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Environmental Science and Pollution Research
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REVIEW ARTICLE

Industrial wastewater treatment using floating wetlands: a review
Jianliang Mao1 · Guangji Hu2 · Wei Deng1 · Min Zhao3,4 · Jianbing Li1,4 
Received: 13 August 2023 / Accepted: 8 December 2023
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2023

Abstract
Industrial wastewater generated from various production processes is often associated with elevated pollutant concentrations
and environmental hazards, necessitating efficient treatment. Floating wetlands (FWs) have emerged as a promising and ecofriendly solution for industrial wastewater treatment, with numerous successful field applications. This article comprehensively reviews the removal mechanisms and treatment performance in the use of FWs for the treatment of diverse industrial
wastewaters. Our findings highlight that the performance of FWs relies on proper plant selection, design, aeration, season
and temperature, plants harvesting and disposal, and maintenance. Well-designed FWs demonstrate remarkable effectiveness in removing organic matter (COD and BOD), suspended solids, nutrients, and heavy metals from industrial wastewater.
This effectiveness is attributed to the intricate physical and metabolic interactions between plants and microbial communities within FWs. A significant portion of the reported applications of FWs revolve around the treatment of textile and oily
wastewater. In particular, the application reports of FWs are mainly concentrated in temperate developing countries, where
FWs can serve as a feasible and cost-effective industrial wastewater treatment technology, replacing high-cost traditional
technologies. Furthermore, our analysis reveals that the treatment efficiency of FWs can be significantly enhanced through
strategies like bacterial inoculation, aeration, and co-plantation of specific plant species. These techniques offer promising
directions for further research. To advance the field, we recommend future research efforts focus on developing novel floating materials, optimizing the selection and combination of plants and microorganisms, exploring flexible disposal methods
for harvested biomass, and designing multi-functional FW systems.
Keywords  Floating wetlands · Pollutant removal · Industrial wastewater · Wastewater treatment
Abbreviations
ADMIAmerican Dye Manufacture Institute
AMDAcid mine drainage
BODBiochemical oxygen demand
Responsible Editor: Alexandros Stefanakis
* Jianbing Li

1

School of Engineering, Environmental Engineering Program,
University of Northern British Columbia (UNBC), 3333
University Way, Prince George, British Columbia V2N 4Z9,
Canada

2



School of Environmental Science and Engineering, Qingdao
University, Qingdao 266071, Shandong Province, China

3

School of Life and Environmental Sciences, Wenzhou
University (WZU), Wenzhou 325035, Zhejiang Province,
China

4

WZU‑UNBC Joint Research Institute of Ecology
and Environment, Wenzhou University (WZU),
Wenzhou 325035, Zhejiang Province, China

CODChemical oxygen demand
CWConstructed wetland
DODissolved oxygen
ECElectrical conductivity
FWFloating wetland
PVCPolyvinyl chloride
TAN Total ammonia nitrogen
TDSTotal dissolved solids
TKNTotal Kjeldahl nitrogen
TNTotal nitrogen
TPTotal phosphorus
TPHTotal Petroleum Hydrocarbons
TSTotal solids
TSSTotal suspended solid

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Introduction
A variety of wastewater is generated in large volumes from
different industrial production processes, such as chemical, petroleum, textile, and mining industries (Zhang et al.
2015). Industrial wastewater contains a diverse array of
organic, inorganic, and biological pollutants, which will
deteriorate the receiving waterbodies if not treated properly (Bi et al. 2019). Conventional technologies for industrial wastewater treatment include gravity separation,
screening, gas flotation, flocculation, activated sludge,
sequential bioreactor, membrane bioreactor, anaerobic baffled reactor, membrane filtration, and advanced oxidation

(Shrestha et al. 2021; Toczyłowska-Mamińska 2017; Yu
et al. 2017). However, these technologies are associated
with several shortcomings such as high cost, sludge production, low operating pH, high maintenance requirement,
and secondary pollution (Ijaz et al. 2016; Jain et al. 2020).
Consequently, there is an urgent need for developing effective and eco-friendly methods for industrial wastewater
reclamation. In response to this need, natural wetlands
have emerged as promising agents for the treatment of
polluted water, and in light of this, various artificial wetlands have been designed and used to treat anthropogenic

Fig. 1  Classification and typical structure of FW

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Environmental Science and Pollution Research

discharges such as municipal wastewater, agricultural
runoff, and industrial effluents (Ijaz et al. 2016; Li et al.
2021a, b; Naeem et al. 2020; Rahi et al. 2020). Artificial
wetlands mainly include subsurface flow wetlands, free
water surface flow wetlands, and floating wetlands (FWs)
(Stefanakis 2018). Among them, FWs are a prominent
type that can be established easily using soilless planting
technology in a flexible and cost-effective manner (Shahid
et al. 2018).
Various terminologies have been used for FWs (Fig. 1),
including floating treatment wetland, constructed floating
wetland, artificial floating wetland, artificial floating island,
ecological floating bed, floating hydroponic system (Davamani et al. 2021; Karstens et al. 2021; Oliveira et al. 2021).
As illustrated in Fig. 1, the structure of FWs mainly consists of plants and a floating mat. Notably, the key distinction between natural and artificial FWs is that plants grow
on the artificial buoyancy materials in the latter. The roots

attached with biofilm can thus grow under the water surface
and the crown of plants is supported above the water surface. Rhizosphere is the environment that interacts closely
with the plant root system. Instead of soil, the water is the
main environment to the root system in FWs, and bacteria
are also observed in rhizosphere (Saleem et al. 2018). A
variety of buoyancy materials have been employed in the


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construction of floating mats, such as bamboo-based meshes,
wire meshes, fibrous material, polystyrene foam, polyvinyl
chloride (PVC) pipes, and polyester sheets (Shahid et al.
2018). PVC-based floating materials are regarded as the
new-generation materials with better stability and buoyancy,
and it is also assessed to be environmentally safe because
of the insignificant release of microplastic particles (Ziajahromi et al. 2020). Additionally, mat materials are also
influential to other critical factors affecting the mat design,
including anchoring, cost, durability, flexibility, functionality, and local availability (Samal et al. 2019). Ensuring
the stability of floating mats to withstand sunlight radiation, water wave action, and wind over extended periods is
essential. Additionally, the parenchymatous ability of plants
could also increase the buoyancy of FWs, which can entrap
gases in tissues and therefore make plants float on the water
surface (Rehman et al. 2019a).
Typically, FWs rely on interactions among plants, water,
atmosphere, and microorganisms to treat pollutants (Shahid
et al. 2020a, b). The main mechanisms of FW for pollutants
removal include entrapment of solids, uptake of nutrients
and metals, development of biofilms, degradation of organic
pollutants, and flocculation of suspended matter (Samal

et al. 2019). Different types of FWs have been installed in
reservoirs, ponds, rivers, and lakes for natural water quality
improvement (Hu et al. 2010; Saeed et al. 2016). With the
development of this technology, FWs have been employed
to treat industrial wastewater, such as acid mine drainage
(Gupta et al. 2020), effluent from the pulp and paper industry (Ayres et al. 2019), and oily wastewater from the petrochemical industry (Darajeh et al. 2016).
Previous literature reviews have extensively explored
the utilization of constructed wetlands (CWs) for the treatment of industrial wastewater (Stefanakis 2018; Vymazal

2013). These reviews have demonstrated the effectiveness
of CWs in mitigating industrial pollutants. However, it
is important to note that traditional CWs often necessitate significant land resources for their implementation.
In contrast, floating wetlands (FWs) present an alternative approach that relies on the robust plant system and
associated biofilm to directly remediate pollutants, eliminating the need for additional land allocation (Colares
et al. 2020). Recent publications have begun to unveil the
considerable potential of FWs in achieving high treatment
efficiency, even for complex industrial pollutants. Nonetheless, there exists a noticeable gap in the literature—a
comprehensive discussion of the application of FWs for
industrial wastewater treatment and a thorough exploration of their advantages and limitations. It is within this
context that this review aims to make a valuable contribution. The primary objective of this review is to provide an
encompassing summary of the development and practical
application of FWs in the treatment of industrial wastewater. This review will summarize the structural components
of FWs, the critical factors influencing the performance of
FWs, the removal mechanism of various industrial pollutants by FWs, and the applications of the FWs of treating
different industrial wastewater. Moreover, the limitations
of FWs in their current state and avenues for their future
development will be discussed in detail, the review scope
and framework are shown in Fig. 2.

Factors affecting the performance of FWs

Various factors can impact the FWs treatment performance
(Fig. 3), and they are discussed below.

Fig. 2  Review scope and
framework

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Environmental Science and Pollution Research

60% to 80%) (Rehman et al. 2018). Aquatic plants are more
commonly used in FWs because the plants are well-adapted
to the complex water environment characterized by different
nutrient concentrations, redox conditions, and trophic status
of water (Vymazal 2013). Plants can also be used in combination because different species have different treatment
capacities for different pollutants and concentrations. The
combination of plants can achieve higher efficiencies in the
treatment of wastewater with complex pollutants (Dzakpasu
et al. 2014). However, it is difficult to assess the function of
individual species and the synergistic effect of plants.

