Ecology and Resilient Infrastructure. September 2018. 174-179
https://doi.org/10.17820/eri.2018.5.3.174

MAIN

  • 1. Introduction

  • 2. Materials and Methods

  •   2.1 Manufacturing method of TiO2-embedded EPS balls

  •   2.2 Experiment on inhibition of algal growth using TiO2-embedded EPS balls

  • 3. Results and Discussion

  •   3.1 Cell number and morphology of C. ellipsoidea

  •   3.2 Chlorophyll-a and Phaeopigments

  • 4. Conclusions

1. Introduction

Algae in freshwater is an important role as a primary producer in aquatic ecosystem. However, if algal blooms occur continuously due to overgrowth of blue green algae, algal blooms cause both aquatic ecosystem disturbance and aesthetic, physical adverse effects on human life (Paul 2008, Rabalais et al. 2009, Raven and Giordano 2014, Backer et al. 2015, Wells et al. 2015). Water eutrophication in lakes and rivers is widespread all over the world, and the occurrence of water eutrophication is a complex function of the various influencing factors (e.g., nutrient enrichment, hydrodynamics, water temperature, salinity, light irradiation, biodiversity, etc.) (Paul 2008, Rabalais et al. 2009, Raven and Giordano 2014, Backer et al. 2015, Wells et al. 2015). Also, climate change, abnormal high temperature, reduced precipitation, and increased sunlight result in the excessive algal blooms (Paul 2008, Rabalais et al. 2009, Raven and Giordano 2014, Backer et al. 2015, Wells et al. 2015). Therefore, various physical, chemical and biological algae countermeasure technologies have been developed (Paul 2008, Wells et al. 2015). However, due to the practical limitations of algae countermeasure applications in lakes and rivers, low- cost, efficient, and sustainable algal growth inhibition technologies have been required to reduce the occurrence of water eutrophication.

Recently, polymer-based photocatalyst composites have received increased attention using various polymer supports (e.g., polyaniline, polycarbonate, polyethylene, polystyrene, polyvinyl alcohol, polyvinyl chloride, etc.) with outstanding mechanical properties and compatibilities (Leong et al. 2014, Jang et al. 2016, Joo et al. 2013, 2016). These polymer-based photocatalyst composites can readily control both surface morphology and chemistry of composites through direct compounding, in situ synthesis, self-assembly, electro- spinning, etc (Leong et al. 2014, Jang et al. 2016, Joo et al. 2013, 2016). Accordingly, self-floating photocatalyst/ polymer composites utilizing both continuous illumination of solar energy and oxygenation in the air/ water interface can be applied in contaminated lakes and wastewater reservoirs.

In this study, expanded polystyrene (EPS) is used as a practical and floating support for photocatalyst/ polymer composites since EPS is an innocuous floating material with its thermal-softness and long durability (Ross and Evans 2003, Lee et al. 2010). Also, simple and cost-effective temperature-controlled melting method of EPS was developed (Joo et al. 2013, 2016), and modified as immobilization technique for mass production of TiO2-embedded EPS (TiEPS) balls in this study. Finally, the photocatalytic activity of TiO2-embedded EPS balls was evaluated using Chlorella ellipsoidea (C. ellipsoidea) as a probe algae under the natural solar light irradiation (285 - 660 nm & 0.02 - 0.14 mW/cm2). From this study, the specific objectives were to develop the mass production procedures of TiO2-embedded EPS (TiEPS) balls, and to evaluate the feasibility for usage of buoyant TiO2-embedded EPS balls to inhibit the excessive growth of algae in lakes and rivers.

2. Materials and Methods

2.1 Manufacturing method of TiO2-embedded EPS balls

Commercial low density uniform EPS balls were purchased, and the diameter of the EPS balls used was 3 cm. In this study, powdered nanoscale P25 TiO2 (Evonik Degussa, Germany) was used. Glycerin was purchased (Daejung Chemicals & Metals Co., Korea), and used as a dispersing medium for TiO2. The suspension of TiO2 particles was heated to 140-150°C, which is the temperature at thermal denaturation of the polymer occurs, using a digital temperature controller and a heating pan equipped with a magnetic stirrer. EPS balls were repeatedly immersed, so that the TiO2 particles were evenly embedded in the EPS balls surface. Then, the surface of the EPS balls was completely freeze-dried using liquid nitrogen to enhance the embedding of TiO2 particles on the surface of EPS balls. Finally, the TiO2-embedded EPS (TiEPS) balls were washed with distilled water at 700 W for 2 minutes using an ultrasonic washing machine (POWER SONIC 420, Hwasin Tech, Korea) to remove excess TiO2 particles that were not rigorously embedded to the surface of the EPS balls. After washing, the TiEPS balls were allowed to air dry at room temperature. The detail mass production processes of TiEPS balls are displayed in Fig. 1.

