Wetlands for Wastewater Treatment

Wetlands for Wastewater Treatment Edith Martinez-Guerra1, Jairo Castillo-Valenzuela2, Veera Gnaneswar Gude3*,

ABSTRACT: An update on the current research and

Wetlands for Wastewater Treatment

development of wetland treatment technologies for

Constructed wetlands (CWs) have been successfully used

wastewater treatment is provided in this paper. This article

for treating different wastewaters for decades and have been

focuses on wetland applications in wastewater treatment (as

identified as a sustainable wastewater management option

an advanced treatment unit or a decentralized system), and

(Wang et al., 2017). For example, Liang Y et al. (2017)

nutrient and pollutant removal (metals, industrial and

published a detailed review on constructed wetlands for

emerging pollutants including pharmaceutical compounds).

saline wastewater treatment. While an overview of the state

A summary of studies involving the effects of vegetation,

of the art of CWs for decentralized wastewater management

wetland design and operation, modeling, hybrid and

in Brazil was also published. This section describes several

innovative systems, landfill leachate treatment, and

studies performed on CWs during the year of 2017. Ming Li et al. (2017) designed a CW for maximal

pathogen removal is also included.

nitrogen removal and minimal nitrous oxide (N 2 O)

————————— 1Research

Environmental

Engineer;

2Environmental

emission. The results show that nitrogen removal and N 2 O

Engineer; 3*Associate Professor

emission in CWs were significantly affected by C/N (Carbon

1Environmental

Laboratory, U.S. Army Engineer Research

and Nitrogen) ratio of the influent. Much higher removal

and Development Center. 3909 Halls Ferry Road,

efficiency of NH 4 +-N (98%) and total nitrogen (90%) was

Vicksburg, Mississippi 39180, United States.

obtained simultaneously in surface flow constructed wetland US

(SFCW) at C/N ratios of 12:1, and low N 2 O emission (8.2

Environmental Protection Agency Region 4, 980 College

mg/m2/d) and the percentage of N 2 O-N emission in total

Station Rd, Athens, Georgia, 30605.

nitrogen (TN) removal (1.44%) were also observed. In

3*Department

addition, wetland systems have also been evaluated for the

2Science

and

Ecosystem

Support

Division,

of Civil and Environmental Engineering

Mississippi State University, Mississippi State, MS 39762

treatment of recycled domestic wastewater. In fact,

e-mail: [email protected]

Almuktar et al. (2017) designed a VFCW meeting the

KEYWORDS: wetlands, natural treatment, vegetation,

irrigation water quality standards and successfully planted

hydrology, pollution, stormwater.

Chilli with the effluent. However, some thresholds (P,

doi: 10.2175/106143018X15289915807281

ammonia-nitrogen, and total coliform) exceeded. The

1537 Water Environment Research, Volume 90, Number 10 - Copyright © 2018 Water Environment Federation

excessive nutrients benefited the plants. Andreo-Martinez et

97.2% of chemical oxygen demand (COD); 33.33, 85.71,

al. (2017) investigated the performance of a horizontal sub-

and 92.5% of Nitrate/Nitrite; 53.5%, 46.5%, and 88.8% of

surface constructed wetland (HSSFCW) in Spain. The

sulphate; and 98.3%, 99.7%, and 99.6% of total suspended

wetland was planted with Phragmites australis, and it was

solids (TSS) were obtained from the anaerobic, anoxic, and

designed to treat artificially aerated domestic wastewater to

aerobic zones respectively. These combinations were found

produce reusable water for agricultural purpose. An average

to be efficient in municipal wastewater treatment.

TP removal of 96.9% was achieved while turbidity, TSS,

Furthermore, some halophytes have shown the ability to

TN, and E. coli removal rates were also improved. In

accumulate salts in their tissues, which make them attractive

addition, an integrated VFCW was designed for the removal

for domestic wastewater treatment (Fountoulakis et al.,

performance

2017).

of

phosphorus

and

biological

dephosphorization process in treating reclaimed water (Du et al., 2017).

