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Enhanced carbon dioxide fixation of Haematococcus pluvialis using sequential operating system in tubular photobioreactors
Accepted Manuscript Title: Enhanced carbon dioxide fixation of Haematococcus pluvialis using sequential operating system in tubular photobioreactors Author: Joo Yeong Lee Min-Eui Hong Won Seok Chang Sang Jun Sim PII: DOI: Reference:
S1359-5113(15)00162-2 http://dx.doi.org/doi:10.1016/j.procbio.2015.03.021 PRBI 10389
To appear in:
Process Biochemistry
Received date: Accepted date:
20-1-2015 30-3-2015
Please cite this article as: Lee JY, Hong M-E, Chang WS, Sim SJ, Enhanced carbon dioxide fixation of Haematococcus pluvialis using sequential operating system in tubular photobioreactors, Process Biochemistry (2015), http://dx.doi.org/10.1016/j.procbio.2015.03.021 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Enhanced carbon dioxide fixation of Haematococcus pluvialis using sequential operating system in tubular photobioreactors
Department of Chemical and Biological Engineering, Korea University, Seoul 136-713,
South Korea
Department of Chemical Engineering, Sungkyunkwan University, Suwon 440-746, South
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Green School, Korea University, Seoul 136-713, South Korea
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Joo Yeong Leea, Min-Eui Hongc, Won Seok Changd, and Sang Jun Sima,b,*
Korea
Research Institute, Korea District Heating Corp., 186 Bundang-dong, Bundang-gu,
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Seongnam-si, Gyeonggi-do, South Korea
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Tel: +82-2-3290-4853
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Fax: +82-2-926-6102
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*Corresponding author: Professor Sang Jun Sim
e-mail: [email protected]
Running title: Effect of sequential PBRs on the CO2 fixation efficiency of microalgae
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Abstract
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Carbon dioxide sequestration by microalgae photosynthesis is an attractive alternative to
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mitigate climate change due to greenhouse gas emission. In our study, Haematococcus
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pluvialis and a sequential operating system were exploited to examine the carbon dioxide
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fixation efficiency in a tubular photobioreactor. We investigated the carbon balance over the
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photobioreactor, including the carbon bound in the biomass, dissolved inorganic carbon in the
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liquid media, and gaseous carbon remained in the headspace and vented out from the
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photobioreactor. The experiments were performed both indoors and outdoors, using air-mixed
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3% CO2 gas and the flue gas from power plant. As a result, the sequential operation system
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using H. pluvialis cultivation improved the carbon dioxide fixation efficiencies from 12.34%
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to 49.37% (indoor), and from 13.55% to 49.15% (outdoor), respectively, compared to single
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bioreactor operation mode. This sequential operating system would be useful for enhanced
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conversion of carbon dioxide from flue gas by microalgae photosynthesis.
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Keywords: Haematococcus pluvialis, flue gas, carbon fixation efficiency, tubular
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photobioreactor
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1. Introduction As consumption of fossil fuels has been increased for centuries due to industrial
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development around the world, greenhouse gas emissions into the atmosphere have
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continuously increased. Since greenhouse gas causes many environmental issues, various
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carbon sequestration technologies have been introduced to reduce greenhouse gas emissions
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[1]. As carbon dioxide is a great part of the greenhouse gases, reduction of carbon dioxide
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plays a substantial role for greenhouse gas sequestration [2].
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Biological fixation of carbon dioxide using microalgae is an attractive option because
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microalgae are not only able to sequester carbon dioxide, but also to produce high-value
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products such as biofuels, pigments and nutrients [3]. Astaxanthin (3,3′-dihydroxy-β-
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carotene-4,4′-dione) is recognized as a high-value keto-carotenoid pigment ($2,500/kg USD)
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and one of the most powerful antioxidants among carotenoids with many applications in
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nutraceuticals, cosmetics, and the food and feed industries [4, 5]. The green microalga
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Haematococcus pluvialis is the richest source of natural astaxanthin (up to 4% of its dry
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mass) [6] and is cultivated on an industrial scale [7, 8].
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Photosynthetic cultivation could be performed in both open pond system and closed
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photobioreactor. Open culture systems have been extensively studied; however, these
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cultivation processes suffer multiple disadvantages including loss of media by evaporation,
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the possibility of contamination by unwanted species and requirement of an area of enormous
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size [9]. Closed systems which utilize photobioreactors for culturing microalgae, on the other
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hand, are much easier to control contamination from heterotrophs and culture parameters
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such as nutrient levels, temperature, amount of inlet carbon dioxide, etc. [10]. Moreover,
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closed systems are able to achieve highly efficient biomass production for enhancement of
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the carbon dioxide fixation rate compared to open pond systems.
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The tubular photobioreactor is one of the most typical cultivation apparatus used in the
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carbon sequestration process by algal culture [11]. A vertical tubular photobioreactor can
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increase the residence time of sparged gas, which could enhance the carbon dioxide
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utilization efficiency [12]. Accordingly, it seems that consideration of the configuration and
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operational mode of photobioreactors is crucial to elevate their performance.
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In the present study, the carbon fixation efficiency in H. pluvialis was improved by
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developing an operational system using serial tubular photobioreactors. In this system, four
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photobioreactors were placed in series and connected to reuse the gas vented out from the
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preceding photobioreactor as injection gas for the next photobioreactor. The experiments
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were performed in indoor and also outdoor system using the unicellular green algae H.
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pluvialis. An indoor PBR system was operated in a 5L photobioreactor (1 column) aerated
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with 3% CO2 mixed gas and illuminated with cool white fluorescent light at 30-60 μmol
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photon/m2/s to clearly demonstrate the effect of a sequential PBR system on the carbon
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dioxide fixation and utilization efficiency. After that, an outdoor PBR system was operated in
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a 20L photobioreactor (4 columns) exposed to flue gas consisted of 2~4% of CO2 and
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illuminated with natural solar radiation at 50~80 μmol photon/m2/s to define benefits of this
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strategy in pilot scale. Consequently, this system extended the retention time and achieved
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lower carbon dioxide levels in the effluent gas vented from the photobioreactors. The serial
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photobioreactors process is a promising strategy for improving carbon dioxide fixation and
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utilization efficiency in microalgae culture systems.
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2. Materials and Methods
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2.1 Algal strain and medium composition Haematococcus pluvialis NIES-144 was obtained from the National Institute for
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Environmental Studies, Tsukuba, Japan. H. pluvialis was grown photoautotrophically in
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NIES-C medium (pH 7.5), which consists of 0.15 g/L Ca(NO3)2, 0.10 g/L KNO3, 0.05 g/L β-
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glycerophosphoric acid disodium salt pentahydrate, 0.04 g/L MgSO4∙7H2O, 0.50 g/L Tris-
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aminomethane, 0.01 mg/L thiamine, 0.10 μg/L biotin, 0.10 μg/L vitamin B12, and 3.00 mL/L
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PIV metal solution [1.0 g/L Na2EDTA, 0.196 g/L FeCl3∙6H2O and (in mg/L) 36.0
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MnCl2∙4H2O, 22.0 ZnSO4∙7H2O, 4.0 CoCl2∙6H2O, and 2.5 Na2MoO4∙2H2O] [13].
