- Email: [email protected]
Aminoclay-induced humic acid flocculation for efficient harvesting of oleaginous Chlorella sp.
Bioresource Technology 153 (2014) 365–369
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Aminoclay-induced humic acid flocculation for efficient harvesting of oleaginous Chlorella sp. Young-Chul Lee a, Seo Yeong Oh a, Hyun Uk Lee b, Bohwa Kim c, So Yeun Lee c, Moon-Hee Choi d, Go-Woon Lee e, Ji-Yeon Park c, You-Kwan Oh c, Taegong Ryu f, Young-Kyu Han g, Kang-Sup Chung f,⇑, Yun Suk Huh a,⇑ a
Department of Biological Engineering, College of Engineering, Inha University, Incheon 402-751, Republic of Korea Division of Materials Science, Korea Basic Science Institute (KBSI), Daejeon 305-333, Republic of Korea c Clean Fuel Department, Korea Institute of Energy Research (KIER), 152 Gajeong-ro, Yuseong-gu, Daejeon 305-343, Republic of Korea d Department of Beauty and Cosmetology, Graduate School of Industry, Chosun University, Gwangju 501-759, Republic of Korea e Testing and Certification Center, Korea Institute of Energy Research (KIER), 152 Gajeong-ro, Yuseong-gu, Daejeon 305-343, Republic of Korea f Rare Metals Research Center, Korea Institute of Geoscience & Mineral Resources, Daejeon 305-350, Republic of Korea g Department of Energy and Materials Engineering, Dongguk University-Seoul, Seoul 100-715, Republic of Korea b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Aminoclay-induced humic acid
flocculation (AC-HA) was investigated. AC-HA showed for efficient harvesting of oleaginous microalgae. AC-HA played a type of network in capturing microalgal cells. Flocculation approach can be utilized for microalgae flocculation.
a r t i c l e
i n f o
Article history: Received 14 October 2013 Received in revised form 25 November 2013 Accepted 30 November 2013 Available online 15 December 2013 Keywords: Aminoclay Humic acid Flocculation Microalgae Harvesting
a b s t r a c t Biofuels (biodiesel) production from oleaginous microalgae has been intensively studied for its practical applications within the microalgae-based biorefinement process. For scaled-up cultivation of microalgae in open ponds or, for further cost reduction, using wastewater, humic acids present in water-treatment systems can positively and significantly affect the harvesting of microalgae biomass. Flocculation, because of its simplicity and inexpensiveness, is considered to be an efficient approach to microalgae harvesting. Based on the reported cationic aminoclay usages for a broad spectrum of microalgae species in wide-pH regimes, aminoclay-induced humic acid flocculation at the 5 g/L aminoclay loading showed fast floc formation, approximately 100% harvesting efficiency, which was comparable to the only-aminoclay treatment at 5 g/L, indicating that the humic acid did not significantly inhibit the microalgae harvesting behavior. As for the microalgae flocculation mechanism, it is suggested that cationic nanoparticles decorated on macromolecular matters function as a type of network in capturing microalgae. Ó 2013 Elsevier Ltd. All rights reserved.
⇑ Corresponding authors. Tel.: +82 42 868 3645 (K.-S. Chung). Tel.: +82 32 860 9177; fax: +82 32 872 4046 (Y.S. Huh). E-mail addresses: [email protected] (K.-S. Chung), [email protected] (Y.S. Huh). 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.11.103
366
Y.-C. Lee et al. / Bioresource Technology 153 (2014) 365–369
1. Introduction Since 2000, microalgae-based biorefinery processes have received intensive academic attention for their practical and industrial applications (Bellou and Aggelis, 2012; Wijffels and Barbosa, 2010; Rodolfi et al., 2009; Farooq et al., 2013; Chen et al., 2011). The available resources of extracted invaluable products such as carbohydrates, proteins, and lipids (oil) from microalgae have been focused on downstream process consisted of harvesting or flocculations, lipids extraction, and re-culture (Lee et al., 2013b,c,e; Markri et al., 2011). For the downstream processes, efficient flocculation of microalgae biomass in harvesting technologies can be a reasonable approach, given the simple and inexpensive methods available for precipitation of microalgae biomass (Xu et al., 2011; Lee et al., 2012, 2013e; Farooq et al., 2013). Recently, cationic aminoclays, as synthesized by simple sol–gel processing under ambient conditions (Chaturbedy et al., 2010; Datta et al., 2010), have been investigated for their use in the destabilization of microalgal cells. Specifically, aminoclays have played unique roles not only in efficient harvesting of fresh and marine microalgae (Lee et al., 2013e; Farooq et al., 2013) but also in selective microalgal lysis of red tide species (Lee et al., 2013d). The protonated amine groups in aminoclay nanoparticles function as positively charged nanoclusters ranging in hydrodynamic diameter from 30 nm to 150 nm (Farooq et al., 2013; Lee et al., 2011a,c), thus effecting flocculation for a broad spectrum of microalgae species without altering the pH environment. Humic acid, one of the most ubiquitous forms of organic matter in water and wastewater environmental systems (Beuckels et al., 2013; Hankins et al., 2006), can significantly effect on microalgae harvesting efficiency in open-pond cultivation or, for the purposes of cost reduction, using wastewater. Previously, Lee et al. found that aminoclay is an efficient flocculant for humic acid to remove from water where humic acids inhibited between interaction of heavy metals and aminoclays (Lee et al., 2011c). These aminoclay-flocculated humic acid macromolecules, therefore, can play efficient microalgae harvesting. Interestingly, the aminoclaydecorated humic acid matrix functions as a network-like precipitant for oleaginous microalgae harvesting without any significant increase of aminoclay loading. 