Oil extraction from Scenedesmus obliquus using a continuous microwave system – design, optimization, and quality characterization Sundar Balasubramanian, James D. Allen, Akanksha Kanitkar, Dorin Boldor ⇑ Department of Biological and Agricultural Engineering, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, United States article info Article history: Received 26 July 2010 Received in revised form 28 September 2010 Accepted 30 September 2010 Available online 8 October 2010 Keywords: Green algae Scenedesmus obliquus Biodiesel Biofuel Microwave assisted extraction abstract A 1.2 kW, 2450 MHz resonant continuous microwave processing system was designed and optimized for oil extraction from green algae (Scenedesmus obliquus). Algae-water suspension (1:1 w/w) was heated to 80 and 95 °C, and subjected to extraction for up to 30 min. Maximum oil yield was achieved at 95 °C and 30 min. The microwave system extracted 76–77% of total recoverable oil at 20–30 min and 95 °C, com- pared to only 43–47% for water bath control. Extraction time and temperature had significant influence (p < 0.0001) on extraction yield. Oil analysis indicated that microwaves extracted oil containing higher percentages of unsaturated and essential fatty acids (indicating higher quality). This study validates for the first time the efficiency of a continuous microwave system for extraction of lipids from algae. Higher oil yields, faster extraction rates and superior oil quality demonstrate this system’s feasibility for oil extraction from a variety of feedstock. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Microalgae are considered a supplemental food source due to their high protein content (39–71% dry matter), pigments, and other bioactive constituents like dietary fibers (as high as 74.6% on dry basis in some species), carotenoids, carbohydrates, ome- ga-3 fatty acids and other lipids that have beneficial uses in the food and pharmaceutical industries (Arterburn et al., 2007; Becker, 2007; Del Campo et al., 2007; Granado-Lorencio et al., 2009; Lahaye, 1991). Microalgae, particularly green algae, is easy to mass cultivate and produce yields of about 10–40 g dry mass per day per m 2 (Becker, 1984; Piorreck et al., 1984). Efforts are also underway to scale-up microalgae production and lipid extraction to even higher magnitude in a cost effective and energy efficient manner to produce oil as food supplements and also with an aim of con- verting it into biodiesel (Demirbas, 2010; Lee et al., 2010). In recent years, increasing fossil fuel prices have accelerated the search for renewable, sustainable energy sources to meet the world’s energy demand. Edible vegetable oils and lipids from non-edible sources like Jatropha, Chinese tallow tree seed, waste frying oil, animal fat, and greases have been investigated as poten- tial oil containing feedstock for biodiesel production (Chen et al., 2010; Singh and Singh, 2010; Terigar et al., 2010a). However, obtaining the large quantities of these lipids feedstock to displace a significant portion of the current fossil fuel use is problematic. Is- sues include slow growth rate of some feedstock, seasonal growth variation, competition of edible oil containing feedstock with nutritional purposes, low oil yields per acre, prime agricultural land use, high feedstock prices and extensive processing of some non-edible feedstock before obtaining quality oil for biodiesel pro- duction (Enweremadu and Mbarawa, 2009; Mandal and Mallick, 2009; Singh and Singh, 2010; Terigar et al., 2010a). Use of microal- gae as a potential oil source is attractive due to its faster growth rates, high oil content and the ability to be harvested frequently over a long period of time (Becker, 1984; Haag, 2007; Minowa et al., 1995). Also, microalgae’s direct utilization of carbon dioxide for growth facilitates CO 2 sequestration and helps reduces green house gases responsible for global warming. In spite of the current high cost of microalgae production, this feedstock is viewed as a very attractive source due to the potential high oil yields (up to 100,000 L of oil/ha/year) which is about 16–70 times the oil yield/ha/year obtained from palm, coconut, castor, and sunflower (Amin, 2009). Some species of microalgae have high oil content (exceeding 80% of their dry mass, Patil et al., 2008), and it is desirable to extract this oil effectively in a cost efficient manner. High water content (above 80%) at harvest- ing (Patil et al., 2008) presents a technological hurdle in developing an industrial scale oil extraction method. Various methods, namely pressurized solvent extraction, Soxhlet extraction, ultra-sonic extraction, extraction by stirring and shaking have been reported for extraction of vegetable oils and other plant essential components (Terigar et al., 2010b) each with inherent merits and drawbacks. Disadvantages include long 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.09.119 ⇑ Corresponding author. Address: 149 EB Doran Building, Department of Biolog- ical and Agricultural Engineering, LSU, Baton Rouge, LA 70803, United States. Tel.: +1 225 578 7762; fax: +1 225 578 3492. E-mail address: DBoldor@agcenter.lsu.edu (D. Boldor). Bioresource Technology 102 (2011) 3396–3403 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech