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AEES 2022 IOP Publishing
IOP Conf. Series: Earth and Environmental Science 1032 (2022) 012026 doi:10.1088/1755-1315/1032/1/012026

Various Types of Constructed Wetland for Wastewater

Treatment- A Review
Arvind Kumar Swarnakar1, Dr. Samir Bajpai2, Dr. Ishtiyaq Ahmad3
1. Research Scholar, Department of Civil Engineering, National Institute of Technology Raipur,
Chhattisgarh, India akswarnakar@nitrr.ac.in
2. Professor, Department of Civil Engineering, National Institute of Technology Raipur, Chhattisgarh,
India
3. Assistant Professor, Department of Civil Engineering, National Institute of Technology Raipur,
Chhattisgarh, India

Abstract. As per the World Health Organization 80% of wastewater is released to the environment
without satisfactory treatment. Constructed Wetlands (CWs) are one of the natural wastewater
(WW) treatment methods. CWs have been recommended as a low technology, low maintenance,
low operation cost, and green technology wastewater treatment system. Many types of CWs are
currently in use. This paper studies these different types based on the climate, area, base materials,
temperature, contaminant removal efficiency, removal mechanism and physicochemical
analysis of various wastewater parameters. It is found that wetlands are successful in removing
organic matter–Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand (COD) and
suspended solids and nutrients–total Nitrogen (TN) and total Phosphorus (TP). CWs need to be
studied as a promising solution not only for effective treatment of wastewater but also as an
economical method to improve the fertility of soil. Further, the paper discusses the scope of future
research in CW to further improve the wastewater treatment technology.

Keywords: Constructed wetland, soil, gravel, wastewater, treatment,

!"Introduction

Natural wetland comprises of vegetation, soil and either water or wastewater. There are
different conventional methods for wastewater treatment such as sand traps (grit chamber), septic
tanks, Imhoff tank, baffled reactor (Anaerobic Baffled Reactor, ABR), anaerobic filter, green filters, Soil
BioTechnology (SBT) or Constructed Soil Biofilter (CSB) or Constructed Soil Filter (CSF), anaerobic
stabilization ponds, aerobic stabilization pond (Maturation Ponds/Oxidation Pond), Rotating
Biological Contactor (RBC), Active Sludge Process (ASP), Upflow Anaerobic Sludge Blanket (UASB),
Trickling Filter (TF), and micro-algae techniques etc. CWs are the manmade system with combination
of base material, vegetation, and organic matter to provide wastewater treatment [1]. CWs require
less infrastructure, investments, raw materials, energy consumption, operation, staff during
operation, maintenance, odors, insects, flow variations, toxic substances, and by-products [2].
Categorization of CWs depends on flow direction, macrophytic growth and hydrology [3]. CWs are
typically used as a secondary treatment unit. The CWs are used for treatment of domestic wastewater,
animal wastewater, mine water, leachate remediation, industrial wastewater, urban stormwater and field
runoff [4]. The main part of the CWs are aggregate, soil and gravel used as filter media and
macrophytes (vegetation) such as Typha, Canna indica, Flax Lily, Banksias, Bottlebrush, P. australis,
common rush, tapered rosette grass, Phragmites australis, common reed, Club-rush, Cattail, Common
water plantain, Reed canary grass, Meadowsweet, Yellow flag, Compact rush used as vegetation [5].
According to water flow in substrate UN- HABITAT has divided CWs in three categories – 1. Vertical
Flow Constructed Wetland (VFCW) 2. Horizontal Flow Constructed Wetland (HFCW) 3.

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IOP Conf. Series: Earth and Environmental Science 1032 (2022) 012026 doi:10.1088/1755-1315/1032/1/012026

Hybrid Flow Constructed Wetlands (HyFCW). Most of the natural wetlands are Free Water Surface (FWS).
Further subdivision is shown in fig.1. This paper briefly describes all types of CWs.