Design
Design of FWs is critical for effective application. Some
important considerations in designing an FW system are as
follows:

Fig. 3  Influential factors on the performance of FWs

Plant selection
The choice of plants is essential to the effective removal of
pollutants from industrial wastewater. There are some key
principles of plant selection in FWs application: the plants
should be native perennial species that have a good growth
rate in hydroponic environments, an extensive root system,
high tolerance to pollutants, and a large capacity to uptake
pollutants (Calheiros et al. 2020; Shahid et al. 2020b). Various species of plants have been used in FWs, such as vetiver
(Chua et al. 2012), Typha domingensis (Di et al. 2019), Brachiaria mutica (Ijaz et al. 2015), Najas minor (Zhou et al.
2016), Salvinia natans and Phragmites australis (Huang
et al. 2017), Oenanthe javanica (Wang et al. 2018), Iris
pseudacorus (Zhang et al. 2019), Pistia stratiotes (Samal
et al. 2021), and Typha orientalis (Ansari et al. 2017). For
industrial wastewater treatment, plant selection depends on
the type of pollutants, water quality, and climatic conditions
(Shahid et al. 2018). Although different plant species have
different phytoremediation potentials, the main pollutant
removal mechanisms include accumulation, exclusion, translocation, osmoregulation, distribution, and concentration
(Rezania et al. 2016). It is important to choose proper plants
for target pollutants under given conditions. For example,
Pistia stratiotes and water hyacinth can remove Pb, Cu, and
Cd from industrial effluent (Aurangzeb et al. 2014; Volf et al.
2015). Vetiver can remove organic matters from wastewater
(Darajeh et al. 2014). Under the same conditions, Phragmites australis removed 20% more chemical oxygen demand
(COD) from oily wastewater than Brachiara mutica (around

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i) Baseline monitoring of wastewater: Baseline water quality and flow direction assessment is necessary for the

design of FWs because the types and concentrations of
pollutants are important to the selection of plants and
application sites (Winston et al. 2013). For example, a
baseline analysis can help researchers select study sites
with a high pollutant load in the inflow (Borne et al.
2013).
ii) Retention period: FWs are often designed or assessed
under varying retention periods depending on the treatment scale. In laboratory-scale settings, retention periods typically range from several hours to weeks, while
large-scale investigations may extend over several
months to years.
iii) Self-buoyancy: Floating plants can achieve self-buoyancy by entrapping gases in their rhizomes and tissues,
enabling them to grow on the water surface (Rehman
et al. 2019b). Floating rafts and mats can also serve as
stable platforms to support non-floating plants growing
on the water surface (Chow et al. 2019; Shin et al. 2015).
iv) Depth of water: Compared with the other types of constructed wetlands, FWs are lack of soil and thus the
plants heavily rely on their roots for nutrients uptake
from the water body (Shahid et al. 2018). Therefore, the
water depth is crucial for root structure development.
For most of the plants in FWs, a water depth of at least
0.8–1.0 m is required for vertical growth (Headley and
Tanner 2008). Increased water depth can promote the
treatment performance of FWs due to increased contact time of roots and microbial biofilm with pollutants
(Tanner and Headley 2011). Water depth is flexible for
different pollutants as a low water depth is preferred for
removing small particles and suspended solids due to
more frequent contact between wastewater and biofilm.
While deep water is suitable to treat coarse suspended

Environmental Science and Pollution Research

solids by sedimentation because there is sufficient free
water zone for solids precipitation (Chen et al. 2012).
Moreover, deep water creates layers with different dissolved oxygen concentrations in the water column, and
thus nitrification and denitrification can be achieved
under aerobic and anaerobic conditions, the co-existence
of both process can efficiently remove N from wastewater (Colares et al. 2020).
Other important design considerations include the size of
wetland and plant coverage (the area ratio of plants to water)
(Chen et al. 2016). Surface area has a significant impact
on the efficiency of FWs; a greater surface area would harbor a larger bacterial population and bring a higher nutrient
removal efficiency (Stewart et al. 2008). An increase in plant
coverage can also increase the treatment efficiency (Winston
et al. 2013). However, increasing plant coverage sometimes
may limit the pollutant removal because this can reduce the
dissolved oxygen level in wastewater, resulting in decreased
aerobic bacteria bioactivity and plant growth rates (Wei et al.
2020). FWs with 100% plant coverage were seen with a low
dissolved oxygen level compared with 50% planting coverage (Chang et al. 2012). Dense plant coverage also limits the
gaseous exchange process, signifying that gas exchange most
likely occurs in the uncovered portions of the water. The
shortage of oxygen and light caused by dense plant coverage
could affect the biofilm attached to plant roots (Chang et al.
2012; Headley and Tanner 2008). The plant coverage ranges
from 5% to > 50% in the reported experimental designs and
field applications (Chang et al. 2012), but it is suggested to
be < 80% for most FW applications (Wu et al. 2015). The
growth rate of plants affects the plant coverage design; with
a higher plant growth rate, FWs may need less coverage to

achieve similar treatment efficiencies (McAndrew and Ahn
2017).

Aeration
Aeration is an important factor that affects the pollutant
removal efficiency of FWs. A high dissolved oxygen (DO)
level brought by aeration can both enhance the microbial
degradation process and be beneficial to the growth of plants
(Pan et al. 2015). One study found that almost all vetiver
under anaerobic conditions did not grow, but healthy roots
grew under aerobic conditions (Darajeh et al. 2016). The
wastewater treatment efficiency of FWs can be maximized
by enhanced aeration (Henny et al. 2020). Aeration creates
aerobic micro-zones that stimulate biofilm growth on the
roots, which promotes the removal of ammonium and nitrate
by aerobic processes such as nitrifying and biodegradation.
The total phosphorus removal can be improved by 4–50%
by employing artificial aeration in CWs (Ilyas and Masih
2018). Nitrate removal was improved from -1.7% to 33.8%

with additional aeration (Dunqiu et al. 2012). FWs supplemented with aeration were proven efficient for municipal
wastewater treatment, and the removal efficiencies of both
total suspended solids (TSS) and biological oxygen demand
(BOD) would reach 93% (Park et al. 2019). However, in
some studies, the increase in oxygen level did not increase
the removal rate of total nitrogen (TN) and total phosphorus (TP) (Wang et al. 2015). In a study, increased aeration
improved the ammonium and phosphorus removal but
decreased denitrification and overall total nitrogen removal
because the denitrification microbials prefer anaerobic conditions (Dunqiu et al. 2012). Another study found that the
aerated water column was associated with less nitrogen and

phosphorus removal than the non-aerated water when using
FWs to treat nutrients-enriched agricultural runoff (Chance
and White 2018).

Season and temperature
Season and temperature are considered a prominent factor in
pollutant removal using FWs (Moortel et al. 2010). During
spring and summer, FWs showed a high capability of pollutants removal because of the high rates of microbial proliferation and plant growth. In contrast, less removal of pollutants was observed in winter because of reduced plant and
bacterial growth (Huang et al. 2017; Shehzadi et al. 2014).
In some studies, a positive relationship was seen between
temperature and nitrogen removal because bacteria involved
in nitrification and denitrification rely heavily on environmental temperature; for example, the highest removal of
TN (46.8–56.8%) and ­NH4-N (51%) were reported within a
temperature range of 5–15 ℃ in a FW (Moortel et al. 2010).
Season and temperature variation can affect the BOD/COD
ratio in wastewater, which further affects the efficiency
of organic matter removal by plants. A high temperature
can enhance the removal of organic matter as the result of
increased microbial activity (Ashraf et al. 2018). With the
decrease in temperature, the capacity of plants to remove
organic matter dramatically declined. In a study, removal
efficiency decreased by 14.57% for TN, 16.47% for N
­ O3-N,
+
16.11% for ­NH4 -N, and 24.06% for TP in the winter batches
over that in the autumn batches (Zou et al. 2016).

Plants harvesting and disposal
Plants harvesting can speed up the removal of pollutants
and limit the internal nutrient cycle in FWs (Wang et al.

2014). Nutrients and pollutants captured by plants are
accumulated in shoots, roots, and leaves (Zare et al. 2018).
During the early stage of plant growth, FWs can remove
pollutants at a high efficiency. According to Wang et al.
(2014), harvesting picked weed and soft-stem bulrush in
July, August, and October can reach maximum nutrients

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removal. It was recommended that plants should be harvested before the end of the growing season to avoid nutrients being released back from the biomass to wastewater
due to plants decay (Borne 2014; Hoffmann et al. 2012).
Because nutrients can transfer between different tissues
of plants, harvesting should be conducted when a high
accumulation of nutrients is observed in the harvestable
parts of plants (Borne 2014). However, early harvesting
could be detrimental to the growth of plants and reduce the
capacity of plants to absorb and store pollutants (Colares
et al. 2020). Moreover, early harvesting makes the bacteria
lose the support of plants and face a shortage of carbon
sources. A good harvesting strategy should consider both
the harvesting schedule and the parts of plants to be harvested. A study reported that harvesting tissues accumulating nutrients above the mat would be more sustainable
and practical than harvesting the entire plants (Wang et al.
2015). Harvesting plant tissues above the mat can keep the
bacteria community stable under the water surface and
also reduce operational and maintenance costs (White and
Cousins 2013), as the reserved roots can then be used for
vegetation restoration in the following spring.

Following plants harvesting is the disposal of the harvested biomass. Improper handling or disposal of harvested plants and tissues may lead to the release of accumulated pollutants back into the environment. This can
result in secondary pollution, offsetting the initial benefits of wastewater treatment. Conventional disposal of
plant biomass includes composting, feeding animals, and
making paper (Bidin et al. 2015). For plants accumulating toxic pollutants like heavy metals, combustion, gasification, and pyrolysis are the common disposal methods.
Combustion transforms plants into ash, which is usually
2–5% of the initial volume of the biomass. The disadvantage of combustion is the release of toxic and greenhouse
gases into the atmospheric environment (Brunerová et al.
2017). In contrast, gasification produces cleaner residue
and generates thermal energy and electricity, but the main
disadvantage of this technology is high cost for meeting
the high temperature (> 700℃) condition (Kathi 2016).
Pyrolysis decomposes biomass at a relatively lower temperature (400–700℃) in an oxygen-free environment into
useful products including pyrolysis oil, gases, and biochar
(Muradov et al. 2010). After proper modification, biochar can be used for wastewater treatment. In a study on
municipal wastewater treatment, harvested reed straw was
pyrolyzed into biochar, which was used as reed biochar
substrate and a carbon source for microorganisms (Huang
et al. 2020). After adding the biochar to FWs, the average
removal efficiencies of TN and TP increased by 57.6% and
46.7%, respectively, and the microbial species for nitrogen removal were also enriched with the additional carbon
source (Huang et al. 2020).

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Environmental Science and Pollution Research

Installation and maintenance of FWs
In the field application of FWs, fertilizers can be used at
the early stage of plants growth to help plants grow better
until the development of floating plants is complete (Arslan

et al. 2017). Plants are usually cultivated in less-polluted or
tap water for adaption to the new environment, and this can
increase the survival rate of the selected plants in wastewater treatment later (Hefni et al. 2017). Floating mats can be
anchored to the edge of the aquatic environment by ropes
to reduce mats drifting caused by strong winds and waves
(Borne et  al. 2015). However, appropriate flexibility is
also needed to adjust the position of floating mats with the
change of water level (Wei et al. 2020). To keep the stability of FWs in windy seasons or areas, the height of plants
should be limited because tall plants may cause the turnover
and drifting of floating mats (Chen et al. 2016). Installing
small floating islands with low-height plants is more suitable for windy environments. After installation, the main
maintenance includes weeding, clearing the blockage of
floating matters on water surface, and repair of broken parts
(Pavlineri et al. 2017). Trimming and removing shoots can
effectively prevent plants from withering due to the shortage
of oxygen (Hawes et al. 2016). Harvesting, mentioned above
for improvement of pollutants removal, is also important for
FWs maintenance; periodic harvesting of plants can provide enough space for plants to regrow (Hussain et al. 2018;
Wei et al. 2020). Additionally, regular monitoring of FWs
is essential to prevent the planting hole or water area from
being blocked caused by the accumulation of plant branches,
plastic species, and other materials and maintain the longterm operation (Borne et al. 2015).

