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Freshwater microalgae harvested via flocculation induced by pH decrease.

Liu J, Zhu Y, Tao Y, Zhang Y, Li A, Li T, Sang M, Zhang C - Biotechnol Biofuels (2013)

Bottom Line: Furthermore, viability of flocculated cells was determined by Evans Blue assay and few cells were found to be damaged with pH decrease.The study provided an economical, efficient and convenient method to harvest fresh microalgae.It has shown the potential to overcome the hurdle of harvesting microalgae to promote full-scale application to biofuels from microalgae.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry, Jinan University, Tianhe District, Guangzhou 510632, China. tzhangym@gmail.com.

ABSTRACT

Background: Recent studies have demonstrated that microalga has been widely regarded as one of the most promising raw materials of biofuels. However, lack of an economical, efficient and convenient method to harvest microalgae is a bottleneck to boost their full-scale application. Many methods of harvesting microalgae, including mechanical, electrical, biological and chemical based, have been studied to overcome this hurdle.

Results: A new flocculation method induced by decreasing pH value of growth medium was developed for harvesting freshwater microalgae. The flocculation efficiencies were as high as 90% for Chlorococcum nivale, Chlorococcum ellipsoideum and Scenedesmus sp. with high biomass concentrations (>1g/L). The optimum flocculation efficiency was achieved at pH 4.0. The flocculation mechanism could be that the carboxylate ions of organic matters adhering on microalgal cells accepted protons when pH decreases and the negative charges were neutralized, resulting in disruption of the dispersing stability of cells and subsequent flocculation of cells. A linear correlation between biomass concentration and acid dosage was observed. Furthermore, viability of flocculated cells was determined by Evans Blue assay and few cells were found to be damaged with pH decrease. After neutralizing pH and adding nutrients to the flocculated medium, microalgae were proved to maintain a similar growth yield in the flocculated medium comparing with that in the fresh medium. The recycling of medium could contribute to the economical production from algae to biodiesel.

Conclusions: The study provided an economical, efficient and convenient method to harvest fresh microalgae. Advantages include capability of treating high cell biomass concentrations (>1g/L), excellent flocculation efficiencies (≥ 90%), operational simplicity, low cost and recycling of medium. It has shown the potential to overcome the hurdle of harvesting microalgae to promote full-scale application to biofuels from microalgae.

No MeSH data available.


Growth curves of microalgae: fresh medium (filled points); flocculated medium (empty points).
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Figure 8: Growth curves of microalgae: fresh medium (filled points); flocculated medium (empty points).

Mentions: Ideally, medium recovered from flocculation could be recycled for next cultivation. The problem with medium recycling is that residual flocculant such as ferric salts and aluminum salts can cause contamination, which eventually cause environmental problems and a great loss of water [35]. However, in this flocculation method induced by pH decrease, since no flocculants were used and the medium was not contaminated, the growth medium after flocculation might be recycled by neutralizing pH and then adding nutrients. The product of neutralizing pH of flocculated BG-11 medium with NaOH was NaNO3, which was a necessary nutrient. So, the recycling of flocculated medium could minimize the cost of nutrients and demand for water. In this respect, the possibility of recycling the flocculated medium was examined. Some microalgal cells flocculated were cultivated in the recycled culture solution and the biomass as a function of growth phase was shown in Figure 8. It was observed that the biomass of each microalgal species cultivated in the recycled growth medium was close to that cultivated in the fresh medium, indicating the flocculated medium could be successfully recycled for cultivation. The fact that the flocculated microalgal cells could be recultivated further suggested that there was no cell lysis during the flocculation process and the molecular function and structure of the photosynthetic apparatus were not affected.


Freshwater microalgae harvested via flocculation induced by pH decrease.

Liu J, Zhu Y, Tao Y, Zhang Y, Li A, Li T, Sang M, Zhang C - Biotechnol Biofuels (2013)

Growth curves of microalgae: fresh medium (filled points); flocculated medium (empty points).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3716916&req=5

Figure 8: Growth curves of microalgae: fresh medium (filled points); flocculated medium (empty points).
Mentions: Ideally, medium recovered from flocculation could be recycled for next cultivation. The problem with medium recycling is that residual flocculant such as ferric salts and aluminum salts can cause contamination, which eventually cause environmental problems and a great loss of water [35]. However, in this flocculation method induced by pH decrease, since no flocculants were used and the medium was not contaminated, the growth medium after flocculation might be recycled by neutralizing pH and then adding nutrients. The product of neutralizing pH of flocculated BG-11 medium with NaOH was NaNO3, which was a necessary nutrient. So, the recycling of flocculated medium could minimize the cost of nutrients and demand for water. In this respect, the possibility of recycling the flocculated medium was examined. Some microalgal cells flocculated were cultivated in the recycled culture solution and the biomass as a function of growth phase was shown in Figure 8. It was observed that the biomass of each microalgal species cultivated in the recycled growth medium was close to that cultivated in the fresh medium, indicating the flocculated medium could be successfully recycled for cultivation. The fact that the flocculated microalgal cells could be recultivated further suggested that there was no cell lysis during the flocculation process and the molecular function and structure of the photosynthetic apparatus were not affected.

Bottom Line: Furthermore, viability of flocculated cells was determined by Evans Blue assay and few cells were found to be damaged with pH decrease.The study provided an economical, efficient and convenient method to harvest fresh microalgae.It has shown the potential to overcome the hurdle of harvesting microalgae to promote full-scale application to biofuels from microalgae.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry, Jinan University, Tianhe District, Guangzhou 510632, China. tzhangym@gmail.com.

ABSTRACT

Background: Recent studies have demonstrated that microalga has been widely regarded as one of the most promising raw materials of biofuels. However, lack of an economical, efficient and convenient method to harvest microalgae is a bottleneck to boost their full-scale application. Many methods of harvesting microalgae, including mechanical, electrical, biological and chemical based, have been studied to overcome this hurdle.

Results: A new flocculation method induced by decreasing pH value of growth medium was developed for harvesting freshwater microalgae. The flocculation efficiencies were as high as 90% for Chlorococcum nivale, Chlorococcum ellipsoideum and Scenedesmus sp. with high biomass concentrations (>1g/L). The optimum flocculation efficiency was achieved at pH 4.0. The flocculation mechanism could be that the carboxylate ions of organic matters adhering on microalgal cells accepted protons when pH decreases and the negative charges were neutralized, resulting in disruption of the dispersing stability of cells and subsequent flocculation of cells. A linear correlation between biomass concentration and acid dosage was observed. Furthermore, viability of flocculated cells was determined by Evans Blue assay and few cells were found to be damaged with pH decrease. After neutralizing pH and adding nutrients to the flocculated medium, microalgae were proved to maintain a similar growth yield in the flocculated medium comparing with that in the fresh medium. The recycling of medium could contribute to the economical production from algae to biodiesel.

Conclusions: The study provided an economical, efficient and convenient method to harvest fresh microalgae. Advantages include capability of treating high cell biomass concentrations (>1g/L), excellent flocculation efficiencies (≥ 90%), operational simplicity, low cost and recycling of medium. It has shown the potential to overcome the hurdle of harvesting microalgae to promote full-scale application to biofuels from microalgae.

No MeSH data available.