Abstract

In this study, the potential of floating treatment wetlands (FTWs), inoculated with selected bacteria, to ameliorate polluted river water was evaluated. Floating cells were prepared by vegetating plants, Typha domingensis and Leptochloa fusca, on a floating mat. The plants were inoculated with three different pollutant-degrading rhizospheric and endophytic bacterial strains. Significantly greater decrease in chemical oxygen demand (COD), biochemical oxygen demand (BOD5) and total organic carbon (TOC) was observed in inoculated FTWs than in the wetlands without bacterial inoculation. However, a slight decrease in pH and EC was seen in most of the treatments. The total nitrogen (TN), nitrate and total phosphorus (TP) contents decreased to 1.77 mg/L, 0.80 mg/L and 0.60 mg/L, respectively. Additionally, the concentration of iron (Fe), nickel (Ni), manganese (Mn), lead (Pb), and chromium (Cr) in the water lowered to 0.41, 0.16, 0.10, 0.25, and 0.08 mg/L, respectively. Overall the performance of T. domingensis was significantly better than L. fusca. The treated effluents meet the water quality guidelines for irrigation and aquatic life. This study revealed that FTWs supplemented with selective bacteria are a promising approach for the restoration and management of polluted river water.

INTRODUCTION

Rivers, originated through the evolutionary process of the earth, are closely related to human civilization. Rivers play an important role in human life by providing myriads of benefits such as shipping, electricity generation, water supply, food and agricultural production (Allan & Castillo 2007; Pan et al. 2012). However, rapid industrialization, agriculture and urbanization have intensified the exploitation of rivers leading to degradation of water quality (Pan et al. 2016). This situation has made it imperative to devise strategies to mitigate such river water degradation. Conventional technologies can be used for remediation of polluted river water but these methods are not perfectly efficient because of economic reasons and technological complexities (Zhao et al. 2012).

Floating treatment wetland (FTW), an innovative approach, offers a practical solution for treatment of polluted river water (Faulwetter et al. 2011; Zhao et al. 2012; Ijaz et al. 2015). A FTW is composed of vegetative plants on a floating mat through which the roots grow and hang within the water column. It depicts properties of both pond and conventional wetlands as it is an inventive combination of these technologies (Headley & Tanner 2008a; Kadlec & Wallace 2008). It can be installed in any pond or river without digging, earth moving or additional land acquisition and does not reduce the storage volume of the water body (Headley & Tanner 2012; Winston et al. 2013). The ability of FTW to withstand water fluctuation and inundation makes it perfect for its application in pond and river systems (Headley & Tanner 2008b). In addition to that, installation of FTW in water bodies also provides habitat for wildlife such as fish, invertebrates and birds (Mietto et al. 2013; White & Cousins 2013; Keizer-Vlek et al. 2014).

In FTW, organic matter, nitrogen and phosphorus are removed by plant–bacteria interactions through decomposition, assimilation, denitrification, sorption, entrapment in roots and finally sedimentation (Wang & Sample 2014; Ijaz et al. 2016a). The roots of plants absorb nutrients directly from the surrounding water and provide support for the attached microbial community (Zhang et al. 2016; Ashraf et al. 2018a). Biofilm on roots and endophytes within the aerial tissue of plants boosts up the decontamination process of wastewater (Weyens et al. 2013; Shehzadi et al. 2014; Ijaz et al. 2015). Bacteria degrade complex organic pollutants, assimilate nitrogen and phosphorus and reduce concentrations of nitrate, phosphate and heavy metals in polluted water by their metabolic and non-metabolic processes (Afzal et al. 2014; Ijaz et al. 2016b; Arslan et al. 2017). Rhizospheric and endophytic bacteria also promote plant growth and surge the resistance to biotic and abiotic stresses (Afzal et al. 2012; Fatima et al. 2015).

Although FTWs have been successfully used in mitigating the pollution load of river waters (Zhao et al. 2012; Fang et al. 2016; Pan et al. 2016), the plant–bacteria synergism in FTWs has not been evaluated for the maximum remediation of polluted river water. The objective of our study was to evaluate the effect of inoculation of bacteria in FTWs on the restoration of polluted river water quality. The water was analysed to meet national irrigation water quality standards. Bacterial persistence was monitored in the water and in the roots and shoots of the plants.

MATERIALS AND METHODS

River water collection

The Ravi River is 725 km long with annual average flow rate of 1,813 million m3. In Lahore district a 72 km stretch of the Ravi River is located. This part of the river has been changed into a sludge drain due to indiscriminate disposal of untreated municipal and industrial effluent (Azfar et al. 2018). To prepare a true mixture, water samples were collected from various points of the river during the month of March 2017. The water samples were analysed for various physico-chemical parameters and heavy metals (Table 1) by using the standard methods (APHA 2012).