Figure 1. Various types of wetlands

2. Removal Mechanisms in Constructed Wetland

The main mechanism of treatment through CWs comprises biogeochemical transformation with solid and
liquid separations. Macrophytes plays a very important role in removing various types of contaminants.
The removal mechanism by macrophytes is shown in fig. 2. Contaminants uptake by root zone involves
rhizodegradation process by microbial activity. The heavy metals are reduced through phytostablization.
Plant enzymes break down the contaminants through phytodegradation. Plants and algae remove the
contaminants from soil and sediments through phytoextraction. Plants release the contaminates from soil
and sediments in atmosphere through phytovolatalization process [6, 7, 8, 9]. Removal of various
contaminants involves various operations and process in CWs. Organic material (BOD) is removed by
biological degradation, sedimentation, and microbial uptake – organic contamination including pesticides
are removed by adsorption, volatilization, photolysis, and biotic degradation, suspended solids are removed
by sedimentation and filtration, Nitrogen is removed by plant uptake, sedimentation, nitrification/
denitrification, microbial uptake, volatilization, Phosphorus is removed by sedimentation, filtration,
adsorption, plant and microbial uptake, pathogens are removed by natural die-off, sedimentation, filtration,
UV degradation, adsorption, heavy metals are removed by sedimentation, adsorption by vegetation and
substrate and plant uptake process.

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AEES 2022 IOP Publishing
IOP Conf. Series: Earth and Environmental Science 1032 (2022) 012026 doi:10.1088/1755-1315/1032/1/012026

Figure 2. Macrophytes mechanism for contaminant removal

2.1 Role of plants in CWs

Different types of CWs plants are – free floating, rooted floating, emergent, submerged, shrub and trees.
Most commonly, emergent herbaceous plants are used in CWs. Phragmites, phragmites australis, cattail,
reeds, vetiver grass, typha latifolia, water grass and canna indica are some wetland plants. Selection of
plants depends on type of constructed wetland systems, substrates, type of wastewater, viability of local
plants and temperature [11]. Soil organic matter plays important role in plant growth in HFCWs [12]. The
vegetation density (numbers in per sq-m area) depends on available filter media area [5-11]. Due to easy
availability, Typha latifolia is a common plant for CWs and it also generates the higher biomass.

2.2 Selection of wetland

Selection of the wetland depends on type of pollutants, material of substrates, local available vegetations,
temperature, Hydraulic Retention Time (HRT= Volume (Area x Water Depth x Porosity) / Discharge) and
Hydraulic Loading Rate (HLR) [10]. As per the United State Environmental Protection Agency (USEPA)
performance of constructed wetland depends on depth of water, slope of ground, and flow velocity. Table
1, 2 and 3 shows the efficiency of the HFCWs with various vegetation, HRT and HLR. Geo
physicochemical parameters of filter media are necessary parameters for selection of CWs [7-49].

3. Vertical Flow Constructed Wetland (VFCWs)

In VFCWs the wastewater in flow is above the substrate. The wastewater is treated through percolates in
root zone. Higher concentration of polluted water can be treated by VFCWs. The major parts of the VFCWs
are shown in figure 2. The inlet of influents flows either by pump or by gravity. Oxidizing of ammonia is
done quite well by VFCWs hence used in food proceeding and landfill leachates as shown in previous
studies by Kadlec R.H. & Wallace S.D. (2009) [4]. The removal efficiency of vertical flow CWs is shown
in table 1. It is used for continuous flow and good n utrient removal as compare to organic matter. It is less
capable of removing total dissolve solids. Water stagnation, mosquitoes and aquatic animals are the

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AEES 2022 IOP Publishing
IOP Conf. Series: Earth and Environmental Science 1032 (2022) 012026 doi:10.1088/1755-1315/1032/1/012026

problem with VFCWs. It has studied the textile waste with sugar bagasse and sylhet sand with plantation
P.australis, D. sanderina and observed 79.2% BOD5, 69.0-89.0% COD, 67.6-89.0% turbidity removal
efficiency in VFCW [13]. It has been observed in pharmaceutical compounds in wastewater removal by
pilot-scale VFCW by using scirpus grossus plants and sand, gravel as media. They practiced with different
HRT (3, 4, and 5 days) and has been observed that 99% ibuprofen, 88% COD, 99% ammonia and 83%
orthophosphate are effectively removed (HRT 5 days and 2 L/min aeration) [14]. Soil base constructed
wetlands can also use for VFCWs.

