Harvesting techniques applied to microalgae: A review Ana I. Barros, Ana L. Gonçalves, Manuel Simões, José C.M. Pires n LEPABE, Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal article info Article history: Received 17 December 2013 Received in revised form 2 September 2014 Accepted 27 September 2014 Keywords: Bioenergy production Economic viability Green processes Harvesting processes Microalgae Sustainable processes abstract Research studies on microalgae have increased in the last decades due to the wide range of applications associated to these photosynthetic microorganisms. Microalgae are an important source of oils and other biomolecules that can be used in the production of biofuels and high-valued products. However, the use of microalgae in these green processes is still not economically viable. One of the main costs associated to microalgal production is related to the harvesting process, as it usually accounts for about 20–30% of total cost. Therefore, this review focuses on the main harvesting processes applied to microalgae, presenting the main advantages and disadvantages of each method, to allow the selection of an appropriate procedure to effectively separate microalgal biomass from the culture medium. To reduce the associated costs, it is common to harvest microalgae in a two-step separation: (i) thickening procedures, in which microalgal slurry is concentrated to about 2–7% of total suspended solids; and (ii) dewatering procedures, which result in the concentration of microalgal slurry to 15–25% of total suspended solids. Selection of the adequate harvesting methods depends on the characteristics of the target microorganism and also on the type and value of the end product. & 2014 Elsevier Ltd. All rights reserved. Contents 1. Introduction ....................................................................................................... 1489 2. Microalgal harvesting methods ........................................................................................ 1490 2.1. Screening ................................................................................................... 1491 2.2. Thickening .................................................................................................. 1491 2.2.1. Chemical coagulation/flocculation......................................................................... 1491 2.2.2. Auto and bioflocculation ................................................................................ 1493 2.2.3. Gravity sedimentation .................................................................................. 1496 2.2.4. Flotation ............................................................................................. 1496 2.2.5. Electrical based processes ............................................................................... 1496 2.3. Dewatering.................................................................................................. 1497 2.3.1. Filtration............................................................................................. 1497 2.3.2. Centrifugation ........................................................................................ 1498 3. Research needs .................................................................................................... 1499 4. Conclusions ....................................................................................................... 1499 Acknowledgements ..................................................................................................... 1499 References ............................................................................................................ 1499 1. Introduction It is well known that microalgae have a huge potential in a wide variety of applications. Concerning environmental ones, microalgae can play an important role in bioremediation of wastewater and carbon dioxide sequestration [1–6]. Furthermore, these photosyn- thetic microorganisms have been considered as a potential renew- able fuel source [7–9]: they can be used as raw material for the production of biodiesel, biomethane, bioethanol, biohydrogen and biobutanol. These biofuels are viewed as the most promising alternative to fossil fuels, being able to provide up to 25% of global Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/rser Renewable and Sustainable Energy Reviews http://dx.doi.org/10.1016/j.rser.2014.09.037 1364-0321/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: þ351 22 508 2262; fax: þ351 22 508 1449. E-mail address: jcpires@fe.up.pt (J.C.M. Pires). Renewable and Sustainable Energy Reviews 41 (2015) 1489–1500