A novel coal additive from microalgae produced from thermal power plant flue gas

Journal of Cleaner Production 133 (2016) 1086e1094

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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro

A novel coal additive from microalgae produced from thermal power plant flue gas Burcu Ertit Tas¸tan a, b, *, Turgay Tekinay a, c, ** €lbas¸ı, Ankara, Turkey Life Sciences Application and Research Center, Gazi University, 06830, Go €lbas¸ı, Ankara, Turkey Health Services Vocational School, Gazi University, 06830, Go c Department of Medical Biology and Genetics, Faculty of Medicine, Gazi University, 06500, Ankara, Turkey a

b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 9 March 2016 Received in revised form 8 June 2016 Accepted 9 June 2016 Available online 13 June 2016

Current techniques for cleaning flue gas produced by coal-fired thermal power plants have high capital and operational costs and are not effective enough. Ongoing research focuses on increasing efficiency of power plants by using coal additives and biological treatment methods especially microalgae for flue gas treatment. Here, we propose use of a resistant microalgae for flue gas treatment and using its biomass as a novel coal additive. Utilization of CO2 from thermal power plant coal samples by bio-stimulated Scenedesmus sp. was investigated for producing a novel coal additive material for use in thermal power plants. Scenedesmus sp. biomass was stimulated by IAA (3-Indoleacetic acid) and VO (Viburnum opulus) promoters. A novel coal additive material with 8.7% lower amounts of ash and 26.17% higher calorific value, termed as “green coal” was produced in this system. The maximum biomass was produced with lowest culture media consumption, minimum time, highest temperature and highest flow rate. The XRF analyses were performed, fatty acid methyl ester levels were determined and morphology of Scenedesmus sp. were observed. The growth of Scenedesmus sp. in open pond system by bubbling with 9.6 vvm of flue gas resulted in volumetric biomass productivity (Pmax) of 0.033 g/L/d and CO2 fixation rate of 1512.22 mg CO2/day. This system has the potential to replace other conventional coal additive and cleaning methods since it needs lower energy expenditure and lower use of chemicals. © 2016 Elsevier Ltd. All rights reserved.

Keywords: Coal additive Coal cleaning process Flue gas Green coal Microalgae

1. Introduction Due to decreasing reserves of fossil fuels and their adverse effects on the environment, alternative clean energy sources are needed. The consumption of coal has a tendency to increase in forthcoming years due to its lower cost compared with other conventional fuels; however use of coal could increase environmental pollution. The unwanted ash and acidic compounds in coal could lead to some problems like slagging, fouling and abrasion during processing of coal in the thermal power plant and researchers study to eliminate these adverse effects (Daood et al., 2014a). Therefore, de-ashing and enhancement of combustion efficiency are essential for sustainable commercial uses. The

* Corresponding author. Life Sciences Application and Research Center, Gazi €lbas¸ı, Ankara, Turkey. University, 06830, Go ** Corresponding author. E-mail addresses: [email protected] (B.E. Tas¸tan), [email protected] (T. Tekinay). http://dx.doi.org/10.1016/j.jclepro.2016.06.053 0959-6526/© 2016 Elsevier Ltd. All rights reserved.

importance of additives on combustion efficiency has recently been investigated. Coal additive technology is based on the use of an additive to reduce emissions and increase the thermal efficiency and produce low C fly ash by improving the burning quality of coal. Use of additives resulted in enhancement of combustion efficiency of coal and decreased the fouling and slagging problems (Wei et al., 2016). There are different type of coal additives, such as iron-based additives (Sowa and Fletcher, 2011), Ca2þ and Fe3þ ions (Tsubouchi and Ohtsuka, 2008), iron, aluminum, calcium and silicon-based oxides (Daood et al., 2014a, 2014b). Microalgae are one of the most promising green energy resources (Pragya and Pandey, 2016). The utilization of flue gas by microalgae is a growing area of research (Sun et al., 2015; Tas¸tan et al., 2013; Doucha et al., 2005). Microalgae have the ability to fix CO2 from flue gas and mitigate the greenhouse gas emissions (Zhao et al., 2015). The microalgae-based CO2 utilization is considered to be renewable, sustainable and environmentally friendly (Ringsmuth et al., 2016). The fixation rate of CO2 in flue gas by microalgae is limited due to acidic and toxic components of flue

B.E. Tas¸tan, T. Tekinay / Journal of Cleaner Production 133 (2016) 1086e1094

Nomenclature IAA VO Pmax BG11 SR CW ED-XRF

m X t t0

3-Indoleacetic acid Viburnum opulus Maximum biomass productivity Blue-green 11 medium Water samples of Sakarya River Cooling water of the Thermal Power Plant Energy Dispersive X-Ray Fluorescence Spectrometer Specific growth rate Dry cell weight concentrations (g/L) Final time Initial time

gas (Lee et al., 2002). Enhancing the biomass productivity with the addition of growth promoters can increase resistance to toxicity of the flue gas and photosynthesis levels (Tas¸tan et al., 2012, 2013). Among various methods proposed for large-scale cultivation of microalgae (Boruff et al., 2015), open ponds are currently the most economic option for commercial scale production (Ashokkumar et al., 2014). Biodiesel (Laamanen et al., 2014), carotenoids (Chagas et al., 2015) and feeds (Das et al., 2015) were produced in these systems, however production of “coal additive material” from microalgae has not been reported. The main goals of this study were to isolate a flue gas resistant microalga, grow it with thermal power plant flue gas in a designed open pond system and transformation of its biomass to a novel coal additive material. The production of “green coal” as a novel coal additive material is reported in this study. 2. Methodology Biological flue gas treatment is a field of research gaining importance due to its sustainability and high cost of alternative methods. Several microalgae species options are available for utilization of flue gas from thermal power plant but there is a need to decide which species should be used as a high flue gas resistant microalgae. Here, we isolated and identified a flue gas resistant microalgae.

