Macrophytes in Constructed wetlands

The vegetation in constructed wetlands (CWs) plays an important role in wastewater treatment. Popularly, the common emergent plants in CWs have been vegetation of natural wetlands. However, there are ornamental flowering plants that have some physiological characteristics similar to the plants of natural wetlands that can stimulate the removal of pollutants in wastewater treatments.

ornamental flowering plants;constructed wetlands;wastewater;pollutants

1. Introduction

Nowadays, the use of constructed wetlands (CWs) for wastewater treatment is an option widely recognized. This sustainable ecotechnology is based on natural wetland processes for the removal of contaminants, including physical, chemical and biological routes, but in a more controlled environment compared with natural ecosystems [1][2][3][1,2,3]. These ecologically engineered systems involve three important components: porous-filter media, microorganism and vegetation [2]. The mechanisms for the transformation of nutrient and organic matter compounds are conducted by biofilms of microorganisms formed in the porous media and the rhizosphere zone [4][5][4,5]. The media materials (soil, sand, rocks, and gravel) provide a huge surface area for microorganisms to attach, contributing to macrophyte growth, and also act as filtration and/or adsorption medium for contaminants present in the water [6]. Regarding the vegetation, one of the most conspicuous features of wetlands is the role that plants play in the production of root and rhizomes in order to provide substrates for attached bacteria and oxygenation of areas adjacent to the root, and absorb pollutants from water. Nitrogen (N), Phosphorus (P) and other nutrients are mainly taken up by wetland plants through the epidermis and vascular bundles of the roots, and are further transported upward to the stem and leaves [7]. This provides carbon for denitrification during biomass decomposition and prevents pollutants from being released from sediments [8][9][10][8,9,10]. The use of the CW technology began in Europe during the 1960s [1], and has been replicated on other continents. The type of vegetation used are plants from natural wetlands, including Cyperus papyrus, Phragmites australis, Typha and Scirpus spp., which have been evaluated for their positive effects on treatment efficiency for nutrient and organic compounds around the globe [8][9][11][8,9,11]. In Americas, such species are typical in CWs, and are found mainly in the United States, where the technology has been used extensively and is implemented in different rural and urban zones [12][13][14][15][16][12,13,14,15,16]. In recent studies (15 years ago), the goal of CW studies involved an investigation into the use of herbaceous perennial ornamental plants in CWs, including the use of species with different colored flowers to make the systems more esthetic, and therefore making it more probable for adoption and replication.

2. Role of Macrophytes in CWs

The plants that grow in constructed wetlands have several properties related to the water treatment process that make them an essential component of the design. Macrophytes are the main source of oxygen in CWs through a process that occurs in the root zone, called radial oxygen loss (ROL) [17]. The ROL contributes to the removal of pollutants because it favors an aerobic micro-environment, and waste removal is therefore accelerated, whereas, in anaerobic conditions (the main environment in CWs), there is less pollutant removal. In a recent study [18] comparing the use of plants in high density (32 plants m−2) and low density (16 plants m−2) CWs, the removal of nitrogen compounds in high density CWs was twice that of CWs using a low density of plants, which is strong evidence of the importance of plants in such systems. The removal rate of total nitrogen (TN) and total phosphorous (TP) were also positively correlated with the ROL of wetland plants, according to a study involving 35 different species [19].
The roots of plants are the site of many microorganisms because they provide a source of microbial attachment [8] and release exudates, an excretion of carbon that contributes to the denitrification process, which increases the removal of pollutants in anoxic conditions [20][21][20,21]. Other physical effects in plant tissue in water include: reduction in the velocity of water flow, promotion of sedimentation, decreased resuspension, and uptake of nutrients. However, for roots and rhizomes in the sediment, the physical effects include: stabilizing the sediment surface, less erosion, nutrient absorption, prevention of medium clogging (in subsurface conditions) and improved hydraulic conductivity. Aerial plant tissue favors in the light attenuation (reduced growth of photosynthesis), reduced wind velocity, storage of nutrients and aesthetic pleasing appearance of the system [2][5][2,5]. A 5-year study evaluated the influence of vegetation on sedimentation and resuspension of soil particles in small CWs [22]. The author showed that macrophytes stimulated sediment retention by mitigating the resuspension of the CW sediment (14 to 121 kg m−2). Macrophytes increased the hydraulic efficiency by reducing short-circuit or preferential flow. Plant presence led to decreasing saturated hydraulic conductivity in horizontal subsurface flow. This study was relevant, since monitoring macrophytes is essential for understanding and controlling clogging in subsurface CWs [22].
The removal of organic and inorganic pollutants in CWs is not only the role of microorganisms. This function is also exerted by plants that are able to tolerate high concentrations of nutrients and heavy metals, and, in some cases, plants are able to accumulate them in their tissues [23]. It has been estimated that between 15 and 32 mg g−1 of TN and 2–6 mg g−1 (dry mass) of TP are removed by CW plants, which was measured in the aboveground biomass [24][25][24,25].
Other uptakes of xenobiotic compounds (organic pollutants) are also the result of the presence of plants, involving processes such as transformation, conjugation and compartmentation [23].

