Harvesting microalgae by CTAB-aided foam flotation increases lipid recovery and improves fatty acid methyl ester characteristics

Thea Coward,Jonathan G.M Lee,Gary S Caldwell

doi:10.1016/j.biombioe.2014.05.019

Thea Coward, Jonathan G.M Lee + Show 1 more

Open Access

https://doi.org/10.1016/j.biombioe.2014.05.019

Copy DOI

Journal: Biomass & Bioenergy	Publication Date: Jun 14, 2014
Citations: 136	License type: cc-by

Affiliation: Newcastle University

Abstract

Foam flotation is an effective and energy efficient method of harvesting microalgae. This study has investigated the influence of growth phase and lipid content on harvesting efficiency. The highest biomass concentration factors were gained during active culture growth. Surprisingly, the quantities of lipid recovered from microalgae harvested by foam flotation using the surfactant cetyl trimethylammonium bromide (CTAB), were significantly higher than from cells harvested by centrifugation. Further, cells harvested by CTAB-aided foam flotation exhibited a lipid profile more suited to biodiesel conversion containing increased levels of saturated and monounsaturated fatty acids. The enhanced lipid recovery was partially explained by the interaction of the cells with the surfactant, CTAB, which adsorbed onto the algae and was carried over into the total lipid extraction process. However, further evidence also suggested that CTAB promoted in situ cell lysis by solubilising the phospholipid bilayer, thus increasing the amount of extractable lipid. This work demonstrates substantial added value of foam flotation as a microalgae harvesting method beyond energy efficient biomass recovery.

Highlights

Microalgae are considered as having great potential as a sustainable, scalable and affordable source of bioproducts including biofuels and high value chemicals [1e3]
cetyl trimethylammonium bromide (CTAB) has proven an advantageous surfactant for algae removal [10,11,13e15,21,23] with reported removal efficiencies approaching 90% [11,13e15]
The highest concentration factors e up to 306.89 ± 31.6 e which occurred on day 12 were significantly higher (p 1⁄4

Summary

Introduction

Microalgae are considered as having great potential as a sustainable, scalable and affordable source of bioproducts including biofuels and high value chemicals [1e3]. A separation process originating from the mineral industry, has become an established method to remove algae from suspension [11e16], with potential for application to harvest microalgae for biofuel production [2,5,6,17e19]. Foam flotation, a technique similar to dissolved air flotation, virtually eliminates the need for the energy intensive step of air compression by generating bubbles and foam with the addition of a cationic surfactant e.g. cetyl trimethylammonium bromide (CTAB) and a low pressure sparger or agitator [16,19]; operational energy consumption is reduced to as little as 0.015 kWh mÀ3 [10]. The surfactant, by improving the electrostatic interactions between the bubbles and the microalgae cells, removes the need for a flocculent [21]. The second hypothesis predicts that cationic surfactant ions adsorb onto the algae making the cell hydrophobic and available for bubble attachment [11,13,15]

Objectives

Methods

Results

Conclusion