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The use of Bassia indica for salt phytoremediationin constructed wetlands

Oren Shelef a,1, Amit Gross b, Shimon Rachmilevitch a,*a French Associates Institute for Agriculture & Biotechnology of Drylands, The Jacob Blaustein Institutes for Desert Research,

Ben-Gurion University of the Negev, Midreshet Ben Gurion 84990, IsraelbZuckerberg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev,

Midreshet Ben Gurion 84990, Israel

a r t i c l e i n f o

Article history:

Received 7 December 2011

Received in revised form

22 April 2012

Accepted 13 May 2012

Available online 23 May 2012

Keywords:

Constructed wetland

Salt phytoremediation

Bassia indica

Desert

a b s t r a c t

The treatment and reuse of wastewater in constructed wetlands offers a low-cost, envi-

ronmentally-friendly alternative for common engineered systems. Salinity in treated

wastewater is often increased, especially in arid and semi-arid areas, and may harm crops

irrigated from wetlands. We have strong evidence that halophyte plants are able to reduce

the salinity of wastewater by accumulating salts in their tissues. Bassia indica is an annual

halophyte with unique adaptations for salt tolerance. We performed three experiments to

evaluate the capability of B. indica for salt phytoremediation as follows: a hydroponic

system with mixed salt solutions, a recirculated vertical flow constructed wetland (RVFCW)

with domestic wastewater, and a vertical flow constructed wetland (VFCW) for treating

goat farm effluents. B. Indica plants developed successfully in all three systems and reduced

the effluent salinity by 20e60% in comparison with unplanted systems or systems planted

with other wetland plants. Salinity reduction was attributed to the accumulation of salts,

mainly Na and K, in the leaves. Our experiments were carried out on an operative scale,

suggesting a novel treatment for green desalination in constructed wetlands by salt phy-

toremediation in desert regions and other ecosystems.

ª 2012 Elsevier Ltd. All rights reserved.

1. Introduction

1.1. Wastewater treatment

Water scarcity has led to the search for alternative water

resources. One solution is the recycling of wastewater (WW)

for irrigation. In Israel, for example, wide areas are irrigated

with treated wastewater, and more than 70% of sewage water

is recycled for agricultural use. Treated wastewater is rich in

nutrients for plants, but is also characterized by a higher

salinity than fresh water. The use of wastewater for irrigation

may reinforce soil salinization since the concentrations of the

dominant ions (Na, Ca, K and Cl) which create the overall

salinity are not reduced (Hillel, 2000).

The salinization of soil and water is a major global envi-

ronmental problem that may cause land degradation, reduc-

tion of water quality and detrimental effects to vegetation

(Schofield et al., 2001). Estimations by the United Nations

Environment Program suggest that 20% of agricultural land

and 50% of cropland in the world is salt-stressed (Flowers and

Yeo, 1995). Salinity in drylands is accelerated by strong sun

radiation and increased evapotranspiration. Larcher (1995)

* Corresponding author. Tel.: þ972 8 6563435; fax: þ972 8 6596742.E-mail addresses: shelefo@bgu.ac.il (O. Shelef), amgross@bgu.ac.il (A. Gross), rshimon@bgu.ac.il (S. Rachmilevitch).

1 Albert Katz International School for Desert Studies.

Available online at www.sciencedirect.com

journal homepage: www.elsevier .com/locate/watres

wat e r r e s e a r c h 4 6 ( 2 0 1 2 ) 3 9 6 7e3 9 7 6

0043-1354/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved.doi:10.1016/j.watres.2012.05.020

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suggested that the salinity rate of irrigated crops should not

exceed EC (electric conductivity) values of 2 dSm�1. The Israeli

Ministry of Environmental Protection determined, through

the Inbar committee, a level of 1.4 dS m�1 as the threshold for

unlimited use of water (Inbar, 2007).

Wastewater treatment is often based on biological systems

such as activated sludge or other engineered units in urban

areas. In rural areas, low-cost, environmentally-friendly

alternative treatments such as constructedwetlands (CW), are

more common. CWs are man-made planted systems that

utilize natural processes to improve water quality for human

benefit (Kadlec and Knight, 1996).

1.2. Role of plants in CWs

Most treatment processes that occur in CWs are driven by

chemical, physical and biological mechanisms. These mech-

anisms include oxidation, fragmentation, desorption, sedi-

mentation, microbial biodegradation and uptake (Vymazal,

2007). The role of plants in the CW cleaning process is not

clear (Imfeld et al., 2009; Stottmeister et al., 2003). Brix (1997)

suggested the following potential attributes of plants in

CWs: (1) increasing retention time by reducing water veloci-

ties; (2) improving hydraulic conductivity by root growth, and

(3) root activity. By utilizing elements such as (N) and phos-

phorus (P), plants may affect the elemental composition of

WW. In addition, plants can prevent odor nuisances, enhance

aesthetic appearance, provide surface area for microbial

growth, and be used as bioindicators for CW management

(Shelef et al., 2011). Plant involvement in nutrient cycling and

the exchange between water and sediment affects the water

and sediment quality (Barko et al., 1991; Biernacki and Doust,

1997; Catling et al., 1994; Petticrew and Kalff, 1992).

1.3. Phytoremediation

Phytoremediation is the use of plants for remedyingwater and

soil pollution. The treatment of heavymetals in contaminated

lands or water reservoirs has attracted most of the research

attention as it seems to be a promising technology to mitigate

pollution without excavation of the contaminants for

mechanical disposal (Salt et al., 1995a; Weis and Weis, 2004).

Another important target for phytoremediation is the treat-

ment of nutrients, mainly N and P (Singh et al., 2010). Raskin

et al. (1994) suggested the following three types of applica-

tion: 1) phytoextraction e when plants transport and

concentrate pollutants from the media to aboveground

harvestable shoots; 2) rhizofiltration - when plant roots store

elements used for the accumulation, precipitation and

concentration of contaminants; and 3) phytostabilization e

elimination of toxins through the stabilization of the growth

media by plants, without necessarily involving bio-

accumulation in plant tissues.

