Harvesting microalgal biomass using magnesium coagulation-dissolved air flotation

Xuezhi Zhang, Lan Wang, Milton Sommerfeld, Qiang Hu

Research output: Contribution to journalArticlepeer-review

44 Scopus citations


Coagulation with magnesium was found to be more effective for harvesting microalgae Chlorella zofingiensis with dissolved air flotation (DAF) than the use of Fe3+, Al3+ or chitosan, and the required coagulant dosage was in the order Mg2+ < chitosan < Al3+ < Fe3+. The Mg2+ dosage required depended on the growth phases and culture medium characteristics. An early exponential culture required the highest Mg2+ dosage (226 mg g−1), while a late stationary culture required the lowest dosage (36 mg g−1). HPO42− and CO32− in the culture medium competed with the microalgal cells for Mg2+ and increased the Mg2+ dosage necessary. No Mg2+ addition was required to harvest the freshwater microalgae Scenedesmus dimorphus grown in a pond with tap water with a high Mg2+ concentration or the marine microalgae Nannochloropsis sp. The critical coagulation pH ranged between 10.8 and 11.8, with a lower pH requirement at a higher Mg2+ concentration. Magnesium hydroxide precipitated with the harvested biomass; however, over 99.5% of the precipitated Mg2+ was recovered by washing the biomass with 0.1 M HCl. Microalgal harvesting with Mg2+ did not introduce extrinsic coagulant; thus, neither the biomass nor the medium was contaminated.

Original languageEnglish (US)
Pages (from-to)43-49
Number of pages7
JournalBiomass and Bioenergy
StatePublished - Oct 1 2016
Externally publishedYes


  • Biomass purification
  • Coagulant recovery
  • Flotation
  • Medium recycling
  • Microalgal harvesting

ASJC Scopus subject areas

  • Forestry
  • Renewable Energy, Sustainability and the Environment
  • Agronomy and Crop Science
  • Waste Management and Disposal


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