2. Methods See Supplementary Data, TEXT. 3. Results and discussion 3.1. HA sedimentation studies using Mg- and Fe-aminoclays HA flocculations were studied according to Mg-aminoclay and Fe-aminoclay dosages. Prior to the flocculation studies, the UV– Vis absorbances were scanned for the Mg- and Fe-aminoclays as well as the HA in aqueous solution as a function of loading with respect to time (Supplementary Data, Fig. S1). The Mg-aminoclay showed a distinct transparent property up to the concentration of 5 g/L. At the 500 nm wavelength, the absorbance intensity was nearly zero (Fig. S1a) (Lee et al., 2011a, 2013a). Contrastingly, the Fe-aminoclay, due to its intrinsic use of ferric ions for Fe-aminoclay synthesis, showed a brown color. At 0.3125 g/L, the absorbance intensity at 600 nm was also zero, but as the concentration was increased to 5 g/L, the absorbance intensity was about 0.4 (Fig. S1b). Moreover, HA also showed zero absorbance intensity at 600 nm, up to the increased loading of 12.5 mg/L (Fig. S1c). As recorded at the 600 nm wavelength, the HA flocculations by the Mg- and Fe-aminoclays as a function of their loadings were
plotted for 180 min (Fig. 1). As the Mg-aminoclay loading was increased (i.e., up to HA + Mg 3), the HA flocculation was enhanced. However, with further increases, the flocculation of HA was inhibited (Fig. 1a), due to the superior water-soluble property of aminoclay according to which cationic aminoclay nanoparticles play a surfactant role in improving the dispersion of (nano)materials in aqueous solution (Datta et al., 2010; Lee et al., 2011a). Such flocculations also were observed for the Fe-aminoclay (Fig. 1b). The higher initial intensities of the HA as flocculated by the aminoclays were related to the aggregation phenomena that arose immediately after the addition of the aminoclay solution to the HA solution. Compared to loading of Mg-aminoclay to HA, the lower loading of Fe-aminoclay showed the optimal sedimentation profiles whose optimal flocculation conditions by Mg- and Feaminoclays were determined to be HA + Mg 3 and HA + Fe 2, respectively. The equilibrium time of HA flocculation was attained at about 180 min, which is comparable to the sedimentation rate of graphene oxide (Lee et al., 2013a). The fitted plots of the sedimentation kinetics of HA + Mg 2, HA + Mg 3, HA + Mg 4, HA + Fe 1, HA + Fe 2, and HA + Fe 3 followed a pseudo first-order equation; the observed kinetic constants, plotted in Fig. S2, were, respectively, 0.0533 (r2 = 0.9094), 0.0537 (r2 = 0.8901), 0.0351 (r2 = 0.7406), 0.0237 (r2 = 0.9088), 0.0524 (r2 = 0.9055), and 0.0155 (r2 = 0.7087) of the observed flocculation constants (abs./min). In general, the Mg-aminoclay showed fast floc formation than the Fe-aminoclay, which might be attributable to the former’s smaller size (30 nm of average hydrodynamic diameter) (Farooq et al., 2013; Lee et al., 2011a,c) compared with that of the latter (100 nm of average hydrodynamic diameter) (Lee et al., 2011a, 2013a). Accordingly, among the Mg-aminoclay treatments, HA + Mg 2 showed the fast separation and most efficient flocculation. 3.2. Characterization of HA flocculants by aminoclays For checking of the amorphous structure and impurities and further confirmation of the organo-functional groups, Fig. S3 plots the XRD patterns of confirms and FT-IR spectra for HA, aminoclay, and HA flocculants by aminoclays. In Fig. S3a, both the HA and the aminoclays show amorphous phases. Initially, the Mg- and Fe-aminoclays revealed d-spacing d001 reflections at 2h = 6.1 and 2h = 6.4, resulting in 1.45 nm and 1.38 nm, respectively. The subsequent broad in-plane peaks of the Mg- and Fe-aminoclays were assigned to d002 = 0.86/0.78 nm/ (2h = 10.48/11.33), d020,110 = 0.40/0.39 nm/(2h = 22.40/22.82), and d130,200 = 0.25/0.28 nm/(2h = 35.31/32.04). The Mg-aminoclay displayed 2:1 trioctahedral smectite phyllosilicate at the distinct d060,330 = 0.16 nm (2h = 59.40) peak, whereas the Fe-aminoclay could not be observed at this peak, thus producing 1:1 layered phyllosilicate (Supplementary Data, Fig. S4a), as is correspondent with the literature (Farooq et al., 2013; Lee et al., 2011a, 2013a,c). By contrast, HA was composed of a mixture of iron silicon carbide (JCPDS 018-0651), graphite (JCPDS 026-1079), and chaoite (JCPDS 022-1069). In the HA flocculations by the Mg- and Fe-aminoclays, there still appeared peaks of graphite and carbide. Also, the Mg- and Fe-aminoclay patterns were maintained at d001 = 1.80/ 2.27 nm/(2h = 4.9/3.9), d020,110 = 0.40/0.39 nm/(2h = 22/23), and d130,200 = 0.26/0.27 nm/(2h = 35/33). The Mg-aminoclay peak at d060,330 = 0.16 nm (2h = 59) was distinctly apparent. Significantly, the regular basal spacings in the aminoclay flocculations of HA were slightly increased, indicating that the HA was intercalated into the aminoclay layers by the process of re-assembly in aqueous solution (Lee et al., 2011c). Next, in an investigation of the aminoclays’ organo-functional groups, their vibration modes were examined (Supplementary Data, Fig. S4b): AOH (3419 cm1), the ACH2Agroups
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Y.-C. Lee et al. / Bioresource Technology 153 (2014) 365–369
(a) 0.5
(b)
HA 5mL + DI 10mL HA 5 mL + DI 9mL + Mg-aminoclay 1mL (HA+Mg 1) HA 5 mL + DI 7mL + Mg-aminoclay 3mL (HA+Mg 2) HA 5 mL + DI 5mL + Mg-aminoclay 5mL (HA+Mg 3) HA 5 mL + DI 3mL + Mg-aminoclay 7mL (HA+Mg 4) HA 5 mL + DI 1mL + Mg-aminoclay 9mL (HA+Mg 5) Mg-aminoclay 5 mL + DI 10mL
1.0
Intensity (abs.)