Several studies have offered means of reducing heavy

metal or other toxic contaminant concentrations (Chaney

et al., 1997; Rascio and Navari-Izzo, 2011; Schwitzguebel

et al., 2009). However, the volumes in which the experi-

ments were carried out were often too small to have any

implications in the practical world (Salt et al., 1995b; Weis and

Weis, 2004). Sklarz et al. (2009) showed that nutrient uptake

may not be significant in relation to water loads in a recircu-

lating vertical flow CW. In the last several years, attempts

have been made to use phytoremediation techniques to find

solutions for soil and water salinization.

1.4. Salt phytoremediation

This approach is based on plants that are especially tolerant to

salt environments. Around 1% of all plant species are halo-

phytes that can complete their life cycle in relatively high

saline environments, as much as 200 mM NaCl or more

(Flowers and Colmer, 2008; Waisel, 1972). Breckle (2002) clas-

sified halophytes as salt-excluders, salt-includers (i.e., Tam-

arix spp.) and salt-accumulators (as Atriplex spp.).

Phytostabilization can be practiced by all these classifications,

e.g., by growing halophytes on salt affected soils to halt soil

degradation (Keiffer and Ungar, 2002; Young et al., 2011).

However, for the purpose of water phytodesalination, salt-

includers are more suitable if they are able to accumulate

sodium in their tissues and reduce the media’s sodium

content and overall salinity. This amelioration of salinity has

been reported in soils (Carty et al., 1997; Hbirkou et al., 2011;

Rabhi et al., 2009; Ravindran et al., 2007; Zhao, 1991).

Bassia indica (Wight) A.J. Scott is an annual halophyte,

widespread on disturbed lands throughout Israel. B. indica

plants exhibit a unique phenomenon of “halotropism” in

which the root seems to search for high salinity in the soil to

enable better conditions for enhanced growth (Shelef et al.,

2010). B. indica was our candidate for salt phytoremediation

due to its following advantages: 1) tolerance for a wide

gradient of salinities; 2) fast growth rate in the summer (up to

9 kg DW (dry weight) in less than a year) that enables a high

uptake under increased evaporation (which increases soil

salinity); 3) accumulation of ions within tissues and not in

specified glands that can be washed easily by water; and 4) B.

indica can be easily removed at the beginning of the blooming

season to avoid seed dispersal.

In the current study, we addressed the problem of soil

salinization due to the use of treated WW that is often more

saline than freshwater, especially in desert environments.We

aimed at testing the potential to recruit halophyte plants for

salt phytoremediation in constructed wetlands. Our main

hypothesis was that halophyte plants can accumulate salts in

their leaves to a level that is high enough to reduce water

salinity in treated WW from CWs. More specifically, we asked

whether B. indica plants can be recruited for salt phytor-

emediation in constructed wetlands; how tolerable B. indica

plants are for the CW environment for differentWW solutions

and for salt solutions; and which elements are accumulated

and in which tissues of the plant.

2. Materials & methods

2.1. Establishment

B. indica seeds were collected in the central Negev highlands

near Midreshet Ben Gurion (30�510N, 34�470E), Israel. Seeds

were sprouted inside pots in a greenhouse, and then seedlings

were moved to hydroponic containers or to a growing

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medium. Established seedlings were planted in the CWs.

Initial DW/height of seedlings was w0.04 g/5 cm in the

hydroponic experiment and w1 g/25 cm in the CWs. The day

of planting was considered the first day of the experiment.

2.2. Experimental setup

The use of B. indica plants for water desalination was studied

in a controlled hydroponic system in a greenhouse and in two

field systems that are regarded here as case studies in oper-

ational scale. Different CWs exhibit different dynamics of

water flow, oxygenation and nutrient loadings. Therefore the

role of plants in CW is strongly affected from the CW

construction. For example, Vymazal (2011) stressed that the

role of plants in horizontal flow CWs (HFCWs) is significantly

different in comparison to their role in VFCWs. Therefore, to

broaden our impression of B. indica salt phytoremediation

abilities we tested it in different CW systems. In the first

system the plants were planted in a recirculating vertical flow

CW treating domestic wastewater, and in the second, they

were planted in a vertical flow CW treating agro wastewater,

as summarized in Table 1 and described below. Average daily

evaporation measured by a “Class A” evaporation pan in the

research area ranged between 2 mm in January and 8.6 in

June, and 8.4 mm in July. The potential evapotranspiration

(PET) calculated by the PenmaneMontieth equation reached

a maximum of 6.2 mm d�1 (Israel Meteorological Service). B.

indica plants with high surface area had relatively elevated

evapotranspiration as compared to evaporation without

plants. To test water balance we measured daily water loss in

the hydroponic containers.

2.3. Hydroponic solutions

B. indica plants were grown in 4 l buckets in a greenhouse for

48 days. Four solutions were used: freshwater (ECw1 dSm�1),

a mild saline solution (EC w5 dS m�1), an intermediate saline

solution (EC w8 dS m�1), and a hyper saline solution (EC

w16 dS m�1). The mild saline solution was ground saline

water, and the other solutions were artificially enriched with

salts to elevate the salinity while keeping the partial propor-

tions of each element in all systems (Table 1). All four solu-

tions were fertilized with a Long Ashton nutrient solution

(Hewitt, 1966; Ottow et al., 2005). Eight plants were planted in

each container with four containers per treatment as repli-

cations. Four containers were used as controls and did not

contain any plants in order to estimate physicochemical

effects such as precipitation and aeration. The control

included one container from each solution (EC w1 dS m�1,

w5 dSm�1,w8 dSm�1 andw16 dSm�1). Altogether we had 20

containers (4 replicates for 4 solutions plus 4 controls). Four

cycles of 10 days were used as repetitions in the control

containers. All twenty containers were aerated with small

aquarium air stones (See Fig. 6 in the supplementary data).