A matured vertical-flow constructed wetland planted with Phragmites australis was compared to three

Barco and Borin (2017) evaluated the depuration

different types of ponds: ponds with wastewater; ponds with

performance and macrophyte plants growth in a full-scale

wastewater and reeds; and ponds with wastewater, reeds and

hybrid CW (composed of a HSSF) treating municipal

aeration- (Al-Isawi and Scholz, 2017). Higher COD, SS.

wastewater. The CW was vegetated with evergreen

NH 4 -N, and PO 4 -P were achieved using the matured VFCW

xerophile species. Results indicated median concentration

than when using the ponds. Moreover, the nitrate-nitrogen

abatements for the entire system of 74.3% for TN, 62.1% for

concentration increased in the aerated ponds reflecting

NH 4 -N, 77.7% for NO 3 -N, 29.6% for TP, 37.4% for PO 4 -P,

higher oxygen availability. Similarly, the effects of

and 46.7% for COD. On the other hand, Rehman et al.

supplementing plant-based carbon sources of a VFCW

(2017) investigated the role of oxygen released by

planted with Arundo donax and Pontederia cordata were

macrophytes (Typha latifolia and Phragmites australis) for

studied (Fu et al., 2017). The results showed that the addition

degrading organic waste, which demonstrated a strong

of the composite carbon source produced the highest

correlation

removal efficiencies of NH 4 +-N 91.5%, NO 3 -N 94.5%, and

between

dissolved

oxygen

(DO),

total

chlorophyll, and fresh plant biomass. The maximum DO in

TN 92.8% in VFCW.

the substratum of CWs proved to play a significant role in

Five types of CWs operated under semi-

reducing hydraulic retention time (HRT) in vegetated CWs

continuous vertical flow mode were analyzed on the

(Rehman et al., 2017). Badejo et al. (2017) used a sequential

treatment of municipal wastewater resulting in significant

activated sludge reactor and vegetated submerged bed

removal efficiencies of each contaminant studied (Kumar

constructed wetland (VSBCW) planted with Vetiveria

and Singh, 2017). The average NH 4 +-N, TN, NO 2 --N, NO 3 --

zizanioides. The percentage removal of 96.6%, 96.9%, and

N, SO 4 2-, and PO 4 3- removal efficiencies were 83.6%,


82.4%, 15.61%, 48.9%, 80.5%, and 78.9% respectively in

Wetlands for Nutrient Removal

semi-continuous CWs. The average NO 2 --N removal

An autotrophic enhanced floating treatment wetland

efficiency shows that highest nitrite accumulation occurred

(AEFTW) and a heterotrophic enhanced floating treatment

in the control CWs. In a similar case, a full-scale integrated

wetland (HEFTW) were designed to remove undesired

VSSFCW was operated over a six-year period for advanced

nitrogen from secondary wastewater effluent (Gao et al.,

treatment of mixed wastewater (Wu et al., 2017). The system

2017). About 89.4% of total nitrogen (TN) was removed

resulted in an average removal efficiency of 70%, 70%,

from AFTW and 88.5% from HEFTW. Valkama et al.

34%, 52%, 45%, 74%, 21%, 43%, and 98% for COD, NH 4 -

(2017) reported that nutrients removal in wetlands were

N, NO 3 -N, TN, TP, TSS, F−, Ni, and E. coli, respectively.

dependent on temperature, oxygen concentration, NO 3 -N

Multistage treatment wetlands can be used to

concentration, and discharge after removing 13% TP and

nitrogen

wastewater

14% NO 3 -N in a wetland in southern Finland. Similarly, in

(Wojciechowska et al., 2017). A pilot-scale multistage

Eastern United States, six large wetlands were used to

treatment receiving non-synthetic wastewater can achieve a

remove NO 3 -N. The NO 3 -N removal was found to be

total nitrogen removal of 95-99%. Lutterbeck et al. (2017)

significant between seasons and soil types (Messer et al.,

conducted a life-cycle analysis of an anaerobic unit

2017). Also in the United States, Wetland conservation

containing four SSFCW and two photoreactors in the

programs have been implemented along the Mississippi

treatment of wastewater. The reductions in chemical oxygen

River Basin. Shrestha et al. (2017) studied draining

demand (COD) varied between 93% and 97%, whereas the

watersheds in southeastern Arkansas and concluded that the

biochemical oxygen demand decreased by 97-98%.