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2.2 Photobioreactors and cultivation conditions
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Cells were grown in transparent film photobioreactors. Agitation and aeration were
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accomplished by use of air-mixed CO2 gas (Indoor system) or flue gas (Outdoor system) with
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a compressor and sparger. [14]. A schematic diagram of the experimental apparatus is shown
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in Fig. 1. In a simple operation, a single PBR with a working volume of 5L (1 column) and
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20L (4 columns) was used for an indoor and outdoor culture system, respectively. In a
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sequential operation, four PBRs with a working volume of 5L and 20L were connected in
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series for an indoor and outdoor culture system, respectively, to utilize the vented gas of the
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front reactor as inlet gas of the rearward reactors, labeled consecutively as PBR1, PBR2,
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PBR3 and PBR4.
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2.2.1 Lab-scale experiments
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The indoor experiments were conducted using single-column type PBRs (1 column) with
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maintenance of the temperature at 23℃. The indoor PBR is consisted of a single bubble
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column which is120cm in height and 10cm in diameter, with 5L for liquid volume and 1L for
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headspace volume. Cells were illuminated with 30-60 μmol photon/m2/s by cool white
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fluorescent lamps. The dark and light cycle was 8:16, and light intensities were measured at
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the surface of the bioreactor using an LI-250 quantum photometer (Lambda Instrument Corp.,
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USA) [15]. The air-mixed 3% CO2 gas was supplied to the PBR through a sparger with 10μm
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pores at the bottom of the PBR at the rate of 0.01~0.02 vessel volume per min (vvm).
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2.2.2 Outdoor system using flue gas The outdoor culture system was demonstrated in a greenhouse using multiple-column
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type PBRs (4 columns) to verify possibilities of scale-up using flue gas. The outdoor PBR
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(multiple-column type), which is consisted of four bubble columns (each column was 120cm
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in height and 10cm in diameter) connected with each other, were prepared (total volume of
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media was 20L, while 5L served as the gas space). The natural sunlight was used as the
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source of light for the outdoor PBRs with a dark/light cycle of about 12:12 h. Cells were
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cultured in outdoors with exposure to the light intensities of 50~80 μmol photon/m2/s, and
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temperature of 26±3℃. The flue gas was also supplied to the PBR through a sparger with
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10μm pores at the bottom of the PBR and the rate of gas flow was increased from 0.01 to
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0.02 vessel volume per min (vvm). The flue gas, composed of N2, CO2, O2, NOx and CO,
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was provided from power plant located nearby Seoul, South Korea. The flue gas consisted of
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2~4% of CO2, which is sufficient for algal cultivation, 11.99±0.73% O2, 21.72±3.72ppm
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NOx, 1.43±4.03ppm CO, water vapor and dust.
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2.3 Carbon mass balance
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Since no carbon source was supplied in the media, the CO2 in the gas was the primary
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source of carbon for biomass production. CO2 injected into the PBR was dispersed into the
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media, cell and headspace of the PBR. The carbon mass balance equation is as follows [16]: (1)
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Cin (g·d-1): mass flow rate of carbon
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Cout (g·d-1): mass flow rate of carbon out of the PBR via venting
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Vl (L): volume of the media
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Vg (L): volume of the headspace
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Mc (g·mol-1): atomic weight of carbon
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(mol·L-1·d-1): rate of change in dissolved inorganic carbon concentration
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(mol·L-1·d-1): rate of change in concentration of carbon bound in the biomass
(mol·L-1·d-1): rate of change in carbon concentration in headspace
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2.4 Analytical methods
Cell growth was determined by measuring the dry weight of the biomass. The dry cell
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weight was measured by filtration of aliquots using filter paper. First, the harvested cells were
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filtered onto pre-weigh glass-fiber filters (Whatman GF/C, 47 mm diameter), rinsed twice
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with 10 mL distilled water, and then dried at 80℃ for 24 h for comparison of the weight
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before and after filtration. Total organic carbon (TOC) was measured by a TOC analyzer
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(TOC 5000, Shimadzu, Kyoto, Japan) with analysis of the samples combusted to CO2 and
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H2O, and the TOC value was calculated as the difference between total carbon and inorganic
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carbon concentration. Dissolved inorganic carbon (DIC) was the sum of carbonic acid,
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bicarbonate and carbonate in the aqueous solution, which can be calculated by the following
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equations [17]:
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(2)
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TA: Total alkalinity in meq/L (measured by titration)
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[H+]: the hydrogen ion activity (i.e.,10-pH) and pH of the culture broth as measured by a
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digital pH meter (Hanna, Rep. of Korea)
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Kw (T), K1 (T), K2 (T): dissociation constants (3)
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(4)
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(5)
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The concentration of CO2 in the gaseous state was measured by a CO2 analyzer (maMoSⅡ
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100, madur, Poland).
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Specific growth rate (d-1) and volumetric biomass productivity (g·L-1·d-1) were calculated
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using the following equations:
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(6)
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(7)
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where X1 and X2 were mass concentrations of the cells (g·L-1) at t1 and t2.
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3. Results and Discussion
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3.1 Carbon supplied into photobioreactor
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Air-mixed 3% CO2 gas and flue gas from power plant were supplied via the sparger in the
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indoor and outdoor systems, respectively. The CO2 concentration of the flue gas varied
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between 2.66% ~ 2.77% and the mean value was 2.7%. Gas including CO2 was employed
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into the PBR to supply the cells with a carbon source, prevent biomass settling, and
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encourage desorption of oxygen [16]. Therefore, the amount of carbon supplied would be
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determined by the CO2 concentration and the flow rate of the injected gas. The total amounts
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of CO2 injected to each PBR (working volume 5L) were 13.24±0.73g·L-1(PBR1),
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11.42±0.09g·L-1(PBR2), 9.42±0.12g·L-1(PBR3) and 7.72±0.71g·L-1(PBR4) for indoor system,
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respectively.
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11.26±1.21g·L-1(PBR2), 9.35±0.62g·L-1(PBR3) and 7.89±1.03g·L-1(PBR4) (working volume
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20L), respectively.
In
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3.2 Carbon assimilated by biomass
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3.2.1 Production of cell biomass
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13.36±0.18g·L-1(PBR1),
H. pluvialis cells can grow photoautotrophically using CO2 as the sole inorganic carbon
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source [18]. The maximum biomass concentration, specific growth rate, biomass productivity
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values are shown in Table 1 and the growth curves of biomass versus time are shown in Fig. 2.
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Biomass densities did not show much differences at first time, however, the differences
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gradually got larger as increasing biomass with demands for CO2. In lab-scale experiments,
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maximum cell densities and specific growth rates for each PBR were 0.68g·L-1 and 0.11d-1
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(PBR1), 0.74g·L-1 and 0.12d-1 (PBR2), 0.55g·L-1 and 0.09d-1 (PBR3), and 0.45g·L-1 and
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0.07d-1 (PBR4), respectively. Meanwhile, the maximum cell densities and specific growth
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rates observed in the outdoor experiments were 0.82g·L-1 and 0.08d-1 (PBR1), 0.81g·L-1 and
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0.07d-1 (PBR2), 0.66g·L-1 and 0.06d-1 (PBR3), and 0.56g·L-1 and 0.04d-1 (PBR4).
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Both indoor and outdoor experiments showed similar cell density and specific growth rate
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for PBR1 and PBR2, while the biomass production was noticeably decreased after PBR2. It
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was presumed that the reduction in biomass production was mainly attributable to the CO2
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concentration. Previous study has also shown the CO2 concentration, photobioreactor
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configuration and light intensity to be crucial factors affecting biomass productivity [19]. In
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the experiments herein, CO2 concentration was the major factor affecting biomass production.