After an establishment period of 5 days the solutions in all

buckets were exchanged, and thereafter every 10 days. Water

was sampled before and after exchanges (approximately

every ten days). Water was added daily to compensate for

evaporation and transpiration losses within the containers.

Water additions were recorded to allow calculation of actual

evaporation and evapotranspiration.

2.4. Recirculating vertical flow CW (RVFCW)

Two identical RVFCWs that are used for treating domestic

WW in Midreshet Ben Gurion, Israel were used. The RVFCWs

are described in detail by Sklarz et al. (2009) and briefly in the

supplementary information (SI Fig. 7). Eighteen B. Indica plants

were planted in one RVFCW while the other was operated

without plants (SI Fig. 7). Plants were grown for 70 days

between July and September 2010. Samples of raw and treated

WW (from both systems) were collectedweekly in the evening

to ensure at least 8 h of treatment. Measurements of plant

growth were also conducted weekly for the duration of the

experiment. Daily global sun radiation was measured in the

Sde Boker Campus meteorology station, Department of Solar

Energy and Environmental Physics in collaboration with the

Israel Meteorological Service.

2.5. Vertical flow CW (VFCW)

The vertical flow CW was located in a boutique dairy farm

producing artisanal goat cheeses in the Negev highlands,

Israel (30�580N, 34�460E). The VFCW treats domestic WW from

a small restaurant and from goat cheese manufacturing. A

detailed description of the system is given in Travis and Gross

Table 1eOutline of three experimental setups for the study of salt phytoremediation by B. Indica that was conducted in thecentral Negev desert around Midreshet Ben Gurion, Israel.

Facility type Water resource Raw watersalinity (dS m�1)

Volume of treatedwater (L)

Volume treatedper day L/day

Plantsnumber

Final plant biomasstotal DWc (g)

Hydroponic

containers

4 artificial solutions 1,5,8,16 4 0.4 8 63

RVFCWa Domestic wastewater 0.9 500 300 18 2828

VFCWb

alternated

Domestic wastewater,

small restaurant and

goat cheese dairy

2.2 3000 2500 100 20,000

a RVFCW ¼ recirculating vertical flow constructed wetland.

b VFCW ¼ vertical flow constructed wetland.

c DW ¼ dry weight.

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(2012). Briefly, following an initial anaerobic treatment stage

WW flowed to one of two similar beds. Feed was alternated

between the two beds every seven days to allow periodic

drying to prevent clogging, control biomass growth, and

maintain aerobic conditions. Average flow to the VFCW was

2.6 m3 per day, fed in approximately 250e300 l batches

throughout the day. The size of each bed was 30 m2, and they

were constructed with locally available crushed limestone

sand and gravel with a total depth of 60 cm: an upper layer

(30 cm) of coarse sand and gravel mix (d10 0.4 mm; d60 3 mm),

underlain by two 15 cm layers of 1 and 3 cm diameter gravel,

respectively (SI Fig. 8). Both beds contained the water plants

Cana sp., Salvia ‘Indigo Spires’ andWedelia trilobata. In the first

experiment over 100 plants of B. indica were planted in March

2010 in the eastern bed and grown for 89 days until June 2010.

In the second experiment 100 seedlings of B. indica were

planted in the western bed for 92 days between July and

October 2010. Plant growth measurements and WW sampling

were carried out weekly. WW samples were taken from the

VFCW inlet and outlet (after treatment). Since only one bed

waswatered everyweek, the comparison between the B. indica

treatment and the control alternated accordingly.

2.6. Plant growth

To estimate plant growth, we used four different measures: 1)

shoot and root dry weight (DW) which was determined after

drying at 65 �C for 48 h; 2) shoot and root surface area (SA) was

measured by preparing digital images with a flat-bed scanner

(Epson Expression 10000 XL, Seiko Epson Corporation, Japan);

the images were analyzed using WinRhizo (WinRhizo Pro

v.2005b, Regent Instruments, Quebec, Canada); 3) basal stem

diameter; and 4) height. The first two measures were

destructive and, therefore, were used only in the hydroponic

experiment. Two plants were harvested from each container

periodically so that at the end of the experiment only two

plants grew in each bucket. Stem diameter and height were

measured weekly in the RVFCW and VFCW systems.

2.7. EC and elemental analysis

Water was sampled periodically before and after the treat-

ments. Electrical conductivity (EC) was measured in the lab in

50 ml centrifuge tubes (Corning inc., USA). 10 ml of WW were

kept at 4 �C for elemental analysis.

Samples were analyzed for EC using two EC meters (CON

510 conductivity/TDS bench meter, EUTECH Instruments,

Singapore, and a portable Multimeter MM 40, CRISON instru-

ments SA, Barcelona), and the averaged results were used.

Elemental analyses for both water and plant extracts were

carried out using an inductively coupled plasma (ICP) optical

emission spectrometer (Varian ICP720-OES, (Eaton et al.,

2005)). To execute elemental analysis on B. indica, we used

dry plants (65 �C for 48 h). The dried plant tissuewas ground to

powder and samples (0.25 g) were digested in a 5 ml acid

mixture of HClO4 and HNO3 (15:85% v/v) in digestion glass

tubes overnight. Digestion was completed by a gradual

increase of temperature from 60 �C to 195 �C according to Zhao

et al. (1994). The resulting extracts were then analyzed by

an ICP.

To estimate the element distribution in plant tissues, we

compared roots and shoots from hydroponic solutions. The

results were the averages of 80 measurements e 40 plants, 2

periods of w10 days of treatment (18e27 and 27e38 days). In

addition, we compared leaves and branches after 40 and 63

days of growth in the VFCW. These results represent an

average of 10 plants (5 plants from each date). Values for EC

and total dissolved solids (TDS) were converted using the

following equation (Lewis, 1980).