conservation of wetlands in the Lower Mississippi River

Additionally, 97% of the Total Kjedahl Nitrogen (TKN),

Basin have significantly improved stream habitat as well as

100% of the ammoniacal nitrogen, and more than 90% of

water quality.

remove

from

high-

strength

total phosphorus were removed from the wastewater. On the

Most of the nutrients found in surface water comes

other hand, Ledon et al. (2017) investigated the life-cycle

from agricultural runoff, which led Darwiche-Criado et al.

greenhouse gaseous emissions and primary exergy resources

(2017) to evaluate the influence of agricultural activities

consumption associated with a HSSF. The results indicate

during a two-year period. It was determined that wetlands

that greenhouse gases (GHG) emissions per capita (12–22

can be used as buffer zones to effectively remove nutrients.

kg CO 2 eq/p.e/yr) and primary exergy resources consumed

Yin et al. (2017) evaluated a thermally modified calcium rich

(24–27 MJ/m3) for the HSSF are lower than those of a

attapulgite as a substrate for rapid phosphorus removal in

conventional

constructed wetlands. Results indicated that more than 95%

wastewater

kgCO 2 eq/p.e/yr and 96 MJ/m3).

treatment

plant

(67.9

of P can be removed in less than one hour with a sorption capacity of 4.5-6 mg P/g. CWs can also serve as sinks for


nutrient compounds (West et al., 2017). Liu et al. (2017)

al. (2017) used a CW coupled with biofilm electrode reactor

reviewed the potential of wetlands on advanced nutrient

(CW-BER) to treat wastewater with a relatively high level

removal from surface waters by a consortium of attached

of total inorganic nitrogen (TIN) concentration. Moreover,

microalgae and bacteria.

Huang et al. (2017) studied the use of silver nanoparticles

Mesquita et al. (2017) evaluated the difference in

(AgNPs) on the removal of nutrients from wastewater. The

removal efficiency of nitrogen and phosphorus compounds

TP removal efficiency was 47.9% at the end of the

based on the seasonal changes in a full-scale gravel-based

experiment (120 d), which mainly depends on the adsorption

horizontal subsurface flow constructed wetland in Portugal.

and precipitation of substrate. Gao et al. (2017) developed a

The results demonstrated that season variations had a

novel electrolysis-integrated horizontal subsurface flow

significant impact on the removal efficiency of TN, NH 4 +-

constructed system (E-HFCWs) to intensify removal of

N, NO x -N, TP, and DP, with higher values in spring-summer

nitrogen and phosphorus from contaminated water. When

period

and 26.1%,

the HRT varied from 2 h to 12 h, the removal rate of nitrate

respectively) than in autumn-winter (0%,-7.7%, -9.8%,

increased from 20% to 84%. Phosphorus (P) removal was

12.9%, and 0%, respectively. Seasonal changes also affected

also greatly enhanced exceeding 90% when the HRT was

the research done by Tan et al. (2017), who investigated the

longer than 4 h in the electrolysis-integrated HFCWs. This

seasonal nitrogen transformations and removal pathways in

improvement is due to the in-situ formation of ferric ions by

a surface flow constructed wetland (93,000 m2 with five

anodizing of sacrificial iron anodes, causing chemical

treatment cells), which treats domestic wastewater in

precipitation, physical adsorption and flocculation of

subtropical Taiwan. These type of wetlands showed higher

phosphorus confirming the role of electrolysis process.

(10.4%,

10.4%,

3.4%,

27.5%,

nitrogen removal rates during the summer due to the high

Natural wetlands, subwatershed and watershed

nitrification in sediments. Bear et al. (2017) monitored a

levels can influence the total phosphorus reduction in water

pilot-scale wetland for over two-year period obtaining a 90%

bodies. For example, Daneshvar et al. (2017) evaluated the

removal of nitrate and significant removal of e-coli during

Saginaw River Watershed, which is the largest watershed in

the summer, significantly higher than those observed in full-

Michigan. The phosphorus reduction was studied in four

scale wetland.

different wetland sizes including two, four, six, and eight ha.

Innovations in wetland modifications for nutrient

The study concluded that the two ha wetland had

removal are being pursued by several researchers. Wang et

significantly lower phosphorus reduction rates, and that the

al. (2017) used a modified single-stage-tidal flow

wetlands located in headwaters and downstream had

constructed wetland (TFCWs) with a step-feeding and

significantly higher phosphorus reduction than the ones

nitrogen transformation pathways in the TFCWs treating

located in the middle of the watershed indicating the

domestic wastewater. On the other hand, Junfeng Wang et

importance of selection and placement of wetlands. In


Jiaozhou Bay, China, four types of wetlands (sandy beaches,

79.9%, and 98.4%, respectively during the dry season; and

mud flats, tidal marshes, and estuarine intertidal zones) were

93.6%, 84.4%, and 94.6%, respectively during the rainy

studied for nutrient removal carried by submarine

season. Shingare et al. (2017) evaluated the efficiency of

groundwater discharge (Qu et al., 2017). It was noted that

Typha latifolia and Cyperus rotundus in treating domestic

nutrients carried out by submarine groundwater discharge

wastewater in CW. The results showed a log reduction of 5.0

provide a more important source for the phosphate-limited

and 4.8 for total coliform, 4.5 and 3.9 for E.coli, and 5.5 and

environment to plankton. Hernandez-Crespo et al. (2017)

5.5 for shigella. Additionally, there was a complete removal

concluded that horizontal subsurface flow constructed

of fecal coliform and Salmonella. Calheiros et al. (2017), on

wetlands (HSSFCW) are more efficient than FWSCW in the

the other hand, reported up to a 3 log removal in

removal of organic matter, suspended solids, and nutrients.

Enterobacteriaceae and up to 2 log removal for E. coli using

The recommended working time of FWSCWs is from 18 to

CWs.

27 m/yr and 55 m/yr for HSSFCW, which is based on effluent COD concentrations.

Maiga et al. (2017) suggested that any type of pathogen can be removed in a constructed wetland. However, the pathogen removal efficiency in full-scale

Wetlands for Pathogens and Viruses Removal

wetlands will depend on variables, such as sunlight,

Microbial communities play an important role in constructed

sedimentation, plants, mechanical filtration and adsorption,

wetlands when removing contaminants from water. Lv et al.

and temperature. Donde and Bangding (2017) performed an

(2017) compared the microbial community metabolic

exhaustive literature review on detection techniques,

function from both saturated and unsaturated CW

removal, and wastewater purification efficiencies of fecal

mesocosms including five planted (Juncus effuses, Typha

coliform bacteria (with emphasis on E. coli) indicators in

latifolia, Berula erecta, Phragmites australis, and/or Iris

CWs.

pseudacorus) and one unplanted mesocosm in the treatment of the pesticide, tebuconazole. The microbial activity and

Wetlands for Emerging Pollutants Removal

metabolic richness of interstitial water from unsaturated

Removal of emerging contaminants such pharmaceutical

CWs were significantly lower than that from saturated CWs.

and personal care products (PPCPs), endocrine disrupting

Lekeufack et al. (2017) studied various configurations of

chemicals (EDCs), antibiotic resistance genes (ARGs) and

vegetated CWs in Cameroon for the treatment of domestic

heavy metals has become an important area of research due

wastewater. The CW was planted with Fuirena umbellata

to the potential for numerous health impacts. These are

(Cyperaceae) to remove fecal bacteria, and it was compared

commonly found in municipal wastewaters, industrial

with an unplanted wetland. The removal efficiency for total

wastewaters and landfill leachates. Yang Zhang et al. (2017)

coliforms, fecal coliforms, and faecal streptocci were 94.7%,

assessed the removal of pharmaceuticals ibuprofen and


iohexol in vegetated CW mesocosms consisting of a variety

the treatment of livestock wastewater. It was reported that

of plants. More than 80% ibuprofen was removed in the CW

the presence of veterinary antibiotics, such as enrofloxacin

planted with Juncus effuses, while more than 80% iohexol

and ceftiofur does not influence the biochemical removal

was removed in the CW with Berula erecta demonstrating

processes that occur naturally in CWs. Huang (2017)

the efficiency of vegetated CWs. Liang Zhang et al. (2017)

evaluated the performance and bacterial community

planted a CW with Juncus, Typha, Berula, Phragmites, and

dynamics of a VFCW during the treatment of antibiotics-

Iris which showed ibuprofen removal rates of 29-99% when

enriched swine wastewater. The concentrations of all the

compared to unplanted ones, 15-85%. It was noted that the

chemical properties including oxytetracycline (OTC),

ibuprofen removal was positively correlated with the oxygen

difloxacin (DIF), copper (Cu) and zinc (Zn), nitrite/nitrate,

concentration in the water. In another study, six pilot-scale

sulphate and total organic carbon (TOC) in down-flow

SSFCWs were loaded with municipal wastewater using

treatment soils were significantly higher than those in up-

emerging organic compounds (EOCs) namely caffeine,

flow treatments on day 30, 60 and 90.

ibuprofen, naproxen, benzotriazole, diclofenac, acesulfame,

Matamoros et al. (2017) investigated the discharge

and carbamazepine as process indicators for biodegradation

of emerging contaminants (ECs) from wastewater plants.

(Kahl et al., 2017). The highest removal efficiency was

Twelve (12) full-scale HFCWs were constructed and used as

observed from the two aerated wetlands and the two-stage

tertiary treatment to remove 16 ECs from secondary treated

vertical flow system, both removing more than 90% of

wastewater.

acesulfame.

ketoprofen, and diclofenac were the most abundant (>2000

Benzotriazole,

5-methylbenzotriazole,

Antibiotics are showing removal resistance in

ng L−1 on average) in the secondary treated wastewater

wastewater. A pilot-scale aerated SSFCW treating municipal

effluent. EC removal levels ranged from 0 to 92%, with an

and hospital wastewater was used for the removal of selected

average removal of 43% recommending the suitability of

pharmaceuticals (Auvinen et al., 2017). The effect of active

HFCWs for this purpose.

aeration was assessed. The removal of metformin and

The removal of four (4) emerging pharmaceuticals

valsartan is significantly increased when continuous aeration

and personal care products using a lab-scale CW planted

is applied (99 ± 1% vs. 68 ± 3% for metformin and 99 ± 1%

with greater duckweed (Spirodela polyrhiza) was evaluated

vs. 17 ± 2% for valsartan), although the microorganisms can

(Jianan Li et al, 2017). Up to 100% removals were achieved

adapt to degrading metformin in anoxic conditions.

for paracetamol (PAR), caffeine (CAF) and tricolsan (TCS)

Moreover, it was noticed that intermittent aeration provides

while the highest removal for DEET was 32.2% in batch

equally efficient removal of the selected pharmaceuticals as

tests. When a stabilization tank was added to the CW, the

continuous aeration. Almeida et al. (2017) investigated how

final removals of the PPCP contaminants were 32.6%,

veterinary antibiotics affect wetlands’ performance during

97.7%, 98.0% and 100% for DEET, PAR, CAF and TCS,


respectively, by CW system alone, while 43.3%, 97.5%,

Design and plant species play an important role in

98.2% and 100%, respectively, were achieved by CW-ST

wetland performance (Zhang, Lv et al., 2017a). For example,

system under continuous conditions. Sgroi et al. (2017)

ibuprofen removal was higher in planted CWs in

studied the removal of emerging organic contaminants and

unsaturated, saturated and aerated saturated designs. Plants

fluorescence signature using a hybrid CW system including

(Juncus, Typha, Berula, Phragmites and Iris) increase

the following configurations: unsaturated vertical subsurface

microbial degradation process due to oxygen availability.