0.8 0.3
0.2
0.1
0.6 0.4 0.2
0.0 10 min
30 min
60 min
120 min
0.0
180 min
10 min
0 min
30 min
Time (min)
60 min
120 min
Time (min)
Fig. 1. Flocculation kinetics of HA by Mg-aminoclay (a) and Fe-aminoclay (b) dosages.
(a) 100 Harvesting efficiency (%)
0.5X 1.0X 1.5X 2.0X 2.5X 3.0X Mg-aminoclay HA
80 60 40 20 0 -20 0
1
2
3
4
5
Time (hour)
(b)
100
80
60
40
20
A H
3. M 0X gam in oc la y
2. 5X
2. 0X
1. 5X
1. 0X
0
0. 5X
0 min
Harvesting efficiency (%)
Intensity (abs.)
0.4
HA 5mL + DI 10mL HA 5mL + DI 9mL + Fe-aminoclay 1 mL (HA+Fe 1) HA 5mL + DI 7mL + Fe-aminoclay 3 mL (HA+Fe 2) HA 5mL + DI 5mL + Fe-aminoclay 5 mL (HA+Fe 3) HA 5mL + DI 3mL + Fe-aminoclay 7 mL (HA+Fe 4) HA 5mL + DI 9mL + Fe-aminoclay 1 mL (HA+Fe 5) Fe-aminoclay 5 mL + DI 10 mL
Fig. 2. Harvesting efficiencies of oleaginous Chlorella sp. by kinetics (a) and at equilibrium condition (b).
180 min
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Y.-C. Lee et al. / Bioresource Technology 153 (2014) 365–369
Table 1 Experimental conditions of Mg-aminoclay-flocculated HA (HA + Mg 3) for microalgae harvesting.
Microalgae solution (1.3 g/L, mL) DI (mL) HA + Mg 3 (mL) Control (mL) Mg-aminoclay (mg) HA (mg)
0.5
1.0
1.5
2.0
2.5
3.0
Mg-aminoclay
HA
7 2.5 0.5 – 12.5 0.5
2 1.0 – 25 1
1.5 1.5 – 37.5 1.5
1.0 2.0 – 50 2
0.5 2.5 – 62.5 2.5
0 3.0 – 75 3.0
5 – – 5 mL of Mg-aminoclay stock solution 25 –
– – 5 mL of HA stock solution – 1
1 (3031/2924 cm1), ANHþ ), ANH2 (1606 cm1), ACH2A 3 (2017 cm 1 1 (1499 cm ), SiACA(1133 cm ), SiAOASi (1042 cm1), ACANA (935 cm1), as well as MgAO (549/470 cm1) and FeAO (690 cm1) were all in good agreement with the previous results (Farooq et al., 2013; Lee et al., 2013a). Moreover, the organofunctional groups of the fresh HA were confirmed: (3693 cm1), AOH (3404 cm1), ACH2A groups (2958/2920/2855 cm1), AC@OA (1566 cm1), and ACAOA (1385 cm1), the stretching and bending vibration modes of the phenolic, hydroxyl, ethoxyl, and aromatic carbons (1103/1038/1007/910/532/470 cm1). Importantly, in the aminoclay flocculations of HA, the HA vibration modes showed identical peaks along with new peaks of ANH2 (1590 cm1) and ACH2A (1495 cm1), which originated from the organofunctional pendents of the aminoclays. The characterization was further examined by SEM and the corresponding elemental analysis (Supplementary Data, Fig. S5). Compared with the HA morphology, the HA flocculations by aminoclay showed grape-like or plate-stacked morphologies when both Mg-aminoclay and Fe-aminoclay caused HA flocculation. These were similar to those resultants from the precipitation of Mg-aminoclay by dye adsorption (Lee et al., 2011b). The presence of Mg-aminoclay and Fe-aminoclay was detected by energy dispersive X-ray (EDX) analysis with Mg; Cl and Fe; Cl, respectively.