Figure 3. Vertical Type Constructed Wetland

Table 1. Removal efficiencies (%) for VFCWs

S. No. Type of WW TSS BOD5 COD NH4-N NO3-N TN TP Reference

1. Household 97.0 96.0 - 88.4 - [16]

2. STP - - 85.0 77-100 - 64- 90.0 [17]

80
3. Municipal 89.4 41.5 55.8 73.0 34.6 - 67.8 [18]
4. Domestic 90.0 - 84.0 92.0 - - - [19]
5. Landfill - - 78.0 87.0 - - - [20]
Leachate

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AEES 2022 IOP Publishing
IOP Conf. Series: Earth and Environmental Science 1032 (2022) 012026 doi:10.1088/1755-1315/1032/1/012026

4. Horizontal Flow Constructed Wetland (HFCWs)

HFCWs comprise of soil or gravel bed with vegetation. The wastewater flows below the top surface around
the root of vegetation. Such wetlands can be called Sub Surface Flow Constructed Wetland system
(SSFCWs). HSFCWs are used as secondary system for small community system [4].
Pretreated wastewater flows by gravity, horizontally or vertically, through the bed substrate where it
contacts a mixture of facultative microbes living in association with the substrate and plant roots resulting
in effective removal of BOD5 and suspended solids (USEPA, 2000). Small scale HFCWs are shown in
fig.3. The aerobic zones occur around roots and rhizomes that leak oxygen into the substrate. Organic
compounds are very effectively degraded aerobically around roots and rhizome bacteria. As per the table
2, good efficiency for removing total suspended solid (TSS), organic matter (BOD) and COD as
compared to nutrients. Mosquitoes and aquatic animal issues are limited in this CWs. HFCWs are used
for all types of wastewaters. The various materials can be used for substrates like shale, soil sediments,
zeolite, limestone, volcanic mineral, alum sludge, oyster shell, wood chip, plant waste, fly ash, slag,
construction waste, ceramsite and activated carbon. Sewage with high E. Coli bacteria and suspended solids
pit soil can be used [15]. Fecal coliform (FC) can effectively remove (82%) by HFCWs under 4.5 mg/L
Dissolved Oxygen (DO) and temperatures 25 °C [21]. Soil base subsurface constructed wetland enhanced
the potential for removing wastewater pollution [11-49].

Table -2. Removal efficiencies (%) for HFCWs

S.No. Type of WW TSS BOD5 COD NH4-N NO3-N TN TP Reference

1. Domestic 95.0 85.5 80.0 29.5 - 42.0 19.5 [22]
2. Municipal - 84.0 69.0 - - 41.0 96.0 [23]
3. Urban Sewage 82.7 91.6 - 55.3 - - 58.2 [24]
4. Sewage - 77.0 60 67.0 69.0 - 85.0 [25]
Treatment
Plant
5. Graywater 86.0 35.0 61.9 - - 87.0 95.0 [26]

Fig 4 shows the layout of the HFCWs. Influents flow under gravity. Table 2 shows the comparative
performance for wastewater treatment in HFCWs.

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AEES 2022 IOP Publishing
IOP Conf. Series: Earth and Environmental Science 1032 (2022) 012026 doi:10.1088/1755-1315/1032/1/012026

Figure 4. Horizontal Flow Constructed Wetland (HFCWs)

5. Hybrid Flow Constructed Wetlands (HCWs)

HFCWs are the combination of VFCWs and HFCWs. HFWS is effective for reduction of pathogens,
ammonia and TN [9]. The various types of CWs can be arranged together to create a combined system,
which is called hybrid constructed wetlands. Such mixed CWs are utilized to accomplish higher
effectiveness of wastewater treatment as opposed to single CW. Investigation of HCWs was initiated by
Seidel in Germany in 1980 [27] – ammonia was oxidized to nitrate, and in the following anoxic HF beds
nitrate was reduced via denitrification [3]. Using a similar setup for the municipal wastewater, using the
gravel, sand and soil with typha plant, the removal efficiency for BOD578%, TKN 66%, TSS 74% and P
86% while pilstia stratiotes removed BOD5 84%, TKN 76%, TSS 82% and P 83% [28]. Fig. 5 shows the
layout of HCWs.