F CO2 V SEM SE

s FAME VM FC TS SA TC BC

1087

biofixation rate (g/d) Culture volume Scanning electron microscopy Standard error Square root of the estimated error variance of the quantity Fatty acid methyl esters Volatile Matter Fixed C Total Sulfur Sulfur in Ash Top Calorific Value Bottom Calorific Value

growing cultures. 2.2. PCR and sequencing In these series of experiments the isolated microalgal cells were identified. Whole cells from an exponentially growing culture of the isolate were used for 18 S rRNA gene amplification in order to identification of the flue gas resistant microalgae. 18 S rRNA region was amplified with primers forward p23SrV_F: 50GGACAGAAAGACCCTATGAA-30 and reverse p23SrV_R: 50TCAGCCTGTTATCCCTAGAG-30 as described by Sherwood and Presting (2007). PCR reaction is carried out in 50 mL reaction mixture. The reaction mixture included in 0.2 mM of each primer, 0.2 mM of each dNTP, 1.5 mM of MgCl2 and 30 ng of template DNA. 1.5 U Taq DNA polymerase is used in the amplification. Amplification by PCR was carried out by an initial denaturation at 95  C for 10 min, followed by 35 cycles of denaturation at 95  C for 45 s, annealing at 60  C for 45 s, and elongation at 72  C for 45 s, with a final extension of 72  C for 10 min. The amplified product was analyzed in 1.2% agarose gel with ethidium bromide at 8 V/cm. The PCR products were visualized under UVP gel imaging system. The amplified PCR product was purified using the QIAGEN gel extraction kit. Applied Biosystems Gene AMP PCR System 9700 is used in sequencing. 2.3. Growth factors

2.1. Microalgae isolation and culture medium The microalgal culture was isolated from Sakarya River located near the Thermal Power Plant Mihalıççık, Eskis¸ehir, Turkey. Samples were spread on Petri plates containing BG 11 medium (Rippka, 1998) with 50.000 IU penicillin and were incubated at 25 ± 2  C under continuous illumination (cool-white fluorescent, 25 mmol/ m2s (1750 lx)). The pH of the BG 11 medium was 8 due to its own chemical composition. Micromanipulation was used to isolate cells from single colonies on these plates. The microalgal cells were purified under aseptic conditions by streaking the cells repeatedly on the BG 11 medium agar plate. At the final step, the purified microalgal cells were transferred to liquid media. In order to validate the axecinity, these liquid cultures were also tested for bacterial contamination by plating on bacteriological media. A series of batch culture experiments in unshaken flasks illuminated by cool-white fluorescent lamps were carried out at 25 mmol/m2s (1750 lx) light intensity. The microalgal cultures were transferred into 100 mL BG 11 medium in 250 mL Erlenmeyer flasks and incubated at 25 ± 2  C under continuous illumination for fifteen days. The medium was inoculated with 0.1 g/L exponentially

3-indoleacetic acid (IAA) (CAS: 87-51-4; SigmaeAldrich) solution was prepared by dissolving 10 mg of the chemical in 20 mL chloroform. A Viburnum opulus solution (VO) was prepared by dissolving 10 mg of the 80  C dried V. opulus (VO) powder in 20 mL chloroform. Desired volume of IAA and VO were added to BG11 media by diluting solutions. 2.4. Flue gas composting system Native industrial mineral coal in Turkey was used in studies. An experimental combustor system was designed to produce flue gas (Tas¸tan et al., 2013). The flue gas used in this study was obtained after burning of coal in this system. The flue gas was transferred through heat resistant silicone pipelines to a gas storage tank (Turk Electric AE 136 AD, volume 5 L) with the help of a compressor before feeding it to the microalgal culture. A schematic illustration of the flue-gas based cultivation system for microalgae is shown in Supplementary Data 1. The evaluated combustion regime was defined as complete combustion. The transfer speed of the gas samples was expressed in terms of vvm units, which were

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calculated on the gas and liquid volumes transferred and collected per minute. The flue gas was analyzed by GCMS-QP2010 SE (Shimadzu) Gas Chromatography Mass Spectrometer equipped with a TD-20 Shimadzu thermal desorption system (Supplementary Data 2). Separation was performed on an RTX 624 capillary column (60 m  0.25 mm diameter, 1.4 mm film thickness) with a temperature programme from 50  C (2 min) to 260  C (20 min), using helium as carrier gas. MS ion source temperature was kept at 200  C and interface temperature at 230  C with solvent cut time for 2.8 min.

containing 2% H2SO4 with 100% methanol for 2 h at 80  C. Then 300 mL of 0.9% NaCl and 300 mL of hexane were added and the mixture was centrifuged at 5000 rpm for 3 min (Matthew et al., 2009). 1 mL of hexane layer was injected into a Shimadzu GCMSQP2010 SE. Separation was performed on an RTX 5MS capillary column (30 m  0.25 mm diameter, 0.25 mm film thickness). Helium was used as the carrier gas at a constant flow of 1 mL/min. Oven temperature was initially set at 90  C for 7 min, and then set at 240  C with a final hold of 10 min. MS ion source temperature was kept at 200  C and interface temperature at 250  C with solvent cut time for 3 min.

2.5. Optimization of growth medium 2.8. Laboratory scale open pond The growth medium was modified by adding cost effective supplements to select the cost effective media composition. The first supplement was the water samples of Sakarya River (SR), (Mihalıççık, Eskis¸ehir, Turkey) which is the closest river to the thermal power plant. The second supplement was the cooling water (CW) of the Thermal Power Plant. Experiments were performed with 11 different culture media compositions that were detailed below at 2.4 vvm flue gas. The compositions of culture media; (1) BG11; (2) BG11 þ 5%SR; (3) BG11 þ 5%CW; (4) BG11 þ 5% SR þ 5%CW; (5) BG11 þ 10%SR þ 10%CW; (6) BG11 þ 25%SR þ 25% CW; (7) BG11 þ 50%SR; (8) BG11 þ 50%CW; (9) 100%SR; (10) 100% CW; (11) 50%SR þ 50%CW. 2.6. Optimization of culture conditions The pH values of the culture medium were adjusted to 6, 7, 8 and 9 to determine the effect of pH on growth of microalgae under the influence of flue gas by the addition of 0.1 M H2SO4 and 0.1 M NaOH solutions accordingly. The effect of photoperiod was determined at 24:0, 16:8 and 12:12 light:dark period at 25 mmol/m2s (1750 lx) light intensity at selected optimum pH. The effect of growth promoters was evaluated with single and binary concentrations of 0.0, 0.5, 1.0 and 2.5 mg/L IAA and VO solutions. Single and binary effects of growth promoters were tested. 0, 0.5, 1 and 2.5 mg/L chloroform was tested as control. The single and binary series of experiments were performed at these concentrations (mg/L); Control group (0IAA, 0VO), 0.5IAA, 0.5IAA þ 0.5VO, 0.5IAA þ 1VO, 0.5IAA þ 2.5VO, 1IAA, 1IAA þ 0.5VO, 1IAA þ 1VO, 1IAA þ 1VO, 2.5IAA, 2.5IAA þ 0.5VO, 2.5IAA þ 1VO, 2.5IAA þ 2.5VO, 0.5VO, 1VO, 2.5VO. The effect of temperature was investigated at 25, 35 and 45  C in a rotary shaker temperature control incubator at 100 rpm (New Brunswick Scientific, Innova 40 R, Eppendorf) at optimum pH and light. The effect of biomass concentrations was investigated at 0.3, 0.4 and 0.5 g/L biomass concentrations at optimum pH, light and temperature. Cultures were incubated for 15 days, 5 days without flue gas and 10 days with flue gas at a flow rate of 2.4 vvm in pH, photoperiod, temperature and biomass experiments. The control samples were cultivated without flue gas at the same conditions with samples. Each of these experiments was performed in triplicates. Effect of flow rate was investigated at 2.4, 4.8 and 9.6 vvm flue gas at optimum pH, light, temperature and biomass concentrations.