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Microalgal cells have optimal CO2 concentrations for growth; therefore, the CO2
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concentration of the injected gas should be carefully controlled to avoid inefficient growth of
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the cells due to insufficient or excessive CO2 supply [20]. Biomass productivity also showed
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a similar tendency, with maximum cell density and specific growth rates of 0.039g·L-1·d-1
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(PBR1), 0.42g·L-1·d-1 (PBR2), 0.031g·L-1·d-1 (PBR3), and 0.020g·L-1·d-1 (PBR4) in the indoor
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experiments, and 0.034g·L-1·d-1 (PBR1), 0.32g·L-1·d-1 (PBR2), 0.023g·L-1·d-1 (PBR3), and
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0.016g·L-1·d-1 (PBR4) in the outdoor system, respectively.
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3.2.2 Total organic carbon in cell
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The total organic carbon percentage (%TOC) in the biomass samples from indoor and
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outdoor experiments was measured. The average %TOC values from the two were 46.82%
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and 44.33%, respectively, with the standard deviations of 1.89% and 0.66%. These values
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were reasonable compared to the reference that stated the typical dry mass %TOC of
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microalgae to be approximately 50% [21]. The dry cell weight and %TOC on a dry mass
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basis were employed to estimate the amount of carbon assimilated into the biomass. We
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calculated the amount of carbon bound in biomass (Cbiomass) with %TOC and dry cell weight,
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0.237 g·L-1(PBR1), 0.25 g·L-1(PBR2), 0.19 g·L-1(PBR3) and 0.12 g·L-1(PBR4) for indoor
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system and 0.24 g·L-1(PBR1), 0.22 g·L-1(PBR2), 0.16 g·L-1(PBR3) and 0.12 g·L-1(PBR4) for
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outdoor experiments.
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3.3 Carbon in liquid media
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Dissolved carbon dioxide in the media of the photobioreactor was available as a carbon
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source for consumption by the cells or was degassed out from the liquid phase into the
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gaseous phase in the headspace, where it could be emitted via the venting system. The
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transfer of CO2 gas to liquid media depends on the inlet gas composition, medium pH and
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alkalinity [22]. Since the dissolution of CO2 acidifies water, the medium pH would be lower
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after the injection of CO2 gas [23]. Nevertheless, the consumption of CO2 dissolved in the
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liquid media through photosynthesis by the biomass would increase the pH of the media,
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which means that increase in the pH, associated with the biomass, is a characteristic of
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photosynthetic cell cultivation [24]. Uptake of the CO2 from the media elevated the pH, not the alkalinity of the liquid;
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however, other cell growth processes, for instance, the uptake of NO3- or H2PO4- during
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photosynthesis, elevated the alkalinity based on the equation below [25].
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(8)
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This explains that more CO2 might be induced to be dissolved in the media, and that not only
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inlet gas but also cell growth is an important factor for CO2 dissolution. As cell growth also
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depends on supplied CO2 using primary carbon source, three factors; biomass production,
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injected carbon amount and dissolved inorganic carbon are all associated with each other.
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In lab-scale experiments, DIC for PBR 1 was 0.34 g·L-1 with 0.50 g·L-1 increased
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biomass and 3.61 g·L-1 injected carbon; 0.32 g·L-1 with 0.54 g·L-1 and 3.11 g·L-1(PBR 2);
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0.30 g·L-1 with 0.40 g·L-1 and 2.57 g·L-1(PBR 3); 0.23 g·L-1 with 0.26 g·L-1 and 2.11 g·L-
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1
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and 3.08 g·L-1(PBR 2); 0.27 g·L-1 with 0.36 g·L-1 and 2.55 g·L-1(PBR 3); 0.22 g·L-1 with 0.26
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g·L-1 and 2.15 g·L-1(PBR 2) for outdoor experiments. Accordingly, amount of dissolved
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carbon in liquid medium would be increased by amount of injected carbon and production of
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biomass (Fig. 3).
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(PBR 4). And 0.36 g·L-1 with 0.54 g·L-1 and 3.64 g·L-1(PBR 1); 0.33 g·L-1 with 0.50 g·L-1
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3.4 Carbon vented out from photobioreactors
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3.4.1 Carbon in headspace of photobioreactor
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The carbon in the headspace increased proportionally to the concentration of carbon in
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the supplied gas. The final carbon concentrations of the headspace for each PBR were
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0.31g·L-1, 0.25g·L-1, 0.12g·L-1 and 0.07g·L-1 in lab-scale experiments, and 0.24g·L-1,
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0.15g·L-1, 0.07g·L-1 and 0.03g·L-1 in the outdoor experiments, respectively. Accumulation of
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carbon dioxide in the headspace could be inferred from supplied gas and respiration of the
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biomass during the dark or night time [16].
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3.4.2 Vented out carbon
The amount of carbon vented out could be calculated using Eq.1. The overall amount of
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carbon vented out was 15.49g, 12.72g, 10.38g and 8.6g for respective PBR in the indoor
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system, and 61.17g, 50.61g, 42.59g, and 35.94g for those in the outdoor system. It was
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assumed that all the carbon in the injected gas was vented out during dark time or night, when
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photosynthesis ceased. Furthermore, additional loss of carbon, which was not currently
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accounted for, may have occurred because of carbon dioxide outgassing from the media
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during the dark time or at night. This outgassed carbon would be vented out with the carbon
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in the supplied gas. Additional investigations are needed to accurately determine the carbon
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distribution in the photobioreactor [16].
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3.5 Overall analysis of carbon distribution in photobioreactor
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The total carbon fixation efficiency was determined by integrating the respective amount
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of carbon removed in each sequential PBR with working volumes of 5L (indoor experiments)
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and 20L (outdoor experiments).
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Fig. 4 shows the ratio of distributed carbon in PBR to injected carbon. As additional
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PBRs were connected, the percentage of carbon bound in biomass increased from 6.54% to
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13.46%, 18.56% and 21.88%; dissolved carbon in liquid media was 5.93% to 12.97%,
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20.12% and 26.26%; carbon in headspace was 1.71% to 3.10%, 3.82% and 4.21%, while
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carbon vented out from PBRs decreased from 85.82% to 70.47%, 57.51% and 47.65% for
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indoor experiments. In outdoor system, carbon bound in biomass extended from 6.59% to
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12.72%, 17.11% and 20.26%; dissolved carbon in liquid media was 7.83% to 15.16%,
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21.30% and 27.05%; carbon in headspace was 1.65% to 2.68%, 3.16% and 3.36%, carbon
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vented out from PBRs, whereas, reduced from 83.93% to 69.44%, 58.44% and 49.31%. When the 4 PBRs were used in a sequential operation, the total carbon fixation efficiency
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(Cbiomass + DIC) was elevated from 12.34% to 49.37% and from 13.55% to 49.15% for the
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indoor and outdoor experiments, respectively, compared to that in a simple operation (Fig. 4).
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Consequently, in the sequential operation system (4 PBRs), the total carbon fixation
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efficiency was improved by 300% (indoor) and 263% (outdoor) as compared to that in the
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simple operation system (1 PBR).
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Photobioreactors are multi-phase (gas-liquid-solid) with a number of interactions, and the
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performance of the PBR in carbon dioxide sequestration depends on the microalgal species,
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PBR configuration, flow rate of the inlet gas, CO2 concentration in the supplied gas and
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operation system [26-28]. The use of this tubular type of reactor and sequential operation
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mode could be regarded as a promising option for the elimination of CO2 by photosynthetic
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microalgal culture [29].
