard radioactive solution and distilled water. This experiment used two types of microalgae, Chlorella Vulgaris was used for Sr-90 decontamination and Hematococcus pluvialis for Cs-137 decontamination. The experimental method is to put the microalgae cultured for 2 weeks into a bottle with a semi-permeable membrane, and then put the bottle in which the microalgae was put into the manufactured radioactive solution, so that the microalgae and the radioactive solution react through the semi-permeable membrane for 48 hours. For the radioactivity concentration analysis of each sample, a gamma-ray nuclide analyzer was used for Cs-137, a γ -ray i sotope, and a Liquid S cintillation Count(LSC) w as u sed f or Sr-90, a β -ray i sotope. As a r esult of the experiment, it was confirmed that about 88.0 % of Cs-137 and about 89.7 % of Sr-90 could be decontaminated, and about 98.6 % of Sr-90 was finally able to be decontaminated by the two-stage decontamination method.

본 연구에서는 미세조류와 박테리아의 공생관계를 이용하여 하수 내 영양염류 제거효율을 평 가하고자 하였다. 또한 최 적 배양조건을 도출하기 위해 온도, 광주기, CO2 주입농도에 따른 Chlorella sp.와 Scenedesmus sp.의 생장특성을 파악하 고, 그에 따른 영양염류 제거효율을 평가하여 미세조류-박테리아의 공생관계를 이용한 폐수 처리 가능성을 연구하였다. 그 결과 미세조류의 최적 배양조건은 25 ~ 30oC, 24시간 내내 광원을 주입해 준 경우, Chlorella sp.는 5% CO2 주입농도 에서, Scenedesmus sp.는 2% CO2 주입농도에서 높은 성장률을 기준으로 산정되었다. 산정 된 배양조건을 영양염류 제거 효율을 평가해본 결과, Chlorella sp.의 경우 COD 63%, BOD 70%, SS 48.3%, T-N 70.5%, T-P 76.4% 나타냈고, Scenedesmus sp.는 COD 66%, BOD 72.3%, SS 56.5%, T-N 67.1%, T-P 70.1%로 나타내었다 .

This study intended to evaluate the removal efficiency of nutrients in wastewarer using the symbiosis relationship of microalgae-bacteria. Also, in order to confirm optimal culture conditions, growth characteristics of Chlorella sp. and Scenedesmus sp. on the temperature, L:D cycle, and CO2 injection were identified, and then the possibility of wastewater treatment by the symbiosis relationship of microalgae-bacteria through the evaluation of nutrients removal efficiency, was identified as well. As the results, Chlorella sp. showed the highest growth rate at 25 ~ 30oC, 24:0 L:D cycle, and 5% of CO2 injection concentration, and Scenedesmus sp. showed it from 25 ~ 30oC, 24:0 L:D cycle, and 2% CO2 injection concentration, respectively. In addition, the nutrients removal efficiency under the optimal culture conditions was resulted in the followings: Chlorella sp. showed the removal efficiency of COD 63%, BOD 70%, SS 48.3%, T-N 70.5%, and TP 76.4% and Scenedesmus sp. showed COD 66%, BOD 72.3%, SS 56.5%, T-N 67.1%, and T -P 70.1%, respectively.

We are in the process of selecting elite lines of Korean domestic microalgae for mass cultivation and biodiesel production in Korea. Twenty microalgal strains from various domestic streams and lakes were collected, axenically purified, and tested for physiological characteristics and lipid production. Many microalgae were able to autotrophically synthesize hydrocarbon chains such as pentadecane (C15H34) and heptadecane (C17H36), which can be directly used as fuel without requiring a transesterification step. Consequently, the genes involved in alkane biosynthesis such as an aldehyde decarbonylase and an acyl-acyl carrier protein (ACP) reductase were present in this microalgae. Genetic clonings and characterization of those domestic genes are currently underway. In addition, a high value fatty alcohol such as hexadecenol (C20H40O) was present in this photosynthetic microorganism. Other common algal biodiesel constituents, palmitic acid (C16:0), palmitoleic acid (C16:1), linoleic acid (C18:2) and linolenic acid (C18:3) were also produced by many strains as major fatty acids. Therefore, numerous domestic microalgae appear to show promise for their application in cost-effective production of microalgae-based biofuel and high-value products. Also we are investigating Korean type microalgae mass cultivation system to grow and induce lipids in various conditions. Over 100-ton raceways have been operated by our laboratory for field cultivation and currently approximately 1000-ton raceways are under construction. A few microalgal strains that are suitable for field mass-cultivation were selected.