Table 1

Characteristics of polluted river water collected from Ravi River, Lahore, Pakistan

ParameterValueWater quality guidelines*
IrrigationFish/aquatic life
pH 8.5 (0.1) 6.5–8.4 6.5–8.5 
EC (mS/cm) 2.3 (0.04) 15 15 
TSS (mg/L) 290 (4.5) NG NG 
COD (mg/L) 405 (6.2) NG NG 
BOD (mg/L) 190.33 (5.5) NG 
TOC (mg/L) 110.00 (2.0) NG NG 
TN (mg/L) 37.47 (1.1) NG NG 
NO3−1 (mg/L) 33.33 (1.5) NG NG 
TP (mg/L) 2.63 (0.1) NG NG 
Fe (mg/L) 1.53 (0.1) 5.0 0.3 
Ni (mg/L) 0.54 (0.01) 0.20 0.05 
Mn (mg/L) 0.85 (0.02) 0.20 0.1 
Pb (mg/L) 0.83 (0.06) 0.1 0.01 
Cr (mg/L) 0.36 (0.02) 0.01 0.05 
ParameterValueWater quality guidelines*
IrrigationFish/aquatic life
pH 8.5 (0.1) 6.5–8.4 6.5–8.5 
EC (mS/cm) 2.3 (0.04) 15 15 
TSS (mg/L) 290 (4.5) NG NG 
COD (mg/L) 405 (6.2) NG NG 
BOD (mg/L) 190.33 (5.5) NG 
TOC (mg/L) 110.00 (2.0) NG NG 
TN (mg/L) 37.47 (1.1) NG NG 
NO3−1 (mg/L) 33.33 (1.5) NG NG 
TP (mg/L) 2.63 (0.1) NG NG 
Fe (mg/L) 1.53 (0.1) 5.0 0.3 
Ni (mg/L) 0.54 (0.01) 0.20 0.05 
Mn (mg/L) 0.85 (0.02) 0.20 0.1 
Pb (mg/L) 0.83 (0.06) 0.1 0.01 
Cr (mg/L) 0.36 (0.02) 0.01 0.05 

*Water Quality Guidelines for Pakistan proposed by World Wide Fund for Nature, Pakistan (WWF 2007). Standard deviations are presented in parentheses. NG: not given in the list.

Bacterial strains

Previously isolated three bacterial strains were used in this study. The bacterial strain, Bacillus cerus, was isolated from the rhizosphere of Cyperus laevigatus. The other two bacterial strains, Aeromonas salmonicida and Pseudomonas gessardii, were isolated from root interiors and the rhizosphere of T. domingensis, respectively (Fatima et al. 2015). These bacterial strains were cultivated in Luria–Bertani (LB) broth at 37 °C, 120 rpm, for 24 h. Bacterial cells were harvested by centrifugation at 4 °C, 10,000 rpm for 10 minutes. The harvested cells were re-suspended in 0.9% (w/v) NaCl solution and their optical density (OD) was adjusted to 0.7 at 600 nm. These suspended cells of the strains were mixed together to get a bacterial consortium.

Plants

Two macrophtyes, Typha domingensis and Leptochloa fusca, were selected for this study. Both plants have worldwide distribution and are capable of coping with harsh environmental conditions. Typha domingensis, commonly known as southern cattail, is a tall, perennial herbaceous plant widely distributed throughout temperate and tropical regions. This plant is highly adapted to extensively fluctuating water levels (Hegazy et al. 2011). Leptocloa fusca, commonly known as kallar grass, is a tufted perennial grass with spongy stems. It is frequently found in wetlands, and brackish and salty marshes. It is also best known for its ability to withstand the stress conditions of saline and sodic soils (Akhter et al. 2004).

Formation of FTWs and experimental design

To prepare the FTW cells, polyethylene tanks (35.5 × 30.5 × 21.5 cm) were used to store water. A floating mat (33 × 28 × 7.6 cm) was prepared from the closed cell polyethylene foam. Five holes of 5 cm diameter were made in each floating mat to provide anchorage to macrophytes. The borders of the floating mats were properly covered with aluminium foil (Figure 1).

Figure 1

Formation of floating treatment wetlands and experimental setup.

Figure 1

Formation of floating treatment wetlands and experimental setup.

One seedling of T. domingensis or ten cuttings of L. fusca were placed in each hole of the mat supported with coconut shaving and the remaining spaces were filled with soil, sand and gravel. The floating mats were transferred to a polyethylene tank filled with fresh water for 4 weeks to let the plants grow to appropriate size. After 30 d, the vegetated mats were shifted to tanks filled with 15 L of polluted water of the Ravi River, and inoculated with 100 mL bacterial consortium. The water was treated for 96 h. Each treatment had three replicates (e.g. T1R1, T1R2, and T1R3) and the experiment was conducted in triplicates with three batches of polluted water. Six different treatments were designed as below:

T1: Vegetation of Typha domingensis in polluted river water

T2: Vegetation of Typha domingensis in polluted river water with bacterial inoculation

T3: Vegetation of Leptochloa fusca in polluted river water

T4: Vegetation of Leptochloa fusca in polluted river water with bacterial inoculation

T5: Only bacterial inoculation in polluted river water

C: Polluted river water without vegetation and bacterial inoculation.