Summary of impact factors
Plant selection is a crucial factor in the effective removal
of pollutants from industrial wastewater using Floating
Wetlands (FWs). Key principles for selecting suitable
plants include choosing native perennial species with
strong adaptability to hydroponic environments, extensive root systems, high pollution tolerance, and efficient
pollutant uptake capabilities. The choice of plant species

should be based on the specific pollutants, water quality,
and climatic conditions of the treatment site. Factors like
water depth, plant coverage, aeration, seasonal variations,
and temperature also significantly impact the pollutant
removal efficiency of FWs. Additionally, proper plant
harvesting, and disposal strategies are essential to maintain the effectiveness of FWs, preventing the release of
captured pollutants. The installation and maintenance of
FWs require careful consideration, including initial fertilization, plant adaptation, and routine maintenance tasks
like weeding and clearing. Overall, effective pollutant


Environmental Science and Pollution Research

removal in FWs relies on a combination of plant selection, thoughtful design, aeration, seasonal factors, and
proper maintenance practices.

Industrial wastewater pollutant removal
using FWs
Industrial wastewater is a collective term, and the species
and loads of pollutants vary drastically by the sources.
The main pollutants in industrial wastewater include
organic matter, nutrients, heavy metals, and total solids.
These pollutants are commonly generated from textile,
oil, food processing, mining, chemical, and pulp and
paper industries. In general, mining wastewater contains
high concentrations of heavy metals. Wastewater from
textile and food processing industries contain high levels
of organics and solids, and food processing effluents contain high concentrations of nutrients (Fig. 4). Industrial
wastewater usually contains high concentrations of organics, TS, and heavy metals, while the concentrations of
nutrients are relatively lower (Bi et al. 2019). Compared

with municipal wastewater, industrial wastewater is toxic,
colored, smelly, and foamy. FWs have different removal
mechanisms for different pollutants by employing plants,
bacteria, and plant-bacteria synergism.

Organic matter
Organic pollutants in industrial wastewater are mainly
from tannery, palm oil, dairy, beverage, pharmaceutical,
textile, and food processing industries (Mutamim et al.
2012). Organic pollutants can be used by microorganisms
and plants as a carbon and energy source to increase biomass; however, some organic pollutants such as phenolic
compounds, benzene, toluene, polycyclic aromatic hydrocarbons, and other types of hydrocarbon are toxic and carcinogenic (Jain et al. 2020). In FWs, biodegradation of
organic pollutants by microorganisms attached to roots
is active near the root area. Biofilm and plant roots can
assimilate dissolved organic matter directly, while large
organic compounds can be transformed into smaller compounds by microorganisms so that the smaller compounds
can be taken up by plants (Barbara 2009). CODis used to
measure the oxygen demand of organic and inorganic pollutants in water, and BOD is employed to gauge the ability
of microorganisms in water to degrade organic substances.
In the application of FWs, they are the key parameters to
assess the degradability of organic matter. A BOD/COD
ratio > 0.5 indicates that the wastewater is suitable for biodegradation treatment (Kumar et al. 2010). Nevertheless,
effective removal of organic pollutants has been achieved
for different types of wastewater with BOD/COD ratios
ranging from 0.6 to 0.8 (Benvenuti et al. 2018; Li and
Guo 2017; Prajapati et al. 2017). For industrial wastewater

Fig. 4  Characteristics of
industrial wastewater treated
using FWs: a) main types and

pollutants and concentration
ranges of b) solids and organics
and c) heavy metals in industrial
wastewater (using Data from
Table 1)

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Table 1  Pollutants initial concentration on studies of FWs treating industrial wastewater
Wastewater
Textile wastewater

Wastewater characteristics

ADMI = 1285  ± 1.55, COD = 1438 ± 12.7 mg/L, BOD = 1230 ± 10.2 mg/L,
TDS = 8230 ± 8.8 mg/L, TSS = 5175 ± 0.7 mg/L
Textile wastewater
ADMI = 1142  ± 21, COD = 1495 ± 20 mg/L, BOD = 1135 ± 20 mg/L,
TDS = 4706 ± 28 mg/L, TSS = 734 ± 8 mg/L
Textile wastewater
ADMI = 1308  ± 11, COD = 1794 ± 7 mg/L, BOD = 1350 ± 13 mg/L,
TDS = 5143 ± 21 mg/L, TSS = 1900 ± 15 mg/L
Textile wastewater
ADMI = 1638  ± 1.6, COD = 1734 ± 1.8 mg/L, BOD = 1478 ± 1.5 mg/L,
TDS = 9060 ± 4.6 mg/L, TSS = 6438 ± 4.1 mg/L

Textile wastewater
TS = 55.67  ± 5.72 mg/L, COD = 150.13  ± 39.06 mg/L, BOD = 317  ± 16.73 mg/L
Textile wastewater
COD = 177.76 mg/L, BOD = 87.178 mg/L
Textile wastewater
TDS = 2560.83 mg/L, TSS = 131.61 mg/L, BOD = 107.46 mg/L, COD = 187.1 mg/L
Textile wastewater
TDS = 400 mg/L, TSS = 92 mg/L, BOD = 121 mg/L, COD = 310 mg/L,
Color = 40 ­m−1
Textile wastewater
TDS = 4961 mg/L, TSS = 4569 mg/L, BOD = 249 mg/L, COD = 471 mg/L,
Color = 35.5 ­m−1
Textile wastewater
TDS = 5251  ± 404 mg/L, TSS = 324  ± 29.7 mg/L, BOD = 283  ± 17.9 mg/L,
COD = 513  ± 37.6 mg/L, Color = 66  ± 4.4 ­m−1
Oil and grease
COD = 538 ± 83 mg/L, BOD = 228 ± 65 mg/L, Oil and grease = 17.4 ± 2.7 mg/L
Palm oil mill effluent
COD = 210 mg/L, BOD = 42.91 mg/L
Palm oil mill effluent
COD = 790–810 mg/L, BOD = 350–400 mg/L
Diesel
Oil = 10,000 mg/L, COD = 10000 mg/L, BOD = 3500 mg/L
Refinery wastewater
TPH = 1720 mg/L, COD = 142.8 mg/L
Oil field-produced wastewater COD = 1336 ± 58.74 mg/L, BOD = 405 ± 19.43 mg/L, hydrocarbons = 316 ± 7.84 mg/L
Crude oil contaminated water COD = 1316 ± 73.5 mg/L, BOD = 365 ± 15.4 mg/L, hydrocarbons = 319 ± 9.7 mg/L
Oil field wastewater
COD = 1324 ± 66.5 mg/L, BOD = 475 ± 15.5 mg/L, oil = 325 ± 10.1 mg/L
Crude oil spilled water

COD = 150–160 mg/L, BOD = 20–25 mg/L, Oil and grease = 0.15 mg/L
Palm oil mill effluent
COD = 750 mg/L, BOD = 350 mg/L, Oil and grease = 15 mg/L
Acid mine drainage
Cd = 0.02 mg/L, Cu = 4.78 mg/L
Acid mine drainage
Fe = 81.4 ± 1.16 mg/L, Al = 70.3 ± 1.11 mg/L, Mn = 21.9 ± 0.27 mg/L,
Zn = 1.372 ± 0.0436 mg/L, Ni = 0.697 ± 0.0413 mg/L, Cu = 0.184 ± 0.00435 mg/L,
Pb = 0.08 ± 0.0341 mg/L, Cr = 0.01 mg/L
Acid mine drainage
Fe = 12 mg/L, Al = 11.3 mg/L, Zn = 0.385 mg/L, Ni = 0.388 mg/L,
Cu = 0.0218 mg/L, Pb = 0.0105 mg/L
Pulp and paper mill effluent
TDS = 1840 mg/L, EC = 2.64 dS/m, BOD = 475.1 mg/L, COD = 880.5 mg/L,
TKN = 192.65 mg/L, ­PO43− = 145.6 mg/L, Cd = 2.45 mg/L, Cr = 1.38 mg/L,
Cu = 5.64 mg/L, Fe = 8.95 mg/L, Mn = 3.66 mg/L, Pb = 1.74 mg/L,
Ni = 1.02 mg/L, Zn = 6.9 mg/L
Chemical contaminated water Benzene = 13 ± 3 mg/L, MTBE = 2.2 ± 0.5 mg/L
Dairy wastewater
TS = 1671.58 ± 177 mg/L, COD = 5866.67 ± 924 mg/L, BOD = 2282.75 mg/L
Sugar mill effluent
EC = 5.44 ± 0.05 dS/m, TDS = 1932.2 ± 11.22 mg/L, BOD = 947.88 ± 6.44 mg/L,
COD = 1620.3 ± 10.23 mg/L, TKN = 126.43 ± 3.12 mg/L,
TP = 124.32 ± 2.14 mg/L
Paperboard mill wastewater
EC = 1.98 ± 0.06 dS/m, TDS = 1000 ± 16.3 mg/L, TSS = 200 ± 3.26 mg/L,
BOD = 44.0 ± 1.43 mg/L, COD = 256 ± 4.17 mg/L, TN = 25 ± 0.81 mg/L,
TP = 8.50 ± 0.28 mg/L, Pb = 0.96 ± 0.02 mg/L, Cd = 0.42 ± 0.01 mg/L
Paper mill wastewater
TP = 0.02–0.88 mg/L, TN = 1.8–7.4 mg/L

Saline industrial wastewater
TDS = 5000 mg/L, COD = 350 mg/L, TN = 13.2 mg/L, TP = 4 mg/L,
Batik Wastewater
TSS = 1424.04 ± 166.62 mg/L, COD = 273.88 ± 24.93 mg/L,
BOD = 37.95 ± 8.14 mg/L, Cr = 0.81 ± 0.06 mg/L
Batik Wastewater
TSS = 1183 mg/L, TAN = 2.38 mg/L, ­NH4+  = 0.96 mg/L, ­NH3 = 1.42 mg/L

13

Reference
Kadam et al. (2018a)
Chandanshive et al. (2020)
Chandanshive et al. (2020)
Kadam et al. (2018b)
Charoenlarp et al. (2016)
Tusief et al. (2020)
Qamar et al. (2019)
Nawaz et al. (2020)
Tara et al. (2019b)
Tara et al. (2019a)
Ijaz et al. (2016)
Tan (2019)
Darajeh et al. (2014)
Fahid et al. (2020)
Li et al. (2012)
Rehman et al. (2019b)
Afzal et al. (2019b)
Rehman et al. (2018)
Effendi et al. (2017)

Darajeh et al. (2016)
Palihakkara et al. (2018)
Kiiskila et al. (2019)
Kiiskila et al. (2017)
Kumar et al. (2016)

Chen et al. (2012)
Queiroz et al. (2020)
Kumar et al. (2019)
Davamani et al. (2021)
Ayres et al. (2019)
Gao et al. (2020)
Tambunan et al. (2018)
Effendi et al. (2018)


Environmental Science and Pollution Research

treatment, a floating treatment wetland was installed to
treat palm oil mill effluents, and the reduction of BOD and
COD was reported to be 96% and 94%, respectively, with
aeration under a BOD/COD ratio of 0.46 (Darajeh et al.
2016). In another study, FWs were used to remediate water
contaminated by spilled crude oil, and significant reductions in BOD (81%), COD (81%), and oil content (91%)
were observed after 4  weeks treatment (Effendi et  al.
2017). In a recent study, an FW augmented with bacteria
was used to treat dye-enriched synthetic wastewater, and
the results showed that the FW significantly reduced COD
from 471 to 30 mg/L and BOD from 249 to 31 mg/L; also,
the treatment efficiency of the augmented FW was much

higher than non-vegetated and only vegetated (i.e., nonaugmented) FWs (Tara et al. 2019a).