3.3. Microalgae harvesting by HA + Mg 3 Based on the HA flocculation results just discussed, the HA + Mg 3 condition was applied to the flocculation step in the microalgae harvesting process. Fig. 2 plots the microalgae harvesting kinetics and efficiencies according to the HA + Mg 3 loadings (see also the photographs in Supplementary Data, Fig. S6). Only HA, due to the negatively charged HA macromolecules, could not flocculate microalgal cells. However, Mg-aminoclay has been reported to be an efficient flocculation agent (Lee et al., 2013e; Farooq et al., 2013). In our results, the presence of organic matter and co-existing ions, the aminoclays’ precipitation of the microalgae biomass was inhibited. But a two-times loading of HA + Mg 3 showed an approximately 100% harvesting efficiency, which is twofold that of the Mg-aminoclay (5 g/L)-loaded HA flocculation agent, compared with the only-Mg-aminoclay treatment (Table 1). However, the only-Mg-aminoclay treatment at 2.5 g/L showed an approximately 80% harvesting efficiency. Additionally, to compare the harvesting efficiency at the identical aminoclay loading, we tested only Mgaminoclay treatment at 5 g/L (data not shown). In the microalgae biomass precipitated by Mg-aminoclay and HA + Mg 3 (2.0 and 3.0), sweep flocculation phenomena appeared (Supplementary Data, Fig. S7) (Farooq et al., 2013). As the flocculants were increased, the precipitation was accelerated at a certain loading by the bridging of cells and their neutralization. Thus, these network-type harvesting agents consisted of humic acid with aminoclays, co-existing HA macromolecules, are not affected by inhibition of microalgae harvesting efficiency. This phenomenon is described as the formation of network-like flocculations by harvesting agents (Supplementary Data, Fig. S8), which is similar to the behavior of magnetite-coated chitosan biomolecules in the microalgae harvesting system (Lee et al., 2012). As a result, cationic
electrolyte- and ion-related flocculants with macro(bio)polymers or two-dimensional graphene oxides can be efficient microalgal harvesting agents irrespective of organic-matter effects. 4. Conclusion Efficient flocculation of oleaginous microalgae is a highly intensive, key process in microalgae-based biorefinement. In the present study, aminoclay-flocculated humic acid was applied as an efficient microalgae harvesting agent. Specifically, cationic aminoclays decorated onto humic acid played an efficient role in precipitating a microalgae biomass without any increase in the aminoclay loading. Further cationic-based nanoparticles (other aminoclays) and cationic ions (alum), with macromolecules such as polymers and carbon materials, currently are being pursued, along with studies on oil extraction from harvested wet-microalgae biomass. Acknowledgements This research was supported by the national research project titled ‘‘The Development of Technology for Extraction of Resources Dissolved in Seawater’’ of the Korea Institute of Geoscience and Mineral Resources (KIGAM) funded by the Ministry of Oceans and Fisheries. We thank Jin Seok Choi of the KAIST Research Analysis Center for the electron microscopic imaging. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.biortech.2013.11. 103. References Bellou, S., Aggelis, G., 2012. Biochemical activities in Chlorella sp. and Nannochloropsis salina during lipid and sugar synthesis in a lab-scale open pond simulating reactor. J. Biotechnol. 164, 318–329. Beuckels, A., Depraetere, O., Vandamme, D., Foubert, I., Smolders, E., Muylaert, K., 2013. Influence of organic matter on flocculation of Chlorella vulgaris by calcium phosphate precipitation. Biomass Bioenergy 54, 107–114. Chaturbedy, P., Jagadeesan, D., Eswaramoorthy, M., 2010. pH-sensitive breathing of clay within the polyelectrolyte matrix. ACS Nano 4, 5921–5929. Chen, C.-Y., Yeh, K.-L., Aisyah, R., Lee, D.-J., Chang, J.-S., 2011. Cultivation, photobioreactor design and harvesting of microalgae for biodiesel production: a critical review. Bioresour. Technol. 102, 71–81. Datta, K.K.R., Kulkarni, G., Eswaramoorthy, M., 2010. Aminoclay: a permselective matrix to stabilize copper nanoparticles. Chem. Commun. 46, 616–618. Farooq, W., Lee, Y.-C., Han, J.-I., Darpito, C.H., Choi, M., Yang, J.-W., 2013. Efficient microalgae harvesting by organo-building blocks of nanoclays. Green Chem. 15, 749–755. Hankins, N.P., Lu, N., Hilal, N., 2006. Enhanced removal of heavy metal ions bound to humic acid by polyelectrolyte flocculation. Sep. Purif. Technol. 51, 48–56. Lee, H., Suh, H., Chang, T., 2012. Rapid removal of green algae by the magnetic method. Environ. Eng. Res. 17, 151–156. Lee, Y.-C., Chang, S.-J., Choi, M.-H., Jeon, T.-J., Rye, T., Huh, Y.S., 2013a. Selfassembled graphene oxide with organo-building blocks of Fe-aminoclay for heterogeneous Fenton-like reaction at near-neutral pH: a batch experiment. Appl. Catal. B 142–143, 494–503. Lee, Y.-C., Huh, Y.S., Farooq, W., Chung, J., Han, J.-I., Shin, H.-J., Jeong, S.H., Lee, J.-S., Oh, Y.-K., Park, J.-Y., 2013b. Lipid extractions from docosahexaenoic acid (DHA)rich and oleaginous Chlorella sp. biomasses by organic-nanoclays. Bioresour. Technol. 137, 74–81.
Y.-C. Lee et al. / Bioresource Technology 153 (2014) 365–369 Lee, Y.-C., Huh, Y.S., Farooq, W., Han, J.-I., Oh, Y.-K., Park, J.-Y., 2013c. Oil extraction by aminoparticle-based H2O2 activation via wet microalgae harvesting. RSC Adv. 3, 12802–12809. Lee, Y.-C., Jin, E., Jung, S.W., Kim, Y.-M., Chang, K.S., Yang, J.-W., Kim, S.-W., Kim, Y.O., Shin, H.-J., 2013d. Utilizing the algicidal activity of aminoclay as a practical treatment for toxic red tides. Sci. Rep. 3 (1292), 1–8. Lee, Y.-C., Kim, B., Farooq, W., Chung, J., Han, J.-I., Shin, H.-J., Jeong, S.H., Park, J.-Y., Lee, J.-S., Oh, Y.-K., 2013e. Harvesting of oleaginous Chlorella sp. by organoclays. Bioresour. Technol. 2013 (132), 440–445. Lee, Y.-C., Kim, E.J., Ko, D.A., Yang, J.-W., 2011a. Water-soluble organo-building blocks of aminoclay as a soil-flushing agent for heavy metal contaminated soil. J. Hazard. Mater. 196, 101–108. Lee, Y.-C., Kim, E.J., Yang, J.-W., Shin, H.-J., 2011b. Removal of malachite green by adsorption and precipitation using aminopropyl functionalized magnesium phyllosilicate. J. Hazard. Mater. 192, 62–70.