3. Survey Results of the Use of Ornamental Flowering Plants in CWs

Many CWs around the world used OFP for the removal of various types of wastewater (Table 1). For example, in China, the most popular plants used is Canna sp., while in Mexico the ornamental plant used is more diverse, including plants with flowers of different colors, shapes and aromatic characteristics (Canna, Heliconia, Zantedeschia, Strelitzia spp).
Table 1. Ornamental flowering plants and removal of wastewater pollutants in CWs (constructed wetlands) around the globe.

Country

Type of Wastewater

Vegetation

Removal Efficiency of Pollutants (%)

Reference

Brazil

Domestic

Heliconia psittacorum

TSS: 88, COD: 95, BOD: 95

Paulo et al. [26]

 

Domestic

Alpinia purpurataArundina bambusifoliaCanna spp.

Heliconia psittacorum

L.F.

COD: 48-90, PO4-P: 20, TKN: 31 and TSS: 34.

Paulo et al. [27]

 

Swine

Hedychium coronarium

Heliconia rostrata

COD: 59, TP: 44, TKN: 34 and NHx 35

COD: 57, TP: 38, TKN: 34 and NHx: 37

Sarmento et al. [28]

   

Hemerocallis flava

COD: 72, BOD: 90, TN: 52, TP: 41 and SST: 72.

Prata et al. [29]

   

Heliconia psittacorum L.F.

 

Teodoro et al. [30]

China

Municipal

Canna indica

COD: 77, BOD: 86, TP: >82, TN: >45

Shi et al. [31]

 

Aquaculture ponds

Canna indica mixed with other species

BOD: 71, TSS: 82, chlorophyll-a: 91.9, NH4-N: 62, NO3-N: 68 and TP: 20.

Li et al. [32]

 

Domestic

Canna indica Linn

COD: 82.31, BOD: 88.6, TP: >80, TN: >85

Yang et al. [33]

 

Municipal

Canna indica

NH4-N: 99, PO4-P: 87

Zhang et al. [34]

 

Drain of some factories

R. carnea, I. pseudacorus, L. salicaria

COD: 58-92, BOD: 60-90

TN: 60-92, TP: 50-97,

Zhang et al. [35]

 

River

Canna sp

COD: 95, N-NH4: 100, N-NO3: 76, TN: 72

Sun et al. [36]

 

Domestic

Canna indica

TP: 60, NH4-N: 30-70, TN: ~25

Cui et al. [37]

 

Aquaculture ponds

Canna indica mixed with other natural wetland plants

BOD: 56, COD: 26, TSS: 58, TP: 17, TN: 48 and NH4-N: 34.