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2.8. Data analysis

The study was made up of three separate experiments with

different types of data sets. The data sets that fit the

requirements of statistical analysis were tested for a Gaussian

distribution with a ShapiroeWilk test. We used a parametric

Tukey procedure to test for significant differences if

a Gaussian distribution was detected. A nonparametric Man-

neWhitney U-test was used whenever the data set did not fit

the requirements of normal distribution. Calculations were

conducted with SAS 9.1 (SAS Institute, Cary, NC). We mention

the number of repetitions (n) and the statistical procedure that

was performed for each measurement.

3. Results

3.1. Plant growth

In the hydroponic system plants developed successfully in all

measured salinities, which ranged from an EC of 1 dS m�1 up

to 16 dS m1 (Fig. 1). Shoot and root biomass and surface area

were similar among all treatments. Overall, the average shoot

growth rate in the hydroponic system was 0.48 g/day with

a root: shoot ratio of 0.26 � 0.04.

Plants also developed successfully in the RVFCW with an

average shoot growth rate of 0.9 g/day. Average height was

150 cm, stem diameter 9.4 mm (Fig. 2), and average plant

biomass of 157 g DW. In the VFCW B. Indica plants grew

continuously, reaching an average of 226 cm height, 13.4 mm

stem diameter (Fig. 3), and average plant biomass of 244 g DW

(average shoot growth rate of 0.33 g/day). Since plant growth

was similar in both experiments in the VFCW, the results of

only the first experiment are given (Fig. 3). We measured six

developed plants in the field and found they can reach

a maximum of 9 kg DW, with an average of 4.7 kg DW per

shoot.

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3.2. Element distribution in plant tissues

Element accumulation in shoot was measured in all systems

(hydroponic, VFCW and RVFCW) to allow mass balance

calculations. However, since it was similar (Na 30e50 mg/

g DW; K 17e30mg/g DW; Ca 10e22mg/g DW) in all systemswe

relate here only to the hydroponic systems, where roots could

be analyzed and to VFCW where leaves were separated from

branches. Based on the results from the hydroponic system,

over 80% of the K, Ca and Na accumulated in the shoots and

less than 20% in the roots (Fig. 4A). These proportions were

similar over time from 27 to 48 days after the beginning of the

experiment (data not shown). Among shoot organs, more

accumulation was measured in the leaves as compared with

the branches (Fig. 4B). Nonetheless, these differences were

much smaller in comparison with the differences between

roots and shoots. Accumulation of Ca and Na in the shoots

branch tissues were 27 and 18%, respectively. Potassium was

distributed evenly between branches (48%) and leaves (52%).

Overall, it was estimated that 80% of the total Na

Fig. 2 e Shoot growth of B. indica grown in a recirculating

vertical flow constructed wetland (n [ 10 at a time). Full

circles and solid lines denote basal stem diameter; dashed

lines with empty triangles represent shoot height.

Fig. 1 e Shoot growth of B. indica in a hydroponic system;

dashed lines and empty symbols represent surface area;

full symbols and solid lines stand for dry weight. Plant

growth was similar in all salinities (n [ 8, p < 0.05).

Fig. 3 e Shoot growth of B. indica in a vertical flow

constructed wetland (n [ 10). Full circles and solid lines

denote basal stem diameter; dashed lines with empty

triangles represent shoot height.

Fig. 4 e A) Element distribution in plant tissues in the

hydroponic system; n [ 80 for each element; B) Element

distribution in plant tissues in the VFCW; n [ 10 for each

element.

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accumulation was allocated in the leaves, 13% in the woody

tissues of the canopy and only 7% in the roots. Regarding Ca,

64% was allocated in the leaves, 24% in the woody tissues and

12% in the roots. Potassium was distributed evenly in both

leaves and branches (80% accumulation) and only 17% in the

roots.

3.3. Effect of plants on salinity of inspected solution

The EC of water treated by B. indica was significantly reduced

comparedwith untreatedwater (Fig. 5AeC). In the hydroponic

system treatment with B. indica resulted in an EC decrease of

61.8% in tap water, 22.2% in saline water of 5 dS m�1 and

a decrease of 12.9% in the remaining two hyper saline solu-

tions (Fig. 5A). The average daily water loss was 110 ml in

occupied buckets, 28% higher than empty buckets with an

average of 86 ml daily evaporation. Unexpectedly, we noticed

a reduction in the EC in the control treatment ranging on

average from 6% to 9% in the different salinities, possibly due

to precipitation of some ions. Nevertheless, this reductionwas

significantly smaller than in the treated solutions.

In the RVFCW the effluent EC in the bed planted with B.

indica was lower (mean 0.84 dS m�1) than the inlet EC (mean

0.9 dSm�1), and usually higher in the control bed (0.95 dSm�1,

Fig. 5B). The maximal difference between the EC measured in

the control bed and in the treatment bed was on September

20. We thenmeasured an EC of 1.05 dS m�1 in the control bed,

28% higher than in the raw WW (0.82 dS m�1). At the same

time the EC in the B. indica treated WW was 0.75 dS m�1, 9%

lower than the inflow. Similar differences between treatments

were measured between the 4th and the 8th weeks of the

experiment where the EC of the control bed exceeded the

inflow EC and the salinity of the B. indica treated WW was

lower than the inflow salinity. At this time the growth of green

tissues of B. indica was at maximum (Fig. 2) and global radia-

tion was high (26e20 MJ per square meter).

A reduction in EC wasmeasured in the VFCW (Fig. 5C). The

reduction in EC was higher in the bed that was enriched with

B. indica plants, in comparison with the control bed that con-

tained only other plant species. The maximal EC reduction

(19.9%) was observed at the end of September, seven weeks

after planting. As described in themethods section, since each

week one bed was active and the other was resting, sampling

took place with a week’s difference between the control and

the B. indica planted bed.

3.4. Accumulation of elements in plants and their effectson water quality

The effect of B. indica plants on element concentrations in four

hydroponic solutions is presented in Table 2. To make sure

Fig. 5 e A) Average (±SE) change of electrical conductivity

(EC) in four different saline growing solutions after 10 d of

treatment with B. indica plants as compared with a control

where no plants were present (n [ 16). *denotes significant

differences ( p < 0.05) between values before and after

treatment. B) The percent EC change in the recirculating

vertical flow constructed wetland (RVFCW) effluent (of the

influent) treated by B. indica over time as compared with

the EC change in unplanted RVFCW (control). Daily global

sun radiation on the sampling days is given in the upper

graph in MJ/m2. C) The percent EC change in the VFCW

effluent (of the influent) treated by B. indica over time as

compared with the EC change in VFCW without B. indica

(control).

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that EC measurements were related to TDS (as determined by

the elemental analysis), we calculated TDS from themeasured

EC (Lewis, 1980) and found that it was similar. For example the

average TDS concentrations measured in the empty buckets

were 429, 2445, 4520 and 10939 mg/l compared to 442, 2581,

4378 and 9885 mg/l average calculated TDS. In the tap water

solution (EC ¼ 1 dS m�1), the plants reduced concentrations of

all the measured elements by 12e85%. P was an exception e it

was reduced by 91%, but taking into account a similar reduc-

tion in the control buckets resulted in an insignificant effect of

the plants in all solutions. Concentrations of Na, Ca, Mg, Fe, S

and microelements were also reduced in the high salinities

(EC ¼ 8 and 16 dS m�1), but to a smaller magnitude (only

w10%). K and P were reduced by 50e90% in all four solutions.

Table 3 presents the total accumulation of elements in B.

indica shoots at the end of the experiment. Accumulation of

Na per g DW was 3.1 higher in the most hyper saline solution

(EC ¼ 16 dS m�1) in comparison with the tap water. For K and

Mg the accumulation increased by 1.7 fold. Ca, Fe, P and S

accumulation reached tissue capacity under tap water and

remained the same with higher salinities.

Table 4 presents the concentration of elements per gained

shoot biomass in comparison with the pretreated solution.

During 10 days of growth plants gained a total of 3.2 g shoot

biomass in the fresh water treatment, 3.5 g 1.7 g and 1.4 g in

the 5, 8 and 16 dS m�1 solutions, respectively. This gained

biomass times the measured concentration per gram DW

shoot (Table 4) is the framework for our estimations of the

capability of B. indica to reduce element concentration in

solutions of different salinity. The most prominent effects

include 35% reduction of Na concentration in the tap water

solution within 10 days, 56% reduction of K, 25% of Mg and

reductions of P and K in all solutions.

3.5. Sodium mass balance

Sodiummass balance in the hydroponic solutions and RVFCW

was conducted and recoveries were acceptable, ranging from

81 to 116% (Table 5). In the hydroponic experiment, accumu-

lation of Na in plants ranged from 2% in the highest salinity to

43% in the lowest. In the RVFCW it was estimated that 730.8 g

Na was introduced into the CW during the experiment and B.

indica plants accumulated in total 66.6 g of Na suggesting over

a 9% reduction. In the control RVFCW, Na concentration was

increased most likely because of evaporation in the summer

time (Fig. 5B). This coincidewith the observations of enhanced

evapotranspiration from the hydroponic study in which the

total water loss measured in the planted containers was up to

30% greater in comparison to evaporation from the empty

containers (controls).

4. Discussion

Seedlings of B. indica exhibited tolerance for a wide range of

mixed salt solutions, completing their life cycle in all solutions

in all three systems (Figs. 1e3). The growth of a xerophyte in

hydroponic systems and particularly in a CW is not obvious,

as this environment is extremely different from their natural

habitat. This wide range of tolerance may be attributed to the

firmness of halophytes that are especially adapted to extreme

environments (Manousaki and Kalogerakis, 2011). Our exper-

iments showed that not only can water plants be used as

macrophytes in CWs, but also other terrestrial plants,

provided that they survive the specific conditions. This may

broaden the services that plants provide in CWs. B. indica grew

to a maximum of 244 g DW in a VFCW in 89 days. However,

potentially they can grow as much as 30 times more. This

limited growth may be explained by: 1) a relatively short

Table 2 e Concentrations of elements in hydroponic solutions. Raw and treated represent concentration in solution beforeand after treatment with B. indica (mg/l); D [ change of concentration during treatment (%) after compensating for thebackground change that was measured in the control buckets. All significant changes are marked in bold.

Salinity of growingsolution EC (dS m�1)

Na K Ca Mg

Raw Treated D Raw Treated D Raw Treated D Raw Treated D

1 51.3 25.4 L51% 31.2 0.9 L85% 67.3 27.2 L12% 20.6 6.4 L57%

5 661.3 545.5 L12% 50.9 13.6 L66% 177.0 180.7 24% 86.3 99.1 24%

8 1229.4 1022.9 L9% 72.9 19.5 L64% 328.2 255.8 L2% 174.2 140.1 L11%

16 3067.4 2409.9 L13% 138.3 65.0 L42% 737.0 570.0 L8% 428.6 320.6 L18%

Fe P S

Raw Treated D Raw Treated D Raw Treated D

1 0.3 0.1 L24% 17.0 1.5 L1% 29.9 18.3 L21%

5 0.3 0.2 L15% 9.2 4.4 37% 183.1 144.7 L10%

8 0.5 0.4 L11% 11.0 3.1 22% 175.3 133.7 L8%

16 0.8 0.6 L10% 12.8 4.5 30% 172.2 134.5 L6%

Table 3 e Element accumulation in shoots of B. indicagrowing in hydroponic solutions. Values in mg per g DWof plant shoot ±se (n [ 24).

Salinity of growingsolution EC (dS m�1)

Na K Ca

1 22.2 � 0.7 21.7 � 0.8 12.9 � 0.5

5 46.6 � 2.6 31 � 0.7 19.4 � 0.8

8 47.2 � 1.5 33.6 � 1.1 13.2 � 0.5

16 69.2 � 1.4 37.5 � 1.3 16.9 � 0.5

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growth time (only 90 days or less, compared with about 200

days in the wild); 2) disturbances such as a non-contiguous

water supply and interspecies competition (in the VFCW);

and 3) malnutrition. Whatever the cause, the phytor-

emediation potential of B. indica may be much higher than it

appears in our experiments.