Water sampling and analysis

During the experiment, water samples were collected from each floating wetland cell every 24 h and stored in sterilized polyethylene bottles at 4 °C. Total suspended solid (TSS), TN, nitrate (NO3), and TP were analysed by the standard methods (APHA 2012). Chemical oxygen demand, BOD5 and TOC were analysed by method 5220D (Closed Reflux, Colorimetric Method), 5210B (5-Day BOD Test), and 5310D (Wet-Oxidation Method), respectively (APHA 2012). Samples for heavy metals analysis were prepared by nitric acid digestion (method 3030 E) (APHA 2012) and analysed by atomic absorption spectroscopy. To assess the extent of improvement in the quality of polluted river water after treatment by FTWs, a fish toxicity test was performed at the end of the experiment as described earlier (Afzal et al. 2008; Rehman et al. 2018).

Determination of inoculated bacteria

In order to analyse the survival of inoculated bacterial strains, the colony forming units were determined in the root, shoot and water samples as described earlier (Ijaz et al. 2015). The colonies were analysed by restriction fragment length polymorphism (RFLP) and their identities were compared with the inoculated strains.

Plant dry biomass

The roost and shoots of the macrophytes were harvested at the end of experiment and were gently washed with tap water and dried by absorbent paper, followed by chopping into small pieces to accelerate the drying process. The chopped samples were oven-dried at 70 °C for 48 h and their dry weight was determined (Wang et al. 2014).

Statistical analysis

Data were analysed by using Statistics 8.1. Analysis of variance (ANOVA) was used to appraise the data collected from all three replicates of each treatment. Mean values were compared by using the least significant difference test (LSD).

RESULT

River water characteristics

The values of water quality parameters are given in Table 1 which indicate the pollution status of the river water. Parameters of COD, BOD5, and TSS signify that the Ravi River water is not as required by wastewater discharge standards of Pakistan (WWF 2007).

Water remediation by FTWs

A reduction in the pH of all treatments was observed during the whole experiment. In vegetated treatments, pH decreased from 8.5 to 7.26, with maximum reduction in T4. Overall decreases in pH in T1, T2, T3 and T4 were on par with each other but significantly differed from nonvegetated and only bacterial augmented treatments (Table 2). Similarly, EC declined in all treatments, and its maximum reduction (2.27 to 1.7 mS/cm) was observed in T2.

Table 2

Reduction in pollutants by FTWs from polluted river water

ParameterTreatmentTime
LSD: α = 5%
0 h24 h48 h72 h96 h
pH T1 8.5BC (0.10) 8.26EFG (0.0) 8.16GHI (0.1) 7.63KL (0.1) 7.25M (0.1) 0.10 
T2 8.5BC (0.1) 8.25FG (0.0) 8.06I (0.1) 7.54L (0.1) 7.2M (0.1) 
T3 8.5BC (0.1) 8.37DE (0.1) 8.2GH (0.0) 7.82J (0.0) 7.26M (0.1) 
T4 8.5BC (0.1) 8.31EF (0.0) 8.21GH (0.0) 7.67K (0.0) 7.16M (0.0) 
T5 8.5BC (0.1) 8.31EF (0.0) 8.33DEF (0.10) 8.2GH (0.1) 8.13HI (0.1) 
8.5BC (0.1) 8.42CD (0.0) 8.56B (0.1) 8.56B (0.1) 8.77A (0.0) 
EC (mS/cm) T1 2.3DEF (0.0) 2.88B (0.0) 2.4CD (0.1) 2.16GH (0.0) 1.97J (0.0) 0.10 
T2 2.3DEF (0.0) 3.11A (0.0) 2.3DEF (0.2) 2.03IJ (0.0) 1.73K (0.1) 
T3 2.3DEF (0.0) 2.1HI (0.1) 2.25FG (0.0) 2.03IJ (0.1) 2.00IJ (0.0) 
T4 2.3DEF (0.0) 3.06A (0.1) 2.28EF (0.0) 2.16GH (0.2) 1.97J (0.0) 
T5 2.3DEF (0.0) 2.48C (0.0) 2.38CDE (0.0) 2.04IJ (0.0) 2.00IJ (0.0) 
2.3DEF (0.0) 2.35DEF (0.0) 2.36DE (0.0) 2.02IJ (0.0) 2.00IJ (0.0) 
TSS (mg/L) T1 289.66A (4.51 76.00B (2.0) 33.67GHI (4.7) 19.0K (1.0) 18.3L (1.2) 9.05 
T2 289.67A (4.5) 78.33B (3.1) 36.00FG (3.5) 19.0K (1.7) 15.7KL (1.5) 
T3 289.67A (4.5) 64.00CD (2.4) 40.6F (1.2) 24.7IJK (3.1) 17.0K (2.0) 
T4 289.67A (4.5) 72.67BC (6.4) 34.3FGH (3.8) 24.3JK (2.5) 16.67K (2.1) 
T5 289.67A (4.5) 73.00BC (3.6) 60.0DE (3.6) 39.33F (1.2) 36.0FG (1.7) 
289.66A (4.5) 77.33B (6.7) 54.0E (2.7) 37.3FG (0.9) 36.0FG (1.0) 
TN (mg/L) T1 37.47A (1.1) 28.53DE (0.2) 15.37K (0.5) 6.77P (0.1) 2.03Q (0.1) 0.96 
T2 37.47A (1.1) 25.90F (0.5) 13.20N (0.2) 7.73O (0.2) 1.77Q (0.1) 
T3 37.47A (1.1) 29.40D (0.3) 22.27G (0.2) 14.2LM (0.3) 7.03OP (0.3) 
T4 37.47A (1.1) 28.43E (0.4) 20.17I (0.3) 13.2MN (0.2) 6.23P (0.2) 
T5 37.47A (1.1) 30.73C (0.5) 25.33F (0.3) 19.0J (0.5) 14.83KL (0.8) 
37.47A (1.1) 32.23B (0.4) 28.57DE (0.7) 25.37F (0.4) 21.23H (0.3) 
NO3−1 (mg/L) T1 33.33A (1.5) 25.47C (0.5) 12.33I (0.6) 3.02L (0.1) 1.17MN (0.2) 1.19 
T2 33.33A (1.5) 23.07E (0.4) 10.23K (0.2) 3.50L (0.1) 0.80N (0.1) 
T3 33.33A (1.5) 25.00CD (1.0) 18.67G (0.3) 10.7JK (0.6) 3.27L (0.2) 
T4 33.33A (1.5) 24.90CD (0.9) 16.27H (0.2) 10.5JK (0.5) 2.33LM (0.2) 
T5 33.33A (1.5) 26.03C (1.0) 21.33F (0.6) 12.80I (0.4) 11.67IJ (0.6) 
33.33A (1.5) 30.13B (0.2) 24.1DE (0.2) 21.67F (1.2) 16.47H (0.5) 
TP (mg/L) T1 2.63A (0.1) 2.10C (0.1) 1.47H (0.1) 1.03J (0.1) 0.83K (0.1) 0.13 
T2 2.63A (0.1) 1.77F (0.1) 1.17I (0.1) 0.80K (0.1) 0.60L (0.1) 
T3 2.63A (0.1) 2.10C (0.1) 1.80F (0.1) 1.27I (0.1) 0.87K (0.1) 
T4 2.63A (0.1) 1.94DE (0.0) 1.50GH (0.1) 1.17I (0.1) 0.63L (0.1) 
T5 2.63A (0.1) 2.10C (0.2) 2.03CD (0.1) 1.87EF (0.1) 1.62G (0.0) 