Mircoalgae require proper conditions for the cell growth. Since microalgae are photosynthetic, proper light source, carbon dioxide concentration, water, and inorganic salts are required for optimal growth conditions. In this study, various light intensities and nitrate concentrations were tested with conditions of 20℃, 24:0 L:D cycle and 2.5 L/min aeration rate in 20 L batch culture. It took 5 days to reach the stationary phase for the culture of T. suecica with the light intensities of 108.9 and 133.1 μmol/m2/s with biomass of 0.89 and 0.88 g dcw/L, respectively. And, biomass productions of 1.07 and 1.00 g dcw/L were obtained with the nitrate concentrations of 18.55 and 24.74 mg/L, respectively. Nitrate was consumed by T. suecica of all tested groups within 5 days after the inoculation. Two-stage culture process through nitrate depletion led to increase oil contents from 7.6 % to 17.3 % (w/w) and contents of C16∼�18 fatty acids from 540.2 mg/g oil to 720.5 mg/g oil at 4th day after nitrate depletion. The biomass production and oil content of T. suecica was enhanced by the optimization of growth conditions and 2-stage culture process.

The aim of the study was the optimization of harvesting method for concentrating microalgae from microalgae mass culture. It is well known that the mass density of microalgae is usually very low and it is not economic to concentrate for the purpose of biodiesel production. To find out an efficient method for microalgae harvest, centrifugation, chemical flocculation, and sedimentation method was tested extensively. For chemical flocculation test, aluminum sulfate, ferrous sulfate, ferric chloride, starch, chitosan etc. were used which illustrated the aluminum sulfate is the most efficient flocculatant. As sedimentation media, various sizes of sand was tested.

Microalgae are widely used as live feeds, cosmetics, human food supplements, biomedicine and etc. Especially, the use of microalgae for a potential renewable liquid fuel source was proposed by many reports. In this study, characteristics of five microalgae: Tetraselmis suecica, Phaeodactylum tricornutum, Chaeotoceros calcitrans, Isochrysis galbana and Nannochloropsis oculata were examined on the ability to store intracellular neutral lipid and growth potential. The microalgae were grown in sterilized seawater with f/2 medium nutrients and photoautotrophically in batch cultures where inorganic CO2 from the atmosphere was the only source of carbon. Aeration was provided by air stone at regular pressure. The temperature was kept at 20℃. The strains were inoculated into the medium (18 L) in a 20-L column tank. Range of inoculation density was adjusted between 20~40ⅹ104cells/ml. A fluorescent spectrometric method was applied for lipid contents analysis. In the results, Specific growth rate of N. oculata was higher (0.325/day) and the lipid content of C. calcitrans estimated by fluorescence intensity (au /106 cells) was higher than other strains.

Biodiesel made from microalgae could be a possible replacement for fossil fuel. The separation of microalgae from their culture medium is a critical process in biotechnology. Membrane techniques seem to be effective, reliable, and safe, despite some limitations such as the progressive fouling and the associated decline in flux. Microalgae harvested from membranes have less chemical contamination and therefore membrane systems are more environmentally friendly than other harvesting techniques. Two cleaning processes: forward flushing and backwashing were assessed to minimize the time required to concentrate the microalgae Tetraselmis.sp. It was concluded that backwashing was a more effective method than forward flushing.

Fossil fuels as the source of transport fuels are now widely recognized as unsustainable due to problems with global warming and limited availability. Renewable biofuels including biodiesel, bio-ethanol, bio-hydrogen, bio-oil and bio-gas have been focused on as an alternative energy source. A variety of biomasses from different sources have been investigated as the feedstock for the production of different biofuels. Microalgae have a higher photosynthetic efficiency than other biomasses. In addition, microalgae have been promoted as a future source of transportation fuels primarily because of their potential to produce up to 10 times the amounts of oil per acre compared with vegetable oils, animal fats and crops. In this study, supercritical fluid extraction of microalgae was performed to study the influence of process parameters such as extraction time, temperature, pressure and ultrasonic power on the yield and composition of the extracted oil. In addition, the effect of the size, amount and packing method of glass beads on the oil extraction was investigated in detail.