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Lee, Y.-C., Park, W.-K., Yang, J.-W., 2011c. Removal of anionic metals by aminoorganoclay for water treatment. J. Hazard. Mater. 190, 652–658. Markri, A., Bellou, S., Birkou, M., Papatrehas, K., Dolapsakis, N.P., Bokas, D., Papanikolaou, S., Aggelis, G., 2011. Lipid synthesized by micro-algae grown in laboratory- and industrial-scale bioreactors. Eng. Life Sci. 11, 52–58. Rodolfi, L., Zittelli, G.C., Bassi, N., Padovani, G., Biondi, N., Bonini, G., Tredici, M.R., 2009. Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass cultivation in a low-cost photobioreactor. Biotechnol. Bioeng. 102, 100–112. Wijffels, R.H., Barbosa, M.J., 2010. An outlook on microalgal biofuels. Science 329, 796–799. Xu, L., Guo, C., Wang, F., Zheng, S., Liu, C.-Z., 2011. A simple and rapid harvesting method for microalgae by in situ magnetic separation. Bioresour. Technol. 102, 10047–10051.
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Aminoclay-induced humic acid flocculation for efficient harvesting of oleaginous Chlorella sp. Young-Chul Lee a, Seo Yeong Oh a, Hyun Uk Lee b, Bohwa Kim c, So Yeun Lee c, Moon-Hee Choi d, Go-Woon Lee e, Ji-Yeon Park c, You-Kwan Oh c, Taegong Ryu f, Young-Kyu Han g, Kang-Sup Chung f,⇑, Yun Suk Huh a,⇑ a
Department of Biological Engineering, College of Engineering, Inha University, Incheon 402-751, Republic of Korea Division of Materials Science, Korea Basic Science Institute (KBSI), Daejeon 305-333, Republic of Korea c Clean Fuel Department, Korea Institute of Energy Research (KIER), 152 Gajeong-ro, Yuseong-gu, Daejeon 305-343, Republic of Korea d Department of Beauty and Cosmetology, Graduate School of Industry, Chosun University, Gwangju 501-759, Republic of Korea e Testing and Certification Center, Korea Institute of Energy Research (KIER), 152 Gajeong-ro, Yuseong-gu, Daejeon 305-343, Republic of Korea f Rare Metals Research Center, Korea Institute of Geoscience & Mineral Resources, Daejeon 305-350, Republic of Korea g Department of Energy and Materials Engineering, Dongguk University-Seoul, Seoul 100-715, Republic of Korea b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Aminoclay-induced humic acid
flocculation (AC-HA) was investigated. AC-HA showed for efficient harvesting of oleaginous microalgae. AC-HA played a type of network in capturing microalgal cells. Flocculation approach can be utilized for microalgae flocculation.
a r t i c l e
i n f o
Article history: Received 14 October 2013 Received in revised form 25 November 2013 Accepted 30 November 2013 Available online 15 December 2013 Keywords: Aminoclay Humic acid Flocculation Microalgae Harvesting
a b s t r a c t Biofuels (biodiesel) production from oleaginous microalgae has been intensively studied for its practical applications within the microalgae-based biorefinement process. For scaled-up cultivation of microalgae in open ponds or, for further cost reduction, using wastewater, humic acids present in water-treatment systems can positively and significantly affect the harvesting of microalgae biomass. Flocculation, because of its simplicity and inexpensiveness, is considered to be an efficient approach to microalgae harvesting. Based on the reported cationic aminoclay usages for a broad spectrum of microalgae species in wide-pH regimes, aminoclay-induced humic acid flocculation at the 5 g/L aminoclay loading showed fast floc formation, approximately 100% harvesting efficiency, which was comparable to the only-aminoclay treatment at 5 g/L, indicating that the humic acid did not significantly inhibit the microalgae harvesting behavior. As for the microalgae flocculation mechanism, it is suggested that cationic nanoparticles decorated on macromolecular matters function as a type of network in capturing microalgae. Ó 2013 Elsevier Ltd. All rights reserved.