Zhang et al. [38]

 

Wastewater from a student dormitory (University)

Canna indica mixed with other natural wetland plants

COD: 50–70, BOD: 60–80, N-NO3: 65–75, TP: 50–80

Qiu et al. [39]

 

Domestic

Canna indica and Hedychium coronarium

TP: 40–70

Wen et al. [40]

 

Polluted river

Iris pseudacorus mixed with other natural wetland plants

TN: 68, NH4-N: 93, TP: 67

Wu et al. [41]

 

Sewage

Iris pseudacorus, mixed with other plants of natural wetlands

TN: 20 and TP: 44

Xie et al. [42]

 

Municipal

Canna indica

COD: 60, NO3-N: 80, TN: 15, TP: 52

Chang et al. [43]

 

Simulated polluted river water

Iris sibirica

COD: 22, TN: 46, NH4-N: 62, TP: 58

Gao et al. [44]

 

Synthetic

Canna sp

Fluoride: 51, Arsenic: 95

Li et al. [45]

 

Simulated polluted river water

Iris sibirica

Cd: 92

Gao et al. [46]

 

Synthetic

Canna indica L.

N: 56–60

Hu et al. [47]

 

Synthetic (hydrophonic sol.)

Canna indica L.

TN: 40–60, N-NO3: 20–95, NH4-N: 20–55

Wang et al. [48]

Chile

Sewage

Zantedeschia aethiopica, Canna spp. and Iris spp

BOD: 82, TN: 53, TP: 60.

Morales et al. [49]

 

Sewage

Tulbaghia violácea, and Iris pseudacorus.

BOD: 57–88, COD: 45–72, TSS: 70–93, PO4-P: 6–20.

Burgos et al. [50]

 

Ww rural community

Zantedeschia aethiopica

Organic matter: 60%, TSS: 90%

Leyva et al. [51]

Colombia

Domestic

Heliconia psíttacorum

NH3: 57

COD: 70

Gutiérrez-Mosquera and Peña-Varón [52]

 

Synthetic landfill leachate

Heliconia psittacorum

COD, TKN and NH4 (all: 65–75)

Madera-Parra et al. [53]

 

Cattle bath

Alpinia purpurata

SST: 58, TP: 85, COD: 63

Marrugo-Negrete et al. [54]

 

Municipal

Heliconia psitacorum

Bisphenol A: 73, Nonylphenols: 63

Toro-Vélez et al. [55]

Costa Rica

Dairy raw manure

Ludwigia inucta, Zantedechia aetiopica, Hedychium coronarium and Canna generalis

BOD: 62, NO3-N: 93, PO4-P: 91, TSS: 84

León and Cháves [56]

Egypt

Municipal

Canna sp

TSS: 92, COD: 88, BOD: 90

Abou-Elela and Hellal [57]

 

Municipal

Canna sp

TSS: 92, COD: 92, BOD: 92

Abou-Elela et al. [58]

India

Paper mill effluent

Canna indica

9,10,12,13-tetrachlor- ostearic acid: 92 and 9,10-dichlorostearic acid: 96

Choudhary et al. [59]

 

Synthetic

Canna indica

Dye: 70–90

COD: 75

Yadav et al. [60]

 

Synthetic greywater

Heliconia angusta

COD:40, BOD: 70, TSS: 62, TDS: 19

Saumya et al. [61]

 

Domestic

Canna generalis

TN: 52, T-PO3: 9

Ojoawo et al. [62]

 

Collection pond

Canna Lily

BOD: 70–96, COD: 64–99

Haritash et al. [63]

 

Hostel greywater

Canna indica

COD, TKN and Pathogen all up 70

Patil and Munavalli, [64]

 

Domestic

Polianthus tuberosa L.

Heavy metals (Pb and Fe: 73–87), (Cu and Zn: 31–34) and Ni and Al: 20–26

Singh and Srivastava [65]

Ireland

Domestic

Iris pseudacorus

TN: 30, TP:28

Gill and O’Luanaigh [66]

Italy

Synthetic

Zantedeschia aethiopica, Canna indica

N: 65–67, P: 63–74, Zn and Cu: 98–99, Carbamazepine: 25–51, LAS: 60–72

Macci et al. [67]

Kenya

Flower farm

Canna spp.

