future science group 397 ISSN 1759-7269 10.4155/BFS.13.25 © 2013 Future Science Ltd Microalgae have a robust photosynthetic capability for fixing CO 2 and converting solar energy into chemical energy. Moreover, they do not need to compete with arable land and freshwater, and have been considered as one of the most promising feedstocks for biofuels [1,2]. Microalgae are typically 2–50 μm in size with a negative charge on the cell surface [3–5], but some microalgae, under certain conditions, have a larger cell size. In most cases they are motile (i.e., swimming or gliding), such as dinoflagellates or raphid diatoms, and form stable suspensions. Unfortunately, microalgal biomass is fairly dilute in cultures (up to 0.3–0.5 g dry biomass/l), resulting in difficulties in harvesting and dewatering algae cost effectively [6]. Microalgae harvesting can typically make up to 20–30% of the total biomass production cost [7–9]. This makes the harvesting process a major bottleneck, hindering the development of the microalgae industry. To date, there are a multitude of techniques being used for microalgae dewatering, but with low economical feasibility. Based on their large biodiversity, microalgae harvesting pro- cesses are to a large extent species specific [10,11]. They are also closely linked to cell density and cultivation conditions [12]. The production of biofuel, such as biodiesel, from microalgae is a multistep process involving cultiva- tion, biomass harvest, lipid extraction and oil conver- sion. Compared with the other processes, harvesting is arguably still the most critical and challenging stage in microalgae biomass production [4,8, 12–15]. When con- sidering commercial-scale processes for dewatering and recovering algal biomass for further downstream pro- cesses, a traditional harvesting method may involve up to two steps; the first is known as primary harvesting/bulk harvesting, and the second is known as secondary dewa- tering/thickening (Figure 1) [8–10,16]. During the primary harvesting process, the microalgae mass ratio to water volume is increased [17]. This step aims to achieve a con- centration containing 2–7% total solid matter, from the initial biomass concentration [16]. Secondary dewatering concentrates the biomass up to 15–25%, which when followed by drying, aims to further concentrate the slurry, increasing the total solid matter up to 90–95%. This step is generally a more energy-intensive step than Critical analysis of current microalgae dewatering techniques Kalpesh K Sharma †1 , Sourabh Garg †1 , Yan Li 1,2 , Ali Malekizadeh 1 & Peer M Schenk* 1 Oil-accumulating microalgae have the potential to enable large-scale biodiesel production without competing for arable land or biodiverse natural landscapes. However, microalgae harvesting/dewatering is a major obstruction to industrial-scale processing for biofuel production. The dilute nature of microalgae in cultivation creates high operational costs for harvesting, thus making microalgal fuel less economical. Within the last decade, signifcant advances have been made to develop new technologies for dewatering or harvesting of microalgae. The choice of which harvesting technique to apply depends on the microalgae cell size and the desired product. Microalgae dewatering processes can broadly be classifed as primary and secondary dewatering. This article provides an overview of current dewatering techniques along with a critical analysis of costs and efciencies, and provides recommendations towards cost-efective dewatering. PERSPECTIVE 1 Algae Biotechnology Laboratory, School of Agriculture and Food Sciences, The University of Queensland, Brisbane, QLD 4072, Australia 2 School of Tropical and Marine Sciences, James Cook University, Douglas, QLD 4811, Australia *Author for correspondence: E-mail: p.schenk@uq.edu.au † These authors contributed equally Biofuels (2013) 4(4), 397–407 For reprint orders, please contact reprints@future-science.com