Alum-induced flocculation of preconcentrated Nannochloropsis salina: Residual aluminium in the biomass, FAMEs and its effects on microalgae growth upon media recycling Vincent M. Rwehumbiza ⇑ , Rosalyn Harrison, Laurenz Thomsen School of Engineering and Science, Jacobs University, Campus Ring 1, 28759 Bremen, Germany highlights " Flocculation of Nannochloropsis salina with alum is an economical biomass production method. " After preconcentration, content of aluminium in lipids and FAMEs decreased. " Aluminium in extracted lipids and fatty acids decreased by 2–3 orders of magnitude. " Aluminium in recycled media did not affect photosynthesis and growth of N. salina. graphical abstract article info Article history: Received 16 February 2012 Received in revised form 3 June 2012 Accepted 5 June 2012 Available online 16 June 2012 Keywords: Aluminium Flocculation Voltammetry Microalgae preconcentration Preconcentration FAMEs Media recycling abstract Flocculation with polyaluminium complexes has been regarded as an unsafe method of harvesting mic- roalgae due to the potentially toxic effects of aluminium. Varying concentrations of Nannochloropsis salina were flocculated with different concentrations of aluminium nitrate sulphate. The level of aluminium in the microalgal biomass, lipids and fatty acid methyl esters (FAMEs) was then determined by differential pulse adsorptive cathodic stripping voltammetry. These flocculation experiments were carried at both the laboratory and pilot scale, demonstrating efficiencies of between 79% and 99%. The highest efficien- cies were observed when the concentrations of N. salina suspensions were either 15 or 20 g L 1 . Despite the application of different doses of flocculant, the equilibrium content of aluminium in the filtrate aver- aged between 0.47 and 0.64 mg L 1 for all tested N. salina biomass concentrations. With increasing mic- roalgae biomass concentration, an exponential decrease in aluminium content per weight of microalgal biomass was observed. After recycling the filtrate, the residual aluminium did not affect growth or pho- tosynthetic performance of N. salina. Moreover, following extraction and conversion of lipids and FAMEs respectively, the residual aluminium decreased by 2–3 orders of magnitude. Aluminium was not detected in FAMEs from microalgae flocculated at a starting concentration of 20 g L 1 N. salina biomass. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Microalgae are eukaryotic microorganisms that fix atmospheric carbon dioxide using sunlight energy. Their high productivity, which rivals that of both aquatic and terrestrial plants make them a reliable natural source of a myriad of metabolites for food, feed, pharmaceutical and energy application [1–3]. Additionally, micro- algae can be used for bioremediation to sequester carbon from industrial flue gases, exhaust fumes and wastewater, and in return produce biomass with many potential uses [4,5]. In order to cater to the ever growing demand for food, animal feed and energy, large scale cultivation and harvesting of microalgae in a feasible and sustainable manner is required. Microalgae cells are microscopic 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.06.008 ⇑ Corresponding author. E-mail address: v.rwehumbiza@jacobs-university.de (V.M. Rwehumbiza). Chemical Engineering Journal 200–202 (2012) 168–175 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej