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The difference in effective light penetration may explain the superiority in photosynthetic efficiency of attached cultivation over the conventional open pond for microalgae.

Wang J, Liu J, Liu T - Biotechnol Biofuels (2015)

Bottom Line: In this research, the growth, photosynthetic oxygen evolution, and specific growth rate for microalgal cells in both open-pond and attached cultivation were studied to determine the effective light penetration at different phases of the cultivation.As the biomass concentration increased from day 4 to day 10, the light could only effectively penetrate 45.5% of the open-pond depth, and then effective light penetration gradually decreased to 31.1% at day 31, when the biomass density reached a maximum value of 0.45 g L(-1) or 90 g m(-2).Higher light penetration efficiency might be the reason why, using attached cultivation, observed values for photosynthetic efficiency were higher than those recorded in conventional open-pond suspended cultures.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong 266101 People's Republic of China.

ABSTRACT

Background: The 'attached cultivation' technique for microalgae production, combining the immobilized biofilm technology with proper light dilution strategies, has shown improved biomass production and photosynthetic efficiency over conventional open-pond suspended cultures. However, how light is transferred and distributed inside the biofilm has not been clearly defined yet.

Results: In this research, the growth, photosynthetic oxygen evolution, and specific growth rate for microalgal cells in both open-pond and attached cultivation were studied to determine the effective light penetration at different phases of the cultivation. As a result, the light conditions inside the culture broth as well as the biofilm were revealed for the first time. Results showed that outdoor, in a conventional 20-cm deep open pond, all of the algal cells were fully illuminated in the first 3 days of cultivation. As the biomass concentration increased from day 4 to day 10, the light could only effectively penetrate 45.5% of the open-pond depth, and then effective light penetration gradually decreased to 31.1% at day 31, when the biomass density reached a maximum value of 0.45 g L(-1) or 90 g m(-2). In the attached cultivation system, under nitrogen-replete condition, almost 100% of the immobilized algal cells inside the biofilm were effectively illuminated from day 0 through day 10 when the biomass density increased from 8.8 g m(-2) to 107.6 g m(-2).

Conclusion: Higher light penetration efficiency might be the reason why, using attached cultivation, observed values for photosynthetic efficiency were higher than those recorded in conventional open-pond suspended cultures.

No MeSH data available.


Related in: MedlinePlus

The schematic diagrams of the photobioreactors for attached cultivation. (A) The schematic diagram for the multiple-layer photobioreactor for attached cultivation (adapted from Liu et al. [22]). (B) The schematic diagram and the actual photograph for the single-layer photobioreactor for attached cultivation used in the research.
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Fig1: The schematic diagrams of the photobioreactors for attached cultivation. (A) The schematic diagram for the multiple-layer photobioreactor for attached cultivation (adapted from Liu et al. [22]). (B) The schematic diagram and the actual photograph for the single-layer photobioreactor for attached cultivation used in the research.

Mentions: The biofilm cultivation of microalgae, in which the algal cells are generally immobilized and fixed onto/into supporting materials in high density and fed with nutrient solutions, is a different cultivation method than conventional aqueous suspended cultures. Open ponds and PBRs have existed for a long time now; however, they often exhibited relatively low biomass productivity [14-21]. Recently, our research group proposed an improved cultivation method based on a reactor where both the immobilized biofilm technology and the light dilution theory work together in a patented design called ‘attached cultivation’ [22]. The basic principles of this ‘attached cultivation’ technique as well as the related photobioreactors include the following: (i) a highly dense wet algal paste attached onto artificial supporting materials to form a thin layer of the algal biofilm and (ii) many layers of these biofilms arranged in an array fashion to dilute the high light so that the light intensity impinging the algal biofilm is much lower than the light that reaches the photobioreactor footprint area (Figure 1A). The biomass productivity potential of this ‘attached cultivation’ method was evaluated both under indoor and outdoor conditions. Results showed that with indoor light of 700 μmol m−2 s−1 and a light dilution rate of 10, the maximum biomass productivity for Scenedesmus was close to 120 g m−2 day−1, with photosynthetic efficiency of ca. 18% (based on visible light). Under outdoor conditions, the maximum biomass productivity reached ca. 80 g m−2 day−1 corresponding to a photosynthetic efficiency of 17.3% (based on visible light) and 8.3% (based on total solar irradiation), which were both seven times higher than the data reported for a conventional open pond under the same environment conditions [22]. Similar biomass productivity and photosynthetic efficiency were also achieved with Botryococcus braunii which grows slowly with aqueous suspended cultivation but exhibits a high biomass productivity of ca. 50 g m−2 day−1 with attached cultivation, corresponding to a photosynthetic efficiency of ca. 15% (based on visible light) [23].Figure 1


The difference in effective light penetration may explain the superiority in photosynthetic efficiency of attached cultivation over the conventional open pond for microalgae.