2.63A (0.1) 2.38B (0.1) 2.39B (0.1) 2.10C (0.0) 1.99CDE (0.0) 
ParameterTreatmentTime
LSD: α = 5%
0 h24 h48 h72 h96 h
pH T1 8.5BC (0.10) 8.26EFG (0.0) 8.16GHI (0.1) 7.63KL (0.1) 7.25M (0.1) 0.10 
T2 8.5BC (0.1) 8.25FG (0.0) 8.06I (0.1) 7.54L (0.1) 7.2M (0.1) 
T3 8.5BC (0.1) 8.37DE (0.1) 8.2GH (0.0) 7.82J (0.0) 7.26M (0.1) 
T4 8.5BC (0.1) 8.31EF (0.0) 8.21GH (0.0) 7.67K (0.0) 7.16M (0.0) 
T5 8.5BC (0.1) 8.31EF (0.0) 8.33DEF (0.10) 8.2GH (0.1) 8.13HI (0.1) 
8.5BC (0.1) 8.42CD (0.0) 8.56B (0.1) 8.56B (0.1) 8.77A (0.0) 
EC (mS/cm) T1 2.3DEF (0.0) 2.88B (0.0) 2.4CD (0.1) 2.16GH (0.0) 1.97J (0.0) 0.10 
T2 2.3DEF (0.0) 3.11A (0.0) 2.3DEF (0.2) 2.03IJ (0.0) 1.73K (0.1) 
T3 2.3DEF (0.0) 2.1HI (0.1) 2.25FG (0.0) 2.03IJ (0.1) 2.00IJ (0.0) 
T4 2.3DEF (0.0) 3.06A (0.1) 2.28EF (0.0) 2.16GH (0.2) 1.97J (0.0) 
T5 2.3DEF (0.0) 2.48C (0.0) 2.38CDE (0.0) 2.04IJ (0.0) 2.00IJ (0.0) 
2.3DEF (0.0) 2.35DEF (0.0) 2.36DE (0.0) 2.02IJ (0.0) 2.00IJ (0.0) 
TSS (mg/L) T1 289.66A (4.51 76.00B (2.0) 33.67GHI (4.7) 19.0K (1.0) 18.3L (1.2) 9.05 
T2 289.67A (4.5) 78.33B (3.1) 36.00FG (3.5) 19.0K (1.7) 15.7KL (1.5) 
T3 289.67A (4.5) 64.00CD (2.4) 40.6F (1.2) 24.7IJK (3.1) 17.0K (2.0) 
T4 289.67A (4.5) 72.67BC (6.4) 34.3FGH (3.8) 24.3JK (2.5) 16.67K (2.1) 
T5 289.67A (4.5) 73.00BC (3.6) 60.0DE (3.6) 39.33F (1.2) 36.0FG (1.7) 
289.66A (4.5) 77.33B (6.7) 54.0E (2.7) 37.3FG (0.9) 36.0FG (1.0) 
TN (mg/L) T1 37.47A (1.1) 28.53DE (0.2) 15.37K (0.5) 6.77P (0.1) 2.03Q (0.1) 0.96 
T2 37.47A (1.1) 25.90F (0.5) 13.20N (0.2) 7.73O (0.2) 1.77Q (0.1) 
T3 37.47A (1.1) 29.40D (0.3) 22.27G (0.2) 14.2LM (0.3) 7.03OP (0.3) 
T4 37.47A (1.1) 28.43E (0.4) 20.17I (0.3) 13.2MN (0.2) 6.23P (0.2) 
T5 37.47A (1.1) 30.73C (0.5) 25.33F (0.3) 19.0J (0.5) 14.83KL (0.8) 
37.47A (1.1) 32.23B (0.4) 28.57DE (0.7) 25.37F (0.4) 21.23H (0.3) 
NO3−1 (mg/L) T1 33.33A (1.5) 25.47C (0.5) 12.33I (0.6) 3.02L (0.1) 1.17MN (0.2) 1.19 
T2 33.33A (1.5) 23.07E (0.4) 10.23K (0.2) 3.50L (0.1) 0.80N (0.1) 
T3 33.33A (1.5) 25.00CD (1.0) 18.67G (0.3) 10.7JK (0.6) 3.27L (0.2) 
T4 33.33A (1.5) 24.90CD (0.9) 16.27H (0.2) 10.5JK (0.5) 2.33LM (0.2) 
T5 33.33A (1.5) 26.03C (1.0) 21.33F (0.6) 12.80I (0.4) 11.67IJ (0.6) 
33.33A (1.5) 30.13B (0.2) 24.1DE (0.2) 21.67F (1.2) 16.47H (0.5) 
TP (mg/L) T1 2.63A (0.1) 2.10C (0.1) 1.47H (0.1) 1.03J (0.1) 0.83K (0.1) 0.13 
T2 2.63A (0.1) 1.77F (0.1) 1.17I (0.1) 0.80K (0.1) 0.60L (0.1) 
T3 2.63A (0.1) 2.10C (0.1) 1.80F (0.1) 1.27I (0.1) 0.87K (0.1) 
T4 2.63A (0.1) 1.94DE (0.0) 1.50GH (0.1) 1.17I (0.1) 0.63L (0.1) 
T5 2.63A (0.1) 2.10C (0.2) 2.03CD (0.1) 1.87EF (0.1) 1.62G (0.0) 
2.63A (0.1) 2.38B (0.1) 2.39B (0.1) 2.10C (0.0) 1.99CDE (0.0) 