Total solids
Total solids (TS) include total suspended solids (TSS)
and total dissolved solids (TDS). TSS indicates the total
quantity of suspended particulate matter in water and
usually consists of phosphates, nitrates, carbonates, and
a series of bicarbonates, which can increase the turbidity of wastewater and reduce light availability for submerged macrophytes and microorganisms (Bi et al. 2019;
Wei et al. 2020). In addition, many harmful substances,
such as heavy metals, polycyclic aromatic hydrocarbons,
and organic matter, can be adsorbed on TSS, and thus the
increase of TSS in water may have ecotoxic effects on
aquatic organisms (Rossi et al. 2006). TDS represents the
total amount of dissolved inorganic and organic solids in
water and is related to the high conductivity and salinity
of wastewater. Textile effluents usually contain higher concentrations (1,000–10,000 mg/L) of TDS than other industrial wastewater (Wei et al. 2020). TSS is mainly removed
via physical sedimentation and filtration processes (Borne
et al. 2013), while TDS removal is also associated with
the uptake by plants. Vegetation and associated roots can
speed up the removal of TSS and TDS (Shahid et al. 2019).
Plant roots play an important role in the removal of suspended solids and particles in wastewater (Benvenuti et al.
2018). The network of plant roots can entrap suspended
solids (Hawes et al. 2016). It also forms an ideal area for
the development of biofilm (Cao et al. 2012), which is
active to entrap and filter fine particles. TSS can also be
removed by sedimentation and precipitated to the bottom
(Chen et al. 2016). It is necessary to clean the sediment
layer to avoid pollutants resuspending (Headley and Tanner 2012). For textile wastewater, results of many studies indicated that FWs can successfully achieve 53–80%
and 53–85% removal of TSS and TDS, respectively

(Charoenlarp et al. 2016; Kadam et al. 2018a; Nawaz et al.
2020; Zhang et al. 2015).

Nutrients
Nitrogen and phosphorus in wastewater are referred to as
nutrients, and both are necessary elements for the growth of
plants (Carey and Migliaccio 2009). However, high levels
of nutrients in the aquatic ecosystem can lead to eutrophication and ultimately result in the degradation of the ecosystem. FW is a low-cost and sustainable approach for nutrient removal from industrial wastewater. In FWs, the main
mechanisms of phosphorus removal are physical, including
complexation, sorption, filtration, precipitation, and fixation
(Lynch et al. 2015; Schwammberger et al. 2019; Stewart
et al. 2008). Compared with constructed wetlands, phosphorus sorption to FWs is limited because of the absence
of soil-based barriers and other filtration materials. Adding suspended substrate in FWs can improve the removal of
phosphorus (Huang et al. 2020). Assimilation by plants and
microorganisms can also reduce phosphorus concentrations,
especially the organic phosphorus (Spangler et al. 2019).
Bacteria degrade organic phosphorus into dissolved forms,
which can be readily taken up by plants and other microorganisms (Bi et al. 2019).
The main process for nitrogen removal is biological
nitrification–denitrification. Nitrifying bacteria on biofilm
­ O2−, which can be
transform ammonia into N
­ O3− and N
assimilated by plants (Borin and Salvato 2012). During the
nitrifying-utilization cycle, nitrate can be restored to ­N2 and
­N2O by denitrifying bacteria and released into the atmosphere. A constructed FW was used for treating nitrogen-rich
mining wastewater in a cold climate, and the results showed
that macrophyte root-associated denitrification was the main
pathway for nitrogen removal, and the nitrogen removal
rates ranged between 32 and 2250 mg N

­ 2O-N/(m2 *day)
through the denitrification (Choudhury et al. 2019).
Moreover, there is an oxic-anoxic gradient in the rhizosphere of FWs, and this gradient helps to form a diversity
of microorganism communities and therefore achieve better nitrification–denitrification (Oliveira et al. 2021). Other
nitrogen removal processes include sedimentation and
uptake by plants. Aquatic plants can adsorb ammonia and
­NO2− to support their growth (Li et al. 2008), and the average nitrogen adsorption rates were reported in a wide range
under different conditions, such as plant growth stage, plant
species, types of wastewater, concentrations of dissolved
oxygen, season, and other environmental factors (Emparan
et al. 2019). For instance, Spangler et al. (2019) investigated
five plant species in FWs for nutrients removal and found
that plants selection and timing of harvesting affect nutrients
removal. Another research reported that the uptake of nitrogen was higher in spring and summer (Dong et al. 2011).

13




The N/P ratio is helpful to generate an effective FW
design. The optimum N/P ratio usually depends on the specific plant species (Li et al. 2017). A study found that the
optimal N/P ratios for nutrient removal by M. elatinoides, E.
crassipes, and A. philoxeroides were 10:1, 20:1, and 20:1,
respectively (Li et al. 2021b). pH is also influential to the
removal of nutrients. A recent study reported that different
pH conditions impacted nitrogen and phosphorus removal
by aquatic macrophytes. For example, almost 100% ammonium nitrogen and phosphate phosphorus were removed at
pH 6.5 and 7.0, respectively, while the removal efficiency
decreased to 60% at pH 5.0 and 6.0 (Qian et al. 2020). FWs

enhanced by other methods can achieve higher nutrients
removal in wastewater treatment. A study investigating the
combination of FW islands with micro-bubble aeration and
filtration media found that the combined system had a high
removal rate for nutrients as micro-bubbles can prevent the
formation of the anaerobic area in the lower zones of the
wastewater (Yoon et al. 2016). Another study reported that
maximum reduction in TN and phosphate was achieved
using plants assisted with endophyte (Ijaz et al. 2015). In
a study, water hyacinth and water lettuce were used to treat
mixed industrial wastewater in an industrial park, and the
phytoremediation reduced 71% of ­NH4+, 74% of TN, 57% of
­PO43−, and 64% of TP (Victor et al. 2016). Another research
investigated endophyte-assisted floating treatment wetland
for the remediation of mixed wastewater (70% of domestic
and 30% industrial effluent from an industrial park), and up
to 90% and 39% reduction of nitrogen and phosphorus were
obtained, respectively (Ijaz et al. 2016).

Heavy metals
Industrial wastewater from mining, electroplating, steel and
non-ferrous metallurgy and some chemical production usually contains high concentrations of heavy metals and some
metal species (e.g., Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn)
are significantly biologically toxic (Shrestha et al. 2021).
Heavy metals in industrial wastewater are in two forms:
dissolved and particulate. Plants can take up the dissolved
fraction (Bi et al. 2019). The uptake process is impacted by
a series of factors, such as plant species, temperature, pH,
heavy metal concentration, and the types of heavy metals
(Dhir et al. 2009). Meanwhile, high salinity was observed

to reduce heavy metal removal efficiency because sodium
ions can compete with heavy metals during the uptake by
plants (Leblebici et al. 2011). In FWs, the physicochemical
processes affecting the transport and fate of heavy metals
include adsorption, complexation, chelation, ion exchange,
reduction–oxidation, uptake of plants and bacteria, entrapment into the biofilm, and metal sulfides formation (Ali et al.
2020; Rezania et al. 2016).

13

Environmental Science and Pollution Research

Plant roots play a significant role in heavy metals removal
as roots and attached biofilms can trap particulate heavy
metals (Borne et al. 2014). Moreover, plant roots can release
exudates, excretion, lysates, and dead tissues to increase the
humic content in water (Canellas et al. 2020), which promotes the flocculation and complexation of dissolved metals
(e.g., Cd, Cu, Ni, Pb, Zn) (Hankins et al. 2006; Kulikowska
et al. 2015). The exudates of roots can also adsorb heavy
metals, facilitating the formation of metal sulfides and
hydroxides (Kim et al. 2010). The decay of dead plant parts
can enhance heavy metals removal by binding to sulfides and
organic matter, metals associated with sulfides form insoluble metal sulfides (Borne et al. 2015; Hankins et al. 2006).
It has been reported that Cu can also be combined with
organic matter (e.g., humic acid) to form stable compounds
(Fuentes et al. 2013). Roots can accumulate a higher amount
of metals than other tissues. For example, roots were found
to accumulate 80% of Zn and 40% of Cu in plants (Saleem
et al. 2019). Biofilm is another important FW component
for metal removal. It was found that the precipitation of several metals can be enhanced by the function of rhizosphere

microorganisms (Ijaz et al. 2015; Shahid et al. 2020).
A variety of plants are capable of removing heavy metals
from wastewater. A study screened the capacity of 34 plants
to remove metals in water (Schück and Greger 2020), and
their results showed that the highest removal efficiency can
be up to 52–94% after 0.5 h and up to 98–100% after 5 days.
FWs implanted with different plants have been widely used
to remove metals from various types of industrial wastewater and waterbody polluted by industrial effluent (Table 2).
In Canada, floating cattail mats were used for acid mine
drainage treatment (Chen et al. 2016), and after 131 days,
the system removed 88% of Fe and 77% of Ni, respectively.
The system also achieved 98% of Ni and 95% of Fe removal
efficiency after operation for 2 years. Recent studies showed
that the inoculation of bacteria can effectively promote the
heavy metal removal efficiency by aquatic plants in wastewater treatment. For example, bacteria augmentation was
found to significantly enhance the heavy metals removal
from (46.4–70.0%) to (65.5–89.7%) of a FW in textile wastewater treatment after 20 days (Nawaz et al. 2020).