⇑ Corresponding authors. Tel.: +82 42 868 3645 (K.-S. Chung). Tel.: +82 32 860 9177; fax: +82 32 872 4046 (Y.S. Huh). E-mail addresses: [email protected] (K.-S. Chung), [email protected] (Y.S. Huh). 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.11.103
366
Y.-C. Lee et al. / Bioresource Technology 153 (2014) 365–369
1. Introduction Since 2000, microalgae-based biorefinery processes have received intensive academic attention for their practical and industrial applications (Bellou and Aggelis, 2012; Wijffels and Barbosa, 2010; Rodolfi et al., 2009; Farooq et al., 2013; Chen et al., 2011). The available resources of extracted invaluable products such as carbohydrates, proteins, and lipids (oil) from microalgae have been focused on downstream process consisted of harvesting or flocculations, lipids extraction, and re-culture (Lee et al., 2013b,c,e; Markri et al., 2011). For the downstream processes, efficient flocculation of microalgae biomass in harvesting technologies can be a reasonable approach, given the simple and inexpensive methods available for precipitation of microalgae biomass (Xu et al., 2011; Lee et al., 2012, 2013e; Farooq et al., 2013). Recently, cationic aminoclays, as synthesized by simple sol–gel processing under ambient conditions (Chaturbedy et al., 2010; Datta et al., 2010), have been investigated for their use in the destabilization of microalgal cells. Specifically, aminoclays have played unique roles not only in efficient harvesting of fresh and marine microalgae (Lee et al., 2013e; Farooq et al., 2013) but also in selective microalgal lysis of red tide species (Lee et al., 2013d). The protonated amine groups in aminoclay nanoparticles function as positively charged nanoclusters ranging in hydrodynamic diameter from 30 nm to 150 nm (Farooq et al., 2013; Lee et al., 2011a,c), thus effecting flocculation for a broad spectrum of microalgae species without altering the pH environment. Humic acid, one of the most ubiquitous forms of organic matter in water and wastewater environmental systems (Beuckels et al., 2013; Hankins et al., 2006), can significantly effect on microalgae harvesting efficiency in open-pond cultivation or, for the purposes of cost reduction, using wastewater. Previously, Lee et al. found that aminoclay is an efficient flocculant for humic acid to remove from water where humic acids inhibited between interaction of heavy metals and aminoclays (Lee et al., 2011c). These aminoclay-flocculated humic acid macromolecules, therefore, can play efficient microalgae harvesting. Interestingly, the aminoclaydecorated humic acid matrix functions as a network-like precipitant for oleaginous microalgae harvesting without any significant increase of aminoclay loading. 2. Methods See Supplementary Data, TEXT. 3. Results and discussion 3.1. HA sedimentation studies using Mg- and Fe-aminoclays HA flocculations were studied according to Mg-aminoclay and Fe-aminoclay dosages. Prior to the flocculation studies, the UV– Vis absorbances were scanned for the Mg- and Fe-aminoclays as well as the HA in aqueous solution as a function of loading with respect to time (Supplementary Data, Fig. S1). The Mg-aminoclay showed a distinct transparent property up to the concentration of 5 g/L. At the 500 nm wavelength, the absorbance intensity was nearly zero (Fig. S1a) (Lee et al., 2011a, 2013a). Contrastingly, the Fe-aminoclay, due to its intrinsic use of ferric ions for Fe-aminoclay synthesis, showed a brown color. At 0.3125 g/L, the absorbance intensity at 600 nm was also zero, but as the concentration was increased to 5 g/L, the absorbance intensity was about 0.4 (Fig. S1b). Moreover, HA also showed zero absorbance intensity at 600 nm, up to the increased loading of 12.5 mg/L (Fig. S1c). As recorded at the 600 nm wavelength, the HA flocculations by the Mg- and Fe-aminoclays as a function of their loadings were
plotted for 180 min (Fig. 1). As the Mg-aminoclay loading was increased (i.e., up to HA + Mg 3), the HA flocculation was enhanced. However, with further increases, the flocculation of HA was inhibited (Fig. 1a), due to the superior water-soluble property of aminoclay according to which cationic aminoclay nanoparticles play a surfactant role in improving the dispersion of (nano)materials in aqueous solution (Datta et al., 2010; Lee et al., 2011a). Such flocculations also were observed for the Fe-aminoclay (Fig. 1b). The higher initial intensities of the HA as flocculated by the aminoclays were related to the aggregation phenomena that arose immediately after the addition of the aminoclay solution to the HA solution. Compared to loading of Mg-aminoclay to HA, the lower loading of Fe-aminoclay showed the optimal sedimentation profiles whose optimal flocculation conditions by Mg- and Feaminoclays were determined to be HA + Mg 3 and HA + Fe 2, respectively. The equilibrium time of HA flocculation was attained at about 180 min, which is comparable to the sedimentation rate of graphene oxide (Lee et al., 2013a). The fitted plots of the sedimentation kinetics of HA + Mg 2, HA + Mg 3, HA + Mg 4, HA + Fe 1, HA + Fe 2, and HA + Fe 3 followed a pseudo first-order equation; the observed kinetic constants, plotted in Fig. S2, were, respectively, 0.0533 (r2 = 0.9094), 0.0537 (r2 = 0.8901), 0.0351 (r2 = 0.7406), 0.0237 (r2 = 0.9088), 0.0524 (r2 = 0.9055), and 0.0155 (r2 = 0.7087) of the observed flocculation constants (abs./min). In general, the Mg-aminoclay showed fast floc formation than the Fe-aminoclay, which might be attributable to the former’s smaller size (30 nm of average hydrodynamic diameter) (Farooq et al., 2013; Lee et al., 2011a,c) compared with that of the latter (100 nm of average hydrodynamic diameter) (Lee et al., 2011a, 2013a). Accordingly, among the Mg-aminoclay treatments, HA + Mg 2 showed the fast separation and most efficient flocculation. 