Biofuels from microalgae—A review of technologies for production, processing, and extractions of biofuels and co-products Liam Brennan a, *, Philip Owende a,b a Charles Parsons Energy Research Programme, Bioresources Research Centre, School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland b School of Informatics and Engineering, Institute of Technology Blanchardstown, Blanchardstown Road North, Dublin 15, Ireland Contents 1. Introduction ..................................................................................................... 000 1.1. Energy outlook and salient environmental issues .................................................................. 000 1.2. Development of biofuel resources .............................................................................. 000 1.3. Potential role of biofuels from microalgae........................................................................ 000 2. Biology of microalgae ............................................................................................. 000 3. Technologies for microalgal biomass production ........................................................................ 000 3.1. Photoautotrophic production .................................................................................. 000 3.1.1. Open pond production systems ........................................................................ 000 3.1.2. Closed photobioreactor systems ........................................................................ 000 3.1.3. Hybrid production systems ............................................................................ 000 Renewable and Sustainable Energy Reviews xxx (2009) xxx–xxx ARTICLE INFO Article history: Received 21 August 2009 Accepted 9 October 2009 Available online xxx Keywords: Microalgae Biomass recovery Bioenergy Conversion Photobioreactor CO 2 sequestration ABSTRACT Sustainability is a key principle in natural resource management, and it involves operational efficiency, minimisation of environmental impact and socio-economic considerations; all of which are interdependent. It has become increasingly obvious that continued reliance on fossil fuel energy resources is unsustainable, owing to both depleting world reserves and the green house gas emissions associated with their use. Therefore, there are vigorous research initiatives aimed at developing alternative renewable and potentially carbon neutral solid, liquid and gaseous biofuels as alternative energy resources. However, alternate energy resources akin to first generation biofuels derived from terrestrial crops such as sugarcane, sugar beet, maize and rapeseed place an enormous strain on world food markets, contribute to water shortages and precipitate the destruction of the world’s forests. Second generation biofuels derived from lignocellulosic agriculture and forest residues and from non- food crop feedstocks address some of the above problems; however there is concern over competing land use or required land use changes. Therefore, based on current knowledge and technology projections, third generation biofuels specifically derived from microalgae are considered to be a technically viable alternative energy resource that is devoid of the major drawbacks associated with first and second generation biofuels. Microalgae are photosynthetic microorganisms with simple growing requirements (light, sugars, CO 2 , N, P, and K) that can produce lipids, proteins and carbohydrates in large amounts over short periods of time. These products can be processed into both biofuels and valuable co-products. This study reviewed the technologies underpinning microalgae-to-biofuels systems, focusing on the biomass production, harvesting, conversion technologies, and the extraction of useful co-products. It also reviewed the synergistic coupling of microalgae propagation with carbon sequestration and wastewater treatment potential for mitigation of environmental impacts associated with energy conversion and utilisation. It was found that, whereas there are outstanding issues related to photosynthetic efficiencies and biomass output, microalgae-derived biofuels could progressively substitute a significant proportion of the fossil fuels required to meet the growing energy demand. ß 2009 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +353 1 716 7458; fax: +353 1 716 7415. E-mail address: liam.brennan@ucd.ie (L. Brennan). G Model RSER-805; No of Pages 21 Please cite this article in press as: Brennan L, Owende P. Biofuels from microalgae—A review of technologies for production, processing, and extractions of biofuels and co-products. Renew Sustain Energy Rev (2009), doi:10.1016/j.rser.2009.10.009 Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser 1364-0321/$ – see front matter ß 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.rser.2009.10.009