Summary of pollutant removal using FWs
Floating Wetlands (FWs) hold great potential for a wide
range of applications in treating pollutants in industrial
wastewater, including organic compounds, total solids,
nutrients, and heavy metals. The treatment mechanisms
involve the activities of root-associated microorganisms
and plants, the formation of biofilms, physical sedimentation, adsorption, ion exchange, redox reactions, and various other processes. These processes work synergistically
to provide pathways for the efficient removal of pollutants


Cd = 3.21 ± 0.02,
Cr = 11.48 ± 1.33,

Pb = 0.39 ± 0.13,
V = 3.64 ± 0.42
NA

Crude oil polluted water

Phragmites australis
Cr = 9.67 ± 0.26,
Fe = 14.4 ± 0.64,
Ni = 7.57 ± 0.38,
Cd = 0.88 ± 0.02
Cd = 2.45, Cr = 1.38, Cu = 5.64, Trapa natans L
Eichhornia crassipes Solms
Fe = 8.95, Mn = 3.66,
Pb = 1.74, Ni = 1.02, Zn = 6.90

Textile industry wastewater

Cr = 1.07–2.17
Cd = 0.11 ± 0.01,
Pb = 0.80 ± 0.09,
Cr = 1.93 ± 0.28
Cd = 0.09, Cr = 4.20, Pb = 0.70

Cr = 3.7, Pb = 0.40, Cd = 0.80

Cd = 0.82 ± 0.02,
Cr = 9.4 ± 0.42,
Cu = 0.60 ± 0.03,
Fe = 13.7 ± 0.27,

Ni = 6.5 ± 0.45,
Pb = 0.62 ± 0.01

Batik wastewater
Textile wastewater

Textile wastewater

Industrial effluent

Textile effluent

Pb = 0.96–2.01, Cd = 0.42–1.90

Paperboard mill wastewater

Pulp and paper mill effluent

Fe = 1.171, Pb = 0.880,
Cr = 0.812, Ni = 0.125,
Cu = 0.503

Textile effluent

Chrysopogon zizanioides,
Typha angustifolia
Typha domingensis

A. baccifera, F. dichotoma

Chrysopogon zizanioides
Vetiveria zizanioides, Ipomoea
aquatica

Chrysopogon zizanioides

Phragmites australis
Typha domingensis

Phragmites australis

NA

Bemaplex Black DRKP Bezma
dye wastewater

Phragmites australis

NA

Cd (33.3%-55.6%), Cr (48.3–
71.7%), and Pb (50–68.6%)
Cr (45.9–56.8%), Pb (37.5%),
and Cd (50–56.3%)
Cd (57.3–69.5%), Cr (86.9–
91.2%), Cu (53.3–58.3%), Fe
(80.4–92.1%), Ni (80.9–
89.5%), and Pb (67.7–72.6%)

Cd (59.2%), Cr (56.5%), Cu

(66.5%), Fe (64.8%), Mn
(44.3%), Ni (46.1%), Pb
(48.9%), and Zn (54.3%)
Pb (51.24–94.79%), Cd
(27.37–95.24%)
Cr (8.85–40.29%)
Cd (18.2–63.6%), Pb (47.5–
73.8%), and Cr (52.3–69.9%)

Cu (75%), Ni (73.3%), Zn
(86.9%), Fe (75%), Mn (70%),
and Pb (76.7%)
Cu (77.5%), Ni (73.3%), Zn
(83.3%), Fe (77.5%), Mn
(66.7%), and Pb (73.3%)
Cu (77.5%), Ni (73.3%), Zn
(89.7%), Fe (81.0%), Mn
(70%), and Pb (65.5%)
Fe (95.4–98.6%), Pb (83.3–
91%), Cr (87.6%-96%),
Ni (72.8–78.4%), and Cu
(98.2–98.6%)
Cr and Fe (> 90%), Ni (> 80%),
and Cd (> 60%)

Cd (32.4%), Cr (13.76%), Pb
(41.03%), and V (26.37%)

Duckweed

Phragmites australis

Metal removal efficiency

Plant Species

Bemaplex Rubine DB dye
wastewater

Bemaplex Navy Blue DRD dye
wastewater

Initial concentration (mg/L)

Wastewater

Table 2  Heavy metal removal from industrial wastewater using FWs

Pakistan

Pakistan

Germany Chen et al. (2012)

8 days

2 years

60 days

Davamani et al. (2021)

Tara et al. (2019a)

Tara et al. (2019b)

Nawaz et al. (2020)

Nawaz et al. (2020)

India
Pakistan

4 days

India

Ijaz et al. (2016)

Kadam, et al. (2018b)

Kadam, et al.(2018a)

Indonesia Effendi et al. (2018)
India
Chandanshive et al. (2020)

4 days

9 days

3 weeks
5 days

India

Pakistan

20 days

40 days

Pakistan

20 days

Nawaz et al. (2020)

Pakistan

20 days

Ekperusi et al. (2019)

Nigeria

Reference

60 days

Retention Period Location

Environmental Science and Pollution Research

13


1.5 years
Cd (87.9%), Cr (95.2%), Cu
(95.2%), Fe (99.3%), Ni
(84.9%), and Pb (93.5%)
Phragmites australis, Typha
domingensis, Leptochloa
fusca, Brachiaria mutica
Cd = 0.91 ± 0.07,
Cr = 0.83 ± 0.03,
Cu = 0.21 ± 0.04,
Fe = 1.52 ± 0.05,
Ni = 0.53 ± 0.02,
Pb = 0.62 ± 0.16
Crude oil contaminated wastewater

Pakistan

Retention Period Location
Metal removal efficiency
Plant Species
Initial concentration (mg/L)
Wastewater

Table 2  (continued)

Afzal, et al. (2019b)

Environmental Science and Pollution Research

Reference



13

from wastewater. Moreover, strategies such as the selection
of suitable plant species and microbial enhancement can
further enhance the pollutant removal efficiency of FWs.
Different types of industrial wastewater can be effectively
treated by well-designed and operated FW systems, thereby
mitigating the adverse environmental impact of wastewater
discharge, and promoting the sustainable utilization of water
resources.

FWs in industrial wastewater treatment
FWs are usually used for industrial wastewater treatment
in developing countries with warm climates, such as India
and Pakistan because the warm climate is suitable for plant
growth (Fig. 5 a). Also, FWs is a land-free wastewater treatment technology, which is suitable for developing countries
where land resources are lacking. However, it should be
noted that while FWs are widely used in developing countries with warm climates, they have the potential for global
applicability. The choice of industrial wastewater treatment
methods needs to take into account local factors such as

the economy, climate, land use, and other circumstances.
According to the reported studies, over 50% industrial
effluents treated using FWs are textile and oily wastewater. Textile and oily wastewater typically contain significant
amounts of organic matter and suspended solids, which
are pollutants that FWs excel at removing. The interaction
between the plants and microbial communities within FWs
and these specific types of wastewater enhances the efficient
removal of organic matter and oils. These pollutants can
serve as nutrients necessary for the growth of plants and
microorganisms. Most importantly, FWs are a cost-effective
and environmentally friendly wastewater treatment technology, well-suited for developing countries, especially in warm
climates. There are also reports on the application of FWs
in the treatment of wastewater from the food processing,
chemical, pulp and paper, and mining industries.

Textile wastewater
Dyes, pigments, oil, surfactants, sulphates, chlorides, and
heavy metals are the common pollutants in textile wastewater (Wei et al. 2020). Dyes can change the watercolor and
reduce the sunlight availability and photosynthetic activity of submerged macrophytes. Textile industrial effluents
are rich in chlorinated compounds, heavy metals, sulfur,
nitrates, naphthol, formaldehyde, benzidine, and remaining
dyes and pigments (Slama et al. 2021). Without sufficient
treatment, the effluents are highly toxic to the aquatic ecosystems (Yaseen and Scholz 2019). FWs have been used
for varioustextile wastewater treatment from different scales
(Table 3). FWs have shown promise in effectively treating


Environmental Science and Pollution Research
Fig. 5  Overview of industrial
wastewater treatment using

FWs: a) the distribution of
study regions and variation of
pollutant removal efficiency
for b) textile wastewater, c)
oily wastewater, and d) other
industrial wastewaters (Data are
extracted from Table 2, Table 3,
and Table 4)

textile wastewater, effectively reducing various pollutants, including color, COD, BOD, heavy metals, and dyes,
through methods such as bacterial augmentation, promoting
the growth of plants, and enhancing removal efficiencies. A
pilot study evaluated the effects of bacterial augmentation
on the efficiency of FWs in the treatment of textile wastewater (Tara et al. 2019b). In this study, Phragmites australis and Typha domingensis were used, and three species of
bacteria were augmented to enhance the treatment efficiency.
After 8 days, the maximum removal efficiencies were 97%
for color, 87% for COD, and 92% for BOD, whereas the
removal efficiencies without bioaugmentation for the above
pollutants ranged from 75 to 80%. Another field study of FW
macrocosms also found that the combination of plants with
pollutant-degrading bacteria would enhance the overall pollutant removal from textile wastewater (Tara et al. 2019a).
In the field study, 15 FWs were operated for 2 years, and the
optimal performance was observed one year after installation. Moreover, a recent study investigated using FWs augmented with specific bacteria to treat different synthetic
effluents made of three types of dye (Nawaz et al. 2020).
The augmented bacteria can also reduce dye-induced toxicity and promoted the growth of plants (Nawaz et al. 2020).
A study using bacterial-augmented FWs to treat wastewater containing an azo dye, namely Reactive Black5, found
that the system could effectively degrade the dye into about
20 different metabolites and successfully remove 95.5% of
color from the wastewater (Tusief et al. 2020). The toxicity
analysis of the metabolites indicated that they were nontoxic

to fishes.

