Harvesting of oleaginous marine microalgae by dewatering is an important step for cost-effective algal biomass feedstock production. This paper reports separation of marine microalgae (Tetraselmis sp. M8) from aqueous medium by froth flotation using various collectors (surfactants) with equal carbon chain length, such as dodecyl pyridinium chloride (DPC), N-dodecylpropane-1,3-diamine hydrochloride (DN2), dodecyl amine hydrochloride (DAH), and sodium dodecyl sulphate (SDS), at different pHs. Algal hydrophobicity, froth stability, and surfactant precipitation were characterised. The laboratory-scale mechanical flotation tests showed that at natural pH 9.5 and a lower pH, DPC outperformed DAH, DN2 and SDS in separating Tetraselmis sp. M8 from seawater. DPC was capable of rendering the microalgae hydrophobic, producing metastable froth, and dissolving readily in water, which are all desirable features of a collector for flotation separation of microalgae from water. Use of DPC at 15 ppm in pilot-scale Jameson cell flotation tests for M8 after outdoor cultivation led to a 23-fold increase in algal concentration with over 99% algal recovery. (C) 2015 Elsevier B.V. All rights reserved.