flow, partial saturated vertical subsurface flow, saturated

Similarly, higher hydraulic residence times and macrophye

horizontal, and free water surface wetlands. The removal

covers improved removal efficiencies of androstenedione,

efficiency of each contaminant varied on the type of

carbamazepine, caffeine, diclofenac, estrone, ibuprofen,

wetland; for example, the free water surface wetland

paracetamol, propranolol and triclosan in a CW treating

achieved a 98% removal of sucralose while the vertical

hospital wastewater (Vystavna et al., 2017). A review

SSFW achieved 9%. However, the free water surface

focused on the effect of different aeration strategies

wetland did not remove any trimethoprim, but the VSSFW

suggested tidal flow, effluent recirculation horizontal and

removed 13%. In contrast, Avila et al. (2017) achieved 30%

vertical flow, and artificial aeration wetlands as best

of sucralose in a VFCW.

performing systems in terms of TSS, COD, and nitrogen

Removal of 11 types of perfluoroalkyl acids

removal efficiencies (Ilyas and Masih, 2017).

(PFAAs) and 7 PFAA precursors was evaluated in a

Almost all of the paracetamol, caffeine and

constructed wetland consisting of aeration lagoon, reed beds,

tricolsan concentrations were removed in a free water

sedimentation tank and polishing ponds (Yin et al., 2017).

constructed wetland planted with Spirodela polyrhiza while

Soil and sediment sorption and plant uptake accounted for

the highest removal for DEET was 32.2% in batch tests.

majority of PFAAs removal (up to 96%) while aeration

Addition of a stabilization tank under continuous flow

lagoons removed most of the PFAA precursors. Removal of

conditions improved the removal efficiencies of all PPCP

caffeine, ibuprofen, naproxen, benzotriazole, diclofenac,

contaminants (Li Zhou et al., 2017). Influence of antibiotics

acesulfame, and carbamazepine was investigated in

(enrofloxacin and ceftiofur) on metal removal by

conventional horizontal flow, unsaturated vertical flow

constructed wetlands was investigated in mesocosms

(single and two-stage), horizontal flow with aeration,

planted with P. australis (Almeida et al., 2017). Above 85%

vertical flow with aeration, and reciprocating wetland

removal of Fe, Cu, Zn was achieved, noting that ceftiofur

systems (Kahl et al., 2017). Aerated and vertical flow

improved metal uptake by P. australis and no adverse

systems performed better than other configurations,

impacts of antibiotics were found. Mesocosms planted with

performance improving with elevated temperatures and

Typha latifolia, Phragmites australis, Irispseudacorus,

oxygen availability.

Juncus effusus, Berula erecta and a control mesocosm


(unplanted) were studied to understand the influence of

al., 2017). Adsorption and microbial degradation were

PPCPs (ibuprofen and iohexol) (Zhang Lv et al., 2017b). The

reported to be the causes for this removal plants playing a

study showed that presence of PPCPs did not have any

major role in this process. Microbial communities are also

influence on the water quality of the wetland effluent but the

affected by the presence of pharmaceutically active

plat type and hydraulic loading rates had varying influences

compounds (PhAC) (Yan et al., 2017). It was reported that

on ibuprofen or iohexol removal. Pretreatment of

Proteobacteria, Acidobacteria, and Bacteroidetes dominated

polybrominated diphenyl ethers containing synthetic

under PhAC exposure, while Desulfobulbus and Treponema

wastewater through a photocatalytic chamber prior to

were the dominant genera. Proteobacteria had a good

entering a sub-surface flow constructed wetland planted with

correlation with PhAC concentrations.

Oryza sativa and Phragmites australis improved removal efficiency from 55% (without pretreatment) to 95% (Chow et l., 2017). A review article focusing on the presence and fate of the organic pollutants was published which includes discussions on 41 organic priority substances and 17 contaminants of emerging concern (Gorito et al., 2017).

