title: Long-term outdoor cultivation by perfusing spent medium for biodiesel production from Chlorella minutissima.
abstract: A unique perfusion process was developed to maintain high concentrations of marine alga, Chlorella minutissima. This method is based on recycling cells by continuous feeding with warm spent sea water from nuclear power plants, which has very similar properties as sea water. A temperature of at least 30 degrees C in a 200 L photo-bioreactor was maintained in this system by perfusion of the thermal plume for 80 days in the coldest season. The maximum cell concentration and total lipid content was 8.3 g-dry wt./L and 23.2 %, w/w, respectively, under mixotrophic conditions. Lipid production was found to be due to a partially or non-growth related process, which implies that large amounts of biomass are needed for a high accumulation of lipids within the cells. At perfusion rates greater than 1.5 L/h, the temperature of the medium inside the reactor was around 30 degrees C, which was optimal for cell growth. For this system, a perfusion rate of 2.8 L/h was determined to be optimal for maintaining rapid cell growth and lipid production during outdoor cultivation. It was absolutely necessary to maintain the appropriate perfusion rate so that the medium temperature was optimal for cell growth. In addition, the lipids produced using this process were shown to be feasible for biodiesel production since the lipid composition of C. minutissima grown under these conditions consisted of 17 % (w/w) of C(16) and 47% (w/w) of C(18). The combined results of this study clearly demonstrated that the discharged energy of the thermal plume could be reused to cultivate marine alga by maintaining a relatively constant temperature in an outdoor photo-bioreactor without the need for supplying any extra energy, which could allow for cheap production of biodiesel from waste energy.
authors.affiliation: College of Bioscience and Biotechnology, Department of Biomaterials Engineering, Kangwon National University, Chuncheon 200-701, Republic of Korea.
authors.forename: Sung Ho
authors.initials: SH
authors.lastname: Oh
authors.forename: Min Chul
authors.initials: MC
authors.lastname: Kwon
authors.forename: Woon Yong
authors.initials: WY
authors.lastname: Choi
authors.forename: Yong Chang
authors.initials: YC
authors.lastname: Seo
authors.forename: Ga Bin
authors.initials: GB
authors.lastname: Kim
authors.forename: Do Hyung
authors.initials: DH
authors.lastname: Kang
authors.forename: Shin Young
authors.initials: SY
authors.lastname: Lee
authors.forename: Hyeon Yong
authors.initials: HY
authors.lastname: Lee
mesh_terms: D056804:Biofuels / Q000382:microbiology*; D019149:Bioreactors / Q000382:microbiology*; D018929:Cell Culture Techniques / Q000379:methods; D049109:Cell Proliferation; D002708:Chlorella / Q000502:physiology*; D007220:Industrial Waste / Q000517:prevention & control*; D010477:Perfusion / Q000379:methods*; D012623:Seawater / Q000382:microbiology*; D014871:Water Microbiology
chemical_list: D056804:Biofuels; D007220:Industrial Waste