T1 (Typha domingensis), T2 (T. domingensis and bacteria), T3 (Leptochloa fusca), T4 (L. fusca and bacteria), T5 (only bacteria), C (without bacteria and vegetation). Each value is the mean of three replicates and alphabetic labels present significant differences between treatments. Standard deviations are presented in parentheses. LSD: least significant difference test.

The maximum decrease in TSS was observed during the first 24 h of the study (Table 2). Statistically TSS reduction in vegetated treatments (T1, T2, T3, and T4) was significantly more than that in nonvegetated treatments (T5 and C). In T2, the COD, BOD5 and TOC decreased to 47, 21 and 15 mg/L from 405, 190 and 110 mg/L, respectively (Figure 2). The treatments having plants along with bacterial inoculation (T2 and T4) caused significantly greater decrease in COD, BOD5 and TOC as compared with treatments (T1 and T3) without bacterial inoculation.

Figure 2

Chemical oxygen demand (COD), biochemical oxygen demand (BOD) and total organic carbon (TOC) reduction in polluted river water (PRW) by floating treatment wetlands vegetated with Typha domingensis (T1), T. domingensis and bacteria (T2), Leptochloa fusca (T3), L. fusca and bacteria (T4), only bacteria (T5), and without vegetation and bacteria (C). Each value is the mean of three replicates. Error bars indicate errors among three replicates. Means sharing the same alphabetic letters are statistically non-significant.

Figure 2

Chemical oxygen demand (COD), biochemical oxygen demand (BOD) and total organic carbon (TOC) reduction in polluted river water (PRW) by floating treatment wetlands vegetated with Typha domingensis (T1), T. domingensis and bacteria (T2), Leptochloa fusca (T3), L. fusca and bacteria (T4), only bacteria (T5), and without vegetation and bacteria (C). Each value is the mean of three replicates. Error bars indicate errors among three replicates. Means sharing the same alphabetic letters are statistically non-significant.

Plant and bacterial systems significantly reduced the concentration of TN and NO3 in the polluted river water (Table 2). Floating wetlands planted with T. domingensis in combination with a bacterial consortium rendered maximum reduction in TN concentration in the polluted water as compared with all other treatments. Similarly the highest decrease of nitrate (NO3) was observed in the floating wetlands carrying plants of T. domingensis and a consortium of bacteria (Table 2). A combination of both plants and bacteria in FTW cells also removed maximum TP.

Removal of heavy metals

Vegetative treatments (T1, T2, T3 and T4) significantly reduced more heavy metal contents in the polluted river water as compared with nonvegetated treatments (T5 and C) (Table 3). The maximum removal of heavy metals was observed in T2 and T4.