Industrial oily wastewater
Industrial oily wastewater can originate from a variety of
sources, including oil refining, oil storage and transportation, petrochemical production, and oil spill response
operations (Lee et al. 2014). Oily wastewater is composed
of substances like dissolved minerals, cyanides, ammonia,
heavy metals, hydrocarbons, and phenol, all of which pose
risks to the environment and human health by skin contact
and consumption of contaminated food and water (Putatunda et al. 2019; Rehman et al. 2019a, b). Oily wastewater
usually contains high concentrations of organic pollutants,
leading to increased levels of COD and BOD in the receiving waterbody (Yu et al. 2017). It is difficult to use conventional oil-contaminated water treatment plants for oil companies, especially in developing countries (Afzal et al. 2019a,
b). As a feasible alternative, FWs have been used to treat
oily wastewater in recent studies (Table 4). A floating bed
planted with four species of perennial grasses was studied
for purification of petroleum refinery wastewater, and the
results showed that the system removed up to 56% of TP,
60% of TN, 67% of COD, and 55% of TPH after 35 days
treatment (Li et al. 2012). A study investigated the treatment
of oil spill-related wastewater using vetiveria zizanioides in
FWs, and the results indicated that 91.39% of oil, 84.60%
of COD, and 84.25% of BOD were reduced in 4 weeks, and
the biomass of plant grew in the oily wastewater was larger
than that of the plant grown in water without oil pollutants
(Effendi et al. 2017). Another study focused on modeling
BOD and COD removal from the palm oil mill secondary

13

13

Floating material

Wastewater characteristics
(concentration in mg/L)

COD = 1438 ± 12.7,
PVC pipe, aluminum metal
A. baccifera
BOD = 1230 ± 10.2,
wire gauze, and PVC plastic
F. dichotoma
TDS = 8230 ± 8.8,
sheet
(floating in tap water for two
TSS = 5175 ± 0.7
months)
PVC pipes, elbows, thermacol COD = 1495 ± 20,
Vetiveria zizanioides
BOD = 1135 ± 20,
sheet and aluminum metal
(floating in tap water for three
TDS = 4706 ± 28,
wire gauze
months)
TSS = 734 ± 8
PVC pipes, elbows, thermacol COD = 1794 ± 7,
Vetiveria zizanioides,
BOD = 1350 ± 13,

sheet and aluminum metal
Ipomoea aquatica
TDS = 5143 ± 21,
wire gauze
(floating in tap water for three
TSS = 1900 ± 15
months)
PVC pipe and elbows
COD = 1734 ± 1.8,
Chrysopogon zizanioides,
BOD = 1478 ± 1.5,
Typha angustifolia
TDS = 9060 ± 4.6,
(planted over floating bed for
TSS = 6438 ± 4.1
a month)
PVC pipe rafts
TS = 55.67  ± 5.72,
Vetiveria zizanioides
(NA)
COD = 150.13  ± 39.06,
BOD = 317  ± 16.73
Free floating
COD = 177.76, BOD = 87.178
Eichhornia crassipes,
Pistia stratiotes
(NA)
Free floating
TDS = 2560.83,
Eichhornia crassipes,

TSS = 131.61,
Pistia stratiotes
BOD = 107.46,
(stored in water tub)
COD = 187.1
Polystyrene-based sheets
TDS = 400, TSS = 92,
Phragmites australis
BOD = 121, COD = 310
(seeding on floating sheets
supported by coconut shavings and soil)
Diamond Jumbolon Roll,
TDS = 4961, TSS = 4569,
Phragmites australis,
aluminum foil
BOD = 249, COD = 471
Typha Domingensis
(seeding on floating sheets
supported by coconut shavings, gravel, sand and soil)
Polystyrene sheets
TDS = 5251  ± 404,
Phragmites australis
TSS = 324  ± 29.7,
(seeding on floating sheets
BOD = 283  ± 17.9,
supported by coconut shavCOD = 513  ± 37.6
ings, and soil)

Plant Species
(Arrangement)

Table 3  Treatment of textile wastewater using FWs

77

72

74

79

74

15.87 21.29 41.07 45.39 72 h

-

91

73

54

1 year

8 days

Pakistan Tara, et al. (2019a)

92

-

86

-

Pakistan Tara, et al. (2019b)

92

87

97

Pakistan Qamar et al. (2019)

Pakistan Tusief et al. (2020)

Pakistan Nawaz et al. (2020)

72 h

5 weeks

83–85 89–90 84–85 84–85 74–79 20 days

-

88

Kadam, et al. (2018b)

Chandanshive et al. (2020)

Chandanshive et al. (2020)

Kadam, et al. (2018a)

Thailand Charoenlarp et al. (2016)

31.69 57.78 -

-

4 days

57

77

70

36

67

43

75

India

India

India

75

72 h

9 days

82

47

56

TSS

India

66

66

TDS

Retention Period Location Reference

61–76 74–79 71–84 75–83 31–51 5 days

81

BOD

Color COD

Removal efficiency (%)


Environmental Science and Pollution Research


Crude oil contaminated
water

Oil field-produced wastewater

Refinery wastewater

Diesel

Palm oil mill effluent

52–67% -

93

98.9

52.18

90

97.4

Jumbolon sheets

Polyethylene foam, covered with peat

Diamond Jumbolon Role

Jumbolon role (cells of
polyethylene resins),
aluminum foil, and
polypropylene random
copolymer pipes

90 days

2 weeks

14 days

3 days

99.1

95

18 months

3 months

Pakistan

Pakistan

China

Pakistan

Malaysia

Malaysia

Pakistan

Retention Period Location

40–55% 35 days

72.28 73.48

90

94

Polystyrene sheets

45

92.78 -

87.5

BOD TPH

25.24

87

COD

Removal efficiency (%)

NA

Diamond Jumbolon Roll

Typha domingensis
COD = 538 ± 83,
BOD = 228 ± 65, Oil and (seeding on floating
sheets supported by tap
grease = 17.4 ± 2.7
water for 30 days)
COD = 210, BOD = 42.91 Eichhornia crassipes
(NA)

COD = 790–810,
Vetiveria zizanioides
BOD = 350–400
(grown in a hydroponic
solution for 5 weeks)
Cyperus laevigatus L
Oil = 10,000,
(seeding on floating
COD = 10,000,
sheets supported by tap
BOD = 3500
water for 30 days)
TPH = 1720, COD = 142.8 Geophila herbacea O
Kumtze (GHK), Lolium
perenn
CV. Caddieshack (LPT),
Lolium perenne Topone
(LPT), Lolium perenne
L (LPL)
(seedling establishment
for 10 days)
Typha domingensis, LepCOD = 1336 ± 58.74,
tochloa fusca
BOD = 405 ± 19.43,
(seeding on floating sheets
TPH = 316 ± 7.84
supported by coconut
shavings, gravel, sand
and soil, grown for
1 month)

Phragmites australis,
COD = 1316 ± 73.5,
Typha domingensis,
BOD = 365 ± 15.4,
Leptochloa fusca, BraTPH = 319 ± 9.7
chiaria mutica
(grown using plastic pots
in a garden)

Oil and grease

Palm oil mill effluent

Floating materials

Wastewater characteristics Plant Species
(mg/L)
(Arrangement)

Wastewater

Table 4  Treatment of industrial oily wastewater using FWs

Afzal et al. (2019b)

Rehman et al. (2019b)

Li et al., (2012)

Fahid et al. (2020)

Darajeh et al. (2014)

Tan (2019)

Ijaz et al. (2016)

Reference

Environmental Science and Pollution Research

13


Darajeh et al. (2016)
Malaysia
4 weeks
96
94
Polystyrene platform

90.28
81.1

Palm oil mill effluent

COD = 150–160,
BOD = 20–25, Oil and
grease = 0.15
COD = 750, BOD = 350,

Oil and grease = 15
Crude oil spilled water

Chrysopogon zizanioides
(grown in a temporary
hydroponic nursery for
5 weeks)

Pakistan
42 days
97
97

Brachiara mutica, Phrag- Diamond Jumbolon Role, 93
and aluminum foil
mites australis
(seeding on floating sheets
supported by coconut
shavings, gravel, sand
and soil, grown for
1 month)
Vetiveria zizanioides
Plastic pots with rockwool 81.69
(NA)
inside
COD = 1324 ± 66.5,
BOD = 475 ± 15.5,
oil = 325 ± 10.1
Oil field wastewater

BOD TPH
COD

4 weeks

Reference
Retention Period Location
Removal efficiency (%)
Floating materials
Wastewater characteristics Plant Species
(mg/L)
(Arrangement)
Wastewater

Table 4  (continued)

13

Indonesia Effendi et al. (2017)

Environmental Science and Pollution Research
Rehman et al. (2018)



effluent by FWs planted with chrysopogon zizanioides in different conditions (Darajeh et al. 2016). The study validated
the model established using response surface methodology
under three factors (i.e., oil concentration, plant density, and
time), and showed the optimum decreases in BOD and COD
were 96% and 94%, respectively, after 4 weeks using 30

plants. The model showed that plant density has the most
significant effect on the BOD and COD removal and had
good prediction performances in terms of COD (adjusted
­R2 = 0.974) and BOD (adjusted R
­ 2 = 0.957) removal (Darajeh et al. 2016).
Bacteria-plant synergism was reported to be able to
enhance the treatment efficiency of FWs. A study quantitatively assessed the performance of endophyte-assisted FWs
in the treatment of oil and grease-contaminated wastewater
(Ijaz et al. 2016), and it found that the plants inoculated
with a consortium of pollutant-degrading and plant growthpromoting endophytic bacteria reduced COD and BOD by
87.0% and 87.5%, respectively. Another study investigated
the plant synergism in FWs for remediation of oil field
wastewater (Rehman et al. 2018), while FWs were used in
combination with hydrocarbon-degrading bacteria. Their
results showed that both experimental plants can remove
organic and inorganic pollutants from oily wastewater,
and bioaugmentation significantly increased the pollutants
removal efficiency from 76 to 97% for oil, 80% to 93% for
COD, and 85% to 97% for BOD in the wastewater. Moreover, the analysis of alkane-degrading gene abundance and
its expression profile further validated a higher microbial
growth and degradation activity in the water around plant
roots and shoots (Rehman et al. 2018). Another study used
similar bioaugmented FWs to remediate oil field wastewater, and the highest reduction efficiencies were observed as
95% for TPH, 90% for COD, and 93% for BOD (Rehman
et al. 2019b). Their study also found that the average fresh
biomass, dry biomass, and length of the plants increased by
31%, 52%, and 25%, respectively, after the treatment. FWs
were installed at a large scale for remediation of oil-contaminated wastewater, and the plants in the FWs were inoculated
with a consortium of 10 different species of hydrocarbondegrading bacteria (Afzal et al. 2019b), with the treatment
reducing 97.4% of COD, 98.9% of BOD, 82.4% of TDS,

99.1% of hydrocarbon content, and 80% of heavy metals
within 18 months.

Wastewater from other industries
FW has been applied for treating other types of industrial
wastewater (Table 5). FWs have been effectively employed
for the treatment of acid mine drainage (AMD), paper
industry effluents, batik industry effluents, and food industry wastewater, demonstrating their potential in reducing
pollutants and improving water quality. In a recent study,


Cd = 0.02, Cu = 4.78

Fe = 81.4 ± 1.16,
Al = 70.3 ± 1.11,
Mn = 21.9 ± 0.27,
Zn = 1.372 ± 0.0436,
Ni = 0.697 ± 0.0413,
Cu = 0.184 ± 0.00435,
Pb = 0.08 ± 0.0341,
Cr = 0.01
Fe = 12, Al = 11.3,
Zn = 0.385, Ni = 0.388,
Cu = 0.0218,
Pb = 0.0105

Acid mine drainage

Acid mine drainage

TDS = 1840, EC = 2.64
dS/m, BOD = 475.1,
COD = 880.5,
TKN = 192.65,
­PO43− = 145.6,
Cd = 2.45, Cr = 1.38,
Cu = 5.64, Fe = 8.95,
Mn = 3.66, Pb = 1.74,
Ni = 1.02, Zn = 6.9

Benzene = 13 ± 3,
MTBE = 2.2 ± 0.5
TS = 1671.58 ± 177,
COD = 5866.67 ± 924,
BOD = 2282.75

Pulp and paper mill
effluent

Chemical contaminated
water
Dairy wastewater

Acid mine drainage

Wastewater characteristics (mg/L)

Wastewater

Floating materials

Phragmites australis
(NA)
Eichhornia crassipes
Eichhornia paniculata
Polygonum ferrugineum
Borreria scabiosoides
(conditioned in containers with fluvial)

Water caltrop
Water hyacinth
(NA)

Polyethylene terephthalate

NA

NA

Chrysopogon zizanioides NA
(grown in potting soil)

Water hyacinth
Free floating
(NA)
Chrysopogon zizanioides Plywood and PVC pipes
(maintained in hydroponic media for up to
4 months)

Plant species

(Arrangement)

Table 5  Treatment of different types of industrial wastewater using FWs

High plant uptake of Fe
(74.6%), Zn (30.1%),
and Cu (140%), with
relatively lower plant
uptake of Pb, Al, and
Ni (< 10%)
Significant reduction of
TDS (37.5–42.4%),
EC (30.3–33.3%),
BOD (38.9–42.0%),
COD (32.0–35.2%),
TKN (49.9–57.2%),
­PO43− (41.1–55.7%),
Cd (40.8–45.3%),
Cr (43.5–50%), Cu
(33.5–47.9%), Fe
(35.2–45.7%), Mn
(55.7–61.2%), Pb
(51.1–58.0%), Ni
(53.9–64.7%), and Zn
(45.7–55.1%)
Benzene (22–100%) and
MTBE (8–93%)
BOD (74.8 ± 7.7%)
on the fifth day, TS
(64.3–65.18%)

Queiroz et al. (2020)

Brazil

14 days

Kumar et al. (2016)

Kiiskila et al. (2017)

Kiiskila et al. (2019)

Germany Chen et al. (2012)

India

USA

USA

-

60 days

30 days

Reference

Sri Lanka Palihakkara et al. (2018)

Retention period Location

Significant reduction in
24 h
Cd (90%) and Cu (40%)
1 years
High removal of Fe
(81%) and Pb (81%),
low removal of Ni
(38%), Zn (35%), Mn
(27%), Cr (21%), Al
(11%) and Cu (8.0%)

Pollutant removal

Environmental Science and Pollution Research

13


13

Batik Wastewater

Batik Wastewater

Saline industrial wastewater

Paper mill wastewater

TSS = 1424.04 ± 166.62,
COD = 273.88 ± 24.93,
BOD = 37.95 ± 8.14,
Cr = 0.81 ± 0.06
TSS = 1183, TAN = 2.38,
­NH4+  = 0.96,
­NH3 = 1.42

Chrysopogon zizanioides Styrofoam and plastic
tube
(stored in a plastic tub
containing water and
nutrient solution)
Chrysopogon zizanioides Plastic tube
(acclimatized for 3 weeks
in floating wetland
system)

PVC tube and plastic
pots

14 weeks

TAN (81.69%), ­NH4+
(77.5%), and N
­ H3
(84.51%)

4 weeks

TDS (19.3–35.0%), COD 1 month
(54.5–74.4%), TN
(43.2–57.6%), and TP
(36.5–59.0%)
4 weeks
Cr (40%), BOD
(98.47%), and COD
(89.05%)

TP (82–83%) and TN
(45–47%)

Gao et al. (2020)

Ayres et al. (2019)

Davamani et al. (2021)

Kumar et al. (2019)

Reference

Indonesia Effendi et al. (2018)

Indonesia Tambunan et al. (2018)

China

Australia

India

40 days
EC (42.42%), TDS
(79.92%), TSS (100%),
BOD (77.27%),
COD (81.25%), TN
(72.00%), TP (61.06%),
Pb (94.79%), and Cd
(95.24%)

Chrysopogon zizanioides Plastic lid
(stored in tap water for
1 week)

Polyethylene foam

India

Retention period Location
4 weeks

Pollutant removal
BOD (83.78%) and COD
(93.64%)

Floating materials

Free floating

Water hyacinth
(placed in a water tub
containing tap water for
1 week)

Plant species
(Arrangement)

Stenotaphrum secundatum
Cynodon dactylon
(NA)
TDS = 5000, COD = 350, Canna indica
TN = 13.2, TP = 4,
(NA)

EC = 5.44 ± 0.05 dS/m,
TDS = 1932.2 ± 11.22,
BOD = 947.88 ± 6.44,
COD = 1620.3 ± 10.23,
TKN = 126.43 ± 3.12,
TP = 124.32 ± 2.14
EC = 1.98 ± 0.06 dS/m,
TDS = 1000 ± 16.3,
TSS = 200 ± 3.26,
BOD = 44.0 ± 1.43,
COD = 256 ± 4.17,
TN = 25 ± 0.81,
TP = 8.50 ± 0.28,
Pb = 0.96 ± 0.02,
Cd = 0.42 ± 0.01

TP = 0.02–0.88,
TN = 1.8–7.4

Sugar mill effluent

Paperboard mill wastewater

Wastewater characteristics (mg/L)

Wastewater

Table 5  (continued)


Environmental Science and Pollution Research


Environmental Science and Pollution Research

a sustainable FW treatment system with vetiver grass was
used for acid mine drainage (AMD) treatment, and the result
showed an increase in pH (from 2.64 to 4.19) after 30 days,
particularly at high planting densities. Vetiver was tolerant
of AMD and achieved high net metal uptake of 140% for Cu,
74.6% for Fe, and 30.1% for Zn. Meanwhile, the investigation of iron formation on the root showed high metal stabilization in the root and low metal translocation from root
to shoot (Kiiskila et al. 2017). As mentioned in Sect. 3.1,
many plants can remove heavy metals, which are the main
pollutants in AMD, from waterbody. Another study investigated the application of water hyacinth-based FW in the
treatment of AMD containing Cu and Cd. The results indicated that water hyacinth had the capability of removing Cu
from 4 to 0.3 mg/L in 6 days and Cd from 0.02 to 0 mg/L in

3 days (Palihakkara et al. 2018). However, higher concentrations of heavy metals were found toxic to plants because
low accumulation and rapid dying were observed. A recent
large-scale study used vetiver grass-based FWs for AMD
treatment (Kiiskila et al. 2019), and the removal efficiencies
were calculated as 81% for Fe, 81% for Pb, 38% for Ni, 35%
for Zn, 28% for ­SO42−, 27% for Mn, 21% for Cr, 11% for Al,
and 8.0% for Cu, respectively, after 1 year’s treatment. Furthermore, the toxicity test showed that the harvested vetiver
biomass was not hazardous.
In the batik industry, vetiver-based FWs were used for
wastewater treatment. The result showed the FWs can effectively remove 40.0% of Cr, 98.47% of BOD, and 89.05%
of COD from the 50% batik wastewater (1:1 for wastewater: freshwater) (Effendi et al. 2018). In another study, an
FW system was used for batik industry wastewater treatment with a significant reduction of N
­ H3 (86.47%), N
­ H 4+

(82.57%), TN (85.01%), BOD (98.13%), and COD (92.45%)
in 75% batik wastewater (Tambunan et al. 2018). In China,
an ecological floating bed system enhanced by arbuscular
mycorrhizal fungi was constructed to treat saline industrial
wastewater, and the results showed that the enhanced treatment removed 15.9% of TDS, 19.9% of COD, 22.5% of TP,
and 23.0% of salt ions in September and 17.5% of TN in
October (Gao et al. 2020). It was also found that arbuscular mycorrhizal fungi improved the removal of pollutants in
wastewater and increased the Na uptake by plants. Another
study investigated the use of Eichhornia genus in FWs for
the treatment of dairy wastewater and found that BOD was
decreased by 74.8% (± 7.7) by four plants after five days
(Queiroz et al. 2020). Thus, Eichhornia genus showed great
potential for dairy wastewater treatment, with a hydraulic
retention time varying between four and five days. Recently,
A pilot-scale investigation was carried out using vetiver

grass (Chrysopogon zizanioides) along with aeration to
treat effluents from the paper board mill industry (Davamani
et al. 2021). The vetiver hydroponic system with aeration
exhibited a significant reduction in electrical conductivity
(39.39%), total soluble salts (81.19%), and TDS (56.19%) in
the wastewater. Significant reduction in BOD (55.68%) and
COD (58.01%) was also observed after 40 days treatment.
The decrease in nutrients like TN (59.24%), TP (47.78%),
and potassium (54.64%) was mainly attributed to the growth
of vetiver grass (Davamani et al. 2021).

Enhancement of FWs
Several methods were used to enhance the efficiency of
FWs in industrial wastewater treatment (Fig. 6 and Table 6).

