cws in china

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Ecological Engineering 35 (2009) 13671378

Contents lists available at ScienceDirect

Ecological Engineering

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / e c o l e n g

Review

Constructed wetlands in China

Dongqing Zhang a,, Richard M. Gersberg b, Tan Soon Keat c

a DHI-NTU Centre, Nanyang Environment & Water Research Institute, N1-B3b-29, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singaporeb Graduate School of Public Health, San Diego State University, Hardy Tower 119, 5500 Campanile, San Diego, CA 92182-4162, USAc Maritime Research Centre, School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore

a r t i c l e i n f o

Article history:

Received 29 May 2009

Received in revised form 27 June 2009

Accepted 20 July 2009

Keywords:

China

Constructed wetlands

Role of wetland plants

Design of constructed wetlands

a b s t r a c t

Large-scale centralized wastewater treatment systems oftenprevail in industrialcountriesand havebeenregarded as a successful approach during the last century. However, to solve the multifold water-related

problems in China with its rapid growth of urbanization and industrialization, complete replication of

this centralized, cost- and energy-intensive technology has proved to be extremely limited in scope and

success. As one of the most important applications of ecological engineering, constructed wetland (CW)

systems for wastewater treatment can offer an optimal alternative and result in beneficial conserva-

tion of natural resources with low capital costs and energy consumption, as well as minimal operation

and maintenance expenditures. CW technology is particularly suitable for rapidly growing small- and

medium-size cities in China. Thispaper aimsat examining themechanismsof pollutantremovalefficiency

in these systems and investigating the merits, status and feasibility of usingconstructed wetland systems

to treatment wastewater in China. Additionally, it investigates existing impediments to application and

implementation of CWs in China, as well as challenges to future development.

2009 Elsevier B.V. All rights reserved.

1. Introduction

Rapid urbanization and industrialization, and highly acceler-

ated economic development in China have resulted in excessive

water consumption and degradation of water resources. Histori-

cally, traditional centralized sewer systems have been regarded as

the optimal solution forwaterpollution control andhave prevailed

in many industrial countries. To a large degree, this centralized

approach did and does solve the problems of sanitation very effi-

ciently. However, at the end of 2002, the official rate of municipal

wastewater treatment was approximately 36.5%, which is far from

adequate given Chinas serious water pollution (U.S. Department

of Commerce, 2005; Wang et al., 2005b). It follows then, that in

order to solve the multifold water-related problems in China, com-

plete replication of centralized water-, energy- and cost-intensivetechnology has proven to be rather limited and not entirely

feasible.

Amongst 660 cities in China, more than half of which are

of medium- (population between 200,000 and 500,000) and

small-size (population less than 200,000) (China Daily Report,

2005), and this is reflected by the fact that 50% of the pop-

ulation of China still resides in these small- to medium-size

Corresponding author. Tel.: +65 8165 6212; fax: +65 6790 6620.

E-mail address: [email protected] (D. Zhang).

urban areas. While big cities are predominantly served by sewagetreatment plants based on conventional intensive technolo-

gies (physicalchemicalbiological treatment), there is increasing

doubt that whether these intensive technologies for sewage

treatment systems are appropriate for medium- and small-size

municipalities (Brissaud, 2007).

Constructed wetlands (CWs) for wastewater treatment have

great potential as an optimal alternative and would be ideal for

Chinas small- to moderate-size cities. Indeed, in other places

worldwide, CWs have proved to be an attractive and stable alter-

native because of their low cost, and energy savings. In addition,

there is the advantage of multi-purpose re-use of the high quality

effluent, self-remediation and self-adaptation to the surrounding

conditions and environment (Song et al., 2006; Brissaud, 2007;

Kivaisi, 2001).It is the objective of this paper to review the progress of

CWs for wastewater treatment in China with the aim of delineat-

ing some of the key treatment efficiency and performance issues

which may be elucidated by the China experience, including the

following:

Design; Specific role of the plant; Effect of climate; Cost/energy/space efficiency; Sustainability.

0925-8574/$ see front matter 2009 Elsevier B.V. All rights reserved.

doi:10.1016/j.ecoleng.2009.07.007
http://www.sciencedirect.com/science/journal/09258574http://www.elsevier.com/locate/ecolengmailto:[email protected]://dx.doi.org/10.1016/j.ecoleng.2009.07.007http://dx.doi.org/10.1016/j.ecoleng.2009.07.007mailto:[email protected]://www.elsevier.com/locate/ecolenghttp://www.sciencedirect.com/science/journal/09258574


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1368 D. Zhang et al. / Ecological Engineering35 (2009) 13671378

Through a review of the Chinese CW experience, we may better

define the scope and issues at hand, and by doing so, overcome

certain key challenges for the future development.

2. Ecological engineering in China

As a relatively new branch of ecology and an interdisciplinary

science, ecological engineering was initially formulated in the

1960s. Ecologicalengineering as describedby Mitsch and Jrgensen

(1989) is engineering in thesensethat it involves thedesign of this

natural environmentusing quantitative approaches and basing our

approaches on basic science.

The term ecological engineering was in the 1960s first inde-

pendently proposed by Prof. Ma Shijun, known as the father of

ecological engineering in China (Mitsch and Jrgensen, 2003a;

Yan et al., 1993; Ma, 1988). He argued in 1978 that in recognition

of the interdependency of social, economic and natural systems,

a cross between social and natural sciences could form the theo-

retical basis for treating the ecological crises the world was facing

(Ma,1988; Yanet al., 1993;Ma, 1978). Ma (1988) definedecological

engineering as . . .a specially designed system of production pro-

cess in which theprinciples of thespecies symbiosisand thecycling

and regeneration of substances in an ecological system are applied

with adopting the system engineering technology and introducing

new technologies and excellent traditional production measures

to make a multi-step use of substance (Mitsch et al., 1993; Mitsch

and Jrgensen, 2003a). Yan et al. (1993) reported that during the

period of 1970 to 1990, the dissemination of the knowledge and

techniques of ecological engineering resulted in a rapid growth of

its popularity all over China. Over 2000 experimental sites for the

ecologicalengineering of agriculture andenvironmental protection

have been founded in allthe provincesof mainland China.Over 100

sites for the ecological engineering of wastewater treatment and

utilization were created as well.

Indeed, the special historical background, ancient Chinese phi-

losophy and rich traditions of Chinese agricultural practices,as wellas the socialeconomical settings in Chinagive ecologicalengineer-

ing in China many rich and distinct characteristics. Mitsch et al.

(1993) concluded that differences between Western and Chinese

systems related to design principles, objectives, human manipula-

tion of ecosystem structure, and recognized values and economics.

Theemphasisof ecological engineering in theWesthas been a part-

nership with nature and research has been carried our primarily

in experimental ecosystems rather than in full-scale applications.

