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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.


Microscopic pictures of microalgal cells: controlled cells: a) Chlorococcum nivale; b) Chlorococcum ellipsoideum; c) Scenedesmus sp.; cells heated at 121 and incubated in 1% Evans’ blue solution for 3 h: d) Chlorococcum nivale; e) Chlorococcum ellipsoideum; f) Scenedesmus sp.; cells flocculated by adjusting pH value of growth medium to 0.5 with nitric acid and incubated in 1% Evans’ blue solution for 3 h: g) Chlorococcum nivale; h) Chlorococcum ellipsoideum; i) Scenedesmus sp.; cells flocculated by adjusting pH value of growth medium to 3.5 with nitric acid and incubated in 1% Evans’ blue solution for 3 h: j) Chlorococcum nivale; k) Chlorococcum ellipsoideum; l) Scenedesmus sp.
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Figure 7: Microscopic pictures of microalgal cells: controlled cells: a) Chlorococcum nivale; b) Chlorococcum ellipsoideum; c) Scenedesmus sp.; cells heated at 121 and incubated in 1% Evans’ blue solution for 3 h: d) Chlorococcum nivale; e) Chlorococcum ellipsoideum; f) Scenedesmus sp.; cells flocculated by adjusting pH value of growth medium to 0.5 with nitric acid and incubated in 1% Evans’ blue solution for 3 h: g) Chlorococcum nivale; h) Chlorococcum ellipsoideum; i) Scenedesmus sp.; cells flocculated by adjusting pH value of growth medium to 3.5 with nitric acid and incubated in 1% Evans’ blue solution for 3 h: j) Chlorococcum nivale; k) Chlorococcum ellipsoideum; l) Scenedesmus sp.

Mentions: Viability of microalgal cells was determined by the Evans blue assay and the cells seemed to be very resistant to relatively low pH values (6.0-3.0). A positive control is also provided. As shown in Figures 7a, 7b and 7c, the controlled cells are light green and the yellow liquid in the cells can be seen clearly. However, for the cells heated at 121 in Figures 7d, 7e and 7f, the dead cells (solid arrows) are dark green which were dyed by Evans blue and the yellow liquid in the cells are not visible. While the alive cells (dash arrows) are light green and similar to the cells shown in Figures 7a, 7b and 7c. As for the cells flocculated by adjusting pH value of growth medium to 0.5 with nitric acid (Figure 7g, 7h and 7i), the dead cell nuclei turned black, the cytoplasm turned green-yellow and the materials surrounding the cells were dyed blue . The cells flocculated by adjusting pH value of growth medium to 3.5 in Figures 7j, 7k and 7l, are similar to the controlled cells in Figure 7a, 7b and 7c, except that few cells were dyed blue. The above results indicated there were no cell lysis and the cell walls were intact. Thus, the cells were not damaged during the process of pH decreasing to 3.5.


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)

Microscopic pictures of microalgal cells: controlled cells: a) Chlorococcum nivale; b) Chlorococcum ellipsoideum; c) Scenedesmus sp.; cells heated at 121 and incubated in 1% Evans’ blue solution for 3 h: d) Chlorococcum nivale; e) Chlorococcum ellipsoideum; f) Scenedesmus sp.; cells flocculated by adjusting pH value of growth medium to 0.5 with nitric acid and incubated in 1% Evans’ blue solution for 3 h: g) Chlorococcum nivale; h) Chlorococcum ellipsoideum; i) Scenedesmus sp.; cells flocculated by adjusting pH value of growth medium to 3.5 with nitric acid and incubated in 1% Evans’ blue solution for 3 h: j) Chlorococcum nivale; k) Chlorococcum ellipsoideum; l) Scenedesmus sp.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Microscopic pictures of microalgal cells: controlled cells: a) Chlorococcum nivale; b) Chlorococcum ellipsoideum; c) Scenedesmus sp.; cells heated at 121 and incubated in 1% Evans’ blue solution for 3 h: d) Chlorococcum nivale; e) Chlorococcum ellipsoideum; f) Scenedesmus sp.; cells flocculated by adjusting pH value of growth medium to 0.5 with nitric acid and incubated in 1% Evans’ blue solution for 3 h: g) Chlorococcum nivale; h) Chlorococcum ellipsoideum; i) Scenedesmus sp.; cells flocculated by adjusting pH value of growth medium to 3.5 with nitric acid and incubated in 1% Evans’ blue solution for 3 h: j) Chlorococcum nivale; k) Chlorococcum ellipsoideum; l) Scenedesmus sp.
Mentions: Viability of microalgal cells was determined by the Evans blue assay and the cells seemed to be very resistant to relatively low pH values (6.0-3.0). A positive control is also provided. As shown in Figures 7a, 7b and 7c, the controlled cells are light green and the yellow liquid in the cells can be seen clearly. However, for the cells heated at 121 in Figures 7d, 7e and 7f, the dead cells (solid arrows) are dark green which were dyed by Evans blue and the yellow liquid in the cells are not visible. While the alive cells (dash arrows) are light green and similar to the cells shown in Figures 7a, 7b and 7c. As for the cells flocculated by adjusting pH value of growth medium to 0.5 with nitric acid (Figure 7g, 7h and 7i), the dead cell nuclei turned black, the cytoplasm turned green-yellow and the materials surrounding the cells were dyed blue . The cells flocculated by adjusting pH value of growth medium to 3.5 in Figures 7j, 7k and 7l, are similar to the controlled cells in Figure 7a, 7b and 7c, except that few cells were dyed blue. The above results indicated there were no cell lysis and the cell walls were intact. Thus, the cells were not damaged during the process of pH decreasing to 3.5.

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.