The laboratory scale open pond was constructed out of glass with an internal diameter of 38 cm, height of 40 cm, width of 95 cm and wall thickness of 4 mm (Fig. 1). Flue gas from the gas cylinder was bubbled into the pond at a controlled flow rate. Air from airpump (LifeTech 50 Hz, India) was bubbled into the pond continuously. The surface layer of the pond was covered with a stretch-film to prevent mix with pollutants. The light sources were placed directly above the liquid surface and the on the sides. This light was supplied by a fluorescent light source at 24:0 h light/dark photoperiod. The intensity at the surface and the sides of the culture was approximately 25 mmol/m2s. Additional water was added daily due to evaporation loss to keep the volume of culture constant at approximately 25 L. The pond was operated at 35 ± 2  C with automatic heater (Tetratec HT300, Germany). 2.9. Transformation to green coal After harvesting microalgae by evaporation and precipitation from the open pond, microalgal biomass was dried by using dry weight method that was detailed below. 1%, 5%, and 10% dried biomass of microalgae were mixed with coal powder. Also, 1%, 5%, and 10% wet biomass of microalgae were mixed with coal. The coal samples were done by adopting standard methods and ground to 200 microns sizes for subsequent analysis. Coal samples without microalgae were used as control group. Green coal (coal þ microalgae) and coal (coal without microalgae) were analyzed. The carbon and total sulfur were estimated using a carbon/sulphur analyzer (ELTRA Carbon/Sulfur Analyzer CS-580, Germany). The calorific values were determined by using Isoperibol Calorimeter (LECO AC500, Germany). The total moisture was determined by using standard methods elsewhere ASTM D 3302e07, the ash content was determined by ASTM D 3174e04, the volatile matter was determined by ASTM D 3175e07, the gross calorific value was determined by ASTM D 5865e07 and ISO 1928:2009. Coal samples were analyzed in two forms: (1) air-dried basis, and (2) dry basis which were dried at 105  C at 2 h. The major and trace element analyses of the control coal and green coal samples were performed using Energy Dispersive X-Ray Fluorescence Spectrometer (ED-XRF), Shimadzu. ED-XRF instrument was calibrated using reference materials (standards) of Shimadzu. The analyses were performed with 4 g powdered coal which was dried 12 h at 110  C. The analytical results of the ED-XRF were given in dry coal basis. 2.10. Analytical methods

2.7. Fatty acid methyl esters analysis At the end of the incubation period microalgal cultures were centrifuged at 5000 rpm for 10 min. The pellets were methylesterified by shaking 750 rpm with 1200 mL extraction buffer

The chlorophyll concentrations were determined according to the method developed by Porra et al. (1989) at 646.6 nm for chlorophyll a and 663.6 nm chlorophyll b. The chlorophyll concentrations were expressed in mg of chlorophyll per milliliter.

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100% BG11

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sample

BG11 + 5% SR

BG11 + 5% SR + 5% PPW

BG11 + 5% PPW

X (g/L)

2 1.5 1 0.5 0

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2.5 BG11 + 5% SR + 5% PPW

X (g/L)

2

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BG11 + 50% SR

BG11 + 25% SR + 25% PPW

1.5 1 0.5 0

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2.5

X (g/L)

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50% SR + 50% PPW

100% PPW

100% SR

BG11 + 50% PPW

1.5 1 0.5 0

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7

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12

14

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7

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12

14

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t (day)

Fig. 1. The effect of culture media composition on flue gas removal of Scenedesmus sp. (T: 25 ± 2  C, illumination: 25 mmol/m2s, flow rate: 2.4 vvm, pH: 8, incubation time:17 days).

Cell growth levels of microorganisms was determined by measuring optic density, dried cell mass and specific growth rate parameters for any set of growth conditions. Optic density was measured at 600 nm with the spectrophotometer. The dried cell mass was saved by the measurement of pellets, which were dried overnight at 80  C (J.R Selecta Digitheat model sterilizator) after centrifugation (3421 g ¼ 5000 rpm for 100 ). Specific growth rate (m) was calculated according to the Eq (1) (Ip and Chen, 2005);

m¼

lnX2  lnX1 t2  t1

(1)

where X2 and X1: dry cell weight concentrations (g/L) at time t2 and t1, respectively. Maximum biomass productivity was calculated according to the Eq (2);

Pmax ¼

X  X0 t  t0

(2)

where X: final and X0: initial biomass concentrations (g/L), t: final and t0: initial time of the culture. The CO2 biofixation rate F (g/d) was calculated from the Eq (3), as described and used by Cheah et al. (2015), Pegallapati and Nirmalakhandan (2013) and Yadav et al. (2015).

F ¼ aPx V

(3)

where a: 1.833 g CO2, Px: productivity, V: the culture volume. Scanning electron microscopy (SEM, Quanta SEM 400, FEI, USA) was used to observe the morphology of Scenedesmus sp. as described above (Balusamy et al., 2015). All of the experiments were performed in triplicate and significant differences among experiments were compared by descriptive statistics (±S.E.). The standard error of data was calculated according to the Eq (4) formulated by Kenney and Keeping (1951); where s represents the square root of the estimated error variance of the quantity.

