Effective extraction of microalgae lipids from wet biomass for biodiesel production Hanifa Taher a , Sulaiman Al-Zuhair a, *, Ali H. Al-Marzouqi a , Yousef Haik b , Mohammed Farid c a Chemical and Petroleum Engineering Department, UAE University, Al-Ain, United Arab Emirates b Mechanical Engineering Department, UAE University, Al-Ain, United Arab Emirates c Chemical and Materials Engineering Department, University of Auckland, New Zealand article info Article history: Received 23 September 2013 Received in revised form 28 January 2014 Accepted 28 February 2014 Available online xxx Keywords: Enzymes Cell disruption Wet microalgae Separation Nitrogen starvation Biodiesel abstract Producing biodiesel from lipid extracted from microalgae is a promising approach for sustainable fuel production. However, this approach is not yet commercialized due to the high costs of upstream processes that are associated with the time consuming and/or energy intensive drying, and lipid extraction processes. In this study, the possibility of avoiding the drying process, and extracting the lipid directly from the wet concentrated cells, using enzymatic disruption to enhance the extraction, has been tested. Results showed that lysozyme and cellulase were both efficient in disrupting cell walls and enhancing lipid extraction from wet samples, with highest lipid extraction yield of 16.6% achieved using lysozyme. The applicability of using supercritical CO 2 (SC-CO 2 ) in extracting lipid from wet biomass was also tested and the highest yield of 12.5% was achieved using lysozyme. In addition, a two-step culturing process was applied, using Scenedesmus sp., to combine both high biomass growth and lipid content. The strain was able to increase its biomass productivity in the first stage, reaching 174 mg l 1 d 1 , with almost constant lipid content. In the second stage, the lipid content was enhanced by six-fold after three weeks of nitrogen starvation, but with lower biomass productivity. ª 2014 Elsevier Ltd. All rights reserved. 1. Introduction Biodiesel, a series of mono-alkyl fatty acid esters, has received an increasing attention, especially with the increasing energy demand and inevitable depletion of fossil fuel reserves [1,2]. Conventionally, biodiesel is produced from oils extracted from oil crops. This is highly controversial and competes with their use as a food stock. In addition, the oil crops require large arable land development, fertilization, and fresh water irrigation. These significant drawbacks limit further industri- alization and urge to find new feedstocks. Waste cooking oils and animal fats have been suggested as alternatives; however the supply of such feedstocks is not consistent and cannot satisfy the large demand for biodiesel production. In addition, poor cold flow properties (cloud and pour points) of oils and saturated fatty acid contents of animal fats reduce the quality of produced biodiesel [3]. On the other hand, oil extracted from microalgae has recently emerged as a potential alter- native source due to the microalgae high growth rate, high * Corresponding author. Tel.: þ971 35319. E-mail address: s.alzuhair@uaeu.ac.ae (S. Al-Zuhair). Available online at www.sciencedirect.com ScienceDirect http://www.elsevier.com/locate/biombioe biomass and bioenergy xxx (2014) 1 e9 Please cite this article in press as: Taher H, et al., Effective extraction of microalgae lipids from wet biomass for biodiesel production, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.02.034 http://dx.doi.org/10.1016/j.biombioe.2014.02.034 0961-9534/ª 2014 Elsevier Ltd. All rights reserved.