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AEES 2022 IOP Publishing
IOP Conf. Series: Earth and Environmental Science 1032 (2022) 012026 doi:10.1088/1755-1315/1032/1/012026

Figure 5. Hybrid Constructed Wetland (HCWs)

HFCWs has some disadvantages like space consuming, capital cost, pretreatment, high supervision and not
extremely lenient to cold atmospheres.

Table 3. Removal efficiencies (%) for HCWs

S.No. Type of WW TSS BOD5 COD NH4-N NO3-N TN TP Reference

1 Domestic 89.0 - 85.0 83.0 - 83.0 64.0 [29]
2. Domestic - - 59.0 79.2 - 79.7 - [30]
3. Dormitory 92.2 88.9 86.0 66.5 65.7 - 63.5 [31]
wastewater
1
4. Urban 96.0 86.0 80.0 88.0 - - 24.0 [32]
Wastewater
5. Anaerobic 95.9 90.1 90.0 - 69.5 - 26.1 [33]
baffled
reactor(ABR)-
HSSF-VSSF
1
99.7% for fecal enterococci

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AEES 2022 IOP Publishing
IOP Conf. Series: Earth and Environmental Science 1032 (2022) 012026 doi:10.1088/1755-1315/1032/1/012026

6. Current scenario in Constructed wetland research

Various researchers have studied performance improvement of CWs by manipulating various parts and
parameters such as, substrate, plants, Hydraulic Retention Time (HRT), Loading Rate (LR), aeration
system, flow pattern, recirculation pattern, various combination for wetlands and plant density [USEPA].
For example, the locally available broken brick used for substratum in SSFCW for removal of nutrients,
plants such as the typha dominensis , cyperus papyrus and dark green bulrush used for treatment for hospital
wastewater resulting in 93% TSS, BOD5 90%, COD 83%, TKN 64%, and 56% phosphate removal [35],
different aeration methods like tide flow (TF), effluent recirculation (ER) and artificial aeration for all type
of CW (VFCW, HFCW and HCW) improving the removal efficiency 89% TSS, 84% COD, 63% total
Nitrogen (TN) and 81% ammonia nitrogen [35]. Recently, steel slag size 10 to 20 mm used as filer media
in multistage pond CWs for removal of contamination in river water resulting in increase in total phosphorus
(TP) reduction for first level HFCW by 151% [36].