SE ¼ √ s2

(4)

3. Results and discussion Selection of appropriate microalgal strains is an important step for CO2 fixation, lipid potential and biomass productivity (Bhola et al., 2014). The flue gas resistant microalga was isolated from the water supply near the coal fired power plant. New microalgal isolate was identified as Scenedesmus sp. by 18 S rRNA sequencing. 3.1. Growth profile of Scenedesmus sp. with flue gas in batch system The changes in dry weight is presented in Fig 1 starting with different media compositions at the same growth conditions. After 17 days of incubation, maximum biomass was obtained in BG11 þ 25%SR þ 25%CW as 1.84 g/L, 33.33% higher than the control. On the other hand biomass amount of samples were lower than controls in BG11, BG11 þ 5%SR þ 5%CW, BG11 þ 10%SR þ 10%CW, BG11 þ 50%CW and 100%SR media. The biomass amount of cells obtained in BG11 þ 5%SR media was 5.88% higher than control. On the other hand biomass amount of samples obtained in 50% SR þ 50%CW was 40% higher than control, but the highest biomass concentration was 0.63 g/L, which is three times lower than biomass concentration obtained in BG11 þ 25%SR þ 25%CW. Therefore, optimum media was selected as BG11 þ 25%SR þ 25%CW for further experiments. Use of wastewater media also indicates that, this process can be cost effective when scaled up. The changes in the dry weight obtained at pH ranges from 6 to 9 were presented in Fig. 2a. As can be seen from Fig. 2a, flue gas improved the growth rates up to pH 8 when compared with control group. Biomass concentration of samples was 3.17% lower than control culture at pH 6 and 4.95% higher at pH 7. When compared with control culture, the maximum growth was obtained at pH 8 as

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Fig. 2. The effect of pH (a), photoperiod (b), outdoor temperature (c), initial biomass concentrations (d), flue gas flow rate (e), SEM micrographs without flue gas (f) and with flue gas (g) on flue gas removal of Scenedesmus sp. (h) GCeMS fatty acid methyl esters black is control, pink is after flue gas treatment (T: 25 ± 2  C, illumination: 25 mmol/m2s, flow rate: 2.4 vvm, pH: 8, incubation time:14 days). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

1.632 g/L. This was 40.69% higher than the control culture. Therefore, optimum pH was selected as pH 8. When starting with the same light intensity, temperature levels and pH 8, the changes in the dry weight obtained at different photoperiods was presented in Fig 2b. Same dry weight yields have been achieved at 12:12 h and 16:8 h light:dark period. The maximum growth was observed at 24:00 h light:dark photoperiod. A comparative study was carried out with respect to the growth profile of Scenedesmus sp. using flue gas. Effect of growth promoters were tested in BG11þ 25% SR þ 25% CW culture media. As seen in Table 1, binary effects of growth promoters increased the biomass concentration of Scenedesmus sp. Maximum growth was obtained at 1 mg/L IAA þ 0.5 mg/L VO concentration as 1.759 g/L. This was 17.89% higher than the control group. Optimum concentration of growth promoters was selected as 1 mg/L IAA þ 0.5 mg/L VO. In previous studies some of the growth promoters such as sodium bicarbonate (Tas¸tan et al., 2012), triacontanol and salicylic acid (Tas¸tan et al., 2013) have been utilized to resist microalgae against toxic components of flue gas. These promoters increased the growth rate of microalgae. In another study, amine based and carbonate based methods have been developed for the integration of flue-gas from power plants with algae production for the capture and utilization of CO2 (Schipper et al., 2013). In the present study IAA and VO increased resistance of microalgae cultivated in flue gas and thus increased the microalgal biomass rates in flue gas treated cells compared to control cells.

As presented in Fig. 2c., the growth of Scenedesmus sp. increased up to 1.925 g/L when temperature was increased from 25  C to 35  C. This was 9.75% higher than control culture. There was no microalgal growth was observed at 45  C. Therefore optimum temperature was selected as 35  C. Changes in dry weight concentrations at different initial biomass concentrations were presented in Fig 2d. The highest dry weight was obtained at 0.1 g/L initial biomass concentration. The maximum biomass was achieved at the initial concentration of 1.925 g/L. The minimum biomass was obtained at the minimum initial biomass concentration (0.868 g/L). The last step for optimization of the biomass production was increasing flue gas flow rates. As shown in Fig 2e. Scenedesmus sp. biomass concentration increased by increasing flow rates. The highest flow rate was 9.6 vvm and the biomass produced at this rate was 2.262 g/L. It was 25% higher than of control culture. BG11þ 25% SR þ 25% CW media, pH 8, 24:00 h light:dark photoperiod, 1 mg/L IAA þ 0.5 mg/L VO growth promoters concentration, 35  C, 0.1 g/L biomass concentration and 9.6 vvm of flue gas were selected as the optimum concentrations. 3.2. Growth profile of Scenedesmus sp. with flue gas in open pond The obtained biomass increased to 0.6 g/L at the end of the 15th days in open pond starting with 0.1 g/L initial biomass concentrations and at the all selected optimum conditions (BG11 þ 25%

Table 1 Effect of growth factors 3-Indoleacetic acid (IAA) and Viburnum opulus (VO) on flue gas removal of Scenedesmus sp. (T: 25 ± 2  C, illumination: 25 mmol/m2s, flow rate: 2.4 vvm, pH: 8, incubation time:14 days). VO (mg/L) 0 IAA (mg/L)

0 0.5 1 2.5

1.492 1.220 1.436 1.500

0.5 ± ± ± ±

0.074 0.026 0.051 0.078

1.332 1.570 1.759 1.416

1 ± ± ± ±

0.005 0.078 0.072 0.005

1.360 1.458 1.528 1.598

2.5 ± ± ± ±

0.021 0.035 0.095 0.013

1.624 1.514 1.598 1.566

± ± ± ±

0.061 0.081 0.106 0.080

1091

SR þ 25%CW media, pH 8, 24:00 h light:dark photoperiod, 1 mg/ LIAA þ 0.5 mg/LVO growth promoters concentration, 35  C, and 9.6 vvm of flue gas). Maximum productivity (Pmax) was 0.033 g/L/d. As shown in Fig. 2f and g, SEM micrographs of Scenedesmus sp. revealed that flue gas is very toxic to cells. The cells have been deformed by the flue gas. A 40 cm deep, gas-bubbled open pond using 9.6 vvm of flue gas had six-times higher productivity levels. This could help microalgal flue gas utilizing in industrial systems become feasible. The growth of Scenedesmus sp. in open pond system by bubbling with 9.6 vvm flue gas gave comparable to what volumetric biomass productivity and CO2 fixation rate (Table 3). Maximum biomass concentration and biomass productivity of 2.262 g/L and 0.154 g/L/ d, respectively, were obtained using 9.6 vvm flue gas for 0.1 L working volume of microalgal culture. The greater CO2 fixation rate achieved in 25 L open pond could be due to increased working volume. The maximum CO2 fixation rate was 1512.22 mg CO2/day in the open pond (Supplementary Data 3). 3.3. Proximate analyses adb: air-dried basis, db: dry basis, VM: Volatile Matter, FC: Fixed C, TS: Total Sulfur, SA: Sulfur in Ash, TC: Top Calorific Value, BC: Bottom Calorific Value.