BOD: 87, COD: 67, TSS: 90, TN: 61

Kimani et al. [68]

Mexico

Municipal

Zantedeschia aethiopoca

COD: 35, TN: 45.6

Belmont and Metcalfe [69]

 

Domestic

ZantedeschiaAethiopica and Canna flaccid

SST: 85.9, COD: 85.8, NO3-N: 81.7, NH4-N: 65.5, NT: 72.6

Belmont et al. [70]

 

Coffee processing

Heliconia psittacorum

COD: 91, Coliformes: 93

Orozco et al. [71]

 

Domestic 

Strelitzia reginae, Zantedeschia esthiopica, Canna hybrids, Anthurium andreanum, Hemerocallis Dumortieri

COD: >75, P: >66, Coliforms: 99

Zurita et al. [72]

 

Domestic

Zantedeschia aethiopica

BOD: 79, TN: 55, PT: 50

Zurita et al. [73]

 

Wastewater form canals

Zantedeschia aethiopica

COD: 92, N-NH4: 85, P-PO4: 80

Ramírez-Carrillo et al. [74]

 

Municipal

Strelitzia reginae, Anthurium, andreanum.

TSS: 62, COD: 80, BOD: 82, TP: >50, TN: >49

Zurita et al. [75]

 

Groundwater

Zantedeschia aethiopica and Anemopsis californica

As: 75–78

Zurita et al. [76]

 

Domestic

Gladiolus spp

BOD: 33, TN: 53, TP: 75

Castañeda and Flores [77]

 

Mixture of greywater (from a cafeteria and research laboratories)

Zantedeschia aethiopica and Canna indica

COD: 65, NT: 22.4, PT: 5.

Zurita and White [78]

 

Domestic

Zantedeschia aethiopica

BOD: 70

Hallack et al. [79]

 

Domestic

Heliconia stricta, Heliconia psittacorum and Alpinia purpurata

BOD: 48, COD: 64, TP: 39, TN: 39

Méndez-Mendoza et al. [80]

 

Municipal

Canna hybrids and Strelitzia reginae

DQO: 86, NT: 30–33, PT: 24–44

Merino-Solís et al. [81]

 

Municipal

Zantedeschia aethiopica and Strelitzia reginae

COD: 75, TN: 18, TP: 2, TSS: 88.

Zurita and Carreón-Álvarez [82]

 

Domiciliar

Spathiphyllum wallisii, Zantedechia aethiopica, Iris japonica, Hedychium coronarium, Alocasia sp, Heliconia sp. and Strelitzia reginae.

N-NH4: 64-93

BOD: 22–96

COD: 25–64

Garzón et al. [83]

 

Community

Zantedeschia aethiopica, Lilium sp, Anturium spp and Hedychium coronarium

NT: 47, PT: 33, COD: 67

Hernández [84]

 

Stillage Treatment

Canna indica

BOD: 87, COD: 70

López-Rivera et al. [85]

 

Artificial

Iris sibirica and Zantedeschia aethiopica

Carbamazepine: 50–65

Tejeda et al. [86]

 

Community

Alpinia purpurata and Zantedeschia aethiopica

 

Marín-Muñiz et al. [87]

 

Polluted river

Zantedeschia aethiopica

NO3-N: 45, NH4-N: 70, PO4-P: 30

Hernández et al. [18]

 

Municipal

Spathiphyllum wallisii, and Zantedeschia aethiopica

 

Sandoval-Herazo et al. [88]

 

University

Strelitzia reginae

 

Martínez et al. [21]

Nepal

Municipal

Canna latifolia

TSS: 97, COD: 97, BOD: 89, TP: >30

Sigh et al. [89]

Portugal

Tannery

Canna indica mixed with other plants

COD: 41–73, BOD: 41–58

Calheiros et al. [90]

 

Community

Canna flaccida, Zantedeschia aethiopica, Canna indica, Agapanthus africanus and Watsonia borbonica

BOD, COD, P-PO4, NH4 and total coliform bacteria (all up to 84)

Calheiros et al. [91]

Spain

Domestic

Iris spp

Bacteria: 37

García et al. [92]

 