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4. Conclusions
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In this study, carbon balance over the photobioreactor was investigated to analyze carbon
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distribution in the photobioreactor, and to enhance the carbon fixation efficiency through use
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of a sequential operation system. In Haematococcus pluvialis culture, the sequential
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operation system using 4 serial photobioreactors demonstrated improved carbon dioxide
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fixation efficiencies of up to 49.37% (indoor) and 49.15% (outdoor), which are 4 fold and
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3.63 fold higher than that of single bioreactor operation mode, respectively. This
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improvement could be applied to maximize carbon capture efficiency by cultivation of
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microalgae in a photobioreactor.
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Acknowledgements
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This study was supported by the Korea Institute of Energy Technology Evaluation and
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Planning and Ministry of Trade, Industry & Energy of Korea as a part of the Project of
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“Process demonstration for bioconversion of CO2 to high-valued biomaterials using
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microalgae” (20122010200010-11-2-100) in “Energy Efficiency & Resources Technology
293
R&D” project, the National Research Foundation of Korea (NRF) grants (grant No. NRF-
294
2013R1A2A1A01015644/2010-0027955), University-Institute Cooperation Program (2013),
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and grants (2014M1A8A1049278) from Korea CCS R&D Center of the NRF funded by the
296
Ministry of Science, ICT, & Future Planning of Korea.
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[5] Guerin M, Huntley ME, Olaizola M. Haematococcus astaxanthin: Applications for human health and nutrition. Trends Biotechnol 2003;21:210-216. [6] Boussiba S. Carotenogenesis in the green alga Haematococcus pluvialis: Cellular physiology and stress response. Physiol Plantarum 2000;108:111-117.
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[7] Bubrick P. Production of astaxanthin from Haematococcus. Bioresource Technol 1991;38:237-239. [8] Li J, Zhu D, Niu J, Shen S, Wang G. An economic assessment of astaxanthin production by large scale cultivation of Haematococcus pluvialis. Biotechnol Adv 2011;29:568-574. [9] Schenk P, Thomas-Hall S, Stephens E, Marx U, Mussgnug J, Posten C, Kruse O,
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[10] Rosenberg J, Oyler G, Wilkinson L, Betenbaugh M. A green light for engineered algae:
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Biodegrad 2001;47:151-155.
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[12] Ono E, Cuello JL. Design parameters of solar concentrating systems for CO2 mitigating algal photobioreactors. Energy 2004;29:1651-1657.
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Haematococcus pluvialis in a sequential heterotrophic–photoautotrophic culture. J Appl
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Phycol 2001;13:395-402.
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bioreactor and its application to outdoor culture of microalgae. Bioproc Biosyst Eng
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2013;36:729-736.
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[15] Yoo JJ, Choi SP, Kim BW, Sim SJ. Optimal design of scalable photo-bioreactor for
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phototropic culturing of Haematococcus pluvialis. Bioproc Biosyst Eng 2012;35:309-
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315.
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[16] Tsang S Optimal Harvesting Strategy For Haematococcus Pluvialis Using A Stella-
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[17] Millero FJ. The thermodynamics of the carbonate system in seawater. Geochimica Et Cosmochimica Acta 4 1979;3:1651-1661. [18] Gaffron, H. Carbon dioxide reduction with molecular hydrogen in green algae. Am J Bot 1940;273-283.
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Based Model. United States: Hawai’i University. Ph.D. thesis 2004.
[19] Cheng L, Zhang L, Chen H, Gao C. Carbon dioxide removal from air by microalgae cultured in a membrane-photobioreactor. Sep Purif Technol 2006;50:324-329.
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[20] Rosello Sastre R, Csogor Z, Perner-Nochta I, Fleck-Schneider P, Posten C. Scale-down
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of microalgae cultivations in tubular photo-bioreactors-a conceptual approach. J
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Biotechnol 2007;132:127-133.
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[21] Becker EW. Microalgae: Biotechnology and Microbiology. New York: Cambridge University Press, 1994;p.11.
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347
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[22] Olaizola M. Microalgal removal of CO2 from flue gases: changes in medium pH and
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flue gas composition do not appear to affect the photochemical yield of microalgal
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cultures. Biotechnol Bioproc Eng 2003;8:360-367.
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[23] Lide DR. CRC handbook of chemistry and physics. Boston: CRC press, 2004;P. 1990.
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[24] Livansky K. Losses of CO2 in outdoor mass algal cultures: determination of the mass
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transfer coefficient KL by means of measured pH course in NaHCO3 solution. Algolo
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Studies 1990;58:87-97.
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[25] Stumm W, Morgan JJ. Aquatic Chemistry: an introduction emphasizing chemical equilibria in natural waters. New York: Wiley Press. 1987;P. 785.
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[26] Eriksen NT, Riisgard FK, Gunter WG, Iversen JJL. On-line estimation of O2 production,
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CO2 uptake, and growth kinetics of microalgal cultures in a gastight photobioreactor. J
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Appl Phycol 2007;19:161-174.
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[27] Fan LH, Zhang YT, Zhang L, Chen HL. Evaluation of amembrane-sparged helical
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tubular photobioreactor for carbon dioxide biofixation by Chlorella vulgaris. J Membr
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Sci 2008;325:336-345.
364 365
[28] Ugwu CU, Aoyagi H, Uchiyama H. Photobioreactors for mass cultivation of algae. Biores Technol 2008;99:4021-4028. [29] Lee BD, Apel WA, Walton MR. Calcium carbonate formation by Synechococcus sp.
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strain PCC 8806 and Synechococcus sp. strain PCC 8807. Biores Technol 2006;97:2427-
368
2434.
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Table Legends
Table 1. Maximum biomass concentration (Xmax, g·L-1), specific growth rate (μ, d-1) and
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photobioreactors which constituted the sequential photobioreactors.
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biomass productivity (Px, g·L-1 d-1) for Haematococcus pluvialis in the four different
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Figure Legends
Fig. 1. The schematic diagram of the experimental apparatus using vertical-column photobioreactor (PBR). 5L- PBR and 20L-PBR were used in indoor and outdoor system,
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respectively. (a) 5L photobioreactor with simple operation, (b) 20L photobioreactor with
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simple operation, (c) 5L photobioreactors in series, (d) 20L photobioreactors in series.
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Fig. 2. Time course of biomass concentration of PBR 1, 2, 3 and 4 during sequential operation in an (a) indoor system and an (b) outdoor system. The 5L-PBR (1 column) and
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20L-PBR (4 columns) were used for an indoor and outdoor culture system, respectively.
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Fig. 3. The concentration of injected carbon, biomass and dissolved inorganic carbon of PBR 1, 2, 3 and 4 during sequential operation in an (a) indoor system and an (b) outdoor system.
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culture system, respectively.
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The 5L-PBR (1 column) and 20L-PBR (4 columns) were used for an indoor and outdoor
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Fig. 4. The percentage (%) of distributed carbon in photobioreactor as carbon bound in biomass (Cbiomass), carbon dissolved in the liquid media (DIC), carbon in headspace (Cheadspace) and vented out carbon to supplied carbon of PBR 1 (simple operation), PBR1-2 (sequential operation), PBR 1-3 (sequential operation) and PBR 1-4 (sequential operation) in an (a) indoor system and an (b) outdoor system. The 5L-PBR (1 column) and 20L-PBR (4 columns) were used for an indoor and outdoor culture system, respectively.
Page 20 of 27
ip t cr
Photobioreactor
Indoor experiments
PBR 1
0.683±0.012
PBR 2
Outdoor experiments
Px
Xmax
μ
Px
0.107±0.009
0.039±0.0077
0.820±0.110
0.077±0.001
0.034±0.002
0.737±0.001
0.115±0.012
0.042±0.0036
0.805±0.181
0.070±0.006
0.032±0.001
PBR 3
0.545±0.052
0.090±0.004
0.031±0.0056
0.662±0.101
0.056±0.008
0.023±0.003
PBR 4
0.449±0.007
0.071±0.003
0.020±0.004
0.564±0.020
0.044±0.003
0.016±0.003
an
μ
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ep te
d
M
Xmax
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Table 1.
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Page 22 of 27
d
ep te
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Fig. 2
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Fig. 3
PBR 1
PBR 3
PBR 4
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(b)
PBR 2
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(a)
PBR 1
PBR 2
PBR 3
PBR 4
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Fig. 4
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Highlights Sequential operating system was applied to evaluate the CO2 fixation efficiency. Haematococcus pluvialis and flue gas were used in microalgae cultivation.
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We identified aspects of cell growth, dissolved carbon in liquid and vented gas.
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The fixation efficiency increased more than 3-fold compared to simple operation.
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S1359-5113(15)00162-2 http://dx.doi.org/doi:10.1016/j.procbio.2015.03.021 PRBI 10389
To appear in:
Process Biochemistry
Received date: Accepted date:
20-1-2015 30-3-2015
Please cite this article as: Lee JY, Hong M-E, Chang WS, Sim SJ, Enhanced carbon dioxide fixation of Haematococcus pluvialis using sequential operating system in tubular photobioreactors, Process Biochemistry (2015), http://dx.doi.org/10.1016/j.procbio.2015.03.021 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Enhanced carbon dioxide fixation of Haematococcus pluvialis using sequential operating system in tubular photobioreactors
Department of Chemical and Biological Engineering, Korea University, Seoul 136-713,
South Korea
Department of Chemical Engineering, Sungkyunkwan University, Suwon 440-746, South
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c
Green School, Korea University, Seoul 136-713, South Korea
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Joo Yeong Leea, Min-Eui Hongc, Won Seok Changd, and Sang Jun Sima,b,*
Korea
Research Institute, Korea District Heating Corp., 186 Bundang-dong, Bundang-gu,
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Seongnam-si, Gyeonggi-do, South Korea
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d
Tel: +82-2-3290-4853
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Fax: +82-2-926-6102
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*Corresponding author: Professor Sang Jun Sim
e-mail: [email protected]
Running title: Effect of sequential PBRs on the CO2 fixation efficiency of microalgae
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Abstract
2
Carbon dioxide sequestration by microalgae photosynthesis is an attractive alternative to
3
mitigate climate change due to greenhouse gas emission. In our study, Haematococcus
4
pluvialis and a sequential operating system were exploited to examine the carbon dioxide
5
fixation efficiency in a tubular photobioreactor. We investigated the carbon balance over the
6
photobioreactor, including the carbon bound in the biomass, dissolved inorganic carbon in the
7
liquid media, and gaseous carbon remained in the headspace and vented out from the
8
photobioreactor. The experiments were performed both indoors and outdoors, using air-mixed
9
3% CO2 gas and the flue gas from power plant. As a result, the sequential operation system
10
using H. pluvialis cultivation improved the carbon dioxide fixation efficiencies from 12.34%
11
to 49.37% (indoor), and from 13.55% to 49.15% (outdoor), respectively, compared to single
12
bioreactor operation mode. This sequential operating system would be useful for enhanced
13
conversion of carbon dioxide from flue gas by microalgae photosynthesis.
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Keywords: Haematococcus pluvialis, flue gas, carbon fixation efficiency, tubular
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photobioreactor
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17 18
1. Introduction As consumption of fossil fuels has been increased for centuries due to industrial
20
development around the world, greenhouse gas emissions into the atmosphere have
21
continuously increased. Since greenhouse gas causes many environmental issues, various
22
carbon sequestration technologies have been introduced to reduce greenhouse gas emissions
23
[1]. As carbon dioxide is a great part of the greenhouse gases, reduction of carbon dioxide
24
plays a substantial role for greenhouse gas sequestration [2].
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Biological fixation of carbon dioxide using microalgae is an attractive option because
26
microalgae are not only able to sequester carbon dioxide, but also to produce high-value
27
products such as biofuels, pigments and nutrients [3]. Astaxanthin (3,3′-dihydroxy-β-
28
carotene-4,4′-dione) is recognized as a high-value keto-carotenoid pigment ($2,500/kg USD)
29
and one of the most powerful antioxidants among carotenoids with many applications in
30
nutraceuticals, cosmetics, and the food and feed industries [4, 5]. The green microalga
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Haematococcus pluvialis is the richest source of natural astaxanthin (up to 4% of its dry
32
mass) [6] and is cultivated on an industrial scale [7, 8].
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Photosynthetic cultivation could be performed in both open pond system and closed
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photobioreactor. Open culture systems have been extensively studied; however, these
35
cultivation processes suffer multiple disadvantages including loss of media by evaporation,
36
the possibility of contamination by unwanted species and requirement of an area of enormous
37
size [9]. Closed systems which utilize photobioreactors for culturing microalgae, on the other
38
hand, are much easier to control contamination from heterotrophs and culture parameters
39
such as nutrient levels, temperature, amount of inlet carbon dioxide, etc. [10]. Moreover,
40
closed systems are able to achieve highly efficient biomass production for enhancement of
41
the carbon dioxide fixation rate compared to open pond systems.
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The tubular photobioreactor is one of the most typical cultivation apparatus used in the
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carbon sequestration process by algal culture [11]. A vertical tubular photobioreactor can
44
increase the residence time of sparged gas, which could enhance the carbon dioxide
45
utilization efficiency [12]. Accordingly, it seems that consideration of the configuration and
46
operational mode of photobioreactors is crucial to elevate their performance.
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In the present study, the carbon fixation efficiency in H. pluvialis was improved by
48
developing an operational system using serial tubular photobioreactors. In this system, four
49
photobioreactors were placed in series and connected to reuse the gas vented out from the
50
preceding photobioreactor as injection gas for the next photobioreactor. The experiments
51
were performed in indoor and also outdoor system using the unicellular green algae H.
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pluvialis. An indoor PBR system was operated in a 5L photobioreactor (1 column) aerated
53
with 3% CO2 mixed gas and illuminated with cool white fluorescent light at 30-60 μmol
54
photon/m2/s to clearly demonstrate the effect of a sequential PBR system on the carbon
55
dioxide fixation and utilization efficiency. After that, an outdoor PBR system was operated in
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a 20L photobioreactor (4 columns) exposed to flue gas consisted of 2~4% of CO2 and
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illuminated with natural solar radiation at 50~80 μmol photon/m2/s to define benefits of this
58
strategy in pilot scale. Consequently, this system extended the retention time and achieved
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lower carbon dioxide levels in the effluent gas vented from the photobioreactors. The serial
60
photobioreactors process is a promising strategy for improving carbon dioxide fixation and
61
utilization efficiency in microalgae culture systems.
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62 63
2. Materials and Methods
64 65 66
2.1 Algal strain and medium composition Haematococcus pluvialis NIES-144 was obtained from the National Institute for
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Environmental Studies, Tsukuba, Japan. H. pluvialis was grown photoautotrophically in
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NIES-C medium (pH 7.5), which consists of 0.15 g/L Ca(NO3)2, 0.10 g/L KNO3, 0.05 g/L β-
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glycerophosphoric acid disodium salt pentahydrate, 0.04 g/L MgSO4∙7H2O, 0.50 g/L Tris-
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aminomethane, 0.01 mg/L thiamine, 0.10 μg/L biotin, 0.10 μg/L vitamin B12, and 3.00 mL/L
71
PIV metal solution [1.0 g/L Na2EDTA, 0.196 g/L FeCl3∙6H2O and (in mg/L) 36.0
72
MnCl2∙4H2O, 22.0 ZnSO4∙7H2O, 4.0 CoCl2∙6H2O, and 2.5 Na2MoO4∙2H2O] [13].
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2.2 Photobioreactors and cultivation conditions
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Cells were grown in transparent film photobioreactors. Agitation and aeration were
76
accomplished by use of air-mixed CO2 gas (Indoor system) or flue gas (Outdoor system) with
77
a compressor and sparger. [14]. A schematic diagram of the experimental apparatus is shown
78
in Fig. 1. In a simple operation, a single PBR with a working volume of 5L (1 column) and
79
20L (4 columns) was used for an indoor and outdoor culture system, respectively. In a
80
sequential operation, four PBRs with a working volume of 5L and 20L were connected in
81
series for an indoor and outdoor culture system, respectively, to utilize the vented gas of the
82
front reactor as inlet gas of the rearward reactors, labeled consecutively as PBR1, PBR2,
83
PBR3 and PBR4.
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2.2.1 Lab-scale experiments
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The indoor experiments were conducted using single-column type PBRs (1 column) with
87
maintenance of the temperature at 23℃. The indoor PBR is consisted of a single bubble
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column which is120cm in height and 10cm in diameter, with 5L for liquid volume and 1L for
89
headspace volume. Cells were illuminated with 30-60 μmol photon/m2/s by cool white
90
fluorescent lamps. The dark and light cycle was 8:16, and light intensities were measured at
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the surface of the bioreactor using an LI-250 quantum photometer (Lambda Instrument Corp.,
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92
USA) [15]. The air-mixed 3% CO2 gas was supplied to the PBR through a sparger with 10μm
93
pores at the bottom of the PBR at the rate of 0.01~0.02 vessel volume per min (vvm).
94 95
2.2.2 Outdoor system using flue gas The outdoor culture system was demonstrated in a greenhouse using multiple-column
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type PBRs (4 columns) to verify possibilities of scale-up using flue gas. The outdoor PBR
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(multiple-column type), which is consisted of four bubble columns (each column was 120cm
99
in height and 10cm in diameter) connected with each other, were prepared (total volume of
100
media was 20L, while 5L served as the gas space). The natural sunlight was used as the
101
source of light for the outdoor PBRs with a dark/light cycle of about 12:12 h. Cells were
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cultured in outdoors with exposure to the light intensities of 50~80 μmol photon/m2/s, and
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temperature of 26±3℃. The flue gas was also supplied to the PBR through a sparger with
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10μm pores at the bottom of the PBR and the rate of gas flow was increased from 0.01 to
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0.02 vessel volume per min (vvm). The flue gas, composed of N2, CO2, O2, NOx and CO,
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was provided from power plant located nearby Seoul, South Korea. The flue gas consisted of
107
2~4% of CO2, which is sufficient for algal cultivation, 11.99±0.73% O2, 21.72±3.72ppm
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NOx, 1.43±4.03ppm CO, water vapor and dust.
110
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2.3 Carbon mass balance
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Since no carbon source was supplied in the media, the CO2 in the gas was the primary
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source of carbon for biomass production. CO2 injected into the PBR was dispersed into the
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media, cell and headspace of the PBR. The carbon mass balance equation is as follows [16]: (1)
114 115
Cin (g·d-1): mass flow rate of carbon
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Cout (g·d-1): mass flow rate of carbon out of the PBR via venting
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Vl (L): volume of the media
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Vg (L): volume of the headspace
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Mc (g·mol-1): atomic weight of carbon
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(mol·L-1·d-1): rate of change in dissolved inorganic carbon concentration
cr
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(mol·L-1·d-1): rate of change in concentration of carbon bound in the biomass
(mol·L-1·d-1): rate of change in carbon concentration in headspace
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2.4 Analytical methods
Cell growth was determined by measuring the dry weight of the biomass. The dry cell
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weight was measured by filtration of aliquots using filter paper. First, the harvested cells were
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filtered onto pre-weigh glass-fiber filters (Whatman GF/C, 47 mm diameter), rinsed twice
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with 10 mL distilled water, and then dried at 80℃ for 24 h for comparison of the weight
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before and after filtration. Total organic carbon (TOC) was measured by a TOC analyzer
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(TOC 5000, Shimadzu, Kyoto, Japan) with analysis of the samples combusted to CO2 and
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H2O, and the TOC value was calculated as the difference between total carbon and inorganic
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carbon concentration. Dissolved inorganic carbon (DIC) was the sum of carbonic acid,
133
bicarbonate and carbonate in the aqueous solution, which can be calculated by the following
134
equations [17]:
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(2)
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TA: Total alkalinity in meq/L (measured by titration)
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[H+]: the hydrogen ion activity (i.e.,10-pH) and pH of the culture broth as measured by a
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digital pH meter (Hanna, Rep. of Korea)
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Kw (T), K1 (T), K2 (T): dissociation constants (3)
141
(4)
142
(5)
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The concentration of CO2 in the gaseous state was measured by a CO2 analyzer (maMoSⅡ
144
100, madur, Poland).
145
Specific growth rate (d-1) and volumetric biomass productivity (g·L-1·d-1) were calculated
146
using the following equations:
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(6)
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(7)
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where X1 and X2 were mass concentrations of the cells (g·L-1) at t1 and t2.
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152 153
3. Results and Discussion
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3.1 Carbon supplied into photobioreactor
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Air-mixed 3% CO2 gas and flue gas from power plant were supplied via the sparger in the
155
indoor and outdoor systems, respectively. The CO2 concentration of the flue gas varied
156
between 2.66% ~ 2.77% and the mean value was 2.7%. Gas including CO2 was employed
157
into the PBR to supply the cells with a carbon source, prevent biomass settling, and
158
encourage desorption of oxygen [16]. Therefore, the amount of carbon supplied would be
159
determined by the CO2 concentration and the flow rate of the injected gas. The total amounts
160
of CO2 injected to each PBR (working volume 5L) were 13.24±0.73g·L-1(PBR1),
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11.42±0.09g·L-1(PBR2), 9.42±0.12g·L-1(PBR3) and 7.72±0.71g·L-1(PBR4) for indoor system,
162
respectively.
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11.26±1.21g·L-1(PBR2), 9.35±0.62g·L-1(PBR3) and 7.89±1.03g·L-1(PBR4) (working volume
164
20L), respectively.
In
outdoor
experiments,
the
values
were
3.2 Carbon assimilated by biomass
167
3.2.1 Production of cell biomass
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13.36±0.18g·L-1(PBR1),
H. pluvialis cells can grow photoautotrophically using CO2 as the sole inorganic carbon
169
source [18]. The maximum biomass concentration, specific growth rate, biomass productivity
170
values are shown in Table 1 and the growth curves of biomass versus time are shown in Fig. 2.
171
Biomass densities did not show much differences at first time, however, the differences
172
gradually got larger as increasing biomass with demands for CO2. In lab-scale experiments,
173
maximum cell densities and specific growth rates for each PBR were 0.68g·L-1 and 0.11d-1
174
(PBR1), 0.74g·L-1 and 0.12d-1 (PBR2), 0.55g·L-1 and 0.09d-1 (PBR3), and 0.45g·L-1 and
175
0.07d-1 (PBR4), respectively. Meanwhile, the maximum cell densities and specific growth
176
rates observed in the outdoor experiments were 0.82g·L-1 and 0.08d-1 (PBR1), 0.81g·L-1 and
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0.07d-1 (PBR2), 0.66g·L-1 and 0.06d-1 (PBR3), and 0.56g·L-1 and 0.04d-1 (PBR4).
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178
Both indoor and outdoor experiments showed similar cell density and specific growth rate
179
for PBR1 and PBR2, while the biomass production was noticeably decreased after PBR2. It
180
was presumed that the reduction in biomass production was mainly attributable to the CO2
181
concentration. Previous study has also shown the CO2 concentration, photobioreactor
182
configuration and light intensity to be crucial factors affecting biomass productivity [19]. In
183
the experiments herein, CO2 concentration was the major factor affecting biomass production.
184
Microalgal cells have optimal CO2 concentrations for growth; therefore, the CO2
185
concentration of the injected gas should be carefully controlled to avoid inefficient growth of
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the cells due to insufficient or excessive CO2 supply [20]. Biomass productivity also showed
187
a similar tendency, with maximum cell density and specific growth rates of 0.039g·L-1·d-1
188
(PBR1), 0.42g·L-1·d-1 (PBR2), 0.031g·L-1·d-1 (PBR3), and 0.020g·L-1·d-1 (PBR4) in the indoor
189
experiments, and 0.034g·L-1·d-1 (PBR1), 0.32g·L-1·d-1 (PBR2), 0.023g·L-1·d-1 (PBR3), and
190
0.016g·L-1·d-1 (PBR4) in the outdoor system, respectively.
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3.2.2 Total organic carbon in cell
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The total organic carbon percentage (%TOC) in the biomass samples from indoor and
194
outdoor experiments was measured. The average %TOC values from the two were 46.82%
195
and 44.33%, respectively, with the standard deviations of 1.89% and 0.66%. These values
196
were reasonable compared to the reference that stated the typical dry mass %TOC of
197
microalgae to be approximately 50% [21]. The dry cell weight and %TOC on a dry mass
198
basis were employed to estimate the amount of carbon assimilated into the biomass. We
199
calculated the amount of carbon bound in biomass (Cbiomass) with %TOC and dry cell weight,
200
0.237 g·L-1(PBR1), 0.25 g·L-1(PBR2), 0.19 g·L-1(PBR3) and 0.12 g·L-1(PBR4) for indoor
201
system and 0.24 g·L-1(PBR1), 0.22 g·L-1(PBR2), 0.16 g·L-1(PBR3) and 0.12 g·L-1(PBR4) for
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outdoor experiments.
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3.3 Carbon in liquid media
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Dissolved carbon dioxide in the media of the photobioreactor was available as a carbon
206
source for consumption by the cells or was degassed out from the liquid phase into the
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gaseous phase in the headspace, where it could be emitted via the venting system. The
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transfer of CO2 gas to liquid media depends on the inlet gas composition, medium pH and
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alkalinity [22]. Since the dissolution of CO2 acidifies water, the medium pH would be lower
210
after the injection of CO2 gas [23]. Nevertheless, the consumption of CO2 dissolved in the
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liquid media through photosynthesis by the biomass would increase the pH of the media,
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which means that increase in the pH, associated with the biomass, is a characteristic of
213
photosynthetic cell cultivation [24]. Uptake of the CO2 from the media elevated the pH, not the alkalinity of the liquid;
215
however, other cell growth processes, for instance, the uptake of NO3- or H2PO4- during
216
photosynthesis, elevated the alkalinity based on the equation below [25].
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217
(8)
219
This explains that more CO2 might be induced to be dissolved in the media, and that not only
220
inlet gas but also cell growth is an important factor for CO2 dissolution. As cell growth also
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depends on supplied CO2 using primary carbon source, three factors; biomass production,
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injected carbon amount and dissolved inorganic carbon are all associated with each other.
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In lab-scale experiments, DIC for PBR 1 was 0.34 g·L-1 with 0.50 g·L-1 increased
224
biomass and 3.61 g·L-1 injected carbon; 0.32 g·L-1 with 0.54 g·L-1 and 3.11 g·L-1(PBR 2);
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0.30 g·L-1 with 0.40 g·L-1 and 2.57 g·L-1(PBR 3); 0.23 g·L-1 with 0.26 g·L-1 and 2.11 g·L-
226
1
227
and 3.08 g·L-1(PBR 2); 0.27 g·L-1 with 0.36 g·L-1 and 2.55 g·L-1(PBR 3); 0.22 g·L-1 with 0.26
228
g·L-1 and 2.15 g·L-1(PBR 2) for outdoor experiments. Accordingly, amount of dissolved
229
carbon in liquid medium would be increased by amount of injected carbon and production of
230
biomass (Fig. 3).
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(PBR 4). And 0.36 g·L-1 with 0.54 g·L-1 and 3.64 g·L-1(PBR 1); 0.33 g·L-1 with 0.50 g·L-1
231 232
3.4 Carbon vented out from photobioreactors
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3.4.1 Carbon in headspace of photobioreactor
234
The carbon in the headspace increased proportionally to the concentration of carbon in
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the supplied gas. The final carbon concentrations of the headspace for each PBR were
Page 11 of 27
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0.31g·L-1, 0.25g·L-1, 0.12g·L-1 and 0.07g·L-1 in lab-scale experiments, and 0.24g·L-1,
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0.15g·L-1, 0.07g·L-1 and 0.03g·L-1 in the outdoor experiments, respectively. Accumulation of
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carbon dioxide in the headspace could be inferred from supplied gas and respiration of the
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biomass during the dark or night time [16].
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3.4.2 Vented out carbon
The amount of carbon vented out could be calculated using Eq.1. The overall amount of
243
carbon vented out was 15.49g, 12.72g, 10.38g and 8.6g for respective PBR in the indoor
244
system, and 61.17g, 50.61g, 42.59g, and 35.94g for those in the outdoor system. It was
245
assumed that all the carbon in the injected gas was vented out during dark time or night, when
246
photosynthesis ceased. Furthermore, additional loss of carbon, which was not currently
247
accounted for, may have occurred because of carbon dioxide outgassing from the media
248
during the dark time or at night. This outgassed carbon would be vented out with the carbon
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in the supplied gas. Additional investigations are needed to accurately determine the carbon
250
distribution in the photobioreactor [16].
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3.5 Overall analysis of carbon distribution in photobioreactor
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The total carbon fixation efficiency was determined by integrating the respective amount
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of carbon removed in each sequential PBR with working volumes of 5L (indoor experiments)
255
and 20L (outdoor experiments).