9.74 ± 1.77 11.34 ± 2.05 2.06 ± 0.04 2.39 ± 0.05 0.90 ± 0.04 1.04 ± 0.05 1809 ± 31.9 2106 ± 37.0 1601 ± 30.8 1963 ± 36.2 8.21 ± 0.97 9.64 ± 1.13 2.01 ± 0.05 2.36 ± 0.06 0.89 ± 0.02 1.04 ± 0.03 1795 ± 168 2109 ± 201 1584 ± 164 1966 ± 197 9.90 ± 0.85 11.66 ± 1.01 1.92 ± 0.04 2.27 ± 0.05 0.82 ± 0.06 0.97 ± 0.08 1786 ± 46.3 2103 ± 56.0 1568 ± 47.7 1953 ± 57.4 48.43 ± 0,32 56.39 ± 0,43 27.70 ± 1,95 32.25 ± 2.29 48.66 ± 1.06 57.16 ± 1.13 28.25 ± 1.83 33.19 ± 2.20 47.02 ± 0.49 55.36 ± 0.55 28.00 ± 0.39 32.97 ± 0.45 1% 14.11 ± 0.16 0 5% 14.86 ± 0.18 0 10% 15.07 ± 0.15 0 Green coal Wet biomass

1583 1785 0 13.49

48.96

56.59

25.94

29.99

11.60

13.41

1.86

2.15

0.91

1.05

2063

adb

1923

46.22 ± 0.24 54.81 ± 0.26 25.43 ± 0 30.15 ± 0.01 12.68 ± 0.22 15.03 ± 0.26 1.88 ± 0 2.23 ± 0 0.84 ± 0.01 1.00 ± 0 1893 ± 19.6 2244 ± 22.5 1669 ± 20.2 2091 ± 23.7 47.50 ± 0.53 56.10 ± 0.56 26.16 ± 0.19 30.89 ± 0.26 11.01 ± 0.24 13.00 ± 0.30 1.82 ± 0 2.15 ± 0 0.93 ± 0.03 1.11 ± 0.03 1877 ± 28.3 2217 ± 35.8 1660 ± 25.9 2069 ± 33.5 44.72 ± 0.42 52.78 ± 0.48 27.84 ± 0.21 32.86 ± 0.25 12.16 ± 0.19 14.36 ± 0.23 1.82 ± 0.02 2.17 ± 0.03 0.83 ± 0.01 0.98 ± 0.02 2205 ± 39.8 2603 ± 47.3 1980 ± 38.7 2445 ± 46.2 1% 15.66 ± 0.02 0 5% 15.33 ± 0.09 0 10% 15.26 ± 0.02 0 Green coal Dry biomass

TC kcal/kg

adb adb adb adb db adb

VM %

db Ash %

db adb adb

Moisture %

Table 2 The proximate analysis of control coal and green coal with dry and wet biomass mixture.

FC %

db

TS %

db

SA %

db

db

BC kcal/kg

db 0% Control

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The proximate analyses including moisture, ash, volatile matter, stable carbon, total sulfur contents, sulfur contents in ash and top and bottom calorific value were made on control coal and green coal samples with wet or dry biomass. Average values of the proximate analysis results are given in Table 2. The moisture content of the green coal samples with dry biomass was higher than the control due to the biomass of microalgae. Therefore, green coal samples with 1%, 5%, and 10% dry biomass have approximately 15.00% moisture. The ash content of the air-dried basis control sample was 48.96% and was 56.59% in dry control samples. The green coal samples with 10% dry biomass have higher volatile matter contents. This can be related to the assimilated C content of microalgae in flue gas and microalgal biomass additive. In another study the high volatile matter content of coal has been related to the carbonate minerals and fossil shells which are found in large amounts in the samples (Sutcu and Karayigit, 2015). The average fixed carbon contents were higher in green coal samples with dry biomass. The average total sulfur contents of the green coal samples with dry biomass and control samples were the same. There was no significant change. In another study, the average total sulfur contents of the open-pit mine and borehole samples were respectively, 3.11% and 3.71% in air-dried basis (Sutcu and Karayigit, 2015). In our study the total sulfur contents of control samples were lower than their findings. Green coal samples with 10% dry biomass increased the calorific value of coal 23.56% times than of control samples. This value was 6.05% higher in 1% dry biomass samples. The maximum increase of calorific value was obtained at dry basis green coal samples with 10% dry biomass. The calorific value was 2063 kcal/kg in control and increased to 2603 kcal/kg in green coal samples with dry biomass. This means that 26.14% calorific increase was obtained in green coal samples with dry biomass. The moisture content of the green coal samples with wet biomass were lower than green coal samples with dry biomass. The ash content of the air-dried basis control sample was 48.96% and was 56.59% of dry basis control samples. These contents were close to air-dried basis and dry basis green coal samples with wet biomass. The average volatile matter contents of air-dried basis and dry basis green coal samples with dry biomass were higher than green coal with wet biomass samples. The average fixed carbon contents of air-dried basis and dry basis green coal samples with wet biomass were greater than green coal samples with dry biomass. Daood et al. (2014a) used a mixture of iron, aluminum, calcium

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Table 3 The fatty acid methyl esters profile of Scenedesmus sp. with control and with flue gas exposed cultures. Scenedesmus sp. with flue gas

