- Email: [email protected]
Advanced wastewater treatment by integrated vertical flow constructed wetland with vetiveria zizanioides in north China
Procedia Earth and Planetary Science 1 (2009) 1258–1262
Procedia Earth and Planetary Science www.elsevier.com/locate/procedia
The 6th International Conference on Mining Science & Technology
Advanced wastewater treatment by integrated vertical flow constructed wetland with vetiveria zizanioides in north China Wang Xiaoa,b,*, Han Bao-pingb, Shi Ying-zhengb, Pang Zong-qiang a,b a
Jiangsu Key Laboratory of Resources and Environmental Information Engineering, Xuzhou 221116, China b China University of Mining and Technology, Xuzhou 221116, China
Abstract The use of tail water for irrigation is becoming increasingly common. However, raw tail water is often contaminated and can cause environmental harm and pose health risks. Nevertheless, it is often used without any significant pre-treatment, a practice mistakenly considered safe. The aim of this study is to explore the removal efficiency of Integrated Vertical Flow Constructed Wetland (IVFCW) with Vetiveria zizanioides, an economically sound, low-tech and easily maintainable treatment system that would allow safe and sustainable use of tail water for landscape irrigation for COD, NH3-N, TN at different hydraulic retention time and different temperature in north China. The IVFCW can remove about 71% of the chemical oxygen demand, 67% of NH3-N and 80% of TN after five days at the hydraulic load of 0.6～0.8m3/m2.d in summer；But at low temperature，all kinds of pollutants has a lower removal efficiency compared with summer. At 10℃, the highest removal ratio of CODCr, NH3-N, TN are only 51.71%, 19.87%, and 29.76%, respectively.
Keywords: Vetiveria zizanioides; Integrated Vertical-flow Constructed Wetland; tail water treatment
1. Introduction Increasing public awareness of environmentally related issues is helping to prompt increase governmental legislation for environmental protection that is demanding ever more stringent water and wastewater treatment standards. However, capital resources to implement and operate more conventional wastewater treatment infrastructures and facilities are becoming limited. Therefore, the development of alternative, small-scale and innovative economical water treatment technologies is being stimulated. The most sustainable solutions for wastewater recycling should be passive, self-adaptive living systems exploiting natural biogeochemical cycles occurring within microbial-based and plant-based unit process. Like their naturally occurring counterparts, ecologically engineered systems provide ecosystem services that are self adaptive
* Corresponding author. Tel.: + 86-13814426986. E-mail address: [email protected].
1878-5220/09/$– See front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.proeps.2009.09.194
W. Xiao et al. / Procedia Earth and Planetary Science 1 (2009) 1258–1262
1259
and low maintenance, and are sources for value added residuals. One such promising technology for wastewater treatment is the constructed wetland. The use of constructed wetlands for wastewater treatment and stormwater treatment has undergone dramatic development since the 1990s[1-3]. Research has shown that Integrated Vertical-flow constructed wetlands have a great potential for organic, nutrient (nitrogen and phosphorus), suspended solids and pathogen removal because of it’s unique oxidation-reduction environment, microbial activity, and community distribution [4-6]. Some evidences show that Vetiveria zizanioides has been used successfully in constructed wetlands for treatment of wastewater [7], has a great ability to remove total nitrogen (TN), ammonia nitrogen(NH3-N), total phosphorus, phosphate, chemical oxygen demand (CODCr), and biochemical oxygen demand, and has a significant effect on improving water quality[8]. This paper reports on the feasibility of biological nutrient removal from wastewater using Integrated Vertical-flow constructed wetlands, planted with Vetiveria zizanioides. The objectives are (a) to assess the system treatment efficiency under semi-Natural conditions, and (b) to assess microbial and plant biomass contributions to biological nutrient removal processes in the wetlands. 2. Materials and methods 2.1. Site description The integrated vertical-flow constructed wetland system was built in 2008 next to the sewage treatment station of China University of Mining and Technology and is used for the secondary treatment of municipal wastewater, with CODCr of 18.7~65.2 mg/L; NH3-N, 9.2~33.4mg/L; TN, 14.6~41.2mg/L; and pH, 7.0~7.2. The wastewater undergoes primary treatment at the Biological Treatment Plant of China University of Mining and Technology and then is channeled to a 1m×1m×0.75m×2 constructed wetland for secondary treatment. The vertical-flow beds are planted with Vetiveria izanioides. The substrate are 15cm gravel, 30cm Coal Slag and 10cm gravel from up to down (fig.1).
Fig. 1. The scheme of IVCW system
2.2. Water quality monitoring In order to allow the vegetation and bio-film to establish, sampling was started after three months of constructed wetland plant growth. Waste water entering and exiting from the IVCW units was monitored between May and December 2008 and average in situ measurements for temperature, and dissolved oxygen determined. Similar measurements were made along the length of the wetlands. Water samples were analyzed for NH3-N, TN, and COD. Analyses were conducted in accordance with standard methods for the examination of water and wastewater. 3. Results and discussion 3.1. Effect of hydraulic loadings on CODCr, NH3-N and TN removal efficiency The selected hydraulic loading are showed in table 1, the aim is to ascertain reasonable hydraulic loading for better removal efficiency of the CODCr, NH3-N, and TN. The effect of different hydraulic loadings on pollutants removal efficiency of the IVCW system are showed in table 1 and fig.2.
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Table 1. The effect of hydraulic loadings on pollutants removal efficiency
CODCr
NH3-N
TN
0.4
39.95
26.56
42.41
0.6
29.98
16.76
0.8
34.05
15.11
1.0
43.75
1.2 1.4
60
The Average Concentrations of Influent (mg/L)
The Average Removal Ratios (%) C/N
CODCr
CODCr
NH3-N
TN
0.9
69.82
40.1
52.26
29.64
1.0
74.74
38.87
50.57
30.75
1.1
71.74
34.35
39.75
26.3
34.59
1.3
67.54
26.41
25.85
42.44
27.13
40.29
1.1
62.91
18.64
23.35
48.9
28.58
37.62
1.3
60.96
16.19
18.16
NH3-N
TN
50 40 30 20 10 0 0.4
The Average Removal Ratios of Pollutants（%）
The Average Concentrations of Pollutants of Influent （mg/L）
Hydraulic Loadings (m3/m2.d)
0.6 0.8 1.0 1.2 1.4 Hydraulic Loading（m3/m2.d）
CODCr
80
NH3-N
TN
70 60 50 40 30 20 10 0 0.4
0.6 0.8 1.0 1.2 Hydraulic Loading（m3/m2.d）
1.4
Fig. 2. The effect of hydraulic loadings on pollutants removal efficiency
As shown in Table 1 and Fig.2., some conclusions are drawn as following: First, along with the increasing of hydraulic loadings, the removal efficiency of CODCr are relatively stable, and it indicated that the wetland system has a resistance to impact of CODCr load. The highest removal ratio occurred at the hydraulic load of 0.6m3/m2.d. The removal ratio of CODCr declined only 13.78% along with the hydraulic loading from 1.4m3/m2.d to 0.4m3/m2.d. Second, the removal ratios of NH3-N and TN are reduced with the hydraulic loading and pollutants concentration increased.There are no significant difference (P＞0.05)in NH3-N and TN removal ratios when the hydraulic loading is low (0.4 m3/m2.d. and 0.6 m3/m2.d) by T-test analysis. But when the hydraulic loading is higher than 0.8 m3/m2.d, the NH3-N and TN removal efficiency decrease significantly, and the differences (P＜0.05) is significantly. There are two reasons can explain the removal efficiency of NH3-N and TN declined with hydraulic loading increasing. One is that the main component of nitrogen is NH3-N. With the increase of hydraulic loading and the deficiency of oxygen release by Vetiveria zizanioides, nitrification and denitrification of the system are subject to certain restrictions. The other is the C:N of influent is just about 1.5~2, which is much lower than the best C:N=7~8. Therefore, considered synthetically, the suitable hydraulic loading showed be 0.6~0.8 m3/m2.d. 3.2. Effect of Temperature on CODCr , NH3-N and TN removal efficiency Temperature has a greatly influence on treatment effect of constructed wetland, the study was carried out from Oct. to Nov. 2008 and Jan. to Feb. 2009 (the aerial part of Vetiveria zizanioides faded). The hydraulic loading was 0.6~0.8m3/m2.d. The average influent concentrations and removal ratios at different water temperature are showed in table 2 and Fig.3. Table 2. The effect of temperature on pollutants removal efficiency of the IVCW system
W. Xiao et al. / Procedia Earth and Planetary Science 1 (2009) 1258–1262
1261
Daily Mean Temperature (℃)
The Average Concentrations of Influent (mg/L) CODCr
NH3-N
TN
CODCr
NH3-N
TN
25
29.98
16.76
24.64
1.2
74.74
38.87
50.57
20
33.45
19.89
28.58
1.2
70.36
34.25
47.78
18
36.34
24.22
34.44
1.1
68.24
33.67
45.65
15
42.88
27.68
36.53
1.2
61.49
30.81
40.56
10
45.67
25.66
34.26
1.3
51.71
19.87
29.79
5
55.31
28.27
38.13
1.5
33.98
7.15
15.89
1
47.16
29.5
39.24
1.2
20.63
0.90
3.39
CODCr
NH3-N
80
TN
The Average Removal Ratios of Pollutants（%）
The Average Concentrations of Pollutants of Influent （mg/L）
60
The Average Removal Ratios (%) C/N
50 40 30 20 10 0
CODCr
NH3-N
TN
70 60 50 40 30 20 10 0
25
20
18
15
10
5
1
Daily Mean Temperature （℃）
25
20 18 15 10 5 Daily Mean Temperature （℃）
1
Fig.3. The effect of temperature on pollutants removal efficiency of the IVCW system
As shown in Table 2 and Fig.3., some conclusions are drawn as following: First, the removal efficiency of CODCr, NH3-N and TN are correspondingly increased along with the increaseing of temperature and reduced with the temperature decreasing. Second, when temperature higher than 15℃, it has little effect on the removal efficiency of pollutants. The average removal ratios of CODCr changed from 61.49% to 74.74%; and the average removal ratios of NH3-N and TN reached 38.87% and 50.57% respectively. When temperature lower than 15℃, the effect on CODCr and TN removal efficiency is more significant than that of NH3-N. This phenomenon is due to that when temperature falled to below 10℃, the microbial activity decreases, the nutritional requirement of Vetiveria zizanioides reduces during dormant period, which lead to the ability of pollutants removal of the system reduces. And the influent concentration of pollutants are high. Because the matrix itself has a certain absorption ability of pollutants and the activity of some micro-organisms has been restored after a certain time, the removal ratio of CODCr can maintained at more than 20%; but the ramoval of NH3-N and TN are mainly depended on nitrification and denitrification, and temperature has a significant impact on the activity of nitrobacteria and denitrifying bacteria. According to some literatures, nitrification are stopped at 4℃[10,11]. So the ramoval efficiency of NH3-N and TN are very poor in winter of the system. 4. Conclusion Firstly, hydraulic loading has direct impact on pollutants removal of IVCW. In general case, the lower hydraulic loading, the higher removal rate of pollutants in the system. Comprehensively considered with the removal efficiency of various pollutants and economic efficiency, the suitble hydraulic loading shoud be 0.6～0.8 m3/m2.d. Secondly, the effect of tempture on the removal efficiency of pollutants are directly. In general case, the higher temperature, the higher the removal ratio of pollutants. When the average temperature higher than 15℃, removal
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efficiency of CODCr, NH3-N and TN were higher, too. Influenced by lower activity of nitrobacteria and the denitrifying bacteria at 1~5℃, NH3-N and TN removal ratios of the system are very low.
Acknowledgements This work was financially supported by Scientific Research Funds of China University of Mining & Technology. The authors would like to thank Master Luan Xiaoli and Qiang Yanyan for the help during construction of the experimental system and entire experiment course.
References [1] R.H. Kadlec and R.L.KnIgM, Treatment Wetlands. CRC Press, Boca Raton, 1996. [2] W. Scott, Advanced designs for constructed wetlands. Biocycle. 42 (2001) 40-43. [3] B. Gu, M.J. Chimney, J. Newman, Limnological characteristics of a constructed wetland in south Florida. Ecol. Eng. 27 (2006) 345-360. [4] W.Y. Zhao, Z.B. Wu and Q.H. Zhou, Removal of dibuty1 phthalate by a staged,vertical-flow constructed wetland. Wetlands. 24 (2004) 202206. [5] Z.B. Wu, G.L. Xu and P.J. Zhou, Removal Effects of Nitrogen in Integ rated Vertical Flow Constructed Wetland Sewage Treating System. Journal of Agro-environmental Science. 23 (2004) 757-760. [6]S. Kantawanichkul, S. Pilaila, W. Tanapiyawanich, Wastewater treatment by tropical plants in vertical-flow constructed wetlands. Water Science and Technology. 40 (1999) 173-178. [7] Y.B. Si, Purification of eutrophicated water body by Vetiveria zizanioids. Chinese Journal of Applied Ecology. 14 (2003) 277-279. [8] M. Tao and F. He, Redox character and purification of different function units in vertical-flow constructed wetland. Resources and Environment in the Yangtze Basin. 17 (2008) 291-294.
Procedia Earth and Planetary Science www.elsevier.com/locate/procedia
The 6th International Conference on Mining Science & Technology
Advanced wastewater treatment by integrated vertical flow constructed wetland with vetiveria zizanioides in north China Wang Xiaoa,b,*, Han Bao-pingb, Shi Ying-zhengb, Pang Zong-qiang a,b a
Jiangsu Key Laboratory of Resources and Environmental Information Engineering, Xuzhou 221116, China b China University of Mining and Technology, Xuzhou 221116, China
Abstract The use of tail water for irrigation is becoming increasingly common. However, raw tail water is often contaminated and can cause environmental harm and pose health risks. Nevertheless, it is often used without any significant pre-treatment, a practice mistakenly considered safe. The aim of this study is to explore the removal efficiency of Integrated Vertical Flow Constructed Wetland (IVFCW) with Vetiveria zizanioides, an economically sound, low-tech and easily maintainable treatment system that would allow safe and sustainable use of tail water for landscape irrigation for COD, NH3-N, TN at different hydraulic retention time and different temperature in north China. The IVFCW can remove about 71% of the chemical oxygen demand, 67% of NH3-N and 80% of TN after five days at the hydraulic load of 0.6～0.8m3/m2.d in summer；But at low temperature，all kinds of pollutants has a lower removal efficiency compared with summer. At 10℃, the highest removal ratio of CODCr, NH3-N, TN are only 51.71%, 19.87%, and 29.76%, respectively.
Keywords: Vetiveria zizanioides; Integrated Vertical-flow Constructed Wetland; tail water treatment
1. Introduction Increasing public awareness of environmentally related issues is helping to prompt increase governmental legislation for environmental protection that is demanding ever more stringent water and wastewater treatment standards. However, capital resources to implement and operate more conventional wastewater treatment infrastructures and facilities are becoming limited. Therefore, the development of alternative, small-scale and innovative economical water treatment technologies is being stimulated. The most sustainable solutions for wastewater recycling should be passive, self-adaptive living systems exploiting natural biogeochemical cycles occurring within microbial-based and plant-based unit process. Like their naturally occurring counterparts, ecologically engineered systems provide ecosystem services that are self adaptive
* Corresponding author. Tel.: + 86-13814426986. E-mail address: [email protected].
1878-5220/09/$– See front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.proeps.2009.09.194
W. Xiao et al. / Procedia Earth and Planetary Science 1 (2009) 1258–1262
1259
and low maintenance, and are sources for value added residuals. One such promising technology for wastewater treatment is the constructed wetland. The use of constructed wetlands for wastewater treatment and stormwater treatment has undergone dramatic development since the 1990s[1-3]. Research has shown that Integrated Vertical-flow constructed wetlands have a great potential for organic, nutrient (nitrogen and phosphorus), suspended solids and pathogen removal because of it’s unique oxidation-reduction environment, microbial activity, and community distribution [4-6]. Some evidences show that Vetiveria zizanioides has been used successfully in constructed wetlands for treatment of wastewater [7], has a great ability to remove total nitrogen (TN), ammonia nitrogen(NH3-N), total phosphorus, phosphate, chemical oxygen demand (CODCr), and biochemical oxygen demand, and has a significant effect on improving water quality[8]. This paper reports on the feasibility of biological nutrient removal from wastewater using Integrated Vertical-flow constructed wetlands, planted with Vetiveria zizanioides. The objectives are (a) to assess the system treatment efficiency under semi-Natural conditions, and (b) to assess microbial and plant biomass contributions to biological nutrient removal processes in the wetlands. 2. Materials and methods 2.1. Site description The integrated vertical-flow constructed wetland system was built in 2008 next to the sewage treatment station of China University of Mining and Technology and is used for the secondary treatment of municipal wastewater, with CODCr of 18.7~65.2 mg/L; NH3-N, 9.2~33.4mg/L; TN, 14.6~41.2mg/L; and pH, 7.0~7.2. The wastewater undergoes primary treatment at the Biological Treatment Plant of China University of Mining and Technology and then is channeled to a 1m×1m×0.75m×2 constructed wetland for secondary treatment. The vertical-flow beds are planted with Vetiveria izanioides. The substrate are 15cm gravel, 30cm Coal Slag and 10cm gravel from up to down (fig.1).
Fig. 1. The scheme of IVCW system
2.2. Water quality monitoring In order to allow the vegetation and bio-film to establish, sampling was started after three months of constructed wetland plant growth. Waste water entering and exiting from the IVCW units was monitored between May and December 2008 and average in situ measurements for temperature, and dissolved oxygen determined. Similar measurements were made along the length of the wetlands. Water samples were analyzed for NH3-N, TN, and COD. Analyses were conducted in accordance with standard methods for the examination of water and wastewater. 3. Results and discussion 3.1. Effect of hydraulic loadings on CODCr, NH3-N and TN removal efficiency The selected hydraulic loading are showed in table 1, the aim is to ascertain reasonable hydraulic loading for better removal efficiency of the CODCr, NH3-N, and TN. The effect of different hydraulic loadings on pollutants removal efficiency of the IVCW system are showed in table 1 and fig.2.
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Table 1. The effect of hydraulic loadings on pollutants removal efficiency
CODCr
NH3-N
TN
0.4
39.95
26.56
42.41
0.6
29.98
16.76
0.8
34.05
15.11
1.0
43.75
1.2 1.4
60
The Average Concentrations of Influent (mg/L)
The Average Removal Ratios (%) C/N
CODCr
CODCr
NH3-N
TN
0.9
69.82
40.1
52.26
29.64
1.0
74.74
38.87
50.57
30.75
1.1
71.74
34.35
39.75
26.3
34.59
1.3
67.54
26.41
25.85
42.44
27.13
40.29
1.1
62.91
18.64
23.35
48.9
28.58
37.62
1.3
60.96
16.19
18.16
NH3-N
TN
50 40 30 20 10 0 0.4
The Average Removal Ratios of Pollutants（%）
The Average Concentrations of Pollutants of Influent （mg/L）
Hydraulic Loadings (m3/m2.d)
0.6 0.8 1.0 1.2 1.4 Hydraulic Loading（m3/m2.d）
CODCr
80
NH3-N
TN
70 60 50 40 30 20 10 0 0.4
0.6 0.8 1.0 1.2 Hydraulic Loading（m3/m2.d）
1.4
Fig. 2. The effect of hydraulic loadings on pollutants removal efficiency
As shown in Table 1 and Fig.2., some conclusions are drawn as following: First, along with the increasing of hydraulic loadings, the removal efficiency of CODCr are relatively stable, and it indicated that the wetland system has a resistance to impact of CODCr load. The highest removal ratio occurred at the hydraulic load of 0.6m3/m2.d. The removal ratio of CODCr declined only 13.78% along with the hydraulic loading from 1.4m3/m2.d to 0.4m3/m2.d. Second, the removal ratios of NH3-N and TN are reduced with the hydraulic loading and pollutants concentration increased.There are no significant difference (P＞0.05)in NH3-N and TN removal ratios when the hydraulic loading is low (0.4 m3/m2.d. and 0.6 m3/m2.d) by T-test analysis. But when the hydraulic loading is higher than 0.8 m3/m2.d, the NH3-N and TN removal efficiency decrease significantly, and the differences (P＜0.05) is significantly. There are two reasons can explain the removal efficiency of NH3-N and TN declined with hydraulic loading increasing. One is that the main component of nitrogen is NH3-N. With the increase of hydraulic loading and the deficiency of oxygen release by Vetiveria zizanioides, nitrification and denitrification of the system are subject to certain restrictions. The other is the C:N of influent is just about 1.5~2, which is much lower than the best C:N=7~8. Therefore, considered synthetically, the suitable hydraulic loading showed be 0.6~0.8 m3/m2.d. 3.2. Effect of Temperature on CODCr , NH3-N and TN removal efficiency Temperature has a greatly influence on treatment effect of constructed wetland, the study was carried out from Oct. to Nov. 2008 and Jan. to Feb. 2009 (the aerial part of Vetiveria zizanioides faded). The hydraulic loading was 0.6~0.8m3/m2.d. The average influent concentrations and removal ratios at different water temperature are showed in table 2 and Fig.3. Table 2. The effect of temperature on pollutants removal efficiency of the IVCW system
W. Xiao et al. / Procedia Earth and Planetary Science 1 (2009) 1258–1262
1261
Daily Mean Temperature (℃)
The Average Concentrations of Influent (mg/L) CODCr
NH3-N
TN
CODCr
NH3-N
TN
25
29.98
16.76
24.64
1.2
74.74
38.87
50.57
20
33.45
19.89
28.58
1.2
70.36
34.25
47.78
18
36.34
24.22
34.44
1.1
68.24
33.67
45.65
15
42.88
27.68
36.53
1.2
61.49
30.81
40.56
10
45.67
25.66
34.26
1.3
51.71
19.87
29.79
5
55.31
28.27
38.13
1.5
33.98
7.15
15.89
1
47.16
29.5
39.24
1.2
20.63
0.90
3.39
CODCr
NH3-N
80
TN
The Average Removal Ratios of Pollutants（%）
The Average Concentrations of Pollutants of Influent （mg/L）
60
The Average Removal Ratios (%) C/N
50 40 30 20 10 0
CODCr
NH3-N
TN
70 60 50 40 30 20 10 0
25
20
18
15
10
5
1
Daily Mean Temperature （℃）
25
20 18 15 10 5 Daily Mean Temperature （℃）
1
Fig.3. The effect of temperature on pollutants removal efficiency of the IVCW system
As shown in Table 2 and Fig.3., some conclusions are drawn as following: First, the removal efficiency of CODCr, NH3-N and TN are correspondingly increased along with the increaseing of temperature and reduced with the temperature decreasing. Second, when temperature higher than 15℃, it has little effect on the removal efficiency of pollutants. The average removal ratios of CODCr changed from 61.49% to 74.74%; and the average removal ratios of NH3-N and TN reached 38.87% and 50.57% respectively. When temperature lower than 15℃, the effect on CODCr and TN removal efficiency is more significant than that of NH3-N. This phenomenon is due to that when temperature falled to below 10℃, the microbial activity decreases, the nutritional requirement of Vetiveria zizanioides reduces during dormant period, which lead to the ability of pollutants removal of the system reduces. And the influent concentration of pollutants are high. Because the matrix itself has a certain absorption ability of pollutants and the activity of some micro-organisms has been restored after a certain time, the removal ratio of CODCr can maintained at more than 20%; but the ramoval of NH3-N and TN are mainly depended on nitrification and denitrification, and temperature has a significant impact on the activity of nitrobacteria and denitrifying bacteria. According to some literatures, nitrification are stopped at 4℃[10,11]. So the ramoval efficiency of NH3-N and TN are very poor in winter of the system. 4. Conclusion Firstly, hydraulic loading has direct impact on pollutants removal of IVCW. In general case, the lower hydraulic loading, the higher removal rate of pollutants in the system. Comprehensively considered with the removal efficiency of various pollutants and economic efficiency, the suitble hydraulic loading shoud be 0.6～0.8 m3/m2.d. Secondly, the effect of tempture on the removal efficiency of pollutants are directly. In general case, the higher temperature, the higher the removal ratio of pollutants. When the average temperature higher than 15℃, removal
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efficiency of CODCr, NH3-N and TN were higher, too. Influenced by lower activity of nitrobacteria and the denitrifying bacteria at 1~5℃, NH3-N and TN removal ratios of the system are very low.
Acknowledgements This work was financially supported by Scientific Research Funds of China University of Mining & Technology. The authors would like to thank Master Luan Xiaoli and Qiang Yanyan for the help during construction of the experimental system and entire experiment course.
References [1] R.H. Kadlec and R.L.KnIgM, Treatment Wetlands. CRC Press, Boca Raton, 1996. [2] W. Scott, Advanced designs for constructed wetlands. Biocycle. 42 (2001) 40-43. [3] B. Gu, M.J. Chimney, J. Newman, Limnological characteristics of a constructed wetland in south Florida. Ecol. Eng. 27 (2006) 345-360. [4] W.Y. Zhao, Z.B. Wu and Q.H. Zhou, Removal of dibuty1 phthalate by a staged,vertical-flow constructed wetland. Wetlands. 24 (2004) 202206. [5] Z.B. Wu, G.L. Xu and P.J. Zhou, Removal Effects of Nitrogen in Integ rated Vertical Flow Constructed Wetland Sewage Treating System. Journal of Agro-environmental Science. 23 (2004) 757-760. [6]S. Kantawanichkul, S. Pilaila, W. Tanapiyawanich, Wastewater treatment by tropical plants in vertical-flow constructed wetlands. Water Science and Technology. 40 (1999) 173-178. [7] Y.B. Si, Purification of eutrophicated water body by Vetiveria zizanioids. Chinese Journal of Applied Ecology. 14 (2003) 277-279. [8] M. Tao and F. He, Redox character and purification of different function units in vertical-flow constructed wetland. Resources and Environment in the Yangtze Basin. 17 (2008) 291-294.