Low energy harvesting of hydrophobic microalgae (Tribonema sp.) by electro-flotation without coagulation

Shasha Qi; Jingrou Chen; Yuansheng Hu; Zhenhu Hu; Xinmin Zhan; Dagmar B Stengel

doi:10.1016/j.scitotenv.2022.155866

Low energy harvesting of hydrophobic microalgae (Tribonema sp.) by electro-flotation without coagulation

Sci Total Environ. 2022 Sep 10;838(Pt 1):155866. doi: 10.1016/j.scitotenv.2022.155866. Epub 2022 May 12.

Authors

Shasha Qi¹, Jingrou Chen², Yuansheng Hu³, Zhenhu Hu⁴, Xinmin Zhan⁵, Dagmar B Stengel⁶

Affiliations

¹ Civil Engineering, College of Science and Engineering, National University of Ireland Galway, Galway, Ireland; School of Civil Engineering, Hefei University of Technology, Hefei, China.
² Civil Engineering, College of Science and Engineering, National University of Ireland Galway, Galway, Ireland.
³ Civil Engineering, College of Science and Engineering, National University of Ireland Galway, Galway, Ireland; Ryan Institute, National University of Ireland Galway, Galway, Ireland. Electronic address: yuansheng.hu@nuigalway.ie.
⁴ School of Civil Engineering, Hefei University of Technology, Hefei, China.
⁵ Civil Engineering, College of Science and Engineering, National University of Ireland Galway, Galway, Ireland; Ryan Institute, National University of Ireland Galway, Galway, Ireland; MaREI Research Centre, National University of Ireland Galway, Galway, Ireland. Electronic address: xinmin.zhan@nuigalway.ie.
⁶ Ryan Institute, National University of Ireland Galway, Galway, Ireland; Botany and Plant Science, School of Natural Sciences, National University of Ireland Galway, Galway, Ireland.

PMID: 35568179
DOI: 10.1016/j.scitotenv.2022.155866

Abstract

Microalgae have great potential for biofuel production and wastewater treatment, but the high cost of harvesting hinders their practical application. In this study, economical harvesting of hydrophobic microalgae by electro-flotation without coagulation was assessed. The harvesting performance of this method for selected species of freshwater microalgae with different degrees of hydrophobicity (Tribonema sp., highly hydrophobic; Scenedesmus sp., moderately hydrophobic; and Pandorina sp., hydrophilic) were compared. It was found that microalgal hydrophobicity played a critical role in electro-flotation. Under the same condition (current 0.3 A, velocity gradient 200 s^-1, biomass concentration 1 g/L), Tribonema sp. could be effectively harvested (96.2 ± 0.4%) after 20 min of electro-flotation, while the harvesting efficiency decreased significantly with Scenedesmus sp. (70.1 ± 5.2%, 20 min) and Pandorina sp. (<10%, 1 h). The influences of current, electrolysis time, mixing intensity (velocity gradient) and biomass concentration on Tribonema sp. (hydrophobic) harvesting were further investigated. Increasing the current within a certain range (0.1 A-0.4 A) was beneficial to harvesting, while it's further increase decreased floating velocity, which was similar to the effect of the velocity gradient. Under the optimal condition, the harvesting efficiency of Tribonema sp. was 96.3% and the energy consumption (0.19 kWh/kg biomass) was much lower than other harvesting techniques, indicating that electro-flotation is a time-saving and economical approach for hydrophobic microalgae harvesting.

Keywords: Electro-flotation; Energy consumption; Hydrophobicity; Microalgae; Velocity gradient.

MeSH terms

Biomass
Flocculation
Hydrophobic and Hydrophilic Interactions
Microalgae*
Scenedesmus*
Stramenopiles*