Peak

Name

Scenedesmus sp. control RT

%Area

RT

%Area

13 19 23 28 29 30 31 35 36 44 45 46 47 48 49 50 51 52 53 54 56 58 61 62 63 64

Nonanedioic acid, dimethyl ester Tetradecanoic acid, methyl ester (CAS) Pentadecanoic asid, methyl ester Methyl 4,7,10,13-hexadecatetraenoate 9,12-Octadecadienoic acid (Z,Z)-, methyl ester (CAS) 9,12,15 -Octadecatrienoic acid, methyl ester, (Z,Z,Z)9- Hexadecenoic acid, methyl ester,(Z)9-Hexadecenoic acid, eicosyl ester,(Z)Hexadecanoic acid, methyl ester (CAS) Heptadecanoic acid, methyl ester (CAS) 2(3H)-Furanone, 5-hepthylhydro-(CAS) 2(3H)-Furanone, 5-hepthylhydroMethyl gamma,linolenoate n-Nonadecanol-1 Methyl stearidonate 9,12-Octadecadienoic acid (Z,Z)-, methyl ester 6-Octadecenoic acid, methyl ester,(Z)8,11,14-Docosatrienoic acid, methyl ester 9-Octodecenoic acid, methyl ester (CAS) Methyl stearate 1,3-Dioxolane-2,2-diethanol Octadecanoic acid, 3-hydroxy-, methyl ester cis-13-Eicosenoic acid, methyl ester Eicosenoic acid, methyl ester (CAS) Docosanoic acid methyl ester (CAS) _ (2-ethylhexyl) phthalate BIs

23.737 29.028 31.816 33.433 33.645 33.823 e e 34.518 36.988 37.275 37.981 38.296 38.388 38.465 38.697 38.862 e 38.947 39.405 e 42.893 43.358 43.908 e e

0.1 0.37 0.25 1.8 2.53 8.19 e e 20.57 0.32 3.78 7.42 1.36 2.02 1.44 11.5 11.5 e 0.24 3.28 e 0.22 0.1 0.13 e e

e 29.029 31.822 33.440 33.648 33.930 33.929 34.379 34.532 36.989 37.283 37.993 38.304 38.401 38.472 38.708 e 38.881 38.960 39.427 40.640 42.901 e 43.910 48.889 49.632

e 0.49 0.26 2.09 1.19 6.39 0.49 1.25 19.52 0.25 4.11 7.89 1.22 3.16 1.39 8.53 e 21.4 0.94 5.80 1.03 0.39 e 0.17 0.18 1.98

RT: Retention Time.

and silicon oxides additive and they succeeded to reduce NO emissions, improve the quality of fly ash with less carbon and finer particle size. We showed that microalgal biomass produced with flue gas can be used as novel coal additive matter for the first time. The average total sulfur contents of air-dried basis and dry basis green coal samples with wet biomass were higher than green coal samples with dry biomass. These contents were also higher than control samples. There were no important calorific value increases in air-dried basis and dry basis green coal samples with wet biomass compared with control and green coal samples with dry biomass. The average calorific values of green coal samples with wet biomass were close to control coal samples. The maximum increase was obtained at green coal samples with 5% wet biomass as 2.23%. The effect of coal burning additives due to its catalysis mainly related to the burning of carbons in the coal. The coal burning additives have the accelerating effect of carbons on the combustion of the coal (Zhang et al., 1997). The influence of the additives on coal is ndez related to the volatile matter content of the additive (Ferna et al., 2009). All of the methyl esters obtained as higher than 1% by GCeMS were taken into consideration and presented in Table 3. Fig. 2h also shows the GCeMS chromatograms of the control group (black) and after flue gas treatment (pink). As seen in Table 3 GCeMS results were different between Scenedesmus sp. control group and flue gas group. Various methyl esters were obtained in Scenedesmus sp. flue gas group such as; 9- Hexadecenoic acid, methyl ester, (Z)-; 9Hexadecenoic acid, eicosyl ester,(Z)-; 8,11,14-Docosatrienoic acid, methyl ester; Docosanoic acid methyl ester (CAS). On the other hand, some of the methyl esters obtained in the control group could not be seen in flue gas group such as; Nonanedioic acid, dimethyl ester; 6-Octadecenoic acid, methyl ester,(Z)-; cis-13-Eicosenoic acid, methyl ester. In another study FAME compositions of Chlorella sp. KR-1 under autotrophic and mixotrophic culture conditions revealed that the maximum composts were Linoleate and Palmitate

(Praveenkumar et al., 2014). It should be noted that, in the present results, the treatment of flue gas could significantly improve algal lipid productivity by increasing the biomass productivity 1.5 times higher than control culture. Praveenkumar et al. (2014) have noted that the glucose and air feedings with the addition of coal-fired flue gas improved algal lipid productivity by increasing both the intercellular lipid content and the biomass productivity. 3.4. Element analyses As seen in Table 4 the major elements are positively correlated with each other. In the samples, Ca, Fe and Si are commonly observed. According to the ED-XRF results, the Ca concentrations were higher than the other major elements in the all coal samples. The average Ca, Fe, Si and S concentrations were 35.74%, 30.21%, 18.99%, and 6.13% in control coal samples, respectively. K, Ti, Sr, Mn, Ni, Cr, Cu, Zr, V and Zn concentrations are lower amounts. The Ca and other element concentrations of the green coal samples with 1% dry biomass were similar to control coal samples. On the other hand, the Ca, Fe and S concentrations of the green coal samples with 10% dry biomass decreased while Si concentrations increased (Table 4). According to the green coal samples with 10% dry biomass data, these variations were a weak correlation between Ca and ash content of the samples. The ash contents and Ca concentrations of green coal samples with dry biomass were lower than control and wet biomass samples. On the other hand, the FeeSi and FeeNi relationships reveal that Si and Ni concentrations decreased with decreasing Fe concentrations. As stated before the Ca concentration probably was related to organic matter in the coal samples (Sutcu and Karayigit, 2015). Therefore green coal samples with wet biomass had the highest Ca concentrations. As seen in Table 4 Ca concentrations increased when wet biomass concentrations increased from 1% to 10%. Fe concentrations of green coal samples with wet biomass were similar to control coal samples. Although, there is no significant