3.2. Characterization of HA flocculants by aminoclays For checking of the amorphous structure and impurities and further confirmation of the organo-functional groups, Fig. S3 plots the XRD patterns of confirms and FT-IR spectra for HA, aminoclay, and HA flocculants by aminoclays. In Fig. S3a, both the HA and the aminoclays show amorphous phases. Initially, the Mg- and Fe-aminoclays revealed d-spacing d001 reflections at 2h = 6.1 and 2h = 6.4, resulting in 1.45 nm and 1.38 nm, respectively. The subsequent broad in-plane peaks of the Mg- and Fe-aminoclays were assigned to d002 = 0.86/0.78 nm/ (2h = 10.48/11.33), d020,110 = 0.40/0.39 nm/(2h = 22.40/22.82), and d130,200 = 0.25/0.28 nm/(2h = 35.31/32.04). The Mg-aminoclay displayed 2:1 trioctahedral smectite phyllosilicate at the distinct d060,330 = 0.16 nm (2h = 59.40) peak, whereas the Fe-aminoclay could not be observed at this peak, thus producing 1:1 layered phyllosilicate (Supplementary Data, Fig. S4a), as is correspondent with the literature (Farooq et al., 2013; Lee et al., 2011a, 2013a,c). By contrast, HA was composed of a mixture of iron silicon carbide (JCPDS 018-0651), graphite (JCPDS 026-1079), and chaoite (JCPDS 022-1069). In the HA flocculations by the Mg- and Fe-aminoclays, there still appeared peaks of graphite and carbide. Also, the Mg- and Fe-aminoclay patterns were maintained at d001 = 1.80/ 2.27 nm/(2h = 4.9/3.9), d020,110 = 0.40/0.39 nm/(2h = 22/23), and d130,200 = 0.26/0.27 nm/(2h = 35/33). The Mg-aminoclay peak at d060,330 = 0.16 nm (2h = 59) was distinctly apparent. Significantly, the regular basal spacings in the aminoclay flocculations of HA were slightly increased, indicating that the HA was intercalated into the aminoclay layers by the process of re-assembly in aqueous solution (Lee et al., 2011c). Next, in an investigation of the aminoclays’ organo-functional groups, their vibration modes were examined (Supplementary Data, Fig. S4b): AOH (3419 cm1), the ACH2Agroups
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(a) 0.5
(b)
HA 5mL + DI 10mL HA 5 mL + DI 9mL + Mg-aminoclay 1mL (HA+Mg 1) HA 5 mL + DI 7mL + Mg-aminoclay 3mL (HA+Mg 2) HA 5 mL + DI 5mL + Mg-aminoclay 5mL (HA+Mg 3) HA 5 mL + DI 3mL + Mg-aminoclay 7mL (HA+Mg 4) HA 5 mL + DI 1mL + Mg-aminoclay 9mL (HA+Mg 5) Mg-aminoclay 5 mL + DI 10mL
1.0
Intensity (abs.)
0.8 0.3
0.2
0.1
0.6 0.4 0.2
0.0 10 min
30 min
60 min
120 min
0.0
180 min
10 min
0 min
30 min
Time (min)
60 min
120 min
Time (min)
Fig. 1. Flocculation kinetics of HA by Mg-aminoclay (a) and Fe-aminoclay (b) dosages.
(a) 100 Harvesting efficiency (%)
0.5X 1.0X 1.5X 2.0X 2.5X 3.0X Mg-aminoclay HA
80 60 40 20 0 -20 0
1
2
3
4
5
Time (hour)
(b)
100
80
60
40
20
A H
3. M 0X gam in oc la y
2. 5X
2. 0X
1. 5X
1. 0X
0
0. 5X
0 min
Harvesting efficiency (%)
Intensity (abs.)
0.4
HA 5mL + DI 10mL HA 5mL + DI 9mL + Fe-aminoclay 1 mL (HA+Fe 1) HA 5mL + DI 7mL + Fe-aminoclay 3 mL (HA+Fe 2) HA 5mL + DI 5mL + Fe-aminoclay 5 mL (HA+Fe 3) HA 5mL + DI 3mL + Fe-aminoclay 7 mL (HA+Fe 4) HA 5mL + DI 9mL + Fe-aminoclay 1 mL (HA+Fe 5) Fe-aminoclay 5 mL + DI 10 mL
Fig. 2. Harvesting efficiencies of oleaginous Chlorella sp. by kinetics (a) and at equilibrium condition (b).
180 min
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Table 1 Experimental conditions of Mg-aminoclay-flocculated HA (HA + Mg 3) for microalgae harvesting.
Microalgae solution (1.3 g/L, mL) DI (mL) HA + Mg 3 (mL) Control (mL) Mg-aminoclay (mg) HA (mg)
0.5
1.0
1.5
2.0
2.5
3.0
Mg-aminoclay
HA
7 2.5 0.5 – 12.5 0.5
2 1.0 – 25 1
1.5 1.5 – 37.5 1.5
1.0 2.0 – 50 2
0.5 2.5 – 62.5 2.5
0 3.0 – 75 3.0
5 – – 5 mL of Mg-aminoclay stock solution 25 –
– – 5 mL of HA stock solution – 1
1 (3031/2924 cm1), ANHþ ), ANH2 (1606 cm1), ACH2A 3 (2017 cm 1 1 (1499 cm ), SiACA(1133 cm ), SiAOASi (1042 cm1), ACANA (935 cm1), as well as MgAO (549/470 cm1) and FeAO (690 cm1) were all in good agreement with the previous results (Farooq et al., 2013; Lee et al., 2013a). Moreover, the organofunctional groups of the fresh HA were confirmed: (3693 cm1), AOH (3404 cm1), ACH2A groups (2958/2920/2855 cm1), AC@OA (1566 cm1), and ACAOA (1385 cm1), the stretching and bending vibration modes of the phenolic, hydroxyl, ethoxyl, and aromatic carbons (1103/1038/1007/910/532/470 cm1). Importantly, in the aminoclay flocculations of HA, the HA vibration modes showed identical peaks along with new peaks of ANH2 (1590 cm1) and ACH2A (1495 cm1), which originated from the organofunctional pendents of the aminoclays. The characterization was further examined by SEM and the corresponding elemental analysis (Supplementary Data, Fig. S5). Compared with the HA morphology, the HA flocculations by aminoclay showed grape-like or plate-stacked morphologies when both Mg-aminoclay and Fe-aminoclay caused HA flocculation. These were similar to those resultants from the precipitation of Mg-aminoclay by dye adsorption (Lee et al., 2011b). The presence of Mg-aminoclay and Fe-aminoclay was detected by energy dispersive X-ray (EDX) analysis with Mg; Cl and Fe; Cl, respectively.
