• International Journal of Technology (IJTech)
  • Vol 11, No 7 (2020)

Sound Wave Exposure as a Strategy for Improving the Tubular Photobioreactor for Cultivating Synechococcus HS-9 as Biofuel Feedstock under Different Photoperiods

Sound Wave Exposure as a Strategy for Improving the Tubular Photobioreactor for Cultivating Synechococcus HS-9 as Biofuel Feedstock under Different Photoperiods

Title: Sound Wave Exposure as a Strategy for Improving the Tubular Photobioreactor for Cultivating Synechococcus HS-9 as Biofuel Feedstock under Different Photoperiods
Yosua Adi Santoso, Rubiantin Mesha Nauli Tambunan, Santoso Soekirno, Nasruddin, Nining Betawati Prihantini

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Cite this article as:
Santoso, Y.A., Tambunan, R.M.N., Soekirno, S., Nasruddin, ., Prihantini, N.B., 2020. Sound Wave Exposure as a Strategy for Improving the Tubular Photobioreactor for Cultivating Synechococcus HS-9 as Biofuel Feedstock under Different Photoperiods. International Journal of Technology. Volume 11(7), pp. 1406-1413

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Yosua Adi Santoso Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia
Rubiantin Mesha Nauli Tambunan Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia
Santoso Soekirno Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia
Nasruddin Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia
Nining Betawati Prihantini Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia
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Abstract
Sound Wave Exposure as a Strategy for Improving the Tubular Photobioreactor for Cultivating Synechococcus HS-9 as Biofuel Feedstock under Different Photoperiods

This study aimed to evaluate the effect of sound wave exposure in different photoperiods on Synechococcus HS-9 cell density and lipid content using tubular photobioreactors (PBRs). In this study, nine PBRs were used: three PBRs were exposed to a sine wave of 279.9 Hz for three hours during the day (A), three PBRs were exposed to a sine wave of 279.9 Hz for three hours during the night (B), and three PBRs remained unexposed to any sound wave to serve as a control (K). All PBRs were studied for 18 days. The results showed that the highest average cell densities of Synechococcus HS-9 in PBR A, B, and K respectively were 8.883×105 cells/mL, 7.242×105 cells/mL, and 6.175×105 cells/mL. The highest lipid percentage, which was 17%, was observed in PBR A; the percentage in PBR B was 16%, and in PBR K, 7%. However, Synechococcus HS-9 in PBR B showed a higher growth rate compared to PBR A and PBR K. Sound waves could have increased cell activity and metabolism which led to the increase in cell densities and lipid percentages in Synechococcus HS-9. The photoperiodic differences might have resulted in a lower photosynthetic rate and cell metabolism, but the sound wave could have helped promote the growth of Synechococcus HS-9 despite the lower photosynthetic rate.

Audible sound; Biomass; Photobioreactor; Photoperiodism; Synechococcus

Introduction

    The dependency on fossil fuels as the main energy source has caused a depletion of fossil fuel reserves (Sukarni et al., 2019) and severe environmental pollution that affects many ecosystems. The development of sustainable and environmentally friendly fuels is needed in order to maintain the balance of the ecosystem and preserve fossil fuels (Machado and Atsumi, 2012). There are some sources of biofuel feedstock, such as food crops (e.g., corn, jatropha, and coconut) and microalgae (Chisti, 2007). Microalgae fixate CO2 from the environment directly through photosynthesis, during which the CO2 is converted to several biomolecules such as lipids. The aforementioned features of microalgae  show  that  microalgae  have  the  potential  to  serve  as biofuel feedstocks and bioremediation agents.        

Cyanobacteria are one group of microalgae that have been considered to be biofuel feedstocks. Cyanobacteria have high growth rates, can easily be genetically manipulated, and do not need to be grown on large and arable plots of land, thus reducing the competition with food crops for growth area (Nozzi et al., 2013; Sarsekeyeva et al., 2015; Farrokh et al., 2019). Synechococcus is one genus of cyanobacteria that has been researched for its capability to produce several bioethanol and lipid products that could be synthesized as biofuel (Mashayekhi et al., 2017). Synechococcus could be found in various habitats including hot springs. In this study, we use Synechococcus (labeled as Synechococcus HS-9) that was isolated from the Rawa Danau hot spring in Banten, Indonesia (Prihantini, 2015). Synechococcus HS-9 has been studied for its biofuel compounds, such as fatty acids (Prihantini et al., 2018).

    PBRs are systems that could be used to increase the biomass of microalgae, including cyanobacteria. PBRs combine several abiotic factors such as growth media, light, photoperiods, and temperature in order to maximize the growth of cyanobacteria (Johnson et al., 2018). Previous research has shown that varying photoperiods could affect the growth of Synechococcus PCC 6715 (Klepacz-Smólka et al., 2020). Besides the aforementioned factors, there are also physico-stimulants that could affect the growth of cyanobacteria, such as sound waves.  A sound wave is a mechanical wave caused by the movement of energy in a medium (Serway and Jewett, 2014). There are several studies which show that sound waves could promote microalgae growth (Jiang et al., 2012; Christwardana and Hadiyanto, 2017). Furthermore, there is an indication that sound waves could enhance the aeration in PBRs (Rizaldi et al., 2019) and the transesterification process of microalgae lipids (Cercado et al., 2018). Audible sound in the form of music can increase the cell density of Synechococcus HS-9 (Santoso et al., 2020).  Nevertheless, to the best of our knowledge, there is no study about the effect of sound wave exposure under different photoperiods (light and dark times) on Synechococcus HS-9. Therefore, this study was conducted in order to measure and compare the growth and lipid production of Synechococcus HS-9 when exposed to sound waves during periods of daylight and night.

Conclusion

    Sound wave exposure could increase the cell density and lipid production of Synechococcus HS-9 in a tubular PBR. The results of this study demonstrated that the average cell densities of Synechococcus HS-9 in PBR A (8.883×105 cells/mL) and PBR B (7.242×105 cells/mL) were higher compared to that in PBR K (6.175×105 cells/mL). The different photoperiods had different effects on Synechococcus HS-9 that were exposed to the sound wave. Synechococcus HS-9 that were exposed to sound waves in the night (dark period) had lower cell densities and lipid yields (16%) compared to 
Synechococcus HS-9 that were exposed to sound waves during the day; however, Synechococcus HS-9 that were exposed to sound waves during the day had higher growth rates (0.244/day). Further studies could be done to examine the economic viability of this system for mass production. These results indicate that sound wave exposure could be used as a strategy for improving the PBR system in conditions of low light.

Acknowledgement

    This study was funded by the Hibah Penelitian Dasar Unggulan Perguruan Tinggi (PDUPT) 2020 grant from the Ministry of Research and Technology/National Research and Innovation Agency (Kementerian Riset dan Teknologi/Badan Riset dan Inovasi Nasional) Indonesia to Dr. Nining Betawati Prihantini, M.Sc. grant no. NKB-2819/UN2.RST/HKP.05.00/2020.

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