1% 36.33 ± 0.76 30.33 ± 1.22 19.24 ± 0.55 5.65 ± 0.03 4.06 ± 0.03 2.13 ± 0.07 0.82 ± 0.04 0.45 ± 0.02 0.25 ± 0.04 0.16 ± 0.01 0.14 ± 0.01 0.13 ± 0.01 0.12 ± 0.01 0.11 ± 0.01 0.08 ± 0.01 e 5% 35.50 ± 0.43 29.99 ± 0.22 20.27 ± 0.37 5.85 ± 0.26 4.04 ± 0.08 2.05 ± 0.01 0.74 ± 0.01 0.46 ± 0.02 0.29 ± 0.01 0.16 ± 0.01 0.16 ± 0.01 0.13 ± 0.01 0.11 ± 0.01 0.17 ± 0.04 0.08 ± 0.01 e 10% 35.75 ± 0.21 30.33 ± 0.61 19.59 ± 0.38 5.78 ± 0.04 3.99 ± 0.14 2.09 ± 0.10 0.82 ± 0.12 0.48 ± 0.04 0.27 ± 0.02 0.16 ± 0.01 0.15 ± 0.01 0.12 ± 0.01 0.13 ± 0.01 0.26 ± 0.18 0.08 ± 0.01 e

1% 37.98 ± 0.45 29.87 ± 0.76 18.69 ± 0.35 5.40 ± 0.09 3.88 ± 0.09 2.08 ± 0.01 0.69 ± 0.12 0.45 ± 0.01 0.26 ± 0.01 0.16 ± 0.01 0.14 ± 0.01 0.13 ± 0.02 0.10 ± 0.01 0.09 ± 0.01 0.08 ± 0.01 e 5% 38.91 ± 0.13 30.01 ± 0.17 17.31 ± 0.44 5.51 ± 0.20 3.81 ± 0.05 2.15 ± 0.05 0.85 ± 0.11 0.48 ± 0.01 0.26 ± 0.02 0.16 ± 0.01 0.15 ± 0.01 0.14 ± 0.01 0.10 ± 0.01 0.09 ± 0.01 0.07 ± 0.01 e 10% 39.01 ± 0.45 30.07 ± 0.84 17.58 ± 0.45 5.61 ± 0.15 3.79 ± 0.32 1.94 ± 0.09 0.70 ± 0.06 0.48 ± 0.07 0.20 ± 0.01 0.13 ± 0.01 0.15 ± 0.01 0.10 ± 0.01 0.08 ± 0 0.09 ± 0.01 0.07 ± 0.01 e

Green coal with dry biomass

Green coal with wet biomass

2.20 ± 0.10 69.12 ± 1.94

7.00 ± 0.36

1.21 ± 0.19 5.79 ± 0.32 8.28 ± 0.27 0

0.55 ± 0.03 2.53 ± 0.16 0

0

0.36 ± 0.01 0

0

2.94 ± 0.18 0 e

P% Rb% Zn% V% Zr% Cu% Cr% Ni% Mn% Sr% Ti% K% S% Si% Fe% Ca%

Scenedesmus sp.

Control coal

Table 4 ED-XRF analysis results of the samples.

0% 35.74 ± 0.66 30.21 ± 0.74 18.99 ± 0.16 6.13 ± 0.18 4.00 ± 0.09 2.15 ± 0.01 0.82 ± 0.09 0.50 ± 0.01 0.28 ± 0.02 0.16 ± 0.01 0.16 ± 0.01 0.14 ± 0.01 0.11 ± 0.01 0.09 ± 0.01 0.08 ± 0.01 e

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correlation between the ash content and Sr, Mn, Ni, Cr, Cu, Zr, V, Zn and Rb elements (Table 4), they show similar variations with ash content within the samples. The ED-XRF analyses and the relationship between Ca, other elements and ash suggest that the green coal samples with dry biomass are effective coal additive matters. The microalgae-based coal additive, which is 100% environmentally friendly unlike other coal additives which uses chemicals, can increase the product efficiency of thermal power plants. This additive can penetrate inside the coal and can enhance the burning by the help of microalgal enzymes, lipids and carotenoids, but further studies are needed. 4. Conclusions Microalgae are the most promising green energy resources in the future. This study has revealed a very different and novel usage perspective of microalgae. Based on our present laboratory scale investigations, green coal has appeared to be a promising technique for high calorific coal beneficiation technique. The coal with 8.7% lower ash and 26.17% higher calorific value, termed as ‘green coal’ may be produced by this process. Our study showed the maximum biomass of 2.262 g/L, which was produced by lowest culture media consumption, minimum treatment time, highest temperature and highest flow rate. The use of microalgal biomass as green coal is a novel area in the literature. It has the potential to replace other conventional coal additive and cleaning methods in terms of less energy, less chemical treatment, less culture media composition and may be used for large-scale trials with other coal additives around the world. Patent pending number 2015-TP101-613. Acknowledgements The authors are grateful to Republic of Turkey Ministry of Science, Industry and Technology as a part of the “Techno-Initiative Capital Support Program” Grant Number: 025648 and The Scientific _ and Technological Research Council of Turkey (TÜBITAK) for financial support. The authors also wish to express their gratitude  Alhan and S¸evda Akyürek for technical to Hatice Elmas Bas¸bug support and to reviewers for their valuable comments. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jclepro.2016.06.053. References Ashokkumar, V., Agila, E., Salam, Z., Ponraj, M., Md Din, M.F., Ani, F.N., 2014. A study on large scale cultivation of Microcystis aeruginosa under open raceway pond at semi-continuous mode for biodiesel production. Bioresour. Technol. 172, 186e193. Balusamy, B., Tas¸tan, B.E., Ergen, S.F., Uyar, T., Tekinay, T., 2015. Toxicity of lanthanum oxide (La2O3) nanoparticles in aquatic environments. Env. Sci. Process. Impact 17, 1265e1270. Bhola, V., Swalaha, F., Kumar, R.R., Singh, M., Bux, F., 2014. Overview of the potential of microalgae for CO2 sequestration. Int. J. Environ. Sci. Tech. 11, 2103e2118. Boruff, B.J., Moheimani, N.R., Borowitzka, M.A., 2015. Identifying locations for largescale microalgae cultivation in Western Australia: a GIS approach. Appl. Energy 149, 379e391. Chagas, A.L., Rios, A.O., Jarenkow, A., Marcílio, N.R., Ayub, M.A.Z., Rech, R., 2015. Production of carotenoids and lipids by Dunaliella tertiolecta using CO2 from beer fermentation. Process Biochem. 50 (6), 981e988. Cheah, W.Y., Show, P.L., Chang, J.S., Ling, T.C., Juan, J.C., 2015. Biosequestration of atmospheric CO2 and flue gas-containing CO2 by microalgae. Bioresour. Technol. 184, 190e201.