Table 3

Reduction in heavy metals by FTWs from polluted river water

MetalTreatmentTime
LSD: α = 5%
0 h24 h48 h72 h96 h
Fe (mg/L) T1 1.53A (0.12) 1.14CDEF (0.09) 0.83HIJ (0.02) 0.63KLM (0.12) 0.47MN (0.06) 0.18 
T2 1.53A (0.12) 0.67JKL (0.50) 0.73JK (0.03) 0.57KLMN (0.03) 0.41N (0.01) 
T3 1.53A (0.12) 0.97FGHI (0.01) 0.83HIJ (0.01) 0.73JK (0.01) 0.52LMN (0.02) 
T4 1.53A (0.12) 1.00FGH (0.00) 0.82IJ (0.01) 0.66JKL (0.01) 0.42N (0.02) 
T5 1.53A (0.12) 1.22BCD (0.03) 1.27BC (0.06) 1.07DEFG (0.06) 0.95GHI (0.00) 
1.53A (0.12) 1.32BC (0.02) 1.37AB (0.12) 1.20BCDE (0.01) 1.03EFG (0.06) 
Ni (mg/L) T1 0.54A (0.01) 0.40G (0.02) 0.27K (0.00) 0.18N (0.00) 0.13O (0.010) 0.02 
T2 0.54A (0.01) 0.36H (0.01) 0.23L (0.01) 0.16N (0.01) 0.09P (0.01) 
T3 0.54A (0.01) 0.45E (0.01) 0.29J (0.03) 0.23L (0.01) 0.18MN (0.01) 
T4 0.54A (0.01) 0.41FG (0.01) 0.34I (0.02) 0.20M (0.01) 0.16N (0.01) 
T5 0.54A (0.01) 0.48CD (0.01) 0.45E (0.01) 0.43F (0.00) 0.43F (0.01) 
0.54A (0.01) 0.50B (0.01) 0.49BC (0.00) 0.49BC (0.00) 0.46DE (0.00) 
Mn (mg/L) T1 0.85A (0.02) 0.57F (0.01) 0.33JK (0.02) 0.15MN (0.01) 0.12O (0.02) 0.03 
T2 0.85A (0.02) 0.51H (0.02) 0.35IJ (0.01) 0.12S (0.00) 0.10P (0.01) 
T3 0.85A (0.02) 0.58F (0.01) 0.37I (0.01) 0.22L (0.02) 0.17M (0.01) 
T4 0.85A (0.02) 0.54G (0.01) 0.30K (0.01) 0.21L (0.02) 0.14NO (0.01) 
T5 0.85A (0.02) 0.71C (0.02) 0.67D (0.01) 0.63E (0.01) 0.57F (0.06) 
0.85A (0.02) 0.75B (0.01) 0.72C (0.01) 0.68D (0.00) 0.64E (0.01) 
Pb (mg/L) T1 0.83A (0.06) 0.51IJ (0.02) 0.42KL (0.01) 0.39LM (0.01) 0.35MN (0.01) 0.04 
T2 0.83A (0.06) 0.45K (0.02) 0.34N (0.01) 0.29O (0.02) 0.25O (0.02) 
T3 0.83A (0.06) 0.65DEF (0.01) 0.61FG (0.02) 0.57GH (0.01) 0.54HI (0.01) 
T4 0.83A (0.06) 0.62EF (0.02) 0.57GH (0.01) 0.54HI (0.02) 0.49J (0.02) 
T5 0.83A (0.06) 0.68BCD (0.00) 0.68BD (0.01) 0.65CDE (0.00) 0.65CDE (0.00) 
0.83A (0.06) 0.71B (0.01) 0.70B (0.01) 0.70B (0.00) 0.68BCD (0.01) 
Cr (mg/L) T1 0.36A (0.02) 0.28D (0.01) 0.23EF (0.02) 0.14J (0.01) 0.10KLM (0.01) 0.02 
T2 0.36A (0.02) 0.20G (0.01) 0.13J (0.01) 0.11K (0.01) 0.08MN (0.01) 
T3 0.36A (0.02) 0.23EF (0.02) 0.18H (0.01) 0.14J (0.02) 0.11KL (0.02) 
T4 0.36A (0.02) 0.22EF (0.01) 0.16I (0.01) 0.09LMN (0.01) 0.08N (0.01) 
T5 0.36A (0.02) 0.31C (0.00) 0.28D (0.01) 0.24E (0.01) 0.24E (0.01) 
0.36A (0.02) 0.33B (0.00) 0.31C (0.03) 0.29D (0.01) 0.28D (0.01) 
MetalTreatmentTime
LSD: α = 5%
0 h24 h48 h72 h96 h
Fe (mg/L) T1 1.53A (0.12) 1.14CDEF (0.09) 0.83HIJ (0.02) 0.63KLM (0.12) 0.47MN (0.06) 0.18 
T2 1.53A (0.12) 0.67JKL (0.50) 0.73JK (0.03) 0.57KLMN (0.03) 0.41N (0.01) 
T3 1.53A (0.12) 0.97FGHI (0.01) 0.83HIJ (0.01) 0.73JK (0.01) 0.52LMN (0.02) 
T4 1.53A (0.12) 1.00FGH (0.00) 0.82IJ (0.01) 0.66JKL (0.01) 0.42N (0.02) 
T5 1.53A (0.12) 1.22BCD (0.03) 1.27BC (0.06) 1.07DEFG (0.06) 0.95GHI (0.00) 
1.53A (0.12) 1.32BC (0.02) 1.37AB (0.12) 1.20BCDE (0.01) 1.03EFG (0.06) 
Ni (mg/L) T1 0.54A (0.01) 0.40G (0.02) 0.27K (0.00) 0.18N (0.00) 0.13O (0.010) 0.02 
T2 0.54A (0.01) 0.36H (0.01) 0.23L (0.01) 0.16N (0.01) 0.09P (0.01) 
T3 0.54A (0.01) 0.45E (0.01) 0.29J (0.03) 0.23L (0.01) 0.18MN (0.01) 
T4 0.54A (0.01) 0.41FG (0.01) 0.34I (0.02) 0.20M (0.01) 0.16N (0.01) 
T5 0.54A (0.01) 0.48CD (0.01) 0.45E (0.01) 0.43F (0.00) 0.43F (0.01) 
0.54A (0.01) 0.50B (0.01) 0.49BC (0.00) 0.49BC (0.00) 0.46DE (0.00) 
Mn (mg/L) T1 0.85A (0.02) 0.57F (0.01) 0.33JK (0.02) 0.15MN (0.01) 0.12O (0.02) 0.03 
T2 0.85A (0.02) 0.51H (0.02) 0.35IJ (0.01) 0.12S (0.00) 0.10P (0.01) 
T3 0.85A (0.02) 0.58F (0.01) 0.37I (0.01) 0.22L (0.02) 0.17M (0.01) 
T4 0.85A (0.02) 0.54G (0.01) 0.30K (0.01) 0.21L (0.02) 0.14NO (0.01) 
T5 0.85A (0.02) 0.71C (0.02) 0.67D (0.01) 0.63E (0.01) 0.57F (0.06) 
0.85A (0.02) 0.75B (0.01) 0.72C (0.01) 0.68D (0.00) 0.64E (0.01) 
Pb (mg/L) T1 0.83A (0.06) 0.51IJ (0.02) 0.42KL (0.01) 0.39LM (0.01) 0.35MN (0.01) 0.04 
T2 0.83A (0.06) 0.45K (0.02) 0.34N (0.01) 0.29O (0.02) 0.25O (0.02) 
T3 0.83A (0.06) 0.65DEF (0.01) 0.61FG (0.02) 0.57GH (0.01) 0.54HI (0.01) 
T4 0.83A (0.06) 0.62EF (0.02) 0.57GH (0.01) 0.54HI (0.02) 0.49J (0.02) 
T5 0.83A (0.06) 0.68BCD (0.00) 0.68BD (0.01) 0.65CDE (0.00) 0.65CDE (0.00) 
0.83A (0.06) 0.71B (0.01) 0.70B (0.01) 0.70B (0.00) 0.68BCD (0.01) 
Cr (mg/L) T1 0.36A (0.02) 0.28D (0.01) 0.23EF (0.02) 0.14J (0.01) 0.10KLM (0.01) 0.02 
T2 0.36A (0.02) 0.20G (0.01) 0.13J (0.01) 0.11K (0.01) 0.08MN (0.01) 
T3 0.36A (0.02) 0.23EF (0.02) 0.18H (0.01) 0.14J (0.02) 0.11KL (0.02) 
T4 0.36A (0.02) 0.22EF (0.01) 0.16I (0.01) 0.09LMN (0.01) 0.08N (0.01) 
T5 0.36A (0.02) 0.31C (0.00) 0.28D (0.01) 0.24E (0.01) 0.24E (0.01) 
0.36A (0.02) 0.33B (0.00) 0.31C (0.03) 0.29D (0.01) 0.28D (0.01) 

