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Continuous harvesting of microalgae biomass using foam flotation

Lookup NU author(s): Muayad Al-Karawi, Dr Gary Caldwell, Dr Jonathan Lee

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This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND).


Abstract

Biomass harvesting and dewatering are major operational costs that constrain the development and expansion of the industrial use of microalgae; particularly for low value biofuels. Flotation-based technologies show promise as low cost, energy-efficient harvesters, producing a thickened algae slurry ahead of further dewatering steps. In this study we demonstrate, for the first time, a surfactant-aided foam flotation column that is designed and optimised for the continuous harvest of microalgae. The following operational parameters were optimised; surfactant concentration, air flow rate, feed flow rate, column height, liquid pool depth, and sparger type (i.e. bubble size). Additionally, the effects of cell surface characteristics (hydrophobicity, zeta potential, and contact angle) were investigated on Chlorella vulgaris flotation performance. Hydrophobicity was enhanced using three surfactants; the cationic cetyltrimethylammonium bromide (CTAB), the anionic sodium dodecyl sulfate (SDS), and the non-ionic TWEEN®20; with CTAB producing the greatest enhancement. Surfactant concentration, column height, and air flow rate had the greatest effect on the algae concentration factor (CF) and recovery efficiency (RE). The optimised design (CTAB = 35 mg L-1, air flow rate = 1 L min-1, feed flow rate= 0.1 L min-1, column height = 146 cm, liquid pool depth = 25 cm, with a fine porous sparger) yielded RE of 95, 93, and 89% with 173, 271, and 143-fold biomass enrichments for freshwater C. vulgaris and marine Isochrysis galbana and Tetraselmis suecica microalgae respectively. Achieving high RE for freshwater and in the case of marine microalgae (irrespective of ionic strength) at moderate surfactant dosages, gives foam flotation the advantage of being a growth media independent harvesting process. The process had a very low power consumption (0.052 KWh m-3 of algae culture). Our findings demonstrate the potential for continuous, low cost, scalable flotation harvesting with particular relevance for the biofuels, water and wastewater treatment industries.


Publication metadata

Author(s): Alkarawi MAS, Caldwell GS, Lee JGM

Publication type: Article

Publication status: Published

Journal: Algal Research

Year: 2018

Volume: 36

Pages: 125-138

Print publication date: 01/12/2018

Online publication date: 27/10/2018

Acceptance date: 18/10/2018

Date deposited: 19/10/2018

ISSN (print): 2211-9264

Publisher: Elsevier BV

URL: https://doi.org/10.1016/j.algal.2018.10.018

DOI: 10.1016/j.algal.2018.10.018


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