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Fig. 4 shows the ratio of distributed carbon in PBR to injected carbon. As additional
257
PBRs were connected, the percentage of carbon bound in biomass increased from 6.54% to
258
13.46%, 18.56% and 21.88%; dissolved carbon in liquid media was 5.93% to 12.97%,
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20.12% and 26.26%; carbon in headspace was 1.71% to 3.10%, 3.82% and 4.21%, while
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carbon vented out from PBRs decreased from 85.82% to 70.47%, 57.51% and 47.65% for
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indoor experiments. In outdoor system, carbon bound in biomass extended from 6.59% to
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12.72%, 17.11% and 20.26%; dissolved carbon in liquid media was 7.83% to 15.16%,
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21.30% and 27.05%; carbon in headspace was 1.65% to 2.68%, 3.16% and 3.36%, carbon
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vented out from PBRs, whereas, reduced from 83.93% to 69.44%, 58.44% and 49.31%. When the 4 PBRs were used in a sequential operation, the total carbon fixation efficiency
266
(Cbiomass + DIC) was elevated from 12.34% to 49.37% and from 13.55% to 49.15% for the
267
indoor and outdoor experiments, respectively, compared to that in a simple operation (Fig. 4).
268
Consequently, in the sequential operation system (4 PBRs), the total carbon fixation
269
efficiency was improved by 300% (indoor) and 263% (outdoor) as compared to that in the
270
simple operation system (1 PBR).
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Photobioreactors are multi-phase (gas-liquid-solid) with a number of interactions, and the
272
performance of the PBR in carbon dioxide sequestration depends on the microalgal species,
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PBR configuration, flow rate of the inlet gas, CO2 concentration in the supplied gas and
274
operation system [26-28]. The use of this tubular type of reactor and sequential operation
275
mode could be regarded as a promising option for the elimination of CO2 by photosynthetic
276
microalgal culture [29].
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4. Conclusions
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In this study, carbon balance over the photobioreactor was investigated to analyze carbon
280
distribution in the photobioreactor, and to enhance the carbon fixation efficiency through use
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of a sequential operation system. In Haematococcus pluvialis culture, the sequential
282
operation system using 4 serial photobioreactors demonstrated improved carbon dioxide
283
fixation efficiencies of up to 49.37% (indoor) and 49.15% (outdoor), which are 4 fold and
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3.63 fold higher than that of single bioreactor operation mode, respectively. This
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improvement could be applied to maximize carbon capture efficiency by cultivation of
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microalgae in a photobioreactor.
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Acknowledgements
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This study was supported by the Korea Institute of Energy Technology Evaluation and
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Planning and Ministry of Trade, Industry & Energy of Korea as a part of the Project of
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“Process demonstration for bioconversion of CO2 to high-valued biomaterials using
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microalgae” (20122010200010-11-2-100) in “Energy Efficiency & Resources Technology
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R&D” project, the National Research Foundation of Korea (NRF) grants (grant No. NRF-
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2013R1A2A1A01015644/2010-0027955), University-Institute Cooperation Program (2013),
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and grants (2014M1A8A1049278) from Korea CCS R&D Center of the NRF funded by the
296
Ministry of Science, ICT, & Future Planning of Korea.
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[16] Tsang S Optimal Harvesting Strategy For Haematococcus Pluvialis Using A Stella-
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of microalgae cultivations in tubular photo-bioreactors-a conceptual approach. J
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[21] Becker EW. Microalgae: Biotechnology and Microbiology. New York: Cambridge University Press, 1994;p.11.
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flue gas composition do not appear to affect the photochemical yield of microalgal
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[24] Livansky K. Losses of CO2 in outdoor mass algal cultures: determination of the mass
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transfer coefficient KL by means of measured pH course in NaHCO3 solution. Algolo
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[25] Stumm W, Morgan JJ. Aquatic Chemistry: an introduction emphasizing chemical equilibria in natural waters. New York: Wiley Press. 1987;P. 785.
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[26] Eriksen NT, Riisgard FK, Gunter WG, Iversen JJL. On-line estimation of O2 production,
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CO2 uptake, and growth kinetics of microalgal cultures in a gastight photobioreactor. J
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Appl Phycol 2007;19:161-174.
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[27] Fan LH, Zhang YT, Zhang L, Chen HL. Evaluation of amembrane-sparged helical
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tubular photobioreactor for carbon dioxide biofixation by Chlorella vulgaris. J Membr
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Sci 2008;325:336-345.
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[28] Ugwu CU, Aoyagi H, Uchiyama H. Photobioreactors for mass cultivation of algae. Biores Technol 2008;99:4021-4028. [29] Lee BD, Apel WA, Walton MR. Calcium carbonate formation by Synechococcus sp.
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Table Legends
Table 1. Maximum biomass concentration (Xmax, g·L-1), specific growth rate (μ, d-1) and
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photobioreactors which constituted the sequential photobioreactors.
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biomass productivity (Px, g·L-1 d-1) for Haematococcus pluvialis in the four different
Page 19 of 27
Figure Legends
Fig. 1. The schematic diagram of the experimental apparatus using vertical-column photobioreactor (PBR). 5L- PBR and 20L-PBR were used in indoor and outdoor system,
ip t
respectively. (a) 5L photobioreactor with simple operation, (b) 20L photobioreactor with
cr
simple operation, (c) 5L photobioreactors in series, (d) 20L photobioreactors in series.
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Fig. 2. Time course of biomass concentration of PBR 1, 2, 3 and 4 during sequential operation in an (a) indoor system and an (b) outdoor system. The 5L-PBR (1 column) and
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20L-PBR (4 columns) were used for an indoor and outdoor culture system, respectively.
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Fig. 3. The concentration of injected carbon, biomass and dissolved inorganic carbon of PBR 1, 2, 3 and 4 during sequential operation in an (a) indoor system and an (b) outdoor system.
pt
culture system, respectively.
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The 5L-PBR (1 column) and 20L-PBR (4 columns) were used for an indoor and outdoor
Ac ce
Fig. 4. The percentage (%) of distributed carbon in photobioreactor as carbon bound in biomass (Cbiomass), carbon dissolved in the liquid media (DIC), carbon in headspace (Cheadspace) and vented out carbon to supplied carbon of PBR 1 (simple operation), PBR1-2 (sequential operation), PBR 1-3 (sequential operation) and PBR 1-4 (sequential operation) in an (a) indoor system and an (b) outdoor system. The 5L-PBR (1 column) and 20L-PBR (4 columns) were used for an indoor and outdoor culture system, respectively.
Page 20 of 27
ip t cr
Photobioreactor
Indoor experiments
PBR 1
0.683±0.012
PBR 2
Outdoor experiments
Px
Xmax
μ
Px
0.107±0.009
0.039±0.0077
0.820±0.110
0.077±0.001
0.034±0.002
0.737±0.001
0.115±0.012
0.042±0.0036
0.805±0.181
0.070±0.006
0.032±0.001
PBR 3
0.545±0.052
0.090±0.004
0.031±0.0056
0.662±0.101
0.056±0.008
0.023±0.003
PBR 4
0.449±0.007
0.071±0.003
0.020±0.004
0.564±0.020
0.044±0.003
0.016±0.003
an
μ
Ac c
ep te
d
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Xmax
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Table 1.
Page 21 of 27
Page 22 of 27
d
ep te
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Fig. 2
Page 23 of 27
Fig. 3
PBR 1
PBR 3
PBR 4
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(b)
PBR 2
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(a)
PBR 1
PBR 2
PBR 3
PBR 4
Page 24 of 27
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Fig. 4
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Page 26 of 27
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Highlights Sequential operating system was applied to evaluate the CO2 fixation efficiency. Haematococcus pluvialis and flue gas were used in microalgae cultivation.
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We identified aspects of cell growth, dissolved carbon in liquid and vented gas.
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The fixation efficiency increased more than 3-fold compared to simple operation.
Page 27 of 27