http://static.apub.kr/journalsite/sites/kseie/2018-005-03/N0190050308/images/kseie_05_03_08_F1.jpg
Fig. 1.

Mass production procedures of TiO2-embedded expanded polystyrene (TiEPS) balls developed in this study.

2.2 Experiment on inhibition of algal growth using TiO2-embedded EPS balls

Chlorella ellipsoidea, which was used to verify the inhibitory effect of TiEPS balls on algal growth, was obtained from KRIBB (Korea Research Institute of Bioscience and Biotechnology) and cultured using BG-11 medium (MB Cell Co., USA). The culture conditions in the lab were as follows: light intensity of 1,800 lux, temperature of 25°C, light cycle of 12 hr (light)/12 hr (dark), and cultivation for 7 days before the outdoor experiment. The initial concentration of C. ellipsoidea was set at 4 L with 1x106 cells/mL of the algal concentration. The outdoor experiment was performed using an acrylic reactor, the height of the water was 10 cm from the bottom, and total 49 TiEPS balls were inserted in each reactors of (B) and (D). The outdoor experiment was conducted using four reactors with various conditions of (A) natural sunlight, (B) natural sunlight + TiEPS balls, (C) dark, and (D) dark + TiEPS balls on the roof of the building during five days (see Fig. 2).

http://static.apub.kr/journalsite/sites/kseie/2018-005-03/N0190050308/images/kseie_05_03_08_F2.jpg
Fig. 2.

Pictorial view of lab-scale outdoor inhibition experiment using TiO2-embedded expanded polystyrene (TiEPS) balls against the growth of Chlorella ellipsoidea with different conditions.

Both supernatant and mixture solution were sampled at certain time, and the changes in both cell number of C. ellipsoidea and concentration of chlorophyll-a (Chl-a) and phaeopigments were observed. The number of C. ellipsoidea was counted using an optical microscope (DN-10A, Samwon Scientific Ltd., Korea) using a hemocyte counter (Marienfeld, Germany) and the concentrations of chlorophyll-a and phaeopigments were measured using ICES Techniques [ICES Techniques in Marine Envirionmental Sciences (No. 30 Chlorophyll-a: Measurement by Spectroscopy ISSN 0903-2606)] (Aminot and Rey 2000, Bartram and Rees 2000).

3. Results and Discussion

  3.1 Cell number and morphology of C. ellipsoidea

In case of natural sunlight only during the outdoor experiment, the growth of C. elliipsoidea increased along the Monod growth curve, and no inhibition of the growth was observed. Therefore, it is considered that there is no significant growth inhibitory factor of C. ellipsoidea under the natural sunlight irradiation. However, the number of cells in the cases of (B), (C) and (D) were not significantly different up to 80 hours, displaying that the growth inhibition effect of C. ellipsoidea was observed.

Based on the comparison of cell number of C. elliipsoidea between mixture solution (Fig. 3(a)) and supernatant (Fig. 3(b)), the cell numbers increased during the sunlight irradiation, and decreased during the night time in case of (A) in the supernatant, whereas the cell numbers increased in the mixture solution regardless of the sunlight irradiation, indicating that cells of C. elliipsoidea migrate vertically during the outdoor experiment.

http://static.apub.kr/journalsite/sites/kseie/2018-005-03/N0190050308/images/kseie_05_03_08_F3.jpg
Fig. 3.

Changes in cell number of Chlorella ellipsoidea in lab-scale inhibition experiment using TiO2-embedded expanded polystyrene (TiEPS) balls with different conditions; number of Chlorella ellipsoidea in mixture solution (a) and in supernatant (b).

Considering the cell numbers decreased faster in cases of (B), (C) and (D) in both mixture and supernatant, both surface reactions in heterogeneous photocatalysis and light shielding could inhibit the growth of C. elliipsoidea. Although dominant inhibitory effects on the growth of C. elliipsoidea were ambiguous, TiEPS balls were found to be effective to inhibit the excessive growth of algae in the stagnant water body.

As shown in Fig. 4, cell morphology was clear and healthy in the case of (A), whereas cell contents were eluted out of the cell, and the circular shape of cell was distorted in the case of (B). This might be attributed to the attack of oxygen species (OH・, O2・-, and H2O2) generated by TiO2 particles on the surface of TiEPS balls against the algal cell membrane. Further study is warranted to elucidate more dominant effects on the algal growth inhibition using intact vs. TiEPS balls.

http://static.apub.kr/journalsite/sites/kseie/2018-005-03/N0190050308/images/kseie_05_03_08_F4.jpg
Fig. 4.

Comparison of cell shape and morphology in the lab-scale inhibition experiment against the growth of Chlorella ellipsoidea. Light only (a), and light with TiO2-embedded expanded polystyrene (TiEPS) balls (b).(Note: red circles indicate the distorted and ruptured cells)

3.2 Chlorophyll-a and Phaeopigments

Chlorophyll-a (Chl-a) is an indirect indicator of the distribution of algae, and phaeopigments are indirect indicator of algae death (Aminot and Rey 2000, Bartram and Rees 2000). As displayed in Fig. 5(a), Chl-a concentrations increased with time in case of light only whereas Chl-a concentrations decreased with time in case of (B), (C), and (D). Similar to the results of cell numbers, TiEPS balls were also found to be effective to inhibit the excessive growth of algae based on the Chl-a.

As displayed in Fig. 5(b), phaeopigment concentrations increased with time in cases of (A) and (B), whereas phaeopigment concentrations decreased with time in cases of (C) and (D). These results suggest that both algal growth and death occurred simultaneously in cases of (A) and (B), whereas both algal growth and death did not occur in cases of (C) and (D). Consequently, synergistic effects of both photocatalysic reactions and light shielding using TiEPS balls were significant in case of (B).

http://static.apub.kr/journalsite/sites/kseie/2018-005-03/N0190050308/images/kseie_05_03_08_F5.jpg
Fig. 5.

Changes in chlorophyll-a and phaeopigments during the lab-scale inhibition experiment using TiO2-embedded expanded polystyrene (TiEPS) balls against the growth of Chlorella ellipsoidea; chlorophyll-a (a), and phaeopigments (b).

These photocatalytic degradation of C. elliipsoidea using TiEPS balls can be explained by the reaction of oxygen species (OH・, O2・-, and H2O2) released from the irradiated TiO2 particles on the surface of TiEPS balls. Similar results have been reported that highly reactive hydroxyl radicals (OH・) can attack the lipid cell membrane through the peroxidation reaction and inhibit the self-protection mechanisms, eventually resulting in cell inactivation (Li et al. 2008, Altin and Sokmen 2015). Therefore, TiEPS balls were feasible to prevent and inhibit the excessive growth of algae in eutrophic water body.

4. Conclusions

Simple and cost-effective temperature-controlled melting and liquid nitrogen-based cooling method of expanded polystyrene (EPS) was developed as immobilization technique for mass production of TiO2- embedded EPS (TiEPS) balls. Then, the photocatalytic activity of TiEPS balls was evaluated using Chlorella ellipsoidea (C. ellipsoidea) as a probe algae under the natural solar light irradiation (285 - 660 nm & 0.02 - 0.14 mW/cm2). Since the photocatalytic reactions occurred around the water surface, highly reactive transitory species effectively inhibit the growth of C. elliipsoidea on the water surface, thus, C. elliipsoidea might migrate to the bottom of reactors. Also, both surface reactions in heterogeneous photocatalysis and light shielding could inhibit the growth of C. elliipsoidea. Although dominant inhibitory effects on the growth of C. elliipsoidea were ambiguous, TiEPS balls were found to be effective to inhibit the excessive growth of algae in the stagnant water body. Further study is warranted to evaluate the inhibitory effects of harmful algae growth in eutrophic rivers and lakes as a mesocosm field study.

Acknowledgements

This research was supported by a grant from “Field Evaluation of Best Available Technique for Algae Control in River” (18AWMP-B098640-04).

References

1 

Altin, I. and Sokmen, M. 2015. Buoyant photocatalyst based on ZnO immobilized on polystyrene beads for pollutants treatment. Clean Soil Air Water 43(7): 1025- 1030.

10.1002/clen.201400303
2 

Aminot, A. and Rey, F. 2000. Standard procedure for the determination of chlorophyll-a by spectroscopic methods. ICES Techniques in Marine Environmental Sciences 30: 1-15.

3 

Backer, L.C., Baptiste, D.M., Prell, R.L., and Bolton, B. 2015. Cyanobacteria and algae blooms: Review of health and environmental data from the harmful algal bloom- related illness surveillance system (HABISS) 2007-2011. Toxins 7(4): 1048-1064.

10.3390/toxins704104825826054PMC4417954
4 

Bartram, J. and Rees, G. 2000. Monitoring Bathing Waters: A practical guide to the design and implementation of assessments and monitoring programmes. CRC Press, New York, USA, pp. 1-352.

10.4324/9780203478264
5 

Jang, D.G., Ahn, C.H., Choi, J.S., Kim, J.H., Kim, J.K., and Joo, J.C. 2016. Enhanced removal of trichloroethylene in water using nano-ZnO/Polybutadiene rubber composites. Catalysts 6(10): 152-166.

10.3390/catal6100152
6 

Joo, J.C., Ahn, C.H., Jang, D.G., Yoon, H.H., Kim, J.K., Campos, L., and Ahn, H.S. 2013. Photocatalysic degradation of trichloroethylene in aqueous phase using nano-ZnO/Laponite composites. Journal of Hazardous Materials 263(2): 569-574.

10.1016/j.jhazmat.2013.10.01724239256
7 

Joo, J.C., Lee, S., Ahn, C.H., Lee, I.J., Liu, Z.H., Park, J.R. 2016. Development of titanium dioxide (TiO2)- immobilized buoyant photocatalyst balls using expanded polystyrene (EPS). Ecology and Resilient Infrastructure 3(4): 215-220.

10.17820/eri.2016.3.4.215
8 

Lee, Y.S., Park, N.H., and Yoon, H.S. 2010. Dynamic mechanical characteristics of expanded polypropylene foams. Journal of Cellular Plastics 46(1): 43-55.

10.1177/0021955X09346363
9 

Li, Q., Mahendra, S., Lyon, D.Y., Brunet, L., Liga, M.V., Li, D., and Alvarez, P.J. 2008. Antimicrobial nanomaterials for water disinfection and microbial control: Potential applications and implications. Water Research 42(18): 4591-4602.

10.1016/j.watres.2008.08.01518804836
10 

Leong, S., Razmjou, A., Wang, K., Hapgood, K., Zhang, X., and Wang, H. 2014. TiO2-based photocatalytic membranes: A review. Journal of Membrane Science 472(15): 167-184.

10.1016/j.memsci.2014.08.016
11 

Paul, V.J. 2008. Cyanobacterial Harmful Algal Blooms: State of the Science and Research Needs. Springer, New York, USA. pp. 239-257.

10.1007/978-0-387-75865-7_1118461772
12 

Rabalais, N.N., Turner, R.E., Diaz, R.J., and Justic, D. 2009. Global change and eutrophication of coastal waters. ICES Journal of Marine Science 66(7): 1528-1537.

10.1093/icesjms/fsp047
13 

Ross, S. and Evans, D. 2003. The environmental effect of reusing and recycling a plastic-based packaging system. Journal of Cleaner Production 11(5): 561-571.

10.1016/S0959-6526(02)00089-6
14 

Raven, J. A. and Giordano, M. 2014. Algae. Current Biology 24(13): 590-595.

10.1016/j.cub.2014.05.03925004359
15 

Weil, E.D. and Levchik, S.V. 2007. Flame retardants for polystyrenes in commercial use or development. Journal of Fire Sciences 25(3): 241-265.

10.1177/0734904107071607
16 

Wells, M.L., Trainer, V.L., Smayda, T.J., Karlson, B.S.O., Trick, C.G., and Kudela, R.M. 2015. Harmful algal blooms and climate change: Learning from the past and present to forecast the future. Harmful Algae 49(1): 68-93.

10.1016/j.hal.2015.07.00927011761PMC4800334
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