Review of Aquatic Plant Research and Wetland Engineering

This assignment involves reviewing a comprehensive list of academic papers and research articles related to aquatic plant studies, wetland engineering, and environmental science. The papers cover topics such as the use of aquatic plants in wastewater treatment, heavy metal accumulation in natural and constructed wetlands, and the role of submergent macrophytes in domestic greywater treatment. Additionally, the assignment includes studies on phytoremediation, biosorption, and the application of root zone method for treating high-strength abattoir waste. The research highlights the potential of aquatic plants and wetland systems in addressing environmental issues such as water pollution and heavy metal contamination.

Running head: FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION
TREATMENT
Function of Large Aquatic Plants In Water Pollution Treatment
Name of the Student:
Name of the University:
Author note:

1FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Executive Summary
Being a worldwide problem, water pollution has a huge impact on the mankind. The
world has invested a lot of manpower and material resources after the environmental
governance. Environmental pollution control has a new breakthrough with the emergence of
phytoremediation technology that has the characteristics of low cost, more ecological and
environmental friendly. This paper summarizes the mechanism of large aquatic plants in
water pollution treatment, the status of water pollution, and the application of large aquatic
plants in order to minimize the content of pollution from water. Moreover, the discussion is
also based on the selection principle of aquatic plants to decrease the water pollution and safe
disposal to used aquatic plants.

2FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Table of Contents
Executive Summary.........................................................................................................................1
Introduction......................................................................................................................................3
Objective and Hypothesis................................................................................................................7
Literature Review............................................................................................................................7
MATERIALS AND METHODS...................................................................................................13
RESULT........................................................................................................................................14
DISCUSSION................................................................................................................................26
CONCLUSION..............................................................................................................................30
List of Tables
Table 1-----------------------------------------------------------------------------------------------------5
Table 2-----------------------------------------------------------------------------------------------------6
Table 3----------------------------------------------------------------------------------------------------11
Table 4----------------------------------------------------------------------------------------------------11
Table 5----------------------------------------------------------------------------------------------------17
Table 6----------------------------------------------------------------------------------------------------18
Table 7----------------------------------------------------------------------------------------------------19
Table 8----------------------------------------------------------------------------------------------------21
Table 9----------------------------------------------------------------------------------------------------23
Table 10--------------------------------------------------------------------------------------------------24
Table 11--------------------------------------------------------------------------------------------------26

3FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Introduction
The earth is said to be as a “blue planet”, as 70% of its surface is covered with water.
However, in reality, 97.5% of it is salt water and the fresh water accounts for only 2.5%.
Moreover, nearly 70% of the fresh water is fixed in the Antarctic and Greenland glaciers, the
rest in the soil moisture or deep groundwater, which cannot be used by humans. Hence, less
than 1% of the earth's fresh water is there to consume by humans directly. These waters are
provided through lakes, rivers, reservoirs and shallow groundwater sources. In other words,
water is the most precious and limited resource for mankind. Furthermore, there are
numerous activities such as erosion, climatic changes, evaporative cooling, hydropower,
promotion of the cycling of inorganic and organic matter and so on. However, with the rapid
development of industrialization and urbanization, many toxic substances like pesticide and
some organic pollution have entered the water system. This has made the problem of water
pollution the most serious environmental problem that the world is facing today. About 42
billion cubic meters of sewage is discharged into the rivers and lakes every year, polluting 5.5
trillion cubic meters of fresh water, which is equivalent to more than 14 percent of global
runoff. Human activities such as mining, metal smelting, chemical industry, coal combustion,
automobile exhaust emissions, domestic wastewater discharge, pesticide and chemical
fertilizer application and atmospheric deposition are the main factors causing pollution in the
water bodies.
Water pollution can cause effect of water ecological system function. Some harmful
substances, like Heavy metal ions and organic pollutants, can keep in water over one hundred
years. These toxic substances are consumed by humans through the food chain. For example,
the little fishes eat the tiny organic particles; big fishes eat those tiny fishes; and human in
turn eats the big fishes. Hence, ultimately the health is getting affected.

4FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Everyone is aware of the fact that water pollution is a serious problem that is effecting
the human survival and sustainable development. It is negatively affecting human health,
agricultural productivity and the stability of natural ecosystems. The establishment and
development of strategies and technologies for the removal of water pollution has become an
important area of scientific and technological research. Compared with the physical
technology and strategy of mechanical decontamination method, the strategy of using green
plants to remove pollutants is a very promising approach to water pollution.
Phytoremediation is a generic term that uses plants for remediating soils, sludge,
sediments and water contaminated with organic and inorganic contaminants. It can be defined
as “the efficient use of plants to remove, detoxify or immobilize environmental contaminants
in a growth matrix (soil, water or sediments) through the natural biological, chemical or
physical activities and processes of the plants”. Plants are unique organisms equipped with
remarkable metabolic and absorption capabilities, as well as transport systems that can take
up nutrients or contaminants selectively from the growth matrix, soil or water.
Phytoremediation involves growing of plants in a contaminated matrix, for a required period
of time in order to remove contaminants from the matrix, or facilitate immobilization
(binding/containment) or degradation (detoxification) of the pollutants. The plants can be
subsequently harvested, processed and disposed (Wang S M, 2006).
Aquatic plants in the ecosystem are primary consumers. They are autotrophic
organisms. They play a key role in maintaining a virtuous cycle of aquatic ecosystems. The
examples include- aquatic plants can store short-term nutrients such as N P K, which inhibits
the growth of lower aquatic plants such as algae, purify contaminants in water, provide
habitat for some organisms, as well as to promote water production, nitrogen cycle.
Pollution factor Phytormediation Plant

5FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Cd Iris, Canna, Rushes, Barracude, Ipomoea,
Metzyllum
Pb Oriental cattail, Cape health Chara, Canna,
Rushes
Cu Reed, Eichhornia crassipes, Algae
Zn Reed, Eichhornia crassipes, Algae
As Eichhornia crassipes, Algae,
Mn Eichhornia crassipes, Algae, Acours calamus
Hg Algae, Progency Chara
Cr Algae, Progency Chara
Co Algae,
N P Eichhornia crassipes, Canna, Calla
COD Eichhornia crassipes, Calamus, Water Iily
BOD5 Eichhornia crassipes, Reed, Cat-tail
Phenol Rush,
Pesticide Canna, Chrysanthemum
Table 1: Common ecological restoration of aquatic plants
Aquatic plants are mainly composed of three major categories: aquatic vascular
plants, aquatic mosses and higher algae. Global application in the sewage treatment is more k
borne vascular plant developed mechanical process. The plant individuals are relatively tall,
usually can be divided into Algae, Emerged plants, Floating leaves plants and submerged
species (Chong, Hu and Qian. 2003).
Life type Growth characteristic Represent plants

6FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Garden Greenland
plants
Rhizome was born in
the sediment Reed, cattails
Potted flowers
The plant body is
completely floating on
the surface of the water,
with a specialized adapt
to the floatinglife of the
organizational structure
Eichhorniacrassipes, Duckweed
Cut flowers
Rhizome was born in
the mud, the leaves
floating in the water
Water Lily, Nymphoides
Indoor water tank
Soil or muddy water
interface following the
services
Cryptomeria
Table 2：Four kinds of life type of aquatic plants ：source：Chong：Hu and Qian. 2003)
Objective and Hypothesis
Due to its cheap and environment friendly nature, phytoremediation technology is a widely
used technology in recent years. With the discovery of some aquatic plants, the control
treatment of heavy metals and organic pollutants in water environment system has been a top
most research topic in the world. Due to this, the aquatic plants have the same characteristic
of hyperaccumulation plants. In this paper, some normal aquatic plants will be discussed, and
aquatic plants mechanism analysis, practical application, control treatment effectiveness and

7FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
developing prospect will be explored. Furthermore, some factors that influence the ability of
aquatic plants to clean water pollution will be listed down and discussed.
Literature Review
1. The Current Situation of Water Pollution In China
The information related to water pollution is reported by the National Environmental
Protection Agency every year. According to the published data, surface water quality in the
seven major rivers of China is outlined as- In the Songhua River and the Liaohe River
systems, the organic pollution is very serious. The polluted river that reaches accounted for
about 50 percent of the evaluated river reaches in length in the year 1986. Currently, organic
pollutants, ammonia N, phenols and nitrate N contents all have a tendency to rise. The water
quality in the Liaohe River is deteriorating ：Mei and Feng 1993). In the Haihe River basin,
water quality is the worst. In a comprehensive pollution index, among the seven major river
basins, the organic pollution and heavy metal pollution comprise of the first and second place
respectively. The principal components of heavy metal pollution are cadmium, mercury and
copper. Phenol, COD and ammonia N concentrations are in excess of the standards. In the
Huanghe River basin, natural water quality is not high. Suspended matter content exceeds the
standard at all monitoring cross-sections. Total ion and chloride contents are at high levels.
Currently, organic pollution is rather serious; amm onia N pollution is growing, while arsenic
pollution is lightening. In the Huaihe River basin, comprehensive water pollution index is in
the second place below the Haihe River, but heavy metal pollution is in the first place. The
dominant pollution results from organic chemicals, and the polluted river reaches was up to
55.8 percent of the evaluated river. Presently water quality of the Huaihe River is getting
worse, especially during the low-flow periods. The contamination from ammonia N, phenols,
nitrite N and lead, mercury, cadmium and chromium is becoming heavier. In the Changjiang

8FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
(Yangtze) River basin, the water quality of the main stream appears to be rather better but
some tributaries, lakes and urban river reaches have been polluted seriously. The annual
average value of suspended matter exceeds the water standard and the ammonia N pollution
is spreading. In the Pear River basin, water quality is good as well and there, the water
pollution is mainly caused due to organic pollutants. In addition, iron concentration is a bit
high. Furthermore, the pollution from ammonia N, organic chemicals nitrite N is becoming
heavier in specific river reaches.
2. Development History of cleaning pollution By Aquatic Plants In China.
The ecological function of aquatic plants in the water body makes it a very useful
component in the prevention and control of water pollution. Due to the increase of water
pollution, an efficient and low cost water pollution treatment technology had started to grab
people’s attention towards itself. Many of the substances resistance to pollution and
management capabilities studies have founded that a variety of large-scale aquatic pollution
control as the core of sewage treatment and water restoration of ecological engineering
technology has been developed.
In the1990s, scientists used floating island in order to carry out repairing work in Wuli
Lake of Wuxi City. They founded that N, P removal efficiency is high and in 2002, by using
the technology of phytoremediation brake Lake, the Yongding River and other polluted water
bodies in Beijing have gained better phytoremediation results. In 2002, the study of Jianjun
Shi showed that the aquatic plants were used to enrich the radioactive elements in the water.
In 2005, the study of Yi wang showed that there was a negative absorption of heavy metal
contaminants in the water environment or reduces the toxicity of heavy metal pollutants
through the system, thus weaken the water toxicity and repair the water body. The general

9FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
root enrichment coefficient of aquatic plants is greater than that of stems and leaves.
Furthermore, the submerged plant is larger than the floating leaves and the floating leaves are
larger than that of water.
China began to improve the environment by restoring the experiment work of aquatic
plants, and hence developed Tai lake, Dianchi Lake, and the East Lake’s eutrophication
control and ecological restoration demonstration research in the early 1990s. The study found
that the disappearance of the Donghu Lake’s cyano-bacteria populations was related to the
stocking filter-feeding fishes. The later researches and tests were based on using silver carps
such as predatory fish, as filters to control the eutrophication for lake water’s phytoplankton
(algae) quantity and improve water quality. Chinese Academy of Sciences, Nanjing lakes
Geography, set up a pilot area of the demonstration project in Wuli Lake Shore, for
establishing the associations among emergent aquatic plants, floating-leaved plants and
submerged plants. During the project, the aquatic plants’ diversity index reached up to 40%,
and the dominant plant in lake water was changed from algae to large aquatic plants. The area
later on found improvement on its water quality and became clear water.
3. Some Information about Aquatic Plants
Plant adsorption is the direct occurrence of roots (or stems and leaves) surface is
considered to be the most rapid removal of heavy metals, NP and organic ion from the water.
It is by chelation ion exchange, selective absorption and other physical and chemical
processes result (Reddy and Debusk, 1987), that plants can be used for cleaning water
pollution and they must have the following characteristics (Yan 2003：:
 Plants have a higher rate of accumulation even in the lower concentration of
pollutants

10FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
 They can be enriched in high concentrations of pollutants in their body (they can live
in water who content high concentration of pollutants)
 They can absorb the accumulation of several heavy metals, N P and the organic ion
pollution (Samecka and Kemper. 2004)
 They can contribute to fast growth, large biomass (height), along with insect
resistance.
Heavy metal
ion
Hg Cu Cd Zn Pb
Ottelia - 15.4 0.10 4.00 40.3
Hornwort 1.00 7.80 5.00 - -
Water hyacinth 0.06 20.0 5.00 10.0 30.2
Nymphoides
Levin
- - 0.20 0.50 -
scirpus
tabernaem-
ontani
- - 30.0 - -
Algae - 5.00 10.0 - -
Table 3: Upper limit of tolerance of some aquatic plants to heavy metals (mg/L) （source（
He（Geng and Luo. 2008)
It is to be mentioned that aquatic plants can clean water pollution as they can absorb
the heavy metal ion and N P from the water bodies. However, if the pollution is very serious,
the heavy metal ion, N P and the organic pollution content in the water is out the upper limit
of tolerance for some of the aquatic plants. In the table 3, the upper limit of tolerance of some
aquatic plants to the heavy metals are listed, the highest upper limit of tolerance to Pb is

11FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Ottelia, it can live in the water whose Pb content is 40.3mg/L. Most aquatic plants can live in
the water which is polluted by Cd, and the scirpus tabernaemontan even can live in the
30mg/L Cd of polluted water. However, a quite large amount of aquatic plants cannot live in
the Hg polluted water as the Hg ions are able to destroy the cell structure of the aquatic
plants：Jia. 2005).
Plant name Maximum height（m（ Nitrogen content Phosphorus Content
Coix 2 24.1-25.6 4.2-5.6
Reed 3 18-21 2.0-3.0
Mosaic reed 2 17.2-35.1 1.7-6.2
Trapa incisa var. sieb. 1 10.9-25.1 1.3-6.9
Incisa var. sieb 1.8 16.8-27.9 4.4-5.3
Chrysanthemum 0.8 12.3-29.9 1.61-5.94
cat-tail 2 5.0-24 0.5-4.0
Rush 1 15 2
Iris 0.5 4.7-25.3 2.3-4.7
Calamus 1.2 11-35 2.3-5.7
Algae - 12.0-48 1.5-11.5
Duckweed - 25-50 4.0-15.0
Eichhornia crassipes - 10-40 1.4-12
Salvinia - 20-48 1.8-9.0
Vallisneria 0.5 16.9-30.5 2.2-4.7

12FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Spruce - 1-38 1.2-6.4
Table 4: Upper limit of tolerance of some aquatic plants to N P (mg/L) （source（Chen et al
2008)
In table 4, the Maximum height and the upper limit of tolerance of some aquatic plants to N P
are listed. The highest upper limit of tolerance of N and P are the Duckweed, in which the
nitrogen content is 25-50 mg/L and the Phosphorus content is 4.0-15.0mg/L.
4. Current Issues about Cleaning Water Pollution by Using Aquatic Plants.
There are many studies on the remediation of the soil pollution by using plants, but it is
not a sufficient. Lots of application of plant pollution remediation, especially heavy metal
repair in water, the absorption and accumulation of pollutants in plants, the tolerance of
different concentrations of pollutants, and tolerant strong aquatic plants screening are also
need to be further take into the account. In addition, due to geographical and market factors,
aquatic plants market factors, aquatic plants market demand and information asymmetry, the
aquatic ecological restoration is likely to produce potential problems. Therefore, this field of
plant ecological restoration needs to carry out a wide range of work and analysis-.
To study the combination multiple types of plant repair effect, the systematic absorption
of aquatic plants and tolerance needs to be researched. To study the ability of aquatic plants to
repair under the condition of multiple pollutants combined pollution, and to solve the
problem of aquatic plants due to complex pollution, the remediation capacity of aquatic
plants, competition, microbial invasion and so may lead to the decline in repair capacity. To
understand the current market aquatic plants on the scale of water treatment and water
pollution, water ecological restoration required aquatic plants species and quantity, in order to
carry out targeted seed reserve and adjustment to ensure smooth implementation of the

13FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
project, to achieve a good treatment effect; and to deal with the different aquatic plants that
live in different depth water and the different types of pollution.
MATERIALS AND METHODS
The information has been compiled from Chinese publications stemming mostly from
the last decade, to show the research results on the role of aquatic plants in controlling water
pollution, and to provide a general outlook of phytoremediation in China. Related references
from scientific journals and university journals are searched and summarized in sections
concerning the accumulation of heavy metals, organic ions, N P ions in plants, aquatic plants
for these toxic ion purification techniques.
By analyzing these data, the application status of phytoremediation in China and
current status of water pollution could be found out. According to the severity of different
water pollution and related researches in China, this paper mainly classifies and summarizes
the relevant research progress of three different types of water pollution and the mechanism
of action of aquatic plants to clean this pollution. Finally, the restrictions on the development
of aquatic plants applications are discussed.
RESULT
It is to be noted that the normal water pollution can be divided into: heavy metal
pollution, organic pollution and N P pollution. The mechanism of action of aquatic plants was
introduced to clean the heavy metal pollution, N P pollution and organic pollution.
Furthermore, there are seven aquatic plants that are listed for introducing the ability of
aquatic plants to clean these pollutions and they are:

14FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
After the sewage enters the artificial wetland, the plants can remove the pollutants in
the sewage through absorption, and adsorption including the absorption and utilization of
nitrogen and phosphorus, and the adsorption and enrichment of heavy metals. In
1997 ： Copper found that the contents of nitrogen and phosphorus in constructed wetlands
planted with Typhaangustifolia and Juncus effuses were 18% -28% and 20% -31%, which
were lower than those in the non-vegetative control substrate. This means that
Typhaangustifolia and Juncus effuses absorbs and use some part of the sewage nitrogen and
phosphorus. In 2001：Cheng demonstrated that Cyperus alternifolius could consume 30% of

15FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
the copper and manganese in the polluted water, and absorb the zinc, cadmium, and lead from
5% to 15%.
1. Adsorption and enrichment of heavy metals by plants
A large number of studies have found out that planted wetlands system has higher
removal capacity of heavy metals in sewage than that of no plant system (Kantawanichkafl et
al., 1999; Ansola et al., 2003). This indicated that the aquatic plants have great ability to
absorb heavy metals. Plants can directly absorb water-soluble heavy metals through the roots,
and can also change the chemical form of pollutants by changing the rhizosphere
environment (pH, Eh), to reduce or eliminate the chemical toxicity and biotoxicity of heavy
metal pollutants (He et al., 2003). Chengsheng Yang et al. further explain the adsorption of
heavy metals in four species of Typha, Reed, Cyperus malaccensis and
Cynodondactylon(Linn.). The experimental results showed that all these four species have
strong adsorption ability to heavy metals, and heavy metals are mainly concentrated in the
underground part of the plant. Mays et al. (2001) explains the treatment of low concentrations
of heavy metal wastewater with constructed wetlands and found that the most heavy metal
elements such as Pb and Cd can be accumulated by wetland plants.

16FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Table 5. The different bioconcentration factor （BF（ and traslocation factor (TF) to Cd and
Pb from different plants stem part and root part （source（Yang et al（2004（
According to the table,Juncus effusus L. has the highest BF to Cd in the stem part as
compared to the other plants which is 0.31. However, the lowest BF to Cd is 0.029 which is
from Cyperus alternifolius stem part. In the part of root, Acorus calamus L has the highest BF
to Cd, which is up to 0.47, but the Phragmites communis has the lowest BF to Cd of 0.12.
In the stem part, the Juncus effusus L. has the highest BF to Pb i.e., 0.094, the lowest
BF to Pb is 0.021 which is from the Scirpus validus Vahl. In the root part, Phragmites
communis provide highest BF to Pb i.e., 0.20. The Scirpus validus Vahl has the lowest BF to
Pb (0.07).
The Juncus effusus L has most significant TF to Cd which is up to 1.39. This means
that the Juncus effusus can efficiently remove the heavy metal from root part to the stem part.
The TF is an essential factor which influences the purifying ability of aquatic plants.

17FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Table 6. The concentration of different plants stems part and root part to Cd (mg/kg（
（source（He（2003（
From the above table, it is to be concluded that, in the stem part group, the highest Cd
concentration is from the Juncus effusus L, which is 0.32 mg/kg, and the lowest Cd
concentration is from the Cyperus alternifolius, which is 0.03mg/kg. Whereas, in the root
part, the highest Cd concentration is from the Acorus calamus L i.e., 0.49 mg/kg and the
Phragmites communishas lowest concentration to Cd and it is about 0.13 mg/kg. Moreover,
in the same plant, the root part concentration to Cd is far higher than stem part concentration
to Cd.

18FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Table 7. The concentration of different plants stems part and root part to Pb (mg/kg：：source：
Wu 1981：
It is clear that the Acorus calamus L stem part has the highest Pb concentration of
38.62 mg/kg, and the Phragmites communisroot part has the best concentration ability to Pb
which is about 85.3 mg/kg. However, the Cyperus alternifolius stem part has the lowest Pb
concentration which is 12 mg/kg, and the Scirpus validus Vahl root part can absorb the lowest
of 28.91 mg/kg. Furthermore, it is also to be noted that all the aquatic plants root part have
more concentration to Pb as compared to stem part.
The tolerance of plants to heavy metals depends on the plant species. There is a
typical absorption relationship among them: Emergent plants> Floating, Floated plants>
Submerged plants (Hu et al., 1981). The different parts of same plant also have different
absorptive capacity, for example, in cattail plants, it absorbs heavy metal in wastewater, the
absorptive capacity of cattail is root> underground stem> leaf in turn, and according to a
specific proportion, it absorbs various kinds of heavy metals from its local environment,

19FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
forming a new dynamic balance to prevent excessive absorption of elements caused by
poisoning (Qi et al., 1999).
 Absorption of nitrogen by plants
Nitrogen is one of the most indispensable elements of plant growth and is therefore called
the life element of plants. Therefore, in order to maintain normal growth and development,
wetland plants must absorb nitrogen as their nutrient from the outside environment. The
nitrogen in the sewage is in the form of organic nitrogen and inorganic nitrogen. Inorganic
nitrogen, as an indispensable nutrient in the process of plant growth, can be absorbed and
utilized in the form of ions ( NH 4
+
and NO3
−
), and part of the organic nitrogen is decomposed
by microorganisms：then it can also be absorbed and utilized by plants. Yuanxiao (2002), Jing
conducted an experiment on purification of domestic wastewater from Cyperus falcipifolius.
The experiment shows that the removal rate of TN is 64% for submerged constructed wetland
planted with Cyperus alternifolia, and the removal rate is higher 28% than that of artificial
wetland without plants, and every gram of dry weight Cyerus alternifolius can absorb 2.25
mg of nitrogen in wastewater. Chris (1996) further found out that per gram of dry reeds and
Phragmites communisin subsurface wetland systems can be used to harvest 15–32 mg of
nitrogen from wastewater. This shows that wetland plants have certain absorption of nitrogen,
but different plants have different absorption capacities.

20FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Table 8. The clean ability of seven aquatic plants for nitrogen：source：Zhang et al., 1999：
According to the table 1：there are seven aquatic plants cleaning ability were listed for
nitrogen. They all have different abilities for cleaning the nitrogen. In the 5d：the removal rate
of Typha orientalis Presl ， Cyperus alternifolius ， Phragmites communis ， Scirpus validus
Vahl ， Juncus effusus L.Sorghum and Acorus calamus L are 84.8%, 83.7%, 88.2%, 85.2%,
88.9%, 91.7% and 88.1% respectively. However, the removal rate of no plant group is only
41.2%. This shows that seven aquatic plants have strong adsorption ability for nitrogen.
During those 3 days, the concentration of nitrogen have great decrease in the all seven group
compared to the no plant group because of the plants nitrification and denitrification. This
means that the plants can absorb a huge amount of nitrogen in a short period of time.
 Absorption of phosphorus by plants

21FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Phosphorus, like nitrogen, is an essential element of plants. Energy is required for plant
life activities：and the transmission and storage of energy depend on phosphate compounds.
The existence of phosphorus in sewage depends on the type of phosphorus in the sewage. The
most common ones are phosphates, polyphosphates, and organic phosphates. The phosphorus
that can be directly absorbed by plant roots is mainly mono-valent phosphate ions ( H2 PO4
−
). Polyphosphates and organic phosphates are not or hardly absorbed by plant roots such as
divalent phosphate ions ( HPO4
2−
), trivalent phosphate ions ( PO4
3−
). The absorption of
roots by mono-valent phosphate ( H2 PO4
−
) and bivalent phosphate ( HPO4
2−
) is a
physiological process that depends on the energy obtained by the plant through respiration
(Stottmeister et al., 2003). The study by Mcjarmet et al. (1995) using the constructed wetland
method to treat municipal wastewater, shows that about 5% of the phosphorus in the
wastewater can be absorbed and utilized by wetland plants. In 1996 ： Jianwei Liu et al.
conducted a comparative study on the removal of phosphorus in sewage from eight kinds of
wetland plants such as rice, imperial grass ： and corn. The results showed that all eight
wetland plants could absorb part of the phosphorus in the sewage. Phosphorus in the sewage
is absorbed by the plant roots and can become organic compounds such as ATP, DNA, and
RNA through assimilation and is removed by harvesting the plant (Zhang et al., 1999).

22FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Table9. The clean ability of seven aquatic plants for phosphorus
The table clearly shows the capacity of these seven aquatic plants is higher than that
of no plants group. The removal rate of Sorghum, Juncus effusus L.Acorus calamus L,
Scirpus validus Vahl, Phragmites communis, Cyperus alternifolius and Typha orientalis Presl
are 79.5%, 81.8%, 72.7%, 79.5%, 81.8%, 89.7% and 81.8% respectively. However, the
removal rate of no plant group is only 31.8%. According to this information, there is no
denying that the aquatic plants have great contribution on cleaning the phosphorus from the
water bodies.

23FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Table10. The different plant parts to the N and P concentration：mg/kg) (source：Liu：2003)
This table shows the concentration of N and P in the leaf, stem and root part from the
seven aquatic plants. According to the table, the highest N concentration is from Sorghum
which is up to 31.28mg/kg. The N concentration level is leaf> stem> root, whereas the P
concentration level is leaf> root> stem. So the leaf has the highest ability to concentrate the N
P. Above all, these seven aquatic plants have great ability to absorb N and P, they all are
suitable aquatic plant species for cleaning N and P pollution.
 Absorption of organic pollution by plants

24FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Aquatic plants can absorb phenols and cyanide pollutants in the water and do not
accumulate in the body after absorption. And these phenols and cyanide pollutants are
converted and decomposed through the action of enzymes and biochemical to make them
lose their toxicity. Phenol and cyanide are gradually decomposed and transformed due to the
effect of rhizosphere microorganisms (Wu 1981; Zheng, 1987, 1988). The role of the root
system is to oxidize and decompose the sediments around the roots by releasing O2. On the
other hand, many anaerobic and aerobic bacterial communities are formed at the bottom of
the water body and in the matrix soil to create conditions for microbial activity and thus form
a "rhizosphere zone."In this way, plant metabolites and residues and dissolved organic carbon
provide a food source for colonies in the wetland. The organic pollution material is removed
by microbial decomposition or biodegradation. In eutrophic water bodies, it is also possible
to rely on microorganisms on the basis of rhizomes of aquatic plants to make denitrifying
bacteria and ammoniated bacteria accelerate transform NH3-N to N02 （ N and N03. The
transformation process of N facilitates the absorption and utilization to N of aquatic plants
and reduces the release of nutrients from the sediment into the water (Liu, 2003). According
to reports, Eichhornia crassipes can absorb pollutants such as phenols, menylamine and
aniline, lignin, detergents, BHC, and DDT (Tan, 1986; Tao, 1998; Dai, 1986). According to
another report, artificial wetlands can effectively reduce the atrazine content in agricultural
wastewater after a buffering distance between100m--280m (Moore et al., 2000). The primary
mechanism of removal is the microbial action of roots (McKinlay etal., 1990).

25FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Table11. Normal aquatic plants for cleaning the DDT and Dimethoate ：source：Dai, 1986：
According to the table 3 ： there are different aquatic plants for cleaning herbicides
pollution, the Potamogeton distinctus A.Benn have great cleaning ability for the DDT. When
the DDT initial concentration is 0.445 ug/L, the bioconcentration factor of Potamogeton
distinctus A.Benn is up to 2220 （ and when the DDT initial concentration is 2.1ug/L, its
concentration factor becomes 3500. Furthermore, the Scirpus validus Vahl has a substantial
capacity for cleaning the Dimethoate whose removal rate is up to 78.6%.
DISCUSSION
The results show the mechanism of action of aquatic plants to clean heavy metal：N P
and organic pollution ： and the high capacity of purifying of listed seven aquatic plants to
heavy metal ： N P and organic pollution. Although these aquatic plants have high purified
ability to pollution, yet it is also clear that the phytoremediation technology is not the main
technology used in water remediation projects. There are two reasons for this phenomenon-
Firstly, a few aquatic plants meet the principle which is a requirement for aquatic plants to
clean water pollution; secondly, there is not still a perfect way to dispose the used aquatic
plants. So the selection principle of plants in the constructed wetland and the current disposal
way to use the aquatic plants were discussed in this part.
1. Selection principle of plants in constructed wetlands

26FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
Aquatic plants in wetlands have a significant influence on the treatment effect of
pollution. Generally, when the main object of removal is BOD and N, the selected plants
need to have a large root system that can provide an attachment interface for microorganisms
and strong oxygen transmission ability; and when the main pollution type are N, P, heavy
metals and certain organic substances, it is essential to select the species that have better
absorption capacity and grow faster. If there are numerous pollutant removal targets, it is
necessary to find species that can effectively play a variety of ecological functions.
Besides, the adaptation to the local climate, plant resistance and resistance to pests and
diseases, plant management, and died plant reprocessing should be taken into
consideration. Therefore, how to choose the appropriate plant species to improve the
treatment efficiency is an essential aspect of the design of constructed wetlands.
 Strong stain resistance, decontamination effect
Strong stain resistance and excellent decontamination effect is the fundamental principle
of wetland plants. Wetland system should be based on the different nature of the sewage to
choose different wetland plants. For example, improper selection, may lead to plant death or
decontamination effect. When the concentration of nitrogen in sewage reaches 54.5
mg / L, the cattail leaves in the constructed wetlands will be dead and hard to recover in the
short term (Gersberg et al., 1990). The constructed wetlands of reed and broad-leaved cattail
combined with an anaerobic digestive system to treat slaughterhouse effluent led to an
accumulation of phosphorus in the effluent (Rivera, 1997). Huang Shida et al
(1995) compared the reed, rushes and iris three plant pollutant purification capabilities and
found that rushes has strongest stripping ability; Gao Jixi et al (1997) selected seven kinds of
wetland plants to carry out research, the test results show that Sagittarius and
Zizania latifolia (Griseb.) Stapf has the highest comprehensive purification rate. These

27FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
studies serve as a convenient means of selecting suitable wetland plants, and people can
consider these plants while constructing constructed wetlands.
 Roots developed
Purification of aquatic plants is closely related to the development of their roots. There are
two main reasons: Firtly, the developed plant roots can secrete more root exudates, create
favorable conditions for the survival of microorganisms, promote the biodegradation of the
rhizosphere and improve the purification ability of the constructed wetlands; and secondly,
the root system plays an important role in fixing the riverbed surface, covering the soil and
maintaining the vigorous vitality of plants and microorganisms, and play great significance
for maintaining the stability of wetland ecosystems. In constructed wetlands, pollutants are
mainly removed by microorganisms that attach to and thrive near the surface of the aquatic
plant root zone. In general, the more developed the root system is, the better the
decontamination effect of wetland systems is (Leveling et al., 2002). Selecting the more
developed root system, the aquatic plants with longer roots can greatly expand the wetland
purification of sewage space, and enhance its ability to purify the sewage.
 Suitable for the local environment
Plants must adapt to the local soil and climatic conditions which are selected to clean local
water pollution; otherwise it is hard to achieve the desired treatment effect. Some developing
countries in the tropics and subtropics area have turned a blind eye to the plants with very
high purification potential in their regions due to funding constraints, so they often copy the
model of developed countries, including using the developed countries aquatic plant species
to clean their own countries pollution, but their treatment effect is not very satisfactory
(Denny, 1997; Kivaisi, 2001). Cheng Shuiping (2001), found cattail, Rushes is the more

28FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
suitable aquatic plants in Wuhan, especially the rushes were the best thing water-purification
plants in the area.
2. Current Disposal of Used Aquatic Plants
As aquatic plants purify heavy metal wastewater, the content of heavy metals in plants is
brought up. If they are left untreated or directly returned to the field or compost and
biogas, they will easily cause pollution transfer and secondary pollution and will be treated as
hazardous waste disposal such as landfill, not only to occupy the land resources, but also a
waste of plant resource utilization value. Therefore, it is necessary to adopt a safe and reliable
resource utilization strategy. Some researchers put forward the countermeasure of utilization
of biological carbon by making use of plant material after purification treatment and
conducted preliminary experimental research.
Adding biochar can increase the pH value of heavy metal contaminated soil, and increase
with the pyrolysis temperature. Biochar can reduce the extractable acid content of Pb and Cd,
thus reducing the bioavailability of heavy metals and showing a good fixing effect on heavy
metals. The higher the pyrolysis temperature of biochar is, the better the fixation is. We
obtained biochar by adding a certain ratio of carbon to soil mixing, and increase the soil
organic carbon content, and make soil and water fertilizer , reduce nutrient loss, beneficial to
soil microbial habitat and activity. The obtained biochar can be applied to the soil as forest
green manure. Biochar is extremely stable in the soil. The absorbed heavy metal is released
slowly in the soil after being carbonized and fixed by the plant, and will not cause secondary
pollution. Moreover, the biochar long-term carbon fixation in the soil is the potential carrier
of carbon fixation.

29FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
CONCLUSION
Phytoremediation is a big project to solve the water and soil pollution by using plants,
in this paper ： the water pollution is the main topic of discussion. Using large-scale aquatic
plant to clean water pollution is an innovative pollution control technology, and has sound
remediation effects on different sewage bodies. Since it is a brand new research field, there
are still many problems to be developed and perfected. Firstly, at present, although there are
relatively numerous studies on the purification ability of single aquatic plants, the types of
plants used are relatively simple. Although there are many aquatic plants resources in
China, a few aquatic plants have been put into practice in fact. There is no denying of the fact
that more aquatic plants will be used for cleaning water pollution in the
future. Secondly, there is still a few numbers of studies on the interaction of aquatic plants to
purify polluted water. There is a great deal of research space for various aquatic
plants. Thirdly, the concentration of pollutants in the water is already too high or too low will
affect the effectiveness of phytoremediation. High levels of contaminants which are over the
plant's resistance to toxicity will lead to the death of plants, and it limits the plant's absorption
of pollutants when the concentration of contaminants is too low. Therefore, the different
clean method needs to be considered when to clean the various pollutant
concentrations. Fourthly, the safe disposal to used aquatic plants is still a problem. When the
plant's decontamination ability reaches saturation or reaches the apoptosis season, the residual
plant will often become a fresh source of pollution, forming secondary
pollution. Therefore, how to timely and adequately dispose of plant debris and resource
utilization still needs further study. Using large-scale aquatic plant to clean pollution has
significant advantages in purifying polluted water. With further research, the scope of its
application will continue to expand. It will provide a cleaner water ecosystem for the human
with the widespread use of the phytoremediation.

30FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT

31FUNCTION OF LARGE AQUATIC PLANTS IN WATER POLLUTION TREATMENT
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