Study on potential plants for use in constructed wetlands to strengthen phosphorus treatment performance from swine wastewater

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY VU THI THOM STUDY ON POTENTIAL PLANTS FOR USE IN CONSTRUCTED WETLAND TO STRENGTHEN PHOSPHORUS TREATMENT PERFORMANCE FROM SWINE WASTEWATER MASTER'S THESIS Hanoi, 2019 VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY VU THI THOM STUDY ON POTENTIAL PLANTS FOR USE IN CONSTRUCTED WETLAND TO STRENGTHEN PHOSPHORUS TREATMENT PERFORMANCE FROM SWINE WASTEWATER MAJOR: ENVIRONMENTAL ENGINEERING CODE: PILOT SUPERVISORS DR NGUYEN THI AN HANG ASSOC PROF DR SATO KEISUKE DR NGUYEN THI HOANG HA Hanoi, 2019 ACKNOWLEDGMENTS First of all, I would like to express the sincere gratitude to my principal supervisor, Dr Nguyen Thi An Hang at VNU Vietnam Japan University, for accepting me as her master student and continuous teaching and supporting me in the process of doing experiments as well as writing essays and making presentations She always encourages and is willing to help me when I have difficulties She is always beside me to teach me how to work effectively This helps me grow up in both personal and professional aspects A special thanks also go to Assoc Prof Dr Sato Keisuke for his recommendations to my research He provided me with the best conditions for implementing my experiments during my internship in Japan He is wholeheartedly devoted to his students I would like to express my deepest thanks to Dr Nguyen Thi Hoang Ha She gave me valuable supports in developing research methods, and enthusiastically guided me to fullfil my thesis I always feel grateful to her for accompanying me for such a long time The second, I would like to send my sciencere thanks to Prof Dr Jun Nakajima for supporting not only me but also all of memerbers in my class during Master course He cares for us like his children And he is our respected father The third, I am grateful to Ms Nguyen Thi Xuyen, the project staff, for always supporting me in conducting experiments as well as analyzing environmental parameters This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 105.99-2018.13, 2018 Asean Research Center (ARC) research grant of Vietnam National University, Hanoi (VNU), and Japan International Cooperation Agency (JICA) research grant for the academic year of 2018-2019 My heartfelt thanks and gratitudes to my family for their unconditional helps with plant sampling, the love and encouragement Hanoi, June 9th, 2019 Vu Thi Thom i TABLE OF CONTENTS ACKNOWLEDGMENTS i LIST OF TABLES ii LIST OF FIGURES iii LIST OF ABBREVIATIONS v INTRODUCTION vi CHAPTER 1: LITERATURE REVIEW 1.1 Overview of the situation of pig husbandry in Vietnam .1 1.1.1 Current status and development orientation of pig breeding 1.1.2 Environmental pollution due to swine wastewater 1.1.3 Technologies for the treatment of swine wastewater .4 1.2 Phosphorous pollution and treatment technologies .5 1.2.1 Phosphorus pollution and its consequences 1.2.2 Phosphorus treatment technologies 1.3 Constructed wetland for wastewater treatment 1.3.1 Definition and classification of CWs 1.3.2 Influential factors and treatment performance 1.4 Removal phosphorus by plants in the CWs 12 1.4.1 Classification of plants used in CWs 12 1.4.2 Removal P mechanisms by plants 14 CHAPTER 2: MATERIALS AND RESEARCH METHODOLOGY .18 2.1 Research object, scale, and scope 18 2.1.1 Research object .18 2.1.2 Research scale & scope .18 2.2 Materials, chemicals and equipment 19 2.2.1 Materials 19 2.2.2 Experimental design 20 2.2.3 Plant sample preparation and P analysis .25 2.2.4 Analysis of other water quality parameters 26 2.3 Data calculation .27 2.4 Data statistical analysis .28 CHAPTER 3: RESULTS AND DISCUSSION .29 3.1 Screening potential plants for use in the CWs 29 3.1.1 Selection of potential plants based on their P content and biomass growth .29 3.1.2 Selection of CWs plants based on other growth characteristics 33 3.2 Factors influencing the growth and uptake of p of Cymbopogon citratus and Ubon paspalum 35 3.2.1 Effect of initial P concentration 35 3.2.2 Effect of pH 42 3.2.3 