Wang J, Liu J, Liu T - Biotechnol Biofuels (2015)

The schematic diagrams of the photobioreactors for attached cultivation. (A) The schematic diagram for the multiple-layer photobioreactor for attached cultivation (adapted from Liu et al. [22]). (B) The schematic diagram and the actual photograph for the single-layer photobioreactor for attached cultivation used in the research.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4389658&req=5

Fig1: The schematic diagrams of the photobioreactors for attached cultivation. (A) The schematic diagram for the multiple-layer photobioreactor for attached cultivation (adapted from Liu et al. [22]). (B) The schematic diagram and the actual photograph for the single-layer photobioreactor for attached cultivation used in the research.
Mentions: The biofilm cultivation of microalgae, in which the algal cells are generally immobilized and fixed onto/into supporting materials in high density and fed with nutrient solutions, is a different cultivation method than conventional aqueous suspended cultures. Open ponds and PBRs have existed for a long time now; however, they often exhibited relatively low biomass productivity [14-21]. Recently, our research group proposed an improved cultivation method based on a reactor where both the immobilized biofilm technology and the light dilution theory work together in a patented design called ‘attached cultivation’ [22]. The basic principles of this ‘attached cultivation’ technique as well as the related photobioreactors include the following: (i) a highly dense wet algal paste attached onto artificial supporting materials to form a thin layer of the algal biofilm and (ii) many layers of these biofilms arranged in an array fashion to dilute the high light so that the light intensity impinging the algal biofilm is much lower than the light that reaches the photobioreactor footprint area (Figure 1A). The biomass productivity potential of this ‘attached cultivation’ method was evaluated both under indoor and outdoor conditions. Results showed that with indoor light of 700 μmol m−2 s−1 and a light dilution rate of 10, the maximum biomass productivity for Scenedesmus was close to 120 g m−2 day−1, with photosynthetic efficiency of ca. 18% (based on visible light). Under outdoor conditions, the maximum biomass productivity reached ca. 80 g m−2 day−1 corresponding to a photosynthetic efficiency of 17.3% (based on visible light) and 8.3% (based on total solar irradiation), which were both seven times higher than the data reported for a conventional open pond under the same environment conditions [22]. Similar biomass productivity and photosynthetic efficiency were also achieved with Botryococcus braunii which grows slowly with aqueous suspended cultivation but exhibits a high biomass productivity of ca. 50 g m−2 day−1 with attached cultivation, corresponding to a photosynthetic efficiency of ca. 15% (based on visible light) [23].Figure 1

Bottom Line: In this research, the growth, photosynthetic oxygen evolution, and specific growth rate for microalgal cells in both open-pond and attached cultivation were studied to determine the effective light penetration at different phases of the cultivation.As the biomass concentration increased from day 4 to day 10, the light could only effectively penetrate 45.5% of the open-pond depth, and then effective light penetration gradually decreased to 31.1% at day 31, when the biomass density reached a maximum value of 0.45 g L(-1) or 90 g m(-2).Higher light penetration efficiency might be the reason why, using attached cultivation, observed values for photosynthetic efficiency were higher than those recorded in conventional open-pond suspended cultures.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, Shandong 266101 People's Republic of China.

ABSTRACT

Background: The 'attached cultivation' technique for microalgae production, combining the immobilized biofilm technology with proper light dilution strategies, has shown improved biomass production and photosynthetic efficiency over conventional open-pond suspended cultures. However, how light is transferred and distributed inside the biofilm has not been clearly defined yet.

Results: In this research, the growth, photosynthetic oxygen evolution, and specific growth rate for microalgal cells in both open-pond and attached cultivation were studied to determine the effective light penetration at different phases of the cultivation. As a result, the light conditions inside the culture broth as well as the biofilm were revealed for the first time. Results showed that outdoor, in a conventional 20-cm deep open pond, all of the algal cells were fully illuminated in the first 3 days of cultivation. As the biomass concentration increased from day 4 to day 10, the light could only effectively penetrate 45.5% of the open-pond depth, and then effective light penetration gradually decreased to 31.1% at day 31, when the biomass density reached a maximum value of 0.45 g L(-1) or 90 g m(-2). In the attached cultivation system, under nitrogen-replete condition, almost 100% of the immobilized algal cells inside the biofilm were effectively illuminated from day 0 through day 10 when the biomass density increased from 8.8 g m(-2) to 107.6 g m(-2).

Conclusion: Higher light penetration efficiency might be the reason why, using attached cultivation, observed values for photosynthetic efficiency were higher than those recorded in conventional open-pond suspended cultures.

No MeSH data available.


Related in: MedlinePlus