Testing the ability of B. indica to reduce the salinity of WW

in CWs resulted in promising findings. Vymazal (2007) sug-

gested that due to poor ventilation plant uptake is low in sub-

surface CWs. Our findings stand in contradiction to this

conclusion. We found a significant reduction of EC in solu-

tions that were treated with B. indica plants (Fig. 5AeC). This

reduction was limited to mild salinities lower than 5 dS m�1.

Plants did not reduce WW salinity below the agriculture

threshold for use (1.4 dS m�1); meaning that salt phytor-

emediation as we constructed it cannot stand alone for salt

susceptible and non-tolerant crops.

In the hydroponic system we measured a small reduction

in ions in the empty containers. We explain this reduction by

the inevitable addition of diluted water to the buckets due to

evaporation and by physicoochemical processes. The reduc-

tion of EC in the treated RVFCW was highest between August

and September. One might claim this reduction is not caused

by plant salt accumulation, butmerely by the shade effect that

reduces evaporation in comparison to the empty RVFCW.

However, the evapotranspiration in the treated RVFCW

exceeded the transpiration effect in the control system.

Moreover, we found a reduction of EC in the VFCW in which

the control pool was not empty, but planted with other

species. In this case both evaporation and transpiration did

not differ greatly between treatment and control, and salt

phytoremediation by B. indica plantswas the direct cause of EC

reduction.

To track the allocation of salts in B. indica plants, we

measured their concentrations in different plant tissues. The

results showed that salts accumulated primarily in the upper

parts of the plants,mainly in the leaves (Fig. 4A). These results

explain the decrease in EC reduction in the RVFCW (Fig. 5B)

towards the end of the experiments, when B. indica started

blooming, the leaves shrunk and some fell, so that the accu-

mulation potential of the plant was diminished. The practical

implication is that B. indicia plants are most effective at their

initial stages of growth, when most of the shoot biomass is

composed of green tissues.When the shoots becomewoodier,

Table 4e Element concentration in solution and accumulation in plants in hydroponic solutions.Water[ concentration ofan element in solution prior to treatment with B. indica (mg/l); plant[ accumulation of an element in B. indica shoot relatedto the biomass that was gained during 10 days of growth (mg/gained gDW/l); reduction [ potential reduction of anelement’s concentration during 10 days of treatment. Prominent reductions are bold marked.

Salinity Na K Ca

EC (dS m�1) Water Plant Reduction Water Plant Reduction Water Plant Reduction

1 51.3 17.9 35% 31.2 17.5 56% 67.3 10.4 15%

5 661.3 40.5 6% 50.9 26.9 53% 177.0 16.9 10%

8 1229.4 19.8 2% 72.9 14.0 19% 328.2 5.5 2%

16 3067.4 23.6 1% 138.3 12.8 9% 737.0 5.8 1%

Mg Fe P S

Water Plant Reduction Water Plant Reduction Water Plant Reduction Water Plant Reduction

20.6 5.1 25% 0.3 0.07 26% 17.0 3.8 22% 29.9 3.5 12%

86.3 9.5 11% 0.3 0.08 24% 9.2 7.0 76% 183.1 3.8 2%

174.2 3.6 2% 0.5 0.04 7% 11.0 2.4 22% 175.3 1.9 1%

428.6 3.7 1% 0.8 0.03 4% 12.8 2.0 16% 172.2 1.4 1%

Table 5 e Sodium mass balance in hydroponic setup and field scale recirculating vertical flow constructed wetland(RVFCW).

Treatment WW ECdS m�1

aInitial Na contentin solution g

bFinal Na contentin solution g

cNa accumulationby plants g (% initial)

Recovery %

Hydroponic 1 0.21 0.1 0.09 (43) 85

Hydroponic 5 2.65 2.2 0.18 (7) 89

Hydroponic 8 4.92 4.1 0.16 (3) 86

Hydroponic 16 12.27 9.6 0.28 (2) 81

RVFCW treated 0.9 730.8 641 66.6 (9) 97

RVFCW control 0.9 730.8 848 No plants 116

a Na concentration in the initial solution.

b Na concentration in the treated solution (g/l) � the solution volume (l).

c Na accumulation in plants was calculated as Na content in plant (mg/g DW) � total plant DW. The values in parenthesis represent percent

accumulation of Na by the plants.

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they lose their main accumulative tissues, so in the blooming

period plants should be removed.

Another practical question that arises regards what

a farmer should dowith the removed plants. Although beyond

the scope of this article, it would beworth considering B. indica

as an energy source as it produces a significant biomass in

a short time. Several authors showed that B. indica or its

relatives Kochia spp. are a fine food additive resource for sheep

and lambs with regard to palatability and nutrition (Kafi et al.,

2010; Kafi and Jami Al Ahmadi, 2008).

Concentrations of Na per g DW of shoot increased with the

higher salinity of the hydroponic solution (Table 3). This

increase was not high enough to create a significant accu-

mulation effect in relation to Na reduction in the high salin-

ities (Table 4). We conclude that the B. indica effects on Na

reduction are limited to medium and low salinities. K

concentrations in the shoots increased two fold with higher

salinities (Table 3), yet the impact of B. indica on K in hyper

salinity decreased (Table 2). It seems that the high salinities

are beyond B. indica’s capacity to create a significant accu-

mulation effect for salt phytoremediation. Yet the accumu-

lative potential of B. indica is very high.

Summing up the accumulation of the dominant elements

(Table 3 and other elements) showed that in solutions of 1, 5, 8

and 16 dSm�1, B. indica plants accumulated salts up to 7, 11, 12

and 14%, of their DW, respectively. These amounts are

expected to be even higher since our results do not include

important elements such as Cl. Given that B. indica plants can

grow to about 1 kg DW in the first stages of their growth and

potentially accumulate salts to about 10% of their DW, we

estimate that a single plant can remove during its lifetime

approximately 100 g of salts. Based on our experience with

different volumes and salinities, we estimate that accumula-

tion of salts by B. indica can reduce salinities up to 20% of the

initial EC in low salinities (up to 2 dS m�1). An individual plant

can treat approximately 500 L of WW during its growth. Our

results showed that a high leaf: woody tissue ratio is corre-

lated to improved salt phytoremediation by B. indica. There-

fore, plants can be cultivated for a high leaf index. The

preferred time for recruiting B. indica for salt phytor-

emediation in CWs is during the early summer (MayeJuly).

Further research is needed to improve this use by agricultural

management, including subjects such as pruning, re-

plantation, cultivation, fertilization and synergism with

additional species.

5. Conclusions

The current study has demonstrated a novel strategy for green

desalination through salt phytoremediation in CWs. B. Indica

plants tolerated a wide range of salinities and accumulated

salts. Accumulation occurred mainly in leaves and branches,

making B. Indica fit for the phytoextraction of Na and other

elements. Na and Kwere the dominant accumulated elements

driving the salinity reduction. B. indica is a good candidate for

salt phytoremediation in CWs due to its rapid and large

annual growth. Optimization of the plant performance in

terms of growth and salt accumulation is needed to further

improve its efficiency.

Acknowledgments

The authors would like to thank Ms. Tanya Gendler for

assisting with the laboratory and field work, Dr. Ludmila Katz

for her part in the elemental analysis, Daniel & Anat Korn-

mehl for letting us work in their farm, Dr. Menahem Sklarz for

his help in the operation of the RVFCW and Dr. Micheal Travis

for the collaboration in the VFCWandmanuscript editing. The

research was partly supported by the Koshland Foundation.

Appendix A. Supplementary material

Supplementary data associated with this article can be found,

in the online version, at doi:10.1016/j.watres.2012.05.020.

r e f e r e n c e s

Barko, J.W., Gunnison, D., Carpenter, S.R., 1991. Sedimentinteractions with submersed macrophyte growth andcommunity dynamics. Aquatic Botany 41, 41e65.

Biernacki, M., Doust, J.L., 1997. Vallisneria americana(Hydrocharitaceae) as a biomonitor of aquatic ecosystems:comparison of cloned genotypes. American Journal of Botany84, 1743e1751.

Breckle, S.W., 2002. Salinity, halophytes and salt affected naturalecosystems. In: Salinity: Environment e Plants e Molecules.Kluwer Academic Publishers, The Netherlands, pp. 53e77.

Brix, H., 1997. Do macrophytes play a role in constructedtreatment wetlands? Water Science and Technology 35,11e17.

Carty, D.T., Swetish, S.M., Crawley, W.W., Priebe, W.F., 1997.Major variables influencing technology solution forremediation of salt affected soils. In: Proceedings of the RockyMountain Symposium of Environmental Issues in Oil and GasOperations; Cost Effective Strategies. olorado School of Mines,Golden, CO, pp. 145e152.

Catling, P.M., Spicer, K.W., Biernacki, M., Doust, J.L., 1994. Thebiology of Canadian weeds.103. Vallisneria americana Michx.Canadian Journal of Plant Science 74, 883e897.

Chaney, R.L., Malik, M., Li, Y.M., Brown, S.L., Brewer, E.P.,Angle, J.S., Baker, A.J.M., 1997. Phytoremediation of soilmetals. Current Opinion in Biotechnology 8, 279e284.

Eaton, A.D., Clesceri, L.S., Rice, E.W., Greenberg, A.E.,Franson, M.A.H.A., 2005. American Public Health Association(APHA) 2005, Standard Methods for the Examination of Water& Wastewater, twenty first ed. American Public HealthAssociation, American Water Works Association, WaterEnvironment Federation, USA, Washington.

Flowers, T.J., Colmer, T.D., 2008. Salinity tolerance in halophytes.New Phytologist 179, 945e963.

Flowers, T.J., Yeo, A.R., 1995. Breeding for salinity resistance incrop plants: where next? Australian Journal of PlantPhysiology 22, 875e884.

Hbirkou, C., Martius, C., Khamzina, A., Lamers, J.P.A., Welp, G.,Amelung, W., 2011. Reducing topsoil salinity and raisingcarbon stocks through afforestation in Khorezm, Uzbekistan.Journal of Arid Environments 75, 146e155.

Hewitt, E.J., 1966. Sand and Water Culture Methods Used in theStudy of Plant Nutrition. In: Technical Communication No. 22.Commonwealth Bureau, London.

wat e r r e s e a r c h 4 6 ( 2 0 1 2 ) 3 9 6 7e3 9 7 6 3975

Author's personal copy

Hillel, D.S., 2000. Salinity Management for Sustainable Irrigation:Integrating Science, Environment, and Economics. WorldBank Publications, Washington, D.C., USA.

Imfeld, G., Braeckevelt, M., Kuschk, P., Richnow, H.H., 2009.Monitoring and assessing processes of organic chemicalsremoval in constructed wetlands. Chemosphere 74, 349e362.

Inbar, Y., 2007. New standards for treated wastewater reuse inIsrael. In: Zaidi, M. (Ed.), Wastewater ReuseeRisk Assessment,Decision-Making and Environmental Security. Springer,Dordrecht, The Netherlands,, pp. 291e296.

Kadlec, R.H., Knight, R.L., 1996. Treatment Wetlands. CRC Press,Boca Raton, Florida.

Kafi, M., Asadi, H., Ganjeali, A., 2010. Possible utilization of high-salinity waters and application of low amounts of water forproduction of the halophyte Kochia scoparia as alternativefodder in saline agroecosystems. Agricultural WaterManagement 97, 139e147.

Kafi, M., Jami Al Ahmadi, M., 2008. Study of Kochia (Kochiascoparia) as a forage crop. In: Abdelly, C., Ozturk, M.,Ashraf, M., Grignon, C. (Eds.), Biosaline Agriculture and HighSalinity Tolerance. Birkhauser, Basel, Switzerland,pp. 177e195.