3.3. Microalgae harvesting by HA + Mg 3 Based on the HA flocculation results just discussed, the HA + Mg 3 condition was applied to the flocculation step in the microalgae harvesting process. Fig. 2 plots the microalgae harvesting kinetics and efficiencies according to the HA + Mg 3 loadings (see also the photographs in Supplementary Data, Fig. S6). Only HA, due to the negatively charged HA macromolecules, could not flocculate microalgal cells. However, Mg-aminoclay has been reported to be an efficient flocculation agent (Lee et al., 2013e; Farooq et al., 2013). In our results, the presence of organic matter and co-existing ions, the aminoclays’ precipitation of the microalgae biomass was inhibited. But a two-times loading of HA + Mg 3 showed an approximately 100% harvesting efficiency, which is twofold that of the Mg-aminoclay (5 g/L)-loaded HA flocculation agent, compared with the only-Mg-aminoclay treatment (Table 1). However, the only-Mg-aminoclay treatment at 2.5 g/L showed an approximately 80% harvesting efficiency. Additionally, to compare the harvesting efficiency at the identical aminoclay loading, we tested only Mgaminoclay treatment at 5 g/L (data not shown). In the microalgae biomass precipitated by Mg-aminoclay and HA + Mg 3 (2.0 and 3.0), sweep flocculation phenomena appeared (Supplementary Data, Fig. S7) (Farooq et al., 2013). As the flocculants were increased, the precipitation was accelerated at a certain loading by the bridging of cells and their neutralization. Thus, these network-type harvesting agents consisted of humic acid with aminoclays, co-existing HA macromolecules, are not affected by inhibition of microalgae harvesting efficiency. This phenomenon is described as the formation of network-like flocculations by harvesting agents (Supplementary Data, Fig. S8), which is similar to the behavior of magnetite-coated chitosan biomolecules in the microalgae harvesting system (Lee et al., 2012). As a result, cationic
electrolyte- and ion-related flocculants with macro(bio)polymers or two-dimensional graphene oxides can be efficient microalgal harvesting agents irrespective of organic-matter effects. 4. Conclusion Efficient flocculation of oleaginous microalgae is a highly intensive, key process in microalgae-based biorefinement. In the present study, aminoclay-flocculated humic acid was applied as an efficient microalgae harvesting agent. Specifically, cationic aminoclays decorated onto humic acid played an efficient role in precipitating a microalgae biomass without any increase in the aminoclay loading. Further cationic-based nanoparticles (other aminoclays) and cationic ions (alum), with macromolecules such as polymers and carbon materials, currently are being pursued, along with studies on oil extraction from harvested wet-microalgae biomass. Acknowledgements This research was supported by the national research project titled ‘‘The Development of Technology for Extraction of Resources Dissolved in Seawater’’ of the Korea Institute of Geoscience and Mineral Resources (KIGAM) funded by the Ministry of Oceans and Fisheries. We thank Jin Seok Choi of the KAIST Research Analysis Center for the electron microscopic imaging. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.biortech.2013.11. 103. References Bellou, S., Aggelis, G., 2012. Biochemical activities in Chlorella sp. and Nannochloropsis salina during lipid and sugar synthesis in a lab-scale open pond simulating reactor. J. Biotechnol. 164, 318–329. Beuckels, A., Depraetere, O., Vandamme, D., Foubert, I., Smolders, E., Muylaert, K., 2013. Influence of organic matter on flocculation of Chlorella vulgaris by calcium phosphate precipitation. Biomass Bioenergy 54, 107–114. Chaturbedy, P., Jagadeesan, D., Eswaramoorthy, M., 2010. pH-sensitive breathing of clay within the polyelectrolyte matrix. ACS Nano 4, 5921–5929. Chen, C.-Y., Yeh, K.-L., Aisyah, R., Lee, D.-J., Chang, J.-S., 2011. Cultivation, photobioreactor design and harvesting of microalgae for biodiesel production: a critical review. Bioresour. Technol. 102, 71–81. Datta, K.K.R., Kulkarni, G., Eswaramoorthy, M., 2010. Aminoclay: a permselective matrix to stabilize copper nanoparticles. Chem. Commun. 46, 616–618. Farooq, W., Lee, Y.-C., Han, J.-I., Darpito, C.H., Choi, M., Yang, J.-W., 2013. Efficient microalgae harvesting by organo-building blocks of nanoclays. Green Chem. 15, 749–755. Hankins, N.P., Lu, N., Hilal, N., 2006. Enhanced removal of heavy metal ions bound to humic acid by polyelectrolyte flocculation. Sep. Purif. Technol. 51, 48–56. Lee, H., Suh, H., Chang, T., 2012. Rapid removal of green algae by the magnetic method. Environ. Eng. Res. 17, 151–156. Lee, Y.-C., Chang, S.-J., Choi, M.-H., Jeon, T.-J., Rye, T., Huh, Y.S., 2013a. Selfassembled graphene oxide with organo-building blocks of Fe-aminoclay for heterogeneous Fenton-like reaction at near-neutral pH: a batch experiment. Appl. Catal. B 142–143, 494–503. Lee, Y.-C., Huh, Y.S., Farooq, W., Chung, J., Han, J.-I., Shin, H.-J., Jeong, S.H., Lee, J.-S., Oh, Y.-K., Park, J.-Y., 2013b. Lipid extractions from docosahexaenoic acid (DHA)rich and oleaginous Chlorella sp. biomasses by organic-nanoclays. Bioresour. Technol. 137, 74–81.
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