Ecological Engineering, as pioneered by Ma in China, has been

applied to a wide variety of natural resource and environmental

problems, ranging from fisheries and agriculture, to wastewater

control and coastline protection (Mitsch et al., 1993; Mitsch and

Jrgensen, 2003a,b; Mitsch, 1997). In addition, in the west, the goal

of ecological engineering projects is usually environmental protec-tion, while in China it is notonlyenvironmental protection, butalso

economic and social benefits (Mitsch et al., 1993).

As one of the most important applications of ecological engi-

neering, constructed wetlands (CWs) systems for wastewater

treatment could offer an optimal alternative and result in bene-

ficially natural resources conversation with low capital costs, low

energy consumption, and minimal operation and maintenance.

The first full-scale CW (SSF system) for wastewater treatment

from small or medium scale towns in the sub-tropics in China

Bainikeng Constructed Wetland was put in operation in July 1990

at Longgang, Shenzhen Special Economic Zone (Yang et al., 1995).

Other early established CWsin China include: theFWS systembuilt

in Changping District, Beijing for municipal sewage treatment (Li

and Jiang, 1995), the in-series FWS for petrochemical effluent treat-

ment designed by Yanshan Petrochemical Company in Beijing (Li

and Jiang, 1995), and an infiltration wetland system for domestic

sewage treatment located on the costal salinealkali soil on Dagang

Oil Field near Tianjin City(Li andJiang, 1995). These are considered

to be milestones of CW application in China (Chen et al., 2008).

3. The design of constructed wetlands

In general, two types of constructed wetlands systems are most

commonly designed and used: the Free Water Surface (FWS) sys-

tems, the Subsurface Flow (SSF) systems including horizontal- or

vertical flow. SFW systems are similar to natural marshes as they

tend to occupy shallow channels and basins through which water

flows at low velocities above and within the substrate. In SSF

systems, wastewater flows horizontally or vertically through the

substrate, which is composed of soil, sand, rock or artificial media.

3.1. Subsurface flow vs. free water surface wetlands

Table 1 summarizes several applications of the FWS sys-

tem in China and presents relative treatment efficiencies.

Compared to the discharge standards set by the Chinese Gov-

ernment (Environment Bureau of the State, 1997) (COD


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D. Zhang et al. / Ecological Engineering35 (2009) 13671378 1369

Table 1

A summary of the treatment efficiency of FWS systems in China.

TSS BOD5 COD NH4-N TN TP Hydraulic loading

rate (m3/day)

Hydraulic retention

time (day)

Changping, Beijinga

Effluent value (mg/l) 17 17.8 5.1 0.42 500 7.3

Removal efficiency (%) 93.8 85.8 64.6 55.1

Qinghe, Beijing

a

Effluent value (mg/l) 6.1 5.6 3.08 0.34 120 5.6


CW1, Tianjina

Effluent value (mg/l) 19.5 18.1 19.54 0.98 200 1.53.0


CW2, Tianjin (infiltration type)a

Effluent value (mg/l) 11.4 10.3 6.15 0.32 1800 10

Removal efficiency (%) 90 85 83.4 86

Public Park, Shanghaib

Effluent value (mg/l) 30 7.7 32 9.7 0.53 1.2

Removal efficiency (%) 70 15.4 17.9 10.2 18.5

Liaohec

Effluent value (mg/l) 3.9 77 1.6 18.75 15

Removal efficiency (%) 88 80 86

Taihu, Zhejiang Provinced

Effluent value (mg/l) 5.93 1.37 3.97 0.103 0.64 m/day


Average efficiency in China (%) 83.50 66.13 38.13 49.11 53.15

a Li and Jiang (1995).b Li et al. (2009).c Ji et al. (2007).d Li et al. (2008).

in Europe (Haberl et al., 1995), even under relatively high loading

rates, the removal efficiencies of TSS (75.50%), BOD5 (82.22%) and

COD (70.09%) in China are slightly better. In particular, the average

removal efficiencies of TN (56.09%) and TP (59.0%) in HSSF systems

in China are much higher than that in Europe (39.8% and 31.7%

respectively).Table 3 summarizes the application of VSSF systems in China.

Compared with HSSF systems, VSSF systems usually require

smaller foot print (Lderitz et al., 2001), and it is therefore an

attractive alternative for southern China where land is scarce and

population density is high. In a pilot VSSF system near Longdao

River in Beijing, CW occupied less than half of the area of conven-

tional CW following adoption of an improved design. The authors

compared Longdao VSSF system with other HSSF systems in other

countries, the removal efficiencies of BOD5 (87.2%), COD (81.8%)

and TSS (85.1%) of the VSSF CWs are verified comparable to the

highest performers, whilethe removal efficienciesof TP (98.8%) and

NH3-N (77.4%) are much higher than that in other countries. Addi-

tionally, the effluent concentrations of all substances were stable

even duringthe winter(Chen et al., 2008). Experiences showedthatin China (see Tables 2 and 3), although VSSF systems are efficient at

BOD5 and TP removal because of good oxygen supply, the removal

rate of TN (43.66%) and NH4-N (56.17%) remains lower in com-

parison of that in HSSF systems (56.09% and 64.59%, respectively),

probably due to the lack of carbon source during denitrification.

Also, despite the smaller foot print, the technical demand and cost

of VSSF systems are relatively higher than that of HSSF ( Yin et al.,

2008).

3.3. Hybrid wetland systems

As wastewater from various sources are generally difficult to

treat in a single-stage wetland system, hybrid wetland systems

which consist of various types of natural systems staged in series

have gained increasing interest in Europe (Vymazal, 2005). For

example, single-stage constructed wetlands cannot achieve high

removal of total nitrogen due to their inability to provide both

aerobic and anaerobic conditions at the same time. While there

may be other better alternatives, combining ponds and vertical

flow constructed wetlands, as well as infiltration percolation andhorizontal flow CWs have proven to be effective (Brissaud, 2007).

In addition, CWs systems combining horizontal- and vertical flow

were shown to be more efficient than non-hybrid system, and

various types of constructed wetlands maybe combined to comple-

ment each other and to achieve higher treatment effect, especially

for nitrogen (Vymazal, 2005; Lderitz et al., 2001; Brissaud,

2007).

There has been good experience on application of hybrid sys-

tems in China. Table 4 presents several applications of hybrid

systems in China. Zhai et al. (2006) reported a new type of hybrid

constructed wetland: an innovative design of vertical-baffled flow

wetland and horizontal subsurface flow wetland (HSFW) has been

introduced in Chongqing University (CQU), China. The experimen-

tal results exhibited a dramatic reduction in the land requirementand the system was found suitable for waste treatment for a

small township. In his report the author indicated that high

hydraulic retention time (HRT) and internal circulation had very

positive effect on pollutant removal the removal rate of TN

could double through an internal circulation, with a flow rate

that 12 times of the influent. The highest pollutants removal

rate of the hybrid CW with internal circulation occurred HRT

of 70h.

