Harvesting of microalgae Desmodesmus sp. F51 by bioflocculation with bacterial bioflocculant Theoneste Ndikubwimana a , Xianhai Zeng b,c, ⁎, Yu Liu a , Ning He a,c , Michael K. Danquah d , Ching-Nen Nathan Chen e,f , Jo-Shu Chang g,h,i , Lu Lin b , Yinghua Lu a,c, ⁎⁎ a Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China b College of Energy, Xiamen University, Xiamen 361005, China c The Key Laboratory for Synthetic Biotechnology of Xiamen City, Xiamen University, Xiamen 361005, China d Department of Chemical Engineering, School of Engineering and Science, Curtin University of Technology, 98009 Sarawak, Malaysia e Institute of Marine Biology, National Sun Yat-sen University, Kaohsiung 804, Taiwan, ROC f Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung 804, Taiwan, ROC g Department of Chemical Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC h University Center for Bioscience and Biotechnology, National Cheng Kung University, Tainan 701, Taiwan, ROC i Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan 701, Taiwan, ROC abstract article info Article history: Received 12 April 2014 Received in revised form 9 September 2014 Accepted 18 September 2014 Available online xxxx Keywords: Microalgae Downstream processing Harvesting Bioflocculation Bioflocculant The small particulate size of microalgae cells and the extremely dilute concentrations of microalgae cultures con- tinue to be major challenges to effective harvesting. In an attempt to find a cost-effective and environmentally friendly harvesting technique, the bioflocculant poly (γ-glutamic acid) (γ-PGA) produced by Bacillus licheniformis CGMCC 2876 was used to concentrate freshwater microalgae Desmodesmus sp. F51. Experimental results showed that the flocculation efficiency was dependent on the initial culture pH. The flocculation efficiency increased from 43.8 ± 1.6% to 98.2 ± 0.1% when the initial culture pH was changed from ~7.2, as the original cul- ture pH, to 3. With the optimum operating parameters of bioflocculant dosage of 2.5 mL/L, flash mixing rate of 150 rpm for 1 min, and slow mixing rate of 80 rpm for 2 min, a flocculation efficiency of 99% was achieved. Mi- croscopic photos of the harvested microalgae cells showed no cell damage and hence no premature release of in- tracellular contents during the process. The bioflocculation process is easy to operate, cost-efficient, environmentally friendly and as effective as chemical flocculation processes applied industrially. The γ-PGA bioflocculant produced by B. licheniformis CGMCC 2876 demonstrated high performance for optimal microalgae recovery and can be applied in commercial-scale microalgae harvesting. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The operational demand and application of biomass for food, biopharmaceuticals, biofuels and chemicals production is expected to increase by more than 50% in the coming decades as a result of the in- crease in human population globally and the endeavor to improve the living standards of developing economies [1–3]. Microalgae are consid- ered as a promising source of biomass to complement agricultural crops. This is due to their fast growth rate, high productivity of lipids, carbohydrates and a variety of other biochemicals, such as proteins and vitamins, alongside the benefits of integrating environmental bioremediation schemes, such as CO 2 bio-sequestration and wastewater treatment [4–8]. However, despite these advantages, culture harvesting and dewatering continue to be a major bottleneck to microalgae bioprocessing, and this is due to the dilute nature of microalgae cultures, small particulate cell size, and highly electronegative cell membrane surface charge [9]. Microalgae dewatering cost accounts for more than 30% of the entire bioprocess cost for product development [10,11]. There are many solid–liquid separation technologies applied for microalgae culture dewatering. These include centrifugation [12], filtra- tion [13], sedimentation [14], dissolved air flotation [15,16], coagulation with inorganic coagulants (such as aluminium sulfate, iron (III) sulfate, and many others) [17], pH change sedimentation [18], electrostatic al- kaline flocculation [19], magnetic separation [20], electro-coagulation flocculation (ECF) [21], and chitosan flocculation [22]. Most of these dewatering processes are performed as standalone operations under lab-scale conditions and would pose serious challenges, such as high en- ergy consumption, long processing times, low recovery and high green- house gas emissions, under large-scale operation [23]. Thus finding a Algal Research xxx (2014) xxx–xxx ⁎ Correspondence to: X. Zeng, College of Energy, Xiamen University, Xiamen 361005, China. ⁎⁎ Correspondence to: Y. Lu, Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China. E-mail addresses: xianhai.zeng@xmu.edu.cn (X. Zeng), ylu@xmu.edu.cn (Y. Lu). ALGAL-00154; No of Pages 8 http://dx.doi.org/10.1016/j.algal.2014.09.004 2211-9264/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Algal Research journal homepage: www.elsevier.com/locate/algal Please cite this article as: T. Ndikubwimana, et al., Harvesting of microalgae Desmodesmus sp. F51 by bioflocculation with bacterial bioflocculant, Algal Res. (2014), http://dx.doi.org/10.1016/j.algal.2014.09.004