Influence of magnesium concentration, biomass concentration and pH on flocculation of Chlorella vulgaris

Abstract

Influence of magnesium concentration, biomass concentration and pH on flocculation of Chlorella vulgarisAlgal Research, vol 3, 24-29. Archived versionAuthor manuscript: the content is identical to the content of the published paper, but without the final typesetting by the publisher Autoflocculation is a promising low-cost method for harvesting microalgae for bulk 21 biomass production or wastewater treatment. Autoflocculation can be caused by 22 precipitation of calcium or magnesium at high pH. In this study, we investigated the 23 interactive effects of pH, magnesium concentration and microalgal biomass 24 concentration on flocculation of Chlorella vulgaris by magnesium hydroxide. The 25 minimum pH for inducing flocculation was lower when magnesium concentration in 26 the medium is higher. A higher pH and/or higher magnesium concentration are 27 required for flocculation when microalgal biomass concentration is increased. The 28 sludge volume formed during flocculation is highly variable and is influenced mainly 29 by the amount of magnesium hydroxide that precipitates during flocculation. The 30 sludge volume increases with pH and with magnesium concentration in the medium. 31There is an optimal pH where flocculation efficiency is maximized (> 95%) and 32 sludge volume is minimal (1 -2% of culture volume). Increasing the pH slightly 33 above this optimum results either in an increase in sludge volume and/or a decrease in 34 flocculation efficiency. We propose that autoflocculation by magnesium hydroxide 35 can be more easily controlled by the dosage of base rather than by targeting a specific 36 pH level.

Harvesting microalgal biomass using magnesium coagulation-dissolved air flotation

“…However, when pH was greater than 10.5, the harvesting efficiency increased with the Mg 2þ concentration and reached more than 94%. Similar results were found in a previous study in which the coagulation efficiency was higher than 90% when the magnesium concentration was higher than 0.3 mM and the pH was higher than 10.5 [17]. It is interesting to note that the increase in the Mg 2þ dosage also lowered the critical pH at which a rapid increase in the harvesting efficiency occurred.…”

Harvesting of Microalgae by Means of Flocculation

“…Like aluminum or ferric hydroxide, magnesium hydroxide is a metal hydroxide and may cause flocculation through a similar mechanism as metal salts (Smith and Davis 2012). Magnesium hydroxide precipitates are positively charged up to pH 11 and can cause flocculation through charge neutralization (Wu et al 2012;García-Pérez et al 2014). Microscopical observations of flocculated microalgae, however, suggest that sweeping flocculation may be equally important as charge neutralization (Besson and Guiraud 2013).…”

“…In seawater, overdosing of base may result in massive precipitation of magnesium hydroxide and a very large sludge volume, which poses problems for further dewatering (e.g., Şirin et al 2011). Therefore, it is recommended to control addition of the base rather than target a specific pH level to maximize flocculation efficiency and minimize the sludge volume (Besson and Guiraud 2013;García-Pérez et al 2014). The amount of base that needs to be added will be a function of the quantity of magnesium hydroxide required to induce flocculation, but also of the buffering capacity of the culture medium (GarzonSanabria et al 2012).…”

“…The flocculation conditions or dosage can also influence flocculation process. For example, when applying autoflocculation by magnesium hydroxide in seawater medium, overdosing of base may result in massive precipitation of magnesium hydroxide and will result in a very large sludge volume (Şirin et al 2011;Besson and Guiraud 2013;García-Pérez et al 2014). , Wright's cryptophyte medium) was used for each flocculation method (Vandamme et al 2014a, b) Subsequent to flocculation, sedimentation is generally used to separate the flocs from the culture medium.…”

Optimization of Alkaline Flocculation for Harvesting of Scenedesmus quadricauda #507 and Chaetoceros muelleri #862

“…Previous studies have investigated the interactive effects of pH, Mg 2+ , Ca 2+ , concentration and microalgal biomass concentration on flocculation of Chlorella. The flocculation activity is highly variable and is influenced mainly by the amount of magnesium hydroxide [8,[11][12][13][14][15]. This method was studied to a number of microalgal strains (such as Chlorella vulgaris [11][12][13], Scenedesmus sp.…”