Keiffer, C.H., Ungar, I.A., 2002. Germination and establishment ofhalophytes on brine-affected soils. Journal of Applied Ecology39, 402e415.

Larcher, W., 1995. Plants under stress. In: Larcher, W. (Ed.),Physiological Plant Ecology, third ed. Springer-Verlag, Berlin,Germany, pp. 321e432.

Lewis, E.L., 1980. The practical salinity scale 1978 and itsantecedents. IEEE Journal of Oceanic Engineering 5, 3e8.

Manousaki, E., Kalogerakis, N., 2011. Halophytes present newopportunities in phytoremediation of heavy metals and salinesoils. Industrial & Engineering Chemistry Research 50,656e660.

Ottow, E.A., Brinker, M., Teichmann, T., Fritz, E., Kaiser, W.,Brosche, M., Kangasjarvi, J., Jiang, X.N., Polle, A., 2005. Populuseuphratica displays apoplastic sodium accumulation, osmoticadjustment by decreases in calcium and solublecarbohydrates, and develops leaf succulence under salt stress.Plant Physiology 139, 1762e1772.

Petticrew, E.L., Kalff, J., 1992. Water-flow and clay retention insubmerged macrophyte beds. Canadian Journal of Fisheriesand Aquatic Sciences 49, 2483e2489.

Rabhi, M., Hafsi, C., Lakhdar, A., Hajji, S., Barhoumi, Z.,Hamrouni, M.H., Abdelly, C., Smaoui, A., 2009. Evaluation ofthe capacity of three halophytes to desalinize theirrhizosphere as grown on saline soils under nonleachingconditions. African Journal of Ecology 47, 463e468.

Rascio, N., Navari-Izzo, F., 2011. Heavy metal hyperaccumulatingplants: how and why do they do it? And what makes them sointeresting? Plant Science 180, 169e181.

Raskin, I., Kumar, P.N., Dushenkov, S., Salt, D.E., 1994.Bioconcentration of heavy metals by plants. Current Opinionin Biotechnology 5, 285e290.

Ravindran, K.C., Venkatesan, K., Balakrishnan, V.,Chellappan, K.P., Balasubramanian, T., 2007. Restoration ofsaline land by halophytes for Indian soils. Soil Biology &Biochemistry 39, 2661e2664.

Salt, D.E., Blaylock, M., Kumar, N.P.B.A., Dushenkov, V.,Ensley, B.D., Chet, I., Raskin, I., 1995a. Phytoremediation e

a novel strategy for the removal of toxic metals from theenvironment using plants. Bio-Technology 13, 468e474.

Salt, D.E., Prince, R.C., Pickering, I.J., Raskin, I., 1995b.Mechanisms of cadmiummobility and accumulation in Indianmustard. Plant Physiology 109, 1427e1433.

Schofield, R., Thomas, D.S.G., Kirkby, M.J., 2001. Causal processesof soil salinization in Tunisia, Spain and Hungary. LandDegradation & Development 12, 163e181.

Schwitzguebel, J.P., Kumpiene, J., Comino, E., Vanek, T., 2009.From green to clean: a promising and sustainable approachtowards environmental remediation and human health forthe 21(st) century. Agrochimica 53, 209e237.

Shelef, O., Golan-Goldhirsh, A., Gendler, T., Rachmilevitch, S.,2011. Physiological parameters of plants as indicators of waterquality in a constructed wetland. Environmental Science andPollution Research.

Shelef, O., Lazarovitch, N., Rewald, B., Golan-Goldhirsh, A.,Rachmilevitch, S., 2010. Root halotropism: salinity effects onBassia indica root. Plant Biosystems 144, 471e478.

Singh, G., Bhati, M., Rathod, T., 2010. Use of tree seedlings for thephytoremediation of a municipal effluent used in dry areas ofnorth-western India: plant growth and nutrient uptake.Ecological Engineering 36, 1299e1306.

Sklarz, M.Y., Gross, A., Yakirevich, A., Soares, M.I.M., 2009. Arecirculating vertical flow constructed wetland for thetreatment of domestic wastewater. Desalination 246, 617e624.

Stottmeister, U., Wiessner, A., Kuschk, P., Kappelmeyer, U.,Kastner, M., Bederski, O., Muller, R.A., Moormann, H., 2003.Effects of plants and microorganisms in constructed wetlandsfor wastewater treatment. Biotechnology Advances 22,93e117.

Travis, M.J.N.W., Gross, A., 2012. Decentralized wetland-basedtreatment of oil-rich farm wastewater for reuse in an aridenvironment. Ecological Engineering 39, 81e89.

Vymazal, J., 2007. Removal of nutrients in various types ofconstructed wetlands. Science of the Total Environment 380,48e65.

Vymazal, J., 2011. Plants used in constructed wetlands withhorizontal subsurface flow: a review. Hydrobiologia 674,133e156.

Waisel, Y., 1972. Biology of Halophytes. Academic Press, NewYork.Weis, J.S., Weis, P., 2004. Metal uptake, transport and release by

wetland plants: implications for phytoremediation andrestoration. Environment International 30, 685e700.

Young, M.A., Rancier, D.G., Roy, J.L., Lunn, S.R., Armstrong, S.A.,Headley, J.V., 2011. Technical note: seeding conditions of thehalophyte Atriplex patula for optimal growth on a saltimpacted site. International Journal of Phytoremediation 13,674e680.

Zhao, F., Mcgrath, S.P., Crosland, A.R., 1994. Comparison of 3 wetdigestion methods for the determination of plant sulfur byinductively-coupled plasma-atomic emission-spectroscopy(Icpaes). Communications in Soil Science and Plant Analysis25, 407e418.

Zhao, K.F., 1991. Desalinization of saline soils by Suaeda-Salsa.Plant and Soil 135, 303e305.

wat e r r e s e a r c h 4 6 ( 2 0 1 2 ) 3 9 6 7e3 9 7 63976