Metals removal Four engineered up-flow wetlands planted with typha latifolia but different filling materials such as peat, zeolite, volcanic cinder and sand were operated for more than 120 days to evaluate the Boron removal capacity from drinking

Landfill leachates are concentrated with various

water (Turker et al., 2017). Peat-media filled engineered

emerging contaminants such as acetaminophen (ACT),

wetland has shown the highest removal efficiency of 91%

bisphenol A (BPA), clofibric acid (CA), caffeine (CF),

while the removal efficiencies of volcanic cinder, sand and

crotamiton (CTMT), diclofenac (DCF), N,N-diethyl-m-

zeolite reactors were 84%, 83% and 57%, respectively.

toluamide (DEET), gemfibrozil (GFZ), lincomycin (LIN),

Similarly, a microcosmic vertical flow constructed wetland

salicylic acid (SA), and sulfamethazine (SMZ). A 5-hectare

planted with Iris sibirica fed 1, 2, 4 and 8 mg/L Cd

hybrid HSSF-CW system including aerated lagoons and reed

(Cadmium) was able to remove 94.9%, 97.4%, 95.6% and

beds in Singapore was shown to remove more than 90% of

96.2%, respectively (Ma et al., 2017). Nearly 50% of the Cd

these contaminants including antibiotic resistance genes (Yi

removal was attributed to substrate adsorption phenomena

et al., 2017). Variations in the PPCP and EDC concentrations

and the rhizospheric microbial and enzymatic activities,

both in raw leachate and their removal efficiencies were

removals being higher in planted wetlands in comparison

attributed to the redox conditions of the closed landfill site.

with unplanted wetlands. These results can be supported by

A laboratory scale VFCW planted with Phragmites australis

the observations made by Gill et al. (2017) who monitored

was able to remove nearly 100% of phenolic compounds

the accumulation of heavy metals such as Cd, Cr, Cu, Ni, Pb,

from synthetic leachate with a superior performance

Zn from highway runoff in sediments and vegetation of a

compared with unplanted constructed wetland (Dan, Fuji et

constructed wetland over a nine-year period. The


accumulation rates were 0.1 (Cd), 15.6 (Cu), 11.6 (Pb) and

ground biomass and below ground biomass in a Phragmites

88.3 (Zn) g per m2 highway drained per year with

australis constructed wetland was evaluated for individual

corresponding removal efficiencies of 5% (Cd), 60% (Cu),

contributions (Mulkeen et al., 2017). It was noted that

31% (Pb) and 86% (Zn), respectively.

analysis of above ground biomass alone could be an

The presence of acetate, propionate, humate, ammonium, and heavy metals did not have an effect on the growth of Phragmites australis but Juncus effuses withered

underestimation considering the accumulation rates by the below ground biomass indicating an optimum time of biomass harvesting to be effective throughout the year.

(Dan, Oka et al., 2017). High removal of heavy metals (Zn, Cr, Ni, Cd, Fe, and Pb) due to rhizofiltration in the upper soil layers was the reason for Phragmites australis while bioconcentration and translocation were the reasons for Juncus effuses. Two horizontal subsurface flow (HSF) and two vertical flow (VF) pilot-scale CWs were operated in parallel to evaluate Chromium (Cr) removal potential from wastewater. Studies with batch and continuous flow conditions under planted and unplanted configurations showed that planted VF constructed wetlands had higher removal efficiencies fitting pseudo-second-order and Langmuir models (Papaevangelou et al., 2017). A HSF constructed wetland planted with Limnocharis flava removed more than 90% of Hg (mercury) from gold mine effluent which is nine-fold higher than the unplanted constructed wetland (Marrugo-Negrete et al., 2017). The influence of hydraulic flow direction on the removal of antibiotic resistance genes (oxytetracycline and difloxacin) was studied using different substrates like brick and oyster shells (Huang Zheng et al., 2017). Higher antibiotic removal was observed in brick columns, however, higher antibiotic resistance genes compared to the environment were observed in the effluents influenced by substrate type and the flow of direction. Removal of metals and nutrients by above