Effect of plant age 45 3.2.4 Effect of plant density 49 3.2.5 Effect of water level 52 3.3 Applicability of the selected plants in the constructed wetland 54 CHAPTER 4: CONCLUSION AND RECOMMENDATION 57 4.1 Conclusion 57 4.2 Recommendations 57 REFERENCE 58 APPENDIX 62 LIST OF TABLES Table 1.1 Annual growth rate of culture sector (%) Table 1.2 Composition and characteristics of swine wastewater Table 1.3 Methods for handing and using liquids at systems Table 1.4 main parameters of swine wastewater after biogas treatment Table 1.5 P removal by Constructed Wetland 11 Table 1.6 Plant species are used to treat swine wastewater .13 Table 1.7 P removal efficiency by plants in CW (Jesus et al., 2017) .15 Table 2.1 The list of investigated plants 19 Table 2.2 Methods for examination of water quality parameters 27 Table 3.1 The P content in plants use for phytoremediation or CWs 31 Table 3.2 The P removal potential of the studied plants 33 Table 3.3 Growth characteristics of potential plants 34 Table 3.4 The P removal efficiency by different plant species 39 Table 3.5 Biomass growth rate of Ubon paspalum at different plant ages 48 Table 3.6 Effect plant density on the biomass growth rate of Ubon paspalum .51 ii LIST OF FIGURES Figure 1.1 Eutrophication: cause and effect .5 Figure 1.2 P removal in CWs Figure 2.1 Scheme of horizontal constructed wetland 23 (at the start of experiment) 23 Figure 2.2 The structure of filter media in CWs and adsorption units 24 Figure 2.3 Plant sample preparation and analysis 25 Figure 2.4 Images of apparatus used in this study 26 Figure 3.1 The P content and its distribution in the studied plants 29 Figure 3.2 Images of the investigated plants in this study 34 Figure 3.3 Effect of initial P concentration on the removal efficiency of Cymbopogon citratus 37 Figure 3.4 Effect of initial P concentration on the removal efficiency of Ubon paspalum 37 Figure 3.5 P concentration left in solution plant with Ubon paspalum 38 Figure 3.6 P concentration left in solution planted with Cymbopogon citratus 38 Figure 3.7 Effect of intial P concentration on P removal rate of Ubon paspalum 40 Figure 3.8 Effect of intial P concentration on P removal rate of Cymbopogon citratus 40 Figure 3.9 Ubon paspalum died at the highest P concentration 41 Figure 3.10 Cymbopogon citratus could adapt with a wide range of initial P concentration 41 Figure 3.11 Normal growth of Cymbopogon citratus at all pH values 42 Figure 3.12 The death of Ubon paspalum at pH values of 9&11 43 Figure 3.13 Speciation of P in solution at various pH conditions 43 Figure 3.14 Effect of pH on P removal efficiency of Ubon paspalum and Cymbopogon citratus 44 Figure 3.15 Effect of pH on P removal rate of Ubon paspalum and Cymbopogon citratus 45 iii Figure 3.16 Effect of plant age on P removal efficiency and P removal rate of Ubon paspalum (hydroponic experiment) 47 Figure 3.17 The effect of plant age on the growth of root system 47 Figure 3.18 Effect of plant age on the biomass growth of Ubon paspalum 48 (experiment with garden soil) 48 Figure 3.19 Effect of plant density on P removal rate of the investigated plants 50 Figure 3.20 Effect of plant density on the P removal efficiency of the investigated plants 50 Figure 3.21 The root growth of Ubon paspalum at different plant densities 52 Figure 3.22 Effect of Ph on P removal rate of plants 53 Figure 3.23 Effect of water level on root growth of Ubon paspalum 54 Figure 3.24 The change of phosphorus in the effluent over the time 54 Figure 3.25 P removal efficiency and Ph after treatment of HFCWs 55 Figure 3.26 The plants growth well after weeks of system operation 56 iv LIST OF ABBREVIATIONS COD Chemical oxygen demand CW BOD EBPR EPA HF HLR HRT SSF SF TN TP TSS VF WHC Constructed Wetland Biological oxygen demand Enhanced biological phosphorus removal Environmental Protection Agency Horizontal flow Hydraulic loading rate Hydraulic retention time Subsurface water flow Surface flow Total nitrogen Total phosphorus Total suspended solids Vertical flow White hard clam v INTRODUCTION Background In Vietnam, in recent years, pig breeding industry has developed rapidly Since most of pig farms have not designed and operated appropriately, wastewater from pig farms cause serious environmental pollution, which poses a high risk to public health and surrounding ecosystems Therefore, the proper treatment of swine wastewater is urgent and necessary At present, swine wastewater in Vietnam is normally treated by biogas technology However, the concentration of pollutants in the effluent is still high, exceeding national discharge standards (QCVN 01-79: 2011/BNNPTNT) Thus, further processing after biogas treatment of swine wastewater is mandatory Constructed wetlands (CWs) is a promising technology, which possesses many advantages, such as cost-effective, green technology (Wu et al., 2015; Yang et al, 2018;), low land, energy, and less-operational requirements (Wu et al., 2015); simple construction and operation (Bunce et al., 2018) However, the wide application of CWs is limited by intensive land requirement, long-term unsustainability (Bunce et al., 2018) Especially, although CWs can achieve high removal efficiency with TSS, COD, BOD, it is demonstrated to be inefficient in nutrient elimination It is wellknown that the treatment performance of phosphorus by CWs is low and unstable Hence, the enhancement of phosphorus removal by CW is of great significance Since phosphorus is eliminated by CWs mainly via substrate adsorption, plant uptake, microbial degradation, selection and application of potential plants in CWs plays an important role Plant-based treatment technology is known as phytoremediation, which receives the great interests of scientists in the world So far, a numerous number of studies on successful phytoremediation of wastewater polluted by phosphorus The most common types of plant species for nutrient removal are Typha latifolia, Cyperus papyrus, Phragmite australiis (Almuktar et al., 2018) TP removal efficiency of vi 3.2.4 Effect of plant density on its growth and P uptake The total amount of removed P by a plant depends not only on the P content in the plant but also on the biomass growth (Schwammberger et al, 2019) However, biomass growth is reporeted to be affected by the plant density (Jethwa and Bajpai, 2016) This experiment was designed to identify the optimum plant density for the best growth and P uptake by Ubon paspalum and Cymbopogon citratus The experiments with hydroponic solutions were conducted with kinds of plant densities (1, 3, and plants per beaker) for both Ubon paspalum and Cymbopogon citratus It was lasted for 21 days (7 turns) Every days, hydroponic solutions were changed and wastewater samples were collected for P analysis to evaluate the P removal rate and P removal efficiency The experiments with soil was performed with categories of plant densities (1, 2, 3, and plants per trough – 0.5 m2) for only Ubon paspalum It lasted for months (March to May 2019) At the start and the end of experiment, the biomass was measured to evaluate the biomass growth rate and P content in different parts of plant Relating the hydroponic experiments, the effect of plant density on the P removal rate and P removal efficiency of the investigated plants were shown in Figures 3.19 & 3.20 It was found that the higher the plant density was, the slower the P removal rate was oberverd for both Ubon paspalum and Cymbopogon citratus Specifically, the P removal rate of Cymbopogon citratus was decreased from 19.63 to 11.22 mg P/ kg biomass/ d when the plant density increased from to plant/ beaker The higher P removal rate at lower plant density can be attributed to less competition between plants when there were fewer plants in the beaker The similar results were released when Webb et al (2013) Accordingly, the P removal rate of Salicornia europaea at high and low plant densities were found to be 19.96 26.09 mg P/ kg biomass/ d, respectively The opposite trend occurred with the P removal efficiency for both Cymbopogon citratus and Ubon paspalum The P removal efficiency of Cymbopogon citratus was elevated from 22.43 to 51.04% when the plant density increased from to plant/ beaker This can be explained by the fact that the 49 nutrient demand was higher for a greater number of the plant in the beaker The same trend happened to Ubon paspalum However, the reduction in the P removal efficiency as the result of increase in plant density for Cymbopogon citratus (28.61%) was higher than that for Ubon paspalum (15.84%) This indicates that more attention P removal rate (mg P/ kg/ d) should be paid to the plant desnity if Cymbopogon citratus was planted in the CWs 25 20 15 10 plant plants plants Plant density (plant/ beaker) Ubon paspalum Cymbopogon citratus P removal efficiency (%) Figure 3.19 Effect of plant density on P removal rate of the investigated plants 60 50 40 30 20 10 plant plants plants Plant density (plant/ beaker) Ubon paspalum Cymbopogon citratus Figure 3.20 Effect of plant density on the P removal efficiency of the investigated plants 50 Concerning the soil tests with Ubon paspalum, the results on the biomass and biomass growth rate were summarized in Table 3.6 The biomass growth rate of Ubon paspalum was decreased from 10.12 to 3.65 g/d when the plant density increased from 10 to 40 plant/ m2 In contrast, the higher accumulative harvested biomass was obtained at the higher plant density from 10 to 30 plants/ m2 The biomass growth was increased from 6070 to 10290 g when the plant density elevated from 10 to 30 plants/ m2 The highest biomass (10290 g) was obtained at the plant density of 30 plant/m2 At the plant density of 10, 20 or 40 plant/m2, the biomass was low (6070, 7735 and 8748 g) compared with the max biomass Thus, these plant densities should not be used Taking into account both biomass and biomass growth rate, the best plant density was 30 plant/m2 This finding was validated by the observation that the root system of Ubon paspalum was longest (up to 0.8 m) at this plant density (Figure 3.21) Table 3.6 Effect plant density on the biomass growth rate of Ubon paspalum Density (plant/ m2) 10 20 30 40 Initial biomass (g) 300 600 900 1200 Accumulative harvested biomass (g) 6370 8335 11190 9948 51 Biomass growth (g) 6070 7735 10290 8748 Biomass growth rate (g/d) 10.12 6.45 5.72 3.65 Density (1 plants/ 0.1 m2) Density (1 plants/ 0.1 m2) Density (3 plants/ 0.1 m2) Density (5 plants/ 0.125 m2) Figure 3.21 The root growth of Ubon paspalum at different plant densities 3.2.5 Effect of water level on its growth and P uptake Water levels significantly affected plant growth rate and nutrient removal capacity (Ngo et al, 2018) Study the effect of flooding on the rate of P uptake and plant growth to determine the appropriate water level in CWs construction This experiment was conducted with three water levels (2, 5, and cm in 500 mL beaker) The experiment results were illustrated in Figure 3.22 It can be seen from Figure 3.22 that the P removal rate was highest at the water level of cm, which was 17.74 and 10.32 mg P/kg biomass/d for both Cymbopogon citratus and Ubon paspalum, respectively The P removal rate was lowest at the water level of cm This is probably because the flooding significantly affected the growth of plants, thus reducing the P uptake ability of the plants The P removal rate at the water level of cm was lower than that at the water level of cm This is because the less P content could be found in the P solution with lower volume This study indicates that the superior P removal rate could be obtained with lower water levels Similarly, Ngo et al (2013) found that Typha orientalis could grow and uptake P better at lower water levels In the contrary, the better P removal rate of Spirodela oligorrhiza was found at higher water depths (Xu and Shen, 2011) This is because Spirodela oligorrhiza was floating plant Therefore, it is more tolerant to flooding 52 than emergent plants Therefore, higher water depths could not hamper its growth and P removal rate (mg P/ kg/ d) P uptake 20 16 12 Water level (cm) Ubon paspalum Cymbopogon citratus Figure 3.22 Effect of water level on P removal rate of plants The removal P rate of Cymbopogon citratus varied from 11.58 to 17.74 mg/kg/d, which was 1.57-1.88 times higher than that of Ubon paspalum The result exhibited that Cymbopogon citratus could survive at all water levels In contrast, Ubon paspalum was dramatically affected by water level of cm For two out of five turns, the stem of plants turned black and the ruined At the water level of cm, new roots did not appear for all the experiment period In contrast, the growth of new roots was enhanced at two lower water level, especially at the water level of cm The effect of water level on the root growth was quite similar to that on P removal rate These results indicated that the water level of cm was the optimal for both investigated plants and Ubon paspalum was more sensitive to flooding than Cymbopogon citratus 53 Figure 3.23 Effect of water level on root growth of Ubon paspalum 3.3 Applicability of the selected plants in the Constructed Wetland P concentration (mg P/L) 10-May 15-May 20-May 25-May 30-May 4-Jun 9-Jun Date of sampling Tank2 Tank4 Tank1 Adsorption unit Tank3 Adsorption unit Figure 3.24 The change of phosphorus in the effluent over the time This experiment was conducted to assess the role of removing P of plants in CWs tanks for Ubon paspalum and tanks for control were established Besides, the role of CW unit and adsoption unit is also assessed The plants before being tranfered to the system is cut and leave 25 cm of stem with a volume of 400 g per tank In the beginning, the plants grew slowly However, after weeks of adapting the tree the growth rate of the plant was faster, the new 54 branch appeared and many new roots, the height of the plants from 25 cm initially 120 14 100 12 10 80 60 40 pH P removal efficiency (%) increased to m 20 0 Tank Tank Tank Tank % P removal Adsorption Adsorption pH Figure 3.25 P removal efficiency and pH after treatment of HFCWs The difference in the efficiency of treatment performance between the planted CWs system and without plant CWs has obtained some initial results For CWs with substrate as WHC, the role of the plants occupies 1.9% while the role of the plants in CWs with yellow sand as substarte was 3.5% The role of plants in the yellow sand system is slightly higher than that of a WHC substrate The P removal efficiency of CWs (containing WHC) is lower than that of the sand system, which may be related to differences in Ph in these two systems pH in tank - WHC (8.1) is higher than tank –yellow sand (7.7) According to previous studies, pH = 5.5 - is suitable for plant growth and absorption In addition to, the difference is not much Because the system's operating time is quite short and plants has not enough time to adapt When the CWs tank with sand is soon saturated, the difference of the role of plants in system CWs will be clearer Curently, the contribution of plants in the P removal efficiency is very small It need to takes longer observation time 55 After 29 days of operation, the treatment efficiency of the system reaches 9598.7% The removal efficiency of P for WHC system (98%) is 21% higher than the average yellow sand system Summary, the removal efficiency of P of the system still follows the good trend in WHC while becoming more saturated in the sand system To improve the effectiveness of the plant's P removal, pay attention to selecting the young plants and putting them in the background soulution after week before transferring them to the The first days of experiment After two weeks operation of experimetn Figure 3.26 The plants growth well after weeks of system operation 56 CHAPTER 4: CONCLUSION AND RECOMMENDATION 4.1 Conclusion • Among investigated plants, Cymbopogon citratus and Ubon paspalum were most potential for use as CWs plants, because of high biomass, fast growth, high P uptake, good tolerance to flooding and perennial and uncommon CWs plants • Concerning influential factors, Cymbopogon citratus grew the best at pH and was tolerant with high P concentration (up to 50 mg/L) and water level (8 cm for week) Ubon paspalum grew the best at pH 7, was less tolerant with high P concentration (25 mg/L) and water level (5 cm for week) than Cymbopogon citratus The younger the Ubon paspalum was, the higher the P removal rate was The best harvest time for Ubon paspalum was months after planting • In the WHC-based CWs, Ubon paspalum adapted well In the start-up period, this plant contributed to 1.9 – 3.5 % to the P removal of CWs 4.2 Recommendations • This study was implemented in a short period of time, which was inadequate for the complete assessment the P accumulation in the plant A longer study with the same plant should be done in the future • This study was conducted with the simulated wastewater containing only P It is highly recommended to conduct further research with the real wastewater and multiple pollutants • The effect of season on the growth and P uptake of plant should also be investigated in the future work 57 REFERENCE Almuktar, S A., Abed, S N., & Scholz, M (2018) Wetlands for wastewater treatment and subsequent recycling of treated effluent: a review Environmental Science and Pollution Research, 25(24), 23595-23623 Bhandari, A., Surampalli, R Y., Champagne, P., Ong, S K., Tyagi, R D., & Lo, I M (2007) Remediation technologies for soils and groundwater Reston, Virginia: ASCE Bodin, H (2013) Wastewater treatment in constructed wetlands: effects of vegetation, hydraulics and data analysis methods (Doctoral dissertation, Linköping University Electronic Press) Bunce, J T., Ndam, E., Ofiteru, I D., Moore, A., & Graham, D W (2018) A review of phosphorus removal technologies and their applicability to small-scale domestic wastewater treatment systems Frontiers in Environmental Science, 6, Chandekar, N., & Godboley, B J (2017) A review on phytoremediation a sustainable solution for treatment of kitchen wastewater Int J Sci Res (IJSR), 6(2), 1850-1855 Chen, C., Zhao, T., Liu, R., & Luo, L (2017) Performance of five plant species in removal of nitrogen and phosphorus from an experimental phytoremediation system in the Ningxia irrigation area Environmental monitoring and assessment, 189(10), 497 Cunningham, S D., & Ow, D W (1996) Promises and prospects of phytoremediation Plant physiology, 110(3), 715 da Silva Cerozi, B., & Fitzsimmons, K (2016) The effect of pH on phosphorus availability and speciation in an aquaponics nutrient solution Bioresource technology, 219, 778-781 Davis, L (1995) A guide to creating wetlands for agricultural wastewater, domestic wastewater, coal mine drainage and stormwater in the Mid-Atlantic Region 1, general considerations USDA-NRCS, US EPA-Region III, and PA Department of Environmental Resources Demars, B O L., & Edwards, A C (2008) Tissue nutrient concentrations in aquatic macrophytes: comparison across biophysical zones, surface water habitats and plant life forms Chemistry and Ecology, 24(6), 413-422 58 Fu, X., & He, X (2015, April) Nitrogen and phosphorus removal from contaminated water by five aquatic plants In 2015 International Conference on Mechatronics, Electronic, Industrial and Control Engineering (MEIC-15) Atlantis Press Nguyễn Sáng (2016) Nghiên cứu xử lý nước thải chăn nuoi phương pháp sinh học kết hợp lọc màng Luận án tiến sĩ, Đại học Khoa học Tự nhiên, ĐHQGHN Gao, J., Song, Z., & Liu, Y (2019) Response mechanisms of leaf nutrients of endangered plant (Acer catalpifolium) to environmental factors varied at different growth stages Global Ecology and Conservation, 17, e00521 Greenway, M (1997) Nutrient content of wetland plants in constructed wetlands receiving municipal effluent in tropical Australia Water Science and Technology, 35(5), 135-142 Greenway, M (2003) Suitability of macrophytes for nutrient removal from surface flow constructed wetlands receiving secondary treated sewage effluent in Queensland, Australia Water Science and Technology, 48(2), 121-128 Haller, W T., & Sutton, D L (1973) Effect of pH and high phosphorus concentrations on growth of water hyacinth Hyacinth Control Journal, 11, 59-61 Jenkins, D., & Hermanowicz, S W (1991) Principles of chemical phosphate removal IN: Phosphorous and Nitrogen Removal from Municipal Wastewater: Principles and Practice nd ed Lewis Publishers, Boca Raton, Florida 1991 p 91110 15 fig, tab, 23 ref Jethwa, K., & Bajpai, S (2016) Role of plants in constructed wetlands (CWS): A review J Chem Pharm Sci, 2, 4-10 Jesus, J M., Danko, A S., Fiúza, A., & Borges, M T (2018) Effect of plants in constructed wetlands for organic carbon and nutrient removal: a review of experimental factors contributing to higher impact and suggestions for future guidelines Environmental Science and Pollution Research, 25(5), 4149-4164 Kamran, M A., Mufti, R., Mubariz, N., Syed, J H., Bano, A., Javed, M T., & Chaudhary, H J (2014) The potential of the flora from different regions of Pakistan in phytoremediation: a review Environmental Science and Pollution Research, 21(2), 801-812 Pasek, M (2019) A role for phosphorus redox in emerging and modern biochemistry Current opinion in chemical biology, 49, 53-58 Leto, C., Tuttolomondo, T., La Bella, S., Leone, R., & Licata, M (2013) Effects of plant species in a horizontal subsurface flow constructed wetland– 59 phytoremediation of treated urban wastewater with Cyperus alternifolius L and Typha latifolia L in the West of Sicily (Italy) Ecological engineering, 61, 282-291 Lou, Y., Lu, X., Wang, G., & Jiang, M (2012) Nitrogen and phosphorus contents of wetland plant tissues in sanjiang plain, northeast china Fresenius Environmental Bulletin, 21(2 A), 503-508 Qin, R., & Chen, H (2016, October) The procession of constructed wetland removal mechanism of pollutants In 2016 4th International Conference on Mechanical Materials and Manufacturing Engineering Atlantis Press Rezakhani, L., Motesharezadeh, B., Tehrani, M M., Etesami, H., & Hosseini, H M (2019) Phosphate–solubilizing bacteria and silicon synergistically augment phosphorus (P) uptake by wheat (Triticum aestivum L.) plant fertilized with soluble or insoluble P source Ecotoxicology and environmental safety, 173, 504-513 Shane, M W., McCully, M E., & Lambers, H (2004) Tissue and cellular phosphorus storage during development of phosphorus toxicity in Hakea prostrata (Proteaceae) Journal of Experimental Botany, 55(399), 1033-1044 Schwammberger, P F., Lucke, T., Walker, C., & Trueman, S J (2019) Nutrient uptake by constructed floating wetland plants during the construction phase of an urban residential development Science of The Total Environment, 677, 390403 Soti, P G., Jayachandran, K., Koptur, S., & Volin, J C (2015) Effect of soil pH on growth, nutrient uptake, and mycorrhizal colonization in exotic invasive Lygodium microphyllum Plant ecology, 216(7), 989-998 Wu, H., Zhang, J., Ngo, H H., Guo, W., Hu, Z., Liang, S., & Liu, H (2015) A review on the sustainability of constructed wetlands for wastewater treatment: design and operation Bioresource technology, 175, 594-601 Xu, J., & Shen, G (2011) Effects of harvest regime and water depth on nutrient recovery from swine wastewater by growing Spirodela oligorrhiza Water Environment Research, 83(11), 2049-2056 Yan, T., Zhu, J., Yang, K., Yu, L., & Zhang, J (2017) Nutrient removal under different harvesting scenarios for larch plantations in northeast China: Implications for nutrient conservation and management Forest Ecology and Management, 400, 150-158 Zhang (2018) DNDC model is able to simulate the vine biomass at different planting ages in vineyards in Ningxia, China Acta Ecologica Sinica, CHNAES00555 60 Zheng, Z C., Li, T X., Zeng, F F., Zhang, X Z., Yu, H Y., Wang, Y D., & Liu, T (2013) Accumulation characteristics of and removal of nitrogen and phosphorus from livestock wastewater by Polygonum hydropiper Agricultural water management, 117, 19-25 Zhou, Q., Zhu, H., Bañuelos, G., Yan, B., Liang, Y., Yu, X., & Chen, L (2017) Effects of vegetation and temperature on nutrient removal and microbiology in horizontal subsurface flow constructed wetlands for treatment of domestic sewage Water, Air, & Soil Pollution, 228(3), 95 http://nhachannuoi.vn/chan-nuoi-lon-tai-viet-nam-thuc-trang-va-trien-vong/ 61 APPENDIX a) CW system in Koka Shiga b) CW system in Mombetsu, Hokkaido c) Material filter used in CWs d) CW system in Higashikagura, Hokkaido e) Doing experiment in Ritsumeikan University Appendix 1: Visiting CWs and doing experiment during internship in Japan 62 a) Swine wastewater sampling b) Ubon paspalum sampling c) Synthetic wastewater sampling d) Ubon paspalum in home garden Appendix 2: Sampling and doing experiment in Vietnam 63