Municipal

Iris pseudacorus

Bacteria: 43

Ansola et al. [93]

Sri Lanka

Municipal

Canna iridiflora

BOD: 66, TP: 89, NH4-N: 82, N-NO3: 50

Weragoda et al. [94]

Taiwan

Domestic

Canna indica

N-NH4: 73, BOD: 11

Chyan et al. [95]

   

Canna indica

N-NH4: 57, N-NO3: 57

Chyan et al. [96]

Thailand

Domestic

Canna spp

COD: 92, BOD: 93, TSS: 84, NH4-N: 88, TP: 90

Sirianuntapiboon and Jitvimolnimit [97]

 

Seafood

Canna siamensis, Heliconia spp and Hymenocallis littoralis

BOD: 91–99, SS: 52–90, TN: 72–92 and TP: 72–77

Sohsalam et al. [98]

 

Domestic

Heliconia psittacorum L.f. and Canna generalis L. Bailey

TSS: Both > 88, COD: 42-83

Konnerup et al. [99]

 

Fermented fish production

Canna hybrid

BOD, COD, TKN: ~ 97

Kantawanichkul et al. [100]

 

Collection system for business and hotel

Cannae lilies, Heliconia

BOD: 92, TSS: 90, NO3-N: 50, TP: 46

Brix et al. [101]

 

Domestic

Crinum asiaticum, Spathiphyllum clevelandii Schott

PO4-P: ~20

Torit et al. [102]

Turkey

Municipal

Iris australis

NH4-N: 91, NO3-N: 89, TN: 91

Tunçsiper [103]

USA

Domestic

Canna flaccida, Gladiolus sp., Iris sp.

Baceria: ~50

Neralla et al. [104]

 

Nursery

Canna· generalis, Eleocharis dulcis, Iris Peltandravirginica.

N: ~50, P: ~60

Palomsky et al. [105]

 

Domestic

Iris pseudacorus L., Canna x. generalis L.H. Bail., Hemerocallis fulva L. and Hibiscus moscheutosL.

BOD > 75, TSS > 88, Fecal baceteria > 93

Karathanasis et al. [14]

 

Tilapia production

Canna sp.

TSS: 90, NO2-N: 91, NO3-N: 76, COD: 12.5 and NH3-N: 7.5

Zachritz et al. [106]

 

Stormwater runoff

Canna x generalis Bailey, Iris pseudacorus L., Zantedeschia aethiopica (L.)

N and P

Canna

(>90), Iris (>30)

Zantedeschia

(>90)

Chen et al. [107]

 

Residential

Aeonium purpureum and Crassula ovate, Equisetum hyemale, Nasturtium, Narcissus impatiens, and Anigozanthos

TSS: 95

BOD: 97

Yu et al. [16]

Vietnam

Fishpond

Canna generalis

BOD: 50, COD: 25–55

Konnerup et al. [108]

United Kingdom

Herbicide polluted water

Iris pseudacorus

Atrazine: 90–100

McKinlay and Kasperek. [109]

 
A review of the available literature showed that ornamental plants are used to remove pollutants from domestic, municipal, aquaculture ponds, industrial or farm wastewater. The removal efficiency of ornamental plants was also evaluated for the following parameters: biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen (TN), total phosphorous (TP), ammonium (NH4-N), nitrates (NO3-N), coliforms and some metals (Cu, Zn, Ni and Al). There is no clear pattern in the use of certain species of ornamental plants for certain types of wastewater. However, it is important to keep in mind that CWs using ornamental plants are usually utilized as secondary or tertiary treatments, due to the reported toxic effects that high organic/inorganic loading has on plants in systems that use them for primary treatment (in the absence of other complementary treatment options) [110][111][110,111]. The use of OFP in CWs generates an esthetic appearance in the systems. In CWs with high plant production, OFP harvesting can be an economic entity for CW operators, providing social and economic benefits, such as the improvement of system landscapes and a better habitat quality. Some authors have reported that polyculture systems enhanced the CW resistance to environmental stress and disease [14][112][14,112].
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