Another successful example is Shatian hybrid CW which con-

sists of two-stage-SSF systems. According to Shi et al. (2004),

first-stage wetland designed in horizontal flow pattern and the

total area of wetland is 4800 m2 with bed depth of 1m and HRT

of 11.5 h. The second-stage wetland takes the form of vertical-

downwards flow, a total of 4 trains arranged in parallel. The total


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Table 2

A summary of the treatment efficiency of HSSF systems in China.


rate (m3/day)

Hydraulic retention

time (day)

Rongcheng, Shangdong Provincea

Effluent value (mg/l) 27.8 23.8 91 11.3 2 20,000 120

Removal efficiency (%) 71.8 70.4 62.2 40.6 29.6

Dongying, Shandong Province

b

Effluent value (mg/l) 8.53 4.61 41.6 7.12 0.86 50,000 21.6

Removal efficiency (%) 88.2 90 75.8 67.31 59.23

Jiaonan, Shandong Provincec

Effluent value (mg/l) 30 11 125 63.8 2.98 30,000


Miyun, Beijingd

Effluent value (mg/l) 50 63 61.8 17.6 270 72


Futian, Shenzhen Provincee

Effluent value (mg/l) 8.37 25.31 6.28 8.27 0.65 5 72

Removal efficiency (%) 90 70 50 46 60

CIW-TS, Tianjinf


Removal efficiency (%) 84.9 94.01 87.02 80.13 80.04 72.96

Taihu, Zhejiang Provinceg


Removal efficiency (%) 39.6 32 52.1 65.7

Baptist University, Hong Kongh

Effluent value (mg/l) 120


Average efficiency in China (%) 75.5 82.22 70.09 64.59 56.09 59.01

a Song et al. (2006).b Wang et al. (2005b).c Song et al. (2008).d Wang et al. (2008).e Yang et al. (2008).f Yin and Shen (1995).

g Li et al. (2008).h Chung et al. (2008).

surface area of the secondary stage wetland is 4640m2 with bed

depth of 0.75 m and HRT of 8 h. A total of 7 species of plants have

been chosen forthis wetland system. Andthe average removal effi-

ciency of TSS, BOD5, COD, TN and TP are 86.78%, 86.4%, 76.72%,

44.93%, and 81.7%, respectively.

Wang et al. (1994) investigated a hybrid system for industrial

wastewater at Yantian industry area in Shenzhen City, Guang-

dong Province, which consists of anaerobic lagoon and three water

hyacinth ponds and two HSSF beds planted with Phragmites aus-

tralis. Despite the very high hydraulic loading (36 cm/day for the

HSSF stage), the authors reported that the removal efficiencies of

TSS (99%), COD (81%), BOD5 (69%), and TP (62%) were very good

and steady in hybrid systems, but the removal efficiency of TN wasrelatively low.

Recently, hybrid constructed wetlands comprise more than two

types of CWs and quite often include a FWS stage in Europe

(Vymazal, 2005). In China, Liu et al. (2007) investigated the water

quality variation in a hybrid CWs in purifying the Yongding River,

Beijing. There were altogether 7 parallel-connected wetland units,

and the influents flowed from the emerging plant pond (1. Sur-

face flow); thefirst-stage plant-gravel bed(2. Subsurface flow); the

floating plantpond (3. Surface flow); the second-stage plant-gravel

bed (4. Subsurface flow); the sand-filtration tank (5. Subsurface

flow). The removal ratios of the main pollutants in Yongding River

by this hybridsystem were TSS (99.1%), COD (52.8%), BOD5 (77.0%),

TN (59.4%), NH4-N (52.8%), NO3-N (60.3%), PO4-P (92.7%), respec-

tively. The purification effect was remarkable.

3.4. Design and performance

In sum, when comparingFWS, HSSF, VSSF andhybrid systems in

China (see Tables 14), experience has showedthat hybrid systems

perform best in the removal of TSS (94.96%), COD (78.52%), and TP

(79.68%). Compared to VSSF systems, HSSF systems showed better

removal efficiency for TSS and COD (75.5% and 70.09%, respec-

tively). As for nitrogen removal, the TN removal efficiency of HSSF

systems was significantly higherthan thatfor VSSF systems. Appar-

ently, despite experience in China pointing to the superior oxygen

supply of VSSF systems, the removal rate of TN (43.66%) remains

lower in comparison of that in HSSF systems (56.09%), probably

due to the lack of carbon source during denitrification. However,surprisingly, even the ammonia removal efficiency of HSSF systems

in China (64.59%) was higher than for the VSSF systems (56.17%),

indicating that at least in these systems reviewed here, that the

HSSF systems are probably better at nitrification that are the VSSF

systems in China.

From Chinese CW experience (see Tables 14), a comparison of

removal efficiencies by FWS, HSSF, VSSF and hybrid systems can be

made between China and Europe, the latter for which Haberl et al.

(1995) reported on the efficiencies of 268 wetlands in operation.

The mean BOD5 removal efficiencies were 66.13%, 82.22%,

82.95%, and 80.10% for FWS, HSSF, VSSF, and hybrid systems,

respectively in China. In comparison with the value in Europe

(79.1%) (Haberlet al., 1995), most systems inChinaseemto perform

in the same range as those in Europe.


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Table 3

A summary of the treatment efficiency of VSSF systems in China.


rate (m3/day)

Hydraulic retention

time (day)

Bainikeng, Shenzhen, Guangdong Provincea

Effluent value (mg/l) 10.9 6.9 38.3 18.5 18.5 1.59 3100

Removal efficiency (%) 92.6 90.5 73.5 10.5 10.6 30.6

Longdao, Beijing

b

Effluent value (mg/l) 7.08 6 19.7 5.2 0.061 2000


CIW-TS, Tianjinc


Removal efficiency (%) 44 54 39 32 30 44

Taihu, Zhejiang Provinced

Effluent value (mg/l) 4.25 0.89 2.37 0.056 0.64 m/d


Laboratory, HongKong; Pilot Project, Guangzhoue

Effluent value (mg/l) 8.37 25.31 6.28 8.27 0.65 0.45 m3/(m2 day) 18

Removal efficiency (%) 90 70 50 46 60

Jinan, Shandong Provincef

Effluent value (mg/l) 2.66 19.5 1.3 38.15 0.25 1000


Wuxi, Zhejiang Provinceg

Effluent value (mg/l) 96 61.8 32.9 41.3 0.4


Jinhe River, Tianjinh


Removal efficiency (%) 35 71.25 64.85 61.24

Chongming, Shanghaii

Effluent value (mg/l) 13.8 2.7 3.7 1.9

Removal efficiency (%) 67 62 53 33


a Yang et al. (1995).b Chen et al. (2008).c Yin and Shen (1995).d Li et al. (2008).e Chan et al. (2008).f Yin et al. (2008).

g He et al. (2006).h Tang et al. (2009).i Wang et al. (2006b).

The mean NH4 removal efficiencies were 64.59%, 56.17%, and

37.37% for HSSF, VSSF, and hybrid systems, respectively in China.

Andthe mean TN removal efficiencies were 49.11%,56.09%, 43.66%,

and 46.76% for FWS, HSSF, VSSF, and hybrid systems, respectively

in China. In Europe, the average NH4 removal rate was 30%, and the

averageofTNremovalrateis39.6%(Haberl et al.,1995). Apparently,

both of the removal rates for NH4-N and TN in these CW systems

in China are higher than that in Europe.

The meanphosphorus removal efficiencieswere 53.15%,59.01%,59.23%, and 79.68% for FWS, HSSF, VSSF, and hybrid systems,

respectively in China. In comparison with the value reported for

Europe (47.1%) (Haberl et al., 1995), the average removal efficien-

cies of TP in China are generally higher than that for Europe.

4. The role of the plant in constructed wetland treatment

There has been some debate on the importance of plants in pol-

lutant removal by constructed treatmentsystems (Wuet al.,2008).

Experience has shown that a wetland system with vegetation has

a higher efficiency of pollutant removal than that without plants,

and the significance of the plants used for wastewater purification

hasbeen emphasized by previous researchers (Brix,1997; Peterson

and Teal, 1995; Gersberg et al., 1983). However, the quantitative

role that the plant plays in wastewater purification is still a sub-

ject of some debate. The removal capabilities of a well-developed

vegetation could be explained by: (i) the rhizosphere connected to

a plant with active oxygenic photosynthesis will allow the trans-

fer of a certain amount of oxygen to the vicinity of the roots; (ii)

in the root system, where there exists a large number of bacteria

whoseoxidationreduction potentialand nitrification rateare both

higher than the area without plants, and each plant root system is

regarded as a mini aerobic/anoxic biologicaltreatmentsystem, and(iii) uptake into the plants.

Generally, the amounts of nutrients removed by vegetation

harvesting are insignificant compared to the load brought into

the system with wastewater (Brix, 1994; Merlin et al., 2002). If

the wetland vegetation is not harvested, most of nutrients could

be temporarily stored in the litter compartment. According to

Verhoeven and Meuleman (1999), during the autumn and winter,

a large part of nutrients will be gradually released again through

leaching and organic matter mineralization. Only a small part of

the nutrients stays in the vegetation as additional long-term stor-

age in aggrading wood or rhizome material. Vymazal (2005) also

concluded that the removal of nitrogen and phosphorus through

plant harvesting is negligible and forms only a small fraction of the

removed amount.


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Table 4

A summary of the treatment efficiency of hybrid systems in China.


rate (m3/day)

Hydraulic retention

time (day)

Chongqing University, Sichuan Provincea

Effluent value (mg/l) 51.5 17.8 20.1 1.12 1555 m3/(m2 day) 70


Shatian, Shenzhen, Guangdong Province

b

Effluent value (mg/l) 7.92 7.68 33.9 9.11 0.56 5300 11.5 (Stage 1) 8 (Stage 2)


Yongding River, Beijingc

Effluent value (mg/l) 12.3 5.91 5.47 4.27 6.38 0.1 0.58 m3/(m2 day) 34.26

Removal efficiency (%) 99.1 77 67.4 52.8 59.4 91.8

Guangdong Provinced

Effluent value (mg/l) 72


Yantian, Shenzhen, Guangdonge

Effluent value (mg/l) 3.2 58 88 12.2 15.5 1.8 36 cm/day

Removal efficiency (%) 99 69 81 17 31 62


a Zhai et al. (2006).b Shi et al. (2004).c Liu et al. (2007).d Cui et al. (2006).e Wang et al. (1994).

4.1. The capacity of plants for supplying oxygen

The role of plants in supplying oxygen is still being debated. In

CW systems, an important function of macrophytes is to transport

oxygen and release them from its root system into the wetland,

influencing the biochemical cycles in the substrate, and supply-

ing oxygen to bacteria growing on plant roots to improve the

decomposition of organic matter and convert ammoniumto nitrate

(Gersberg et al., 1986; Barko et al., 1991; U.S. EPA, 2000). However,

such capacity of oxygen transfer is limited. Brix et al. (1996) found

a negligible oxygen input of 0.02g/(m2 day). And Zhu and Silora(1994) pointed out that no obvious nitrification could be observed

when dissolved oxygen concentration is lower than 0.5 mg/l. Fur-

thermore, in anaerobic soils, oxygen is transferred to the roots

primarily for plant respiration and only excess oxygen is leaked

to the micro-zone at the rhizosphere (Brix, 1990).

In China, the data on the ability of plant in translocation oxy-

gen is also rare. Yin et al. (2004) reported that the ability of

oxygen translocation are 0.0212g/(m2 day), 0.55.2 g/(m2 day)

and 0.259.6g/(m2 day) by reed, submerged- and floating plant

respectively, these values showing the wide range of translocation

abilities of these aquatic plants.

However, despite this fact, in research on nitrogen removal and

microorganism in a SSF system in Sihong County, Xia et al. (2006)

reported that compared with the removal of COD and BOD5, thenitrifying process was slow. Because oxygen is mainly used for

removal of organic matter and the nitrifying reaction begins only if

BOD5 is reduced to a significant extent, thesmallamount of oxygen

(0.20.4mg/l) in this CW system limited the activity of the nitrifier

Nitrosomonas, which limited any further removal of nitrogen (by

sequential nitrificationdenitrification) from CWs.

4.2. Role of the plant in nitrogen removal

The nitrogen removal mechanisms in wetland systems are

very complex. The processes that affect nitrogen removal dur-

ing wastewater treatment in CWs are manifold. Basically, it

includes NH3 volatilization, nitrification, denitrification, nitrogen

fixation, plant and microbial uptake, mineralization (ammonifi-

cation), nitrate reduction to ammonium (nitrate-ammonification),

fragmentation, sorption, desorption and leaching (Vymazal, 2006).

Of the many kinds of removal mechanisms, however, only a small

subset of these processes ultimately play an important role in total

nitrogen removal while most processes just convert nitrogen to

its various forms. Two major processes have been identified and

they are: (i)storage,which is achieved by assimilationinto biomass

(e.g., plant and microbial uptake) or adsorption to the substrate

(e.g., soil); and (ii) removal through the N cycle: nitrification and

denitrification (Jamieson et al., 2003).

In a FWS in Dianchi Valley (Kunming City), Lu et al. (2009)investigating the N distribution pathway and removal efficiency,

concludedthatplants were importantfor thewetland,as theplants

provided good growth conditions for microbes, which removed the

majority of N from the CWs. Over a 5-year period, the wetland

received slightly more than 2000 kg/ha of nitrogen, mostly from

farmland drainage. The nitrogen removal was mostly due to plant

uptake (1110 kg/ha) and soil accumulation (570 kg/ha), with the

contribution of denitrification being estimated at around 7%. The

authors concludedthat this was becauseZizania caduciflora and Ph.

agmites had large biomass and thus had good N and P absorption

capability.

However, muchexperienceat higherhydraulic application rates

(high nitrogen loading rates), show that the processes of sequen-

tial nitrificationdenitrification play an increasingly major role ascompared to plant uptake (Gersberg et al., 1986). For example,

in a controlled comparison of ammonia-N removal efficiencies in

vegetated vs. unvegetated contracted wetland beds, Gersberg et

al. (1986) showed that the presence of plants did indeed make a

significant (p < 0.05) difference in removal efficiency (although not

via N-incorporation into plant biomass. These authors found that

ammonia removal efficiencies were 2894% for various types of

wetland plants versus only 11% for unvegetated wetlands. They

concluded that clearly sequential nitrificationdenitrification was

responsible for the higher rates of ammonia removal in these

planted wetlands.

Similarly, Tang et al. (2009) in the study of seven experimen-

tal pilot-scale VSSF systems in Tianjing, also reported that, with

respect to NH4-N removal, the planted wetland showed higher


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removal performances than that of the unplanted wetlands. The

improvement was significant and accounted for a 17.18% increase

as compared to that in unplanted wetland in NH4-N mean removal

efficiency (p < 0.05). The authors also indicated that insufficient

microbial activity in unplanted wetland substrate is likely to limit

NH4-N removal. Meanwhile, the planted wetland showed a better

TN removal than theunplanted wetland, andthe presence ofTypha

latifolia in a significant (p < 0.05) additional TN removal of 21.78%.

This observation verified that wetland plants can make significant

contribution to TN removal.

In a study of the HSSF system at Baptist University in Hong

Kong, Chung et al.(2008) indicated that plant uptakeonly removed

2.63.1% N in the microcosms, and denitrification was the main

removal pathway. Loss of N through denitrification was 34 and

50% in 10-day HRT and 5-day HRT unplanted treatment respec-

tively. In planted treatment, loss of N through denitrification was

20% and 32% in 10-day HRT and 5-day HRT treatment. The average

removal efficiencies in NH4-N were 9597% and 9294% planted

and unplanted treatment, respectively. Meanwhile, the average

removal efficiencies in TKN were 6366% and 4052% for planted

and unplanted treatment, respectively, and removal of TKN was

comparatively lower in unplanted treatments, because anoxic con-

ditions were found in unplanted treatments due to ponding of

wastewater, and this limited the rate of removal. In this study, loss

ofN through denitrificationwas 1941%of totalN inputfor alltreat-

ment. Additionally, the plants could reduce total N to significantly

lower levels than unplanted treatments. The high removal rate of

NH4-N in planted treatments showed that nitrification was very

active but the high NH4-N removal was enlarged by the increased

rate of evapotranspiration during plant growth.

Wu et al. (2008) investigated the capabilities of mangrove SSF

microcosms in treating primary settled municipal wastewater col-

lected from a local sewage treatment work in Hong Kong. The

removal efficiencies in the planted systems were 76.1691.83%

for ammonium-N, 47.8963.37%for inorganic-N, and 75.1579.06%

for total Kjeldahl nitrogen. And the authors also indicated that for

total nitrogen, the planted system had significantly higher removal(55.5683.33%) than the unplanted treatments (22.2233.33%).

Nitrification and denitrification process are believed to be an

important mechanism for nitrogen removal, and in this study,

decreases of ammonia in effluent were followed by increases

in nitrate. Additionally, the planted systems had significantly

lower effluent nitrate concentrations than the unplanted ones.

The authors concluded that apparently the mangrove plants not

only absorb nitrate for their growth, but they also enhance the

efficiency of both nitrification and denitrification processes. Fur-

thermore, even though the plants could take up nitrate in the

soil pore water and their roots could provide a large surface

area for microbial growth, in this study, the amount of nitro-

gen accumulated in the plants was only 2.883.28% of total

nitrogen.

4.3. Role of the plant in phosphorus removal

Jiang et al.(2008) investigated a two-stage SSF (combining with

HSSF and VSSF) in Longgang district of Shenzhen city (Guangdong

Province), andreportedthatin thefirst-stage CW,results of TP con-

centration indicated that this was superior for TP removal, and the

main area for TP accumulation. In the 15cm and 36cm depth layer,

87.92% and 86.24% of TP was accumulated in the superior half part,

and this was totally in agreement with the removal situation of

wastewater. The authors further examined P transfer into different

plantsand reported in thefirst-stageof theCW, theorderof TP con-

centration in organs ofPh. australis Trin, Miscanthus sacchariflorus,

Thalia dealbata was flowers, roots, leaves and caudex, while that of

Scirpus validus was roots, caudex and flowers. In the second-stage

CW of Canna generalis and Cyperus papyrus, phosphorus transfer

was coincident with phosphorus distribution in plants in the order

of seeds, followed by leaves, roots and caudex. The unregularity of

phosphorus transfer in the CW system demonstrated that it was

greatly influenced by plant growth environment and species.

Similarly, Chung et al. (2008) reported that removal of PO4-

P was at least twofold higher in the planted treatment and the

presence of plants could effectively remove PO4-P because it is

readily available for plant uptake. Low removal of TP in unplanted

treatments was expected, removal was sixfold lower than planted

treatments. The authors also indicated that vegetation, detritus,

fauna and microorganisms are an important sink for P in the short

term, but substrate is the main sink for P in long term. However, in

the long term, TP removal will be decreased in the vegetated treat-

ment due to the saturation of P adsorption in the substrate. In a

mass balance ofP, the uptake ofP byplants was only1% if the total

amount of P, the presence of plants has increased the P removal

rate and improved the treatment efficiencies.

Despite the finding above, since phosphorus removal is not

mediated by a microbial transformation process (as in the case

with nitrogen),plants would notbe expected to play a major role in

phosphorus removal at higher hydraulic application rates. Indeed,

Wang et al. (2005a) reported that even in the growing season,

the vegetation did not show significant uptake capacity for phos-

phate removal, and the phosphate was taken up by vegetation

roots mostly from the sediments. In a similar study, Yang et al.

(2008) investigated the treatment efficiency in a pilot-scale man-

grove wetland in Futian, Shenzhen for municipal sewage treatment

and the removal efficiency data indicated that plant growth had

playeda minor role in phosphateremoval which was confirmed by

an insignificant correlation between phosphate removal and the

increase in plant height.

4.4. Role of plant in COD, BOD5 and TSS removal

The removal COD and BOD5 rely largely on the good combina-tionbetween physical and microbialmechanisms. Due to a physical

separation mechanism and low porosity of the soil media, the

organic solids could be filtered and trapped in the bed of CWs for

a long time, thereby allowing for better biodegradation of organic

solids. Thehigh removal rates forCOD andBOD5 arecaused bysedi-

mentationof SS andby rapid decomposition processes in thewater

and upper soil layers. Organic matter is consumed and reduced

by bacteria and other microbes both aerobically and anaerobically

(U.S. EPA, 1993).

Yang et al. (2007) presented a comparative study of the effi-

ciency of contaminant removal between several emergent plants

species and between vegetated and unvegetated wetlands con-

ducted in Shenzhen, Guangdong Province for domestic wastewater

treatment. The authors reported that there were no significant dif-ferences in the removal of organic matter between vegetated and

unvegetated wetlands.

Similarly, Tang et al. (2009) investigated and assessed the effect

of plants [T. latifolia L. (cattail)] through severs experimental pilot-

scale SSF CWs in Tianjin. A statistical analysis indicated that there

was not a significant difference in COD removal rate between the

planted wetland and the unplanted wetland, and the presence of

T. latifolia only led to an insignificant (p < 0.05) increase of 2.94%

with respect to the mean COD removal efficiency. Therefore, plants

played a negligiblerole in chemical oxygen demand (COD)removal.

Apparently, despite the fact that BOD5 and COD removal in CWs

are mediated through biological degradation of the organic mat-

ter, it would appear that in most wetland systems either anaerobic

decomposition plays a major role, or alternatively, aeration of the


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substrate along (without plants) is sufficient oxygen demand of

organic removal.

4.5. Role of plant species on removal efficiency

In the report of investigation on twelve small gravel-based SSF

CWs systems and larger SSF CWs systems were installed at the

Virginia Techs Kentland Research Farm and at the Powell RiverProjects, Huang et al. (2000) indicated that plant species had no

impact on TKN or NH4-N concentrations in the wetland effluent

or removal of these N species from the wetland. However, other

researchers indicated that the removal efficiency of pollutant is

varied by the plant species (Gersberg et al., 1986; Peterson and

Teal, 1995).

In China, many studies revealed that different wetland sys-

tems performed differently with plant species and productivity

varied. Yang et al. (2007) concluded that there was a significant

difference in the removal of total nitrogen (TN) and total phos-

phorus (TP). Wetlands plants with Canna indica Linn., Pennisetum

purpureum Schum., and Phragmites communis Trin. had generally

higherremovalratefor TN andTP than wetlands planted with other

species. Theauthors also indicatedthatfine root (root diameter3)biomass rather than the mass of the entire root system played an

import role. Moreover, removal efficiency varied with season and

plantgrowth,e.g., wetlands vegetatedby P. purpureum significantly

outperformedwetlandswith otherplants in Mayand June,whereas

wetlands vegetated by Ph. communis and C. indica demonstrated

higher removal efficiency from August to December.

In a similar study, Yang et al. (1995) investigated a CW system

at Bainikeng, Shenzhen and indicated that different plant species

resulted in great differences in removing efficiency: effluent BOD5was 17.1mg/l for Cyperus malaccensis, 18.2mg/l for Ph. communis

(sampling at secondarygravel bed); and5.3 mg/l forCyperus malac-

censis, and 7.78mg/l for Lepironia articata (sampling at the fourth

gravel bed). The authors concluded that C. malaccensis is the most

efficient one at removing BOD5 while L. articata is the least.Even using same plant type, the treatment efficiency varies

largely by species. Yang et al. (2008) invested the treatment effi-

ciency in a pilot-scale mangrove wetland in Futian, Shenzhen for

municipal sewage treatment and also indicated that although 70%

of the organic matter, 50% of TN, 60% of NH 3-N, 60% of the TP, and

90% of the coliforms were removed, Sonneratia caseolaris was the

most efficientone with allthe effluent samples below thedischarge

standards for COD, BOD5, and NH3-N, whereas the percentage of

samples meeting the discharge standards varied from 71.43% to

85.71% for A. corniculatum and Kandelia candel. The removal of

TP was the lowest among the nutrients with 42.86% ( K. candel)

to 74.43% (A. corniculatum) of the samples meeting the discharge

standards.

Investigating the growth vitality and their removal ability of

the pollutants in domestic sewage, nine aquatic plant species com-

monly used in northern China and transplanted in a HSSF CWs in

Beijing region, Wang et al. (2008) reported that among the tested

plant species, Iris pseudacorus (with the capacity of high N & P

removal efficiency) ranked first in setting up the constructed wet-

land,followed by Typha angustifolia,Acorus calamus, and Triarrhena

sacchariflora, whereas Alisma plantago and Arundo donax were not

recommended due to their sensitivity in cold winter in northern

China.

5. Climate effects

Treatment performance in constructed wetlands may be less

consistent than in conventional treatment since they are strongly

influenced by climate and weather (U.S. EPA, 2000). The best

prospects for successful wetland treatment should be in the

warmer regions. However, in cold weather, wetlands continue to

function, but rates of microbial decomposition may be slow if the

wetland either freezes solid or under a cover of ice. Maehlum et al.

(1995) and Jenssen et al. (1996) stated that nitrogen cycling was

inhibited in colder months due to the decrease of oxygen avail-

ability. Besides lower winter temperatures, low oxygen availability

which is already a common limiting factor in FSSF systems during

the growing season, may be even more severe in winter. Simi-

lar results were also obtained by Maehlum and Stalnacke (1999),

in which they found that the differences in efficiency between

cold and warm periods were less than 10% for all parameters, and

the temperature effects were partially compensated for by longer

hydraulic retention time.

Wang et al. (2006a,b) reported that the removal efficiency of

ammonia nitrogen in October (71.6%) was much higher than that

in May (32.9%), although the water pH and temperature, which

are the most important factors affecting the volatilization rate of

NH3-N, in May were similar to that in October. That means the

volatilization was not a major removal mechanism for ammonia

nitrogen.

Song et al. (2006) investigated the seasonal and annual perfor-

mance of a full-scaled CW in Rongcheng, Shandong Province. He

concluded that there was a significantly seasonal component to

this wetland for BOD5, COD, ammonia nitrogen and total phospho-

rus, when measured on a percentage reduction basis: and (i) the

mean BOD5 and COD percent reduction were approximately 10%

less efficient in wintercomparedto springand summer, as physical

processes such as sedimentation are important in organic matter

removal and are unaffected by winter conditions; (ii) ammonia

nitrogen removal was about 40% less efficient in winter than

in summer and was associated with an increase in temperature

and plant growth; and (iii) there was less variability in sea-

sonal phosphorus removal (around 20% less efficient winter) when

compared to ammonia nitrogen, due to sedimentary binding of

phosphorus.Peng et al. (2005) reported for a multi-stage pondwetlands

ecosystem located in Dongying, Shandong Province, that in cold

season the removal efficiency of BOD5, COD, and NH3-N was

about 84.5%, 40%, 19.6%respectively, whereas in warm season, that

increased to 91.8%, 73% and 71.4% respectively.

Yin and Shen (1995) reported that a CW with reed beds for

industrial and municipal wastewater treatment located in Tanjin,

North China, could successfully operate under ice layers when the

average temperature was lower than 4 C and the lowest tem-

perature ranges from 21.2 C to 26.3 C. And effluent quality are

9.04mg/l, 13 mg/l, 5.5 mg/l and 0.25 mg/l for BOD5, SS, TN and TP,

respectively, which are better than secondary treatment level, e.g.,

BOD5


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Table 5

A comparison of the cost of a conventional wastewater treatment processes and CW system.

Design capacity

(m3/day)

Total capital

cost (US$)

Unit capital

cost (US$/m3)

Treatment cost

(US$/m3)

O/M cost

(US$/m3 )

Conventional WWTP in Chinaa 220 0.15 0.13

Conventional activated sludge process in Chinab 115 0.116

Constructed wetland in Chinab 28.82 0.022

Dongying, Shangdong Provincec 100,000 8.2 million 82 0.012

Longdao River, Beijing Cityd 200 29,191 146 0.03 0.014Dagong Oil Field, Tianjin Citye 2000 41,176 20 0.025 0.031

Wei Fang, Shangdong Provincee 180,000 102 0.021

Hong Kongb 0.45m3/(m2 day) 37.64 0.019

a Li and Wang (2006).b Chan et al. (2008).c Wang et al. (2005a).d Chen et al. (2008).e Li and Jiang (1995), Yin and Shen (1995).

et al. (2005a) reported that the BOD5 removal rate ranged from

75.6%to 90.7%in winterand 85.5%to 83.0%in summerrespectively,

with effluent BOD5 of 3.2916.7 mg/l in winter and 1.505.91mg/l

in summer. Similarly, Yang et al.(2007) alsoindicated that the con-

centration of pollutant in the effluent was significantly higher inOctober andDecembercomparedto summer. During thesemonths,

the mangrove plants hadslower growth and the microbialactivities

were also lower due to the low temperature.

However, Lu et al. (2009) reported that the removal rate of N

in winter was not far lower than in other seasons and the con-

taminant removal rate of the CWs had less than 10% difference

between the warm and cold period. The authors concluded that

the good performance of the CWs during winter was mainly due to

three reasons: (i) the initial harvest prevented N release caused by

the decomposition of plant matter and strengthened oxygen dif-

fusion from the atmosphere; (ii) the free water surface CWs was

built in Kunming City, which is in the north-subtropical zone, and

the average water temperature in winter was higher than the min-

imum required temperatures of nitrification and denitrification;and (iii) the intermittent inflow was beneficial to the processes of

nitrification and denitrification.

6. Cost/energy/land requirements and limitations

6.1. Cost

In China, wastewater in most small- and medium cities as

well as rural areas has not been properly treated, because of the

invariability of wastewater treatment facilities. The use of CWs sys-

tem for the treatment of polluted water has attracted increasing

attention in the last decades due to its minimal costs for construc-

tion, operation and maintenance. Table 5 compares the investment

and operation cost for a traditional wastewater treatment plant(WWTP) and CWs in China. Although conventional WWTP and

activated sludge processes are efficient for wastewater treatment,

their cost-effectiveness can only be achieved in densely populated

urban areas. In contrast, the application of CW is more afford-

able for the wastewater treatment demands of small communities.

Table 5 shows that although CW systems do not present appar-

ent advantage in construction cost, the treatment and O/M cost of

CW systems is much lower than that of conventional WWTP and

activated sludge processes.

Wang et al. (2006a) reported that the total capital cost of an

ecosystem consisting of integrated ponds and constructed wet-

land system (located in Dongying City, Shandong Province) was

US$ 82/(m3 day), which is about half of the conventional systems

based on activated sludge process. The O/M cost is US$ 0.012/m3

,

only one fifth that of conventional treatment systems. Li and Jiang

(1995) reported that the capital investment and operation cost of a

large-scale reed bedFWS in Weifang City, Shandong Province were

35% and 14% of that of A2O (anaerobic/anoxic/oxic) treatment sys-

tems. Similarly, the investment cost for a CWs with reed beds forwastewater treatment in Tianjin, North China was summed up to

US$ 20/(m3 day) and the operation cost was US$ 0.025/(m3 day)

(Yin and Shen, 1995). Chen et al. (2008) also reported that with

the treatment capacity of 200 m3/day, the construction cost in

the Longdao River CW (located in Beijing) was calculated to

be US$ 0.02/m3, and average treatment cost was summed up

to US$ 0.03/m3, which is equal one-fifth of that in traditional

WWTP.

6.2. Energy

Constructed wetlands are an attractive and promising alter-

native (both for industrialized and developing countries) to

conventional technologies to treat wastewater due to their lowenergy consumption.

Lderitz et al. (2001) compared three different strategies for

wastewater treatment and disposal for three villages, namely

dischargeto a large-scale sewagetreatment plant20 kmaway,con-

struction of a central mechanicalbiological wastewatersystem for

the three villages, or construction of a wetland for every local com-

munity. The authors concludedthat a semi-centralized constructed

wetland needed 83% less energy than that of a central technical

system and 72% less energy than the discharge to a central treat-

ment located 20 km away. In addition, in the case of energy, the

advantage of the CW in operational efficiency dominates.

In China, data and reports on energy consumption for con-

structed wetland are very rare. From 1985 to 1990, National

Planning Committee, National Science and Technology Committeeand National Environmental Protection Agencyorganized a nation-

wide study on sewage wetland treatment systems. The research

projects wereinstalledin differentclimaticzonesNorthwest:Xin-

jiang Autonomous Region (arid area, the north temperate zone);

Northeast: Shenyang City(the north temperatezone); North China:

Beijing and Tianin (the medium temperate zone) and South-

west: Kunming City (the north-subtropical zone). At the treated

wastewater included municipal sewage, paper industry effluent,

petrochemical processing wastewater and beer brewery efflu-

ent. And the treated sewage capacity ranges from 120 m3/day to

500m3/day, the resultant technical-economic comparative analy-

sis indicatedthat energyconsumption for the different CW systems

was only 1525% of that of conventional activated sludge technol-

ogy (Li and Jiang, 1995).


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6.3. Space and land requirements

CWs systems for wastewater treatment are usually land inten-

sive and may require more space than conventional wastewater

treatment systems (Kivaisi, 2001; Wittgren and Maehlum, 1997;

Brissaud, 2007). The high land requirement for CWs is the main

barrier for expanding the application of CWs in China. Also, CW

cannot be applied in densely populated areas where land prices

are often too high.

The land requirements of CWs for wastewater treatment vary

widely. Chinas distinct problem is that 81% of its water resources

are in the countrys southern part but the largest part of arable

land (64%), is in the north, where the nations political and

economic centre is located (Varis and Vakkilainen, 2006). Since

there is considerable diversity of geography, climate, land- and

water resources distribution between northern- and southern

China, the availability of land use for CW construction varies

correspondingly.

Therefore, although Zhai et al. (2006) indicated that the land

requirement of traditional CWs for wastewater treatment is from

10 m2/(m3 day) to 70 m2/(m3 day), experience of CW construction

in southern China indicated that the land requirement is much

smaller than that in the northern region. For instance, accord-

ing to Li and Wang (2006), in the constructed wetland systems

of Shatian (Shenzhen, Guangdong Province), the land requirement

was approximately 1.88 m2/m3 and 1.2m2/capita, in the case of

assumed consumption of 300 l/(capita day). Additionally, with the

consideration of preliminary treatment, the total land requirement

is 4m2/m3. Also, in the constructed wetland of Bainikeng (Shen-

zhen, Guangdong Province) the land requirement for wastewater

treatment was around 2.7 m2/m3.

Southern China belongs to a subtropical climate zone, with rela-

tively high temperatures and a humid climate, which is favourable

for water plants growth. However, in Southern China, the average

population density is 210persons/km2 (Zhai et al., 2006). In this

region, land resources are scarce with a high population density.

Furthermore, the price of land is so high that land cost forms a highpercentage of total investment for CWs. Therefore, CW treatment

may be economical relative to other options only where land is

available and affordable. As the available land possessed per capita

in China is much lower than that of international standard,wetland

systems with small land requirement and good effluent perfor-

mance are more suitable for application. Great effort should be

madethereforetowards improvingthe treatment efficiency of CWs

and decreasing the land requirement.

7. Sustainability

In 1987, the concept of sustainable development was defined at

Brundtland Commission as: development that meets the needs ofthe present without compromising the ability of future generation

to meet their own needs (Brundtland Commission, 1987). In the

last decade, costbenefit analysis has been considered as the major

evaluation system for sustainable development activities. How-

ever, such monetary costbenefit evaluation procedures do not

consider allof theresources involved.Although it is difficult,to give

an adequate definition of sustainability, the measurement and

assessment on sustainability of at least three aspects, embracing

the economic cost that determines the operation and maintenance

of the system, input/output efficiency that is necessary for scarce

resource allocation, and the ecological cost of restoration that is

important to deal with the interaction between the biosphere and

societal environment, have to be thoroughly included (Chen et al.,

2009).

Emergy analysis at the scale of biosphere and society is an eval-

uation system free of human bias, which can represent both the

environmental and economic values of a given system (Odum,

1988; Brown and Ulgiati, 1999). Emergy accounting as an ecologi-

cal approach came outof creative combination of thermodynamics

and systems ecology (Odum, 1996; Geber and Bjoerklund, 2001),

and this approach represents a measure for comparison of envi-

ronmental good, energy quality, and economic valuation (Odum,

1988; Brown and Herendeen, 1996).

In China, Zhou et al. (2009) measured the energy and resource

consumption and conducted a comparative study on a constructed

wetland (Longdao River, Beijing) and conventional wastewater

treatment with cyclic activated sludge system (CAAS) (Hang-

tiancheng, Beijing). In this study, emergy-based indices such as the

ratio of purchased/fee, local/imported and the ratio of electricity

emergy used were chosen to characterize the two treatment sys-

tems in self-sufficiency and environmental effect, respectively. The

report revealed that the ratio of purchased inputs to free inputs

for CWs were 3.4, compared with the ratio of 1450 for CAAS. The

ratio of local inputs to imported for CWs was 0.35, almost three

times more than those for CASS, revealing that the system of CASS

depended more on external resources and were driven mainly by

the imported emergy. Similarly, the ratio of the electricity con-

sumption for CWs is 3.9% while 37.1% for CASS. This indicates

that more local renewable resources and less ecological cost are

involved, thus promoting the economic benefit due to less energy

consumption and the lowering of environmental stress.

Zuo et al. (2004) initialled a comparative study on the sustain-

ability of original and constructed wetlands in Yancheng Biosphere

Reserve (YBR) located in Jiangsu Province. The authors employed

two new emergy indices, base emergy change (Bec) and the net

profit (Np) in order to compare the ecological-economic benefits

of different kinds of wetlands. Results indicated that a water fowl

pond, constructed for ecological reasons at the edge of the core

zone of YBR, has much more Bec than the original wetlands and

fishponds, while its Np is negative and much lower than the other

sites. Fishponds built for economic reasons in the buffer zone havenegative Bec while the Np is the highest. However, the emergy

yield ratio (Yr) of the original wetlands is the highest. In some

way, it could be said that the negative Bec in the fishponds may

meana purely exploitation activity searching for economic benefits

by exhausting natural resources, and fishpond creation should be

stopped to ensure better conservation of the original wetlands and

rare bird species. ThepositiveBec andnegativeNp of thewaterfowl

pond indicated an effective wayforward for biodiversity conserva-

tion, which wasproved by theincreasing numbers of birds andbird

species observed.

8. Conclusions

To solve the multifold water-related problems in China,

completely replication of centralized water-, energy- and cost-

intensive technology has proved to be extremely limited and not

feasible, especially in fast growing small- to medium-sized urban

area in China. Constructed wetlands have gained increasing atten-

tion and been implemented as wastewater treatment facilities in

many parts of the world because of their low-cost and energy-

savings. This paper reviews the progress of CWs for wastewater

treatment in China, and delineate some of the key treatment effi-

ciency and performance issues which may be elucidated by the

China experience.

Comparison on the existing of FWS, HSSF, VSSF and hybrid sys-

tems in China that we have data for indicates that hybrid systems

perform best in the removal of TSS, BOD5, COD, and TP. Compared


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to VSSF systems, HSSF systems showed better removal efficiency

forBOD5 and TP (82.22% and 59.01%, respectively), although for TSS

removal the VSSF showed much better removal efficiency (75.52%).

As for nitrogen removal, the TN removal efficiency of HSSF systems

was significantly higher than that for VSSF systems. And surpris-

ingly, even the ammonia removal efficiency of HSSF systems in

China (56.2%) was higher than for the VSSF systems (43.3%). Addi-

tionally, this comparison of removal efficiencies by CWs in China

to CW treatment of 268 systems throughout Europe (Haberl et al.,

1995) indicatedthat the removal ratesfor nearlyall the parameters,

were higher in China than Europe.

Experience in China show that plants can play a key role and

make a significant difference in treatment efficiency. Numerous

comparative studies have verified that the planted wetlands show

higher removal efficiency of TN and NH4-N than that unplanted

wetlands.However,plants play a much lesserrole in theremoval of

TP, COD and BOD5. For COD and BOD5, it would appear that in most

wetland systems either anaerobic decomposition plays a major

role or, alternatively, aeration of the substrate (without plants) is

sufficient to satisfy the oxygen demand of organics removal.

Although CW systems in China do not have an apparent

advantage in construction costs, the costs for treatment and oper-

ation/maintenance of CW systems are much lower than those

of conventional WWTP and activated sludge processes. Similarly,

results of technical-economic comparative analysis of various CW

systems in China indicate that energy consumption for different

CW systems was far less than that of conventional activatedsludge

technology. Land requirements for CWs present one of the factors

mostlimitingtheir broader use,especially in southern China,where

land resources are scarce and population density is high.

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