1094

B.E. Tas¸tan, T. Tekinay / Journal of Cleaner Production 133 (2016) 1086e1094

Daood, S.S., Ord, G., Wilkinson, T., Nimmo, W., 2014a. Fuel additive technology e NOx reduction, combustion efficiency and fly ash improvement for coal fired power stations. Fuel 134, 293e306. Daood, S.S., Ord, G., Wilkinson, T., Nimmo, W., 2014b. Investigation of the influence of metallic fuel improvers on coal combustion/pyrolysis. Energy Fuel 28, 1515e1523. Das, P., Thaher, M.I., Hakim, M.A.Q.M.A., Al-Jabri, H.M.S.J., 2015. Sustainable production of toxin free marine microalgae biomass as fish feed in large scale open system in the Qatari desert. Bioresour. Technol. 192, 97e104. Doucha, J., Straka, F., Livansky, K., 2005. Utilization of flue gas for cultivation of microalgae (Chlorella sp.) in an outdoor open thin-layer photobioreactor. J. Appl. Phycol. 17 (5), 403e412. ndez, A.M., Barriocanal, C., Díez, M.A., Alvarez, R., 2009. Influence of additives Ferna of various origins on thermoplastic properties of coal. Fuel 88, 2365e2372. Ip, P.F., Chen, F., 2005. Production of astaxanthin by the green microalga Chlorella zofingiensis in the dark. Process Biochem. 40, 733e738. Kenney, J.F., Keeping, E.S., 1951. Standard Error of the Mean in Mathematics of Statistics, Pt. 2, second ed. Van Nostrand 110, Princeton, NJ, pp. 132e133. Laamanen, C.A., Shang, H., Ross, G.M., Scott, J.A., 2014. A model for utilizing industrial off-gas to support microalgae cultivation for biodiesel in cold climates. Energy Convers. Manage 88, 476e483. Lee, J.S., Kim, D.K., Lee, J.P., Park, S.C., Koh, J.H., Cho, H.S., Kim, S.W., 2002. Effects of SO2 and NO on growth of Chlorella sp. KR-1. Bioresour. Technol. 82, 1e4. Matthew, T., Zhou, W., Rupprecht, J., Lim, L., Thomas-Hall, S.R., Doebbe, A., Kruse, O., Hankamer, B., Marx, U.C., Smith, S.M., Schenk, P.M., 2009. The metabolome of Chlamydomonas reinhardtii following Induction of anaerobic H2 production by sulfur depletion. J. Biol. Chem. 284 (35), 23415e23425. Pegallapati, A.K., Nirmalakhandan, N., 2013. Internally illuminated photobioreactor for algal cultivation under carbon dioxide-supplementation: performance evaluation. Renew. Energ 56, 129e135. Porra, R.J., Thompson, W.A., Kreidemann, P.E., 1989. Determination of accurate extinction coefficients and simultaneous equations for assaying chlorophylls a and b extracted with four different solvents: verification of the concentration of chlorophyll standards by atomic absorption spectroscopy. Biochim. Biophys. Acta 975, 384e394. Pragya, N., Pandey, K.K., 2016. Life cycle assessment of green diesel production from microalgae. Renew. Energ 86, 623e632. Praveenkumar, R., Kim, B., Choi, E., Lee, K., Park, J.Y., Lee, J.S., Lee, Y.C., Oh, Y.K., 2014. Improved biomass and lipid production in a mixotrophic culture of Chlorella sp. KR-1 with addition of coal-fired flue-gas. Bioresour. Technol. 171, 500e505.

Ringsmuth, A.K., Landsberg, M.J., Hankamer, B., 2016. Can photosynthesis enable a global transition from fossil fuels to solar fuels, to mitigate climate change and fuel-supply limitations? Renew. Sust. Energy Rev. 62, 134e163. Rippka, R., 1998. Isolation and purification of cyanobacteria. Methods Enzym. 167, 3e27. Schipper, K., van der Gijp, S., van der Stel, R., Goetheer, E., 2013. New methodologies for the integration of power plants with algae ponds. Energy Procedia 37, 6687e6695. Sherwood, A.R., Presting, G.G., 2007. Unıversal primers amplıfy a 23S rDNA plastid marker in eukaryotıc algae and cyanobacterıa. Phycol. Soc. Amer. 43, 605e608. Sowa, J.M., Fletcher, T.H., 2011. Investigation of an iron-based additive on coal pyrolysis and char oxidation at high heating rates. Fuel Process. Technol. 92, 2211e2218. Sun, Z., Zhang, D., Yan, C., Cong, W., Lu, Y., 2015. Promotion of microalgal biomass production and efficient use of CO2 from flue gas by monoethanolamine. J. Chem. Technol. Biotechnol. 90 (4), 730e738. Sutcu, E.C., Karayigit, A.I., 2015. Mineral matter, major and trace element content of the Afs¸ineElbistan coals, Kahramanmaras¸, Turkey. Int. J. Coal Geol. 144e145, 111e129. € nmez, G., 2012. SO2 and NO2 tolerance of Tas¸tan, B.E., Duygu, E., Atakol, O., Do microalgae with the help of some growth stimulators. Energy Convers. Manag. 64, 28e34. _ €nmez, G., 2013. Utilization of LPG and gasoline Tas¸tan, B.E., Duygu, E., Ilbas ¸ , M., Do engine exhaust emissions by microalgae. J. Hazard. Mater. 246e247, 173e180. Tsubouchi, N., Ohtsuka, Y., 2008. Nitrogen chemistry in coal pyrolysis: catalytic roles of metal cations in secondary reactions of volatile nitrogen and char nitrogen. Fuel Process. Technol. 89, 379e390. Wei, B., Wang, X., Tan, H., Zhang, L., Wang, Y., Wang, Z., 2016. Effect of siliconealuminum additives on ash fusion and ash mineral conversion of Xinjiang high-sodium coal. Fuel 181, 1224e1229. Yadav, G., Karemore, A., Dash, S.K., Sen, R., 2015. Performance evaluation of a green process for microalgal CO2 sequestration in closed photobioreactor using flue gas generated in-situ. Bioresour. Technol. 191, 399e406. Zhang, L.M., Tan, Z.C., Wang, S.D., Wu, D.Y., 1997. Combustion calorimetrie and thermogravimetric studies of graphite and coals doped with a coal-burning additive. Thermochim. Acta 299, 13e17. Zhao, B., Su, Y., Zhang, Y., Cui, G., 2015. Carbon dioxide fixation and biomass production from combustion flue gas using energy microalgae. Energy 89, 347e357.