Researchers have also studied different types of wastewaters such as removal of petrochemical waste
through HFCW by using gravel and sand media, plants typha and phragmites, removing the BOD5 (85%),
COD (89%) and turbidity (66%). Similarly study on different plant species, like acacia nilotica, cotton,
brassica napus carried out for decontaminating oilfield wastewater. BTEX (benzene, toluene, ethylbenzene
and xylene), PAH (Polycyclic Aromatic Hydrocarbons) and aliphatic/ aromatic petroleum hydrocarbon can
be removed by CW for refinery wastewater [37].
Heavy metals like Cu, Zn, Ni, Fe, Pb, Cd, B, Cr, Al, Co, As and Se from industrial wastewater, mine tailing
waste, tannery wastewater, oil refinery, domestic wastewater can be removed from SFCW. Media used for
removal of heavy metals from CW are sediments, compost, gravel, soil, ash with plants macrophyte, typha
latifolia, macrophyte myriophyllum spicatum and algal species [38,39]. The removal efficiency of heavy
metal from CW are reported as 69%- 96% [38,39,40].
Pharmaceutical, hospital and personal care products (PPCB), medical waste and cosmetic waste has been
seen effectively removed by CWs. Phytoremidiation in various types of CW is a well stablished treatment
method now [39,40, 41]. The removal of various PPCB was observed to be in the range of 70% to 90% by
various CWs [42,43].
Agro based synthetic fertilizer, pesticides, fungicides, insecticides and herbicides leach with soil and
contaminate the river, lakes, ponds, and ground water. CW removal efficiency for agricultural wastewater
for COD (92%), BOD5 (98%), TN (91%), TP (96%), TSS (96%), 94-99% E.Coli, Fecal Coliform (FC), and
Total Coliform (TC) from single stage CWs in various conditions has been reported [44]. The researchers
attributed the contribution of CW for treating agro-base runoff and industrial wastewater [45].
Group of researchers [46] recently observed that wastewater from textile dyeing process can be effectively
treated by CW resulting in removal efficiencies–COD (87%), BOD5 (86%), TSS (49%), TDS (46%),
Orange3R (84%), alcohol oxidase (85%), lignin peroxidase (150%) and color (75%).
Compost and landfill leachates have a high amount of organic matter and it can be treated by CW [47]. A
pilot-scale study was done in Iran where HSSFCW planted with vetiver grass and fine gravel is used as
filter media. It is observed that 75% of BOD5, 53% of COD and 74% of TN were removed successfully
[47]. Microbial fuel cell (MFC)-based horizontal flow (HF) constructed wetlands are novel systems that
use interconnected electrodes (cathode and anode), saturated media, plant, and electrochemically active
microbial population for wastewater polishing [48,49]. One study reported that the Microbial Fuel Cell
(MFC) HFCW with aluminum plates anode and cathode in HFCW with stone aggregate as filter media and
vetiver grass planted in CW, has 93% phosphorus, 83% coliform, 55-92% nitrogen and 80-100% organic
impurities removal [50].

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AEES 2022 IOP Publishing
IOP Conf. Series: Earth and Environmental Science 1032 (2022) 012026 doi:10.1088/1755-1315/1032/1/012026

Microplastics (MP) are the emerging as one of the major environmental pollutants on the earth. In MP
Synthetic Organic Polymer Plastics (SOPP) have been used majorly in households, clothing, agriculture,
personal care products [51]. The increased dependency on plastic material has skyrocketed the demand for
plastic products which eventually end up as a waste in the environment. The research shows that MPs travel
from municipal solid waste landfill to aquatic systems [52]. Natural wetlands are also proving to be effective
in removing MPs, a pollutant of emerging concern. Mangrove wetlands are proving to be effective in
removing MPs from aquatic streams [53]. CWs can be a suitable treatment strategy in removing MPs before
they reach natural water sources.

7. Conclusion and further directions

Due to a small pollution load in domestic and municipal wastewater, CWs can be an effectively part of
treatment. CW provides high removal efficiency for organic contaminants, nutrients–nitrogen and
phosphorus, and pathogenic microorganisms. Highly toxic contaminants and heavy metals from industrial
wastewaters can also be effectively treated by CWs. Toxic heavy metals removal like lead, cadmium, iron,
mercury, arsenic, copper, chromium, zinc, nickels, silver and manganese through CWs have been reported
by many researchers. CWs provide many advantages over conventional wastewater treatment systems.
CWs provide an economical, low technology, less expensive and high energy-saving treatment technology.
CWs also show promise in providing effective treatment not only for the domestic, municipal wastewater
but also for difficult to treat industrial wastewaters. Waterborne pathogens can also be reduced by wetland
systems. CWs are environmentally friendly and natural resource treatment systems that contribute to the
public health. CWs also show potential in removal of emerging contaminants of concerns that are difficult
to remove by conventional treatment methods. Recent research shows that some endocrine disrupting
chemicals were reduced by 48 to 99% by CWs [54]. More research is also required for removal of MPs by
CWs. A long term monitoring of geo-physicochemical properties of CW under various operating conditions
will give further research for better understanding of the key factors responsible for the optimization of CW
[55]. CW has great potential efficiency for removal of all types of water pollution and wetland technology
has made great strides in the last few years.

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