Vegetation in Wetlands Plant biodiversity in CWs can enhance its treatment capabilities. For example, early spring species such as Rumex japonicas, Oenanthe hookeri, Phalaris arundinacea and Reineckiacarnea can be used to remove phosphorus from CWs. In a study done by Geng et al. (2017), communities including Oenanthe hookeri outperformed other communities in removing P. According this study, species composition exert stronger effect than species richness on the removal of P from wastewater. Kan et al. (2017) combined benthic fauna (Tubifex orientalis) substrate-microbes

surface-flow

constructed

wetlands

(SFCWs) by adding T. tubifex removals of 81.14 ± 4.16% and 70.49 ± 7.60% were achieved, which were 22.27% and 27.35% (nitrogen and phosphorus) higher than that without T. tubifex. Additionally, with T. tubifex, higher proportions of particulate (22.66 ± 3.96%) and colloidal phosphorus (20.57 ± 3.39%) observed promoted phosphorus settlement and further absorption by T. orientalis. In fact, Saggai et al. (2017) investigated the diversity (25 plant species) of plants for metaremediation of human wastewater in an arid climate. The removal efficiencies of BOD, COD, TSS, total phosphorus, ammonia, and nitrate were maintained at high


levels, approximately 90%, 80%, 94%, 60% and 50%,

showed that a TP removal efficiency of 78.2-89.8% was

respectively. An extremely high reduction of total coliform

achieved under different inlet loading rates (Luo et al.,

bacteria and streptococci was observed (approximately

2017). A similar plant, Myriophyllum spicatum, was used to

99%) without a specific disinfection step.

remove nutrients (Verhofstad et al., 2017). During the

The removal of nutrients from saline wastewater

testing period, an average of 17.0 mg N.m−2.d−1 and 2.7 mg

using vegetated CWs has also been studied. The study

P.m−2.d−1was sequestered via plant biomass. Also, for swine

evaluated how plant species, influent loads, and salinity

wastewater, a full-scale integrated CW (ICW) with a

influence the performance. The used wetland plants included

bioreactor and three wetland units was used to remove

Phragmites

Vetiveria

nitrogen from swine wastewater (Zhang et al., 2017). Two

zizanioides, and Canna indica. 100% N at both low and high

of the wetlands were vegetated with Myriophyllum

influent loads, and 10% and 93.8% of P at low and high

aquacticum and the other one was vegetated with Ipomoea

influent loads were removed by Canna indica. (Liang et al.,

aquatica, Zizania latifolia, and Nasturtium officinale. ICW

2017). In addition, different plants have been studied to

showed high N removal efficiency with average removal rate

remove not just nutrients from saline water but also to

of 98% for NH 4 +-N and 96% for total nitrogen, and it was

remove salt from high salinity wastewater. Jesus et al. (2017)

reported that the responsible development of functional

reported that Spartina maritima and Juncus maritimus are

microbial communities could contribute to efficient N

halophytic plants that could be used to enhance the removal

removal.

australis,

Typha

orientalis,

of nutrients in saline water; however, they demonstrated that

Vegetated

CWs

have

shown

proficient

salt removal with these plants might be impractical in future

performance in the treatment of domestic wastewater. Two

work.

with

of four wetlands were planted with Cyperus articulatus, a

Potamogeton crispus to enhance the performance of SFCW

Colombian native aquatic macrophyte, to evaluate the

at low temperature (Jian Zhang et al., 2017). NH 4 -N and TP

removal of dissolved organic matter and nitrogenous

treatment efficiency was higher in spring (between 80 and

compounds from domestic wastewater (Caselles-Osorio et

90%) and decreased during the summer. TP treatment

al., 2017). The other two wetlands remained unplanted and

performance

winter,

used as controls for the experiment. A removal efficiency of

confirming that SFCWs are being affected by climate

91% of organic matter was achieved from the planted

change; however, seasonal plant collocation has a potential

wetlands, which is higher than the 80% removal in unplanted

benefit to CWs.

wetlands. NH 4 +-N removal was significantly improved in

Phragmites

australis

increased

was

during

used

autumn

along

and

Three-stage pilot-scale surface flow CWs planted

planted systems, averaging 85% vs. 40% for unplanted

with Myriophyllum aquaticum were used to treat swine

systems (p < 0.05). Furthermore, Two pilot-scale

wastewater from a lagoon over three years. The results

intermittently operated HSSFCWs, one planted with Acorus


calamus and the other one with Phragmites australis were

(imidacloprid, range: