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Physicochemical Approach to Alkaline Flocculation of Chlorella vulgaris Induced by Calcium Phosphate Precipitates.

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    0487866 - ÚCHP 2019 RIV NL eng J - Journal Article
    Brányiková, Irena - Filipenská, Monika - Urbanová, K. - Růžička, Marek - Pivokonský, Martin - Brányik, T.
    Physicochemical Approach to Alkaline Flocculation of Chlorella vulgaris Induced by Calcium Phosphate Precipitates.
    Colloids and Surfaces B-Biointerfaces. Roč. 166, June 1 (2018), s. 54-60. ISSN 0927-7765
    R&D Projects: GA ČR(CZ) GA18-05007S
    Institutional support: RVO:67985858 ; RVO:67985874
    Keywords : microalgae * calcium phosphate * precipitates * surface interactions
    Subject RIV: CI - Industrial Chemistry, Chemical Engineering; BK - Fluid Dynamics (UH-J)
    OBOR OECD: Chemical process engineering; Environmental sciences (social aspects to be 5.7) (UH-J)
    Impact factor: 3.973, year: 2018

    Alkaline flocculation has been studied due to its potential as a low-cost harvesting method for microalgae. However, surface properties (zeta potential, contact angles) as inputs into physicochemical interaction models have not yet been applied systematically. In this work, forced alkaline flocculation of the freshwater microalgae Chlorella vulgaris induced by calcium phosphate precipitates was studied as a model system. Response surface methodology was used to quantify the effect of independent variables (concentration of Ca2+ (0.5 − 0.5 mM) and PO43− (0.05 − 0.35 mM, pH (8 − 12) and ionic strength (1 − 19 mM) on the zeta potential (ZP) of microalgae, and the turbidity (T) of inorganic precipitates. Flocculation tests and their modified versions were carried out. The flocculation efficiencies obtained were interpreted with respect to predictions of physicochemical interaction models. It was found that flocculation was possible under conditions where appropriate precipitates were formed in the presence of cells. Under these conditions, flocculation of negatively charged Chlorella vulgaris was induced not only by positively charged, but also by negatively charged calcium phosphate precipitates at an early phase of nucleation. The driving force for interactions between oppositely charged cells and precipitate particles was electrostatic attraction, while the attraction between equally charged entities may have resulted from a negative total balance of apolar (Lifsitz-van der Waals) and polar (acid-base) interactions. Medium components did not interfere with flocculation, while cellular organic matter decreased flocculation efficiency only to a very limited extent.
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