Fig. 6  Different methods for
enhancing the performance of
FWs

13




Environmental Science and Pollution Research

Table 6  Enhancement methods in FWs for industrial wastewater treatment
Wastewater

Plant species

Enhancement method

Reference

Oily and grease wastewater

Typha domingensis

Rehman et al. (2019a)

Diesel contaminated water

Cyperus laevigatus L

Oil field-produced wastewater

Typha domingensis
Leptochloa fusca

Oil field wastewater

Brachiara mutica
Phragmites australis

Inoculation bacteria (Klebsiella sp. strain LCRI87,
Pseudomonas sp. strain BRRI54, and Acinetobacter sp.
CYRH21)
Inoculation bacteria (Acinetobacter sp.61KJ620863,
Bacillus megaterium 65 KF478214, and Acinetobacter

sp.82 KF478231)
Inoculation bacteria (Bacillus subtilis LORI66, Klebsiella sp. LCRI87, Acinetobacter Junii TYRH47, and
Acinetobacter sp. BRSI56)
Inoculation bacteria (Bacillus subtilis strain LORI66,
Klebsiella sp. strain LCRI87, Acinetobacter Junii strain
TYRH47, Acinetobacter sp. strain LCRH81)
Aeration
Low-temperature protection (snow fencing and wood
pallet)

Palm oil mill secondary effluent Chrysopogon zizanioides
Acid mine drainage
Carex lacustris
Typha latifolia
Juncus canadensis
Mine effluent
Comarum palustre L
Equisetum fluviatile L
Carex rostrata Stokes
Filipendula ulmaria
Menyanthes trifoliata L
Textile effluent
Fimbristylis dichotoma,
Ammannia baccifera
Textile effluent
Chrysopogon zizanioides
Typha angustifolia
Blue dye enriched textile water Eichhornia crassipes
Pistia stratiotes
Synthetic textile dye wastewater Phragmites australis

Textile effluent
Textile effluent

Phragmites australis
Typha domingensis
Phragmites australis

Sugar mill effluent
Paperboard mill wastewater
Saline industrial wastewater

water hyacinth
Chrysopogon zizanioides
Canna indica

Rehman et al. (2019b)
Rehman et al. (2018)
Darajeh et al. (2016)
Gupta et al. (2020)

Co-plantation

Choudhury et al. (2019)

Co-plantation

Kadam et al. (2018a)

Co-plantation and microbial fuel cell

Kadam et al. (2018b)

Inoculation bacteria (Bacillus cereus. and. Bacillus
subtilis)
Inoculation bacteria (Acinetobacter junii strain NT-15,
Rhodococcus sp. strain NT-39, and Pseudomonas
indoloxydans
strain NT-38)
Inoculation bacteria (Acinetobacter junii, Pseudomonas
indoloxydans, and Rhodococcus sp)
Inoculation bacteria (Acinetobacter junii strain NT-15,
Rhodococcus sp. strain NT-39, and Pseudomonas
indoloxydans
strain NT-38)
Continuous Stirred Tank Reactor
Aeration
Fungi enhancement (Arbuscular mycorrhizal fungi
Glomus etunicatum)

Tusief et al. (2020)

Bacterial inoculation is the most popular approach because
the interaction between plants and microbes can greatly
facilitate the removal of pollutants. The local microbes
attached to plants are usually insufficient enough to treat
highly contaminated industrial wastewater, and thus inoculation of extra bacteria would increase the population and
degradation capability of microbial communities. The
selection of bacteria is usually based on the capability of
biodegradation of target pollutants (Rehman et al. 2019a).

These inoculated bacteria not only enhance the pollutant
remediation process but also mitigate pollutant-induced toxicity in plants and promote plant growth by secreting various

13

Fahid et al. (2020)

Nawaz et al. (2020)

Tara et al. (2019b)
Tara et al. (2019a)

Kumar et al. (2019)
Davamani et al. (2021)
Gao et al. (2020)

plant growth-promoting hormones (Wei et al. 2020). This
enhancement method has been widely used in oily and textile industrial wastewater treatment. The main reason for this
is that the screening and cultivation techniques for microorganisms capable of degrading dyes and oil are relatively
mature. The enhancement in treatment efficiency of textile
and oily wastewater by bacteria-augmented FWs has been
discussed in Sects. 4.1 and 4.2. Some studies also investigated the removal efficiency of specific industrial organic
pollutants. For example, a plant-bacterial synergism FWs
was established to remove phenol from wastewater, and the
bacterial augmentation improved the removal from 0.146 to


Environmental Science and Pollution Research

0.166 g/(m2*day), while the presence of bacterial consortia also increased the plant biomass (Saleem et al. 2018).

Another study found that hydrocarbons-degrading bacteria
enhanced the removal efficiency of sodium dodecyl sulphate
to 97.5% by an FW inoculated with B. mutica (Yasin et al.
2021).
Co-plantation is also a promising method as plants have
different capacities for specific pollutants removal, and the
combination of plants can achieve efficient treatment for
complex pollutants. For instance, the combined approach
involving both T. angustifolia and P. scrobiculatum proved
to be notably superior in treating textile dyes and real industrial effluents compared to using individual plants alone.
This enhanced efficacy in decolorizing textile effluents was a
result of the synergistic involvement of oxido-reductive dyedegrading enzymes from both plant species within the consortium (Chandanshive et al. 2017). In a study, an FW with
Ammannia baccifera and Fimbristylis dichotoma reduced
79% of American Dye Manufacture Institute (ADMI) value
(ADMI is used to quantify the residual color of waste water
due to the presence of colored minerals and dyes, humic
breakdown substances and iron) in textile effluent after
9 days, while individual plants can only reduce 67 and 70%
of this value (Kadam et al. 2018a). Another study found a
co-planted FW microbial fuel cell system can remove 76% of
color from textile wastewater, whereas 59 and 62% removal
were observed individually in 4 days (Kadam et al. 2018b),
while the fuel cell system can produce a power of 0.0769 W/
m2 at a current density of 0.3846 A/m2 during the wastewater treatment process.
As mentioned above, aeration is not only considered as a
design factor but also regarded as a significant enhancement,
which is usually added to FW for a better organic pollutants
removal efficiency, which is suitable for oily and paper mill
wastewater treatment (Darajeh et al. 2016; Davamani et al.
2021). Aeration systems can be used to improve the microorganism activities and promote plants growth. A hydroponic

phytoremediation study reported that the aeration-assisted
treatment of paper mill wastewater improved COD removal
from 56.25% to 81.25% (Davamani et al. 2021). Cold climate may also have potential to treat industrial wastewater
with local plants. For example, to improve the performance
of FWs for AMD treatment in a northern climate, a novel
floating treatment wetland was designed with a layer of snow
fencing attached to the bottom of a FW for structural support and protection against the collapse of system after ice
buildup during the winter (Gupta et al. 2020). The results
showed the plants can regenerate and sustain the sulfate
reduction in the system after winter. A study using water
hyacinth combined with a continuous stirred tank reactor
was carried out for the treatment of sugar mill effluent, and
found that the continuous mixing of effluent prevented the
sedimentation and coagulation of several pollutants in the

medium (Kumar et al. 2019). An effluent mixing impeller
physically promoted the reaction in the system, and the system achieved the highest reduction of BOD (83.78%) from
947.88 mg/L and COD (93.64%) from 1620.3 mg/L (Kumar
et al. 2019).

Summary and recommendations
In the past decades, FWs have been mainly used in the
remediation of eutrophic waterbodies, sewage and domestic wastewater, and stormwater runoffs. Comparison to constructed wetlands, FWs have advantages of low-cost and no
land demanding. In recent years, FWs have gradually been
used for industrial wastewater treatment and showed promising treatment performance. In this paper, the components of
FWs and the key factors affecting the performance of FWs
are systematically introduced. Then the pollutant removal
mechanisms are discussed. FWs can efficiently reduce the
concentration of organic matters, total solids, nutrients, and
heavy metals from wastewater. Focusing on industrial wastewater treatment, the application and performance of FWs on

a variety of industrial wastewater treatment are analyzed.
Among them, most of the applications are reported in textile
and oily wastewater treatment, and the majority of applications are around developing countries with warm climate.
Having reviewed recent design of FWs, this paper highlights
enhancement methods in treating industrial wastewater in
terms of their pollutant removal performance. There is sufficient evidence that bacterial inoculation, co-plantation and
aeration can significantly improve the removal of pollutants
in FWs systems. However, FWs are associated with some
limitations: industrial wastewater with high concentrations
of pollutants would not be suitable for FW treatment because
pollutants at a high concentration would threaten plants’ survival. Some industrial wastewater sources are lack of the
necessary nutrients and organic carbon, which can limit
plant growth. Another key limitation is that the installation
of FW treatment systems relies on the local environment,
including temperature, water depth, surface area, and water
flow rates. In many cases, establishing an in-situ FW treatment system can be challenging and increase the technology's cost. Further studies are still needed to improve the
application and performance of FWs. The following recommendations are made:
a. Several methods have been developed to enhance the
performance of FWs, and the most common enhancement of FWs is done by inoculating bacteria. It is still
the mainstream to study more types of bacteria-plants
combo to improve the performance of FWs. The key of
this enhancement method is the cultivation and assessment of bacteria, and more types of bacteria can be

13




applied. Another enhancement is to test new combinations of different plants as different species are efficient
in the removal of complex pollutants; the efficient plant

combination can achieve a multifunctional system for
wastewater treatment.
b. Improving FW design is another important aspect. The
disposal of harvested plants and/or tissues should be
more flexible to avoid secondary environmental pollution. Developing novel floating mats offers important
improvement potential for FWs. The floating mats added
with substrate have the potential to improve the treatment efficiency because the mixture of substrate as biocarrier provides space for growth of organism and can
be used as sorbent or reaction medium for pollutants
removal. Additionally, using multi-functional designs,
such as multi-class FWs and FWs combined with constructed wetlands (CWs), can further improve pollutant
removal efficiency. To optimize the design, based on
abundant data of former research, artificial intelligence
technology can be induced to improve the design of
FWs, as well as for detection and prediction of FWs
performance.
c. With the development of FWs in industrial wastewater
treatment, a comprehensive performance assessment and
application guidance framework needs to be established.
For different types of industrial wastewater, the applicable plants, enhancement methods, applicable pollution
concentration range, applicable environment and climate
need to be classified and summarized. The rationality
and effectiveness of FW design in industrial wastewater treatment should be evaluated using mathematical
models for more economical and feasible designs. Valid
models can aid in optimizing system design, monitoring
performance, predicting pollutant removal efficiency,
optimizing resource utilization, assessing environmental
impact, and supporting decision making. This contributes to enhancing the efficiency and cost-effectiveness
of FWs systems while ensuring environmentally friendly
wastewater treatment practices. Another key point for
improving the performance assessment is to expand

the assessment scope. The assessment should not only
consider pollutant removal, but also think of ecological impacts of the FWs. For example, pollutant removal
and environmental remediation technologies application combined with life cycle assessment has been an
important trend in assessment system, with can help
understand the entire environmental impacts, such as
greenhouse gas emission reduction, carbon sequestration, and its direct and indirect contribution to sustainability goals. Moreover, the new assessment also should
consider social and economic impacts.

13

Environmental Science and Pollution Research
Acknowledgements  This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC). The
authors are very grateful to the anonymous reviewers for their comments and suggestions that helped in improving the manuscript.
Author Contributions  Jianliang Mao: conceptualization, literature
search and data analysis, writing and preparation of original draft, and
writing including reviewing and editing. Guangji Hu: conceptualization, data curation, reviewing and revising. Wei Deng: reviewing and
editing. Min Zhao: supervision and reviewing. Jianbing Li: conceptualization, resources, reviewing and editing, supervision, project administration, and funding acquisition.
Data Availability  As this paper is a review article, it does contain original data or specific datasets. The information and conclusions presented
in this review are based on previously published studies, and references
to these sources are provided in the bibliography.

Declarations 
Ethics approval and consent to participate  Not applicable.
Consent for publication  Not applicable.
Competing interests  The authors declare no competing interests.

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