T1 (Typha domingensis), T2 (T. domingensis and bacteria), T3 (Leptochloa fusca), T4 (L. fusca and bacteria), T5 (only bacteria), and C (without bacteria and vegetation). Each value is the mean of three replicates and alphabetic labels present significant differences between treatments. Standard deviations are presented in parentheses. LSD: least significant difference test.

Survival and colonization of inoculated bacteria

Significant numbers of inoculated bacteria were observed in the roots, shoots and water (Table 4). The bacteria colonized more in the roots than shoots. The number of inoculated bacteria continuously increased in the roots and shoots. In water, the concentration of inoculated bacteria increased in the first 48 h and then decreased. However, in nonvegetated treatments (T5), the number of inoculated bacteria continuously decreased.

Table 4

Survival of inoculated bacteria in roots, shoots and water of FTWs

TreatmentCFU (103/g root)
CFU (103/g shoot)
CFU (105/mL water)
24 h48 h72 h96 h24 h48 h72 h96 h24 h48 h72 h96 h
T2 2.57D (0.4) 4.90C (0.8) 6.27B (0.6) 7.17A (0.3) 2.17E (0.3) 3.10D (0.3) 4.50B (0.3) 5.10A (0.3) 17.4G (1.1) 21.9DE (0.6) 25.37C (0.8) 27.03B (0.7) 
T4 1.40E (0.4) 2.37D (0.4) 4.17C (0.4) 6.13B (0.3) 1.17F (0.2) 2.73D (0.4) 3.83C (0.4) 4.27B (0.2) 17G (1.0) 19.17F (0.8) 21.6E (1.4) 23.3D (0.5) 
T5 – – – – – – – – 18.17FG (1.4) 28.73A (0.8) 19.2F (0.7) 14.63H (0.4) 
LSD: α = 5% 0.79 0.43 1.45 
TreatmentCFU (103/g root)
CFU (103/g shoot)
CFU (105/mL water)
24 h48 h72 h96 h24 h48 h72 h96 h24 h48 h72 h96 h
T2 2.57D (0.4) 4.90C (0.8) 6.27B (0.6) 7.17A (0.3) 2.17E (0.3) 3.10D (0.3) 4.50B (0.3) 5.10A (0.3) 17.4G (1.1) 21.9DE (0.6) 25.37C (0.8) 27.03B (0.7) 
T4 1.40E (0.4) 2.37D (0.4) 4.17C (0.4) 6.13B (0.3) 1.17F (0.2) 2.73D (0.4) 3.83C (0.4) 4.27B (0.2) 17G (1.0) 19.17F (0.8) 21.6E (1.4) 23.3D (0.5) 
T5 – – – – – – – – 18.17FG (1.4) 28.73A (0.8) 19.2F (0.7) 14.63H (0.4) 
LSD: α = 5% 0.79 0.43 1.45 

T1 (Typha domingensis), T2 (T. domingensis and bacteria), T3 (Leptochloa fusca), T4 (L. fusca and bacteria), T5 (only bacteria), and C (without bacteria and vegetation). Each value is the mean of three replicates and alphabetic labels present significant differences between treatments. Standard deviations are presented in parentheses. LSD: least significant difference test.

Plant dry biomass

The total dry biomass of roots and shoots of T. domingensis was higher than L. fusca (Table 5). The dry biomass of treatments inoculated with the bacterial consortium was higher than treatments without bacterial inoculation.

Table 5

Plant dry biomass under different treatments

TreatmentRoot (g)Shoot (g)
T1 46 (4) 124.6 (9) 
T2 79.3 (8.5) 162.6 (7.5) 
T3 18.3 (2.1) 135 (4.4) 
T4 21.6 (2.5) 164 (6) 
TreatmentRoot (g)Shoot (g)
T1 46 (4) 124.6 (9) 
T2 79.3 (8.5) 162.6 (7.5) 
T3 18.3 (2.1) 135 (4.4) 
T4 21.6 (2.5) 164 (6) 

T1 (Typha domingensis), T2 (T. domingensis and bacteria), T3 (Leptochloa fusca), and T4 (L. fusca and bacteria). Each value is a mean of three replicates with standard deviation in parentheses.

DISCUSSION

In this study, the pH of the polluted river water was gradually decreased with the passage of time. The release of organic acids by the roots of plants and their associated microbial pollutant degradation activities contribute to lowering the pH of the water (Zhai et al. 2013). Electrical conductivity (EC) is a handy and useful indicator of total salt content in water (Morrison et al. 2001; Zhao et al. 2013). In the present study, EC decreased with the passage of time. A slight increase in EC after 24 h may result due to release of some liquid exudates from the roots of the plants (Ijaz et al. 2016b). The decrease in EC with time was as a result of nutrient uptake by the plants and the binding of dissolved elements with suspended particles (Zhao et al. 2013).

In this study, considerable removal of TSS from the polluted river water by the application of FTWs was observed. Natural sedimentation is the key factor by which large particles settle down to the bottom of ponds. Following sedimentation, vegetation also plays an important role in TSS removal. The expanding roots of FTWs provide a large surface area for the attachment of soluble solids. Earlier studies also reported that TSS contents tend to decline in water with FTW as a consequence of the trapping of soluble solids by roots (Morrison et al. 2001).

In this study, vegetated FTWs, with or without bacterial inoculation, efficiently removed the organic and inorganic pollutants from polluted river water. However, the performance of FTWs inoculated with bacteria was better and faster than those without inoculation. It suggests that the inoculation of plants with bacteria enhances their natural ability to utilize their metabolic mechanisms to eliminate various types of pollutants from wastewater (Vymazal 2014; Fang et al. 2016). In addition to this, the better performance of inoculated FTWs can be attributed to the ability of bacteria to mineralize organic pollutants (Afzal et al. 2014; Shehzadi et al. 2014; Ijaz et al. 2015). The bacteria on roots, hanging in the water column, contribute to the degradation of organic matter leading to reduction in COD and BOD5 (Khan et al. 2013; Shehzadi et al. 2016). In this study, the rapid and higher reduction in COD, BOD5 and TOC in bacterial inoculated treatment is probably due to the degradation of organic matter by the high number of bacteria in the water and on the roots.

In rivers, the discharge of domestic wastewater and agricultural runoff are the major source of TN, leading to eutrophication (Zhao et al. 2012). Nitrification, denitrification, uptake by plants and microbes and volatilization are the processes responsible for removal of nitrogen from water (Tanner et al. 1999). However, in FTWs, roots are exposed to water only, which may enhance the nutrient uptake by plants (Stewart et al. 2008; Li et al. 2010). In this study, FTWs efficiently removed N and NO3 from the river water. The use of T. domingensis in FTWs removed nitrogen and NO3 more efficiently than L. fusca, which might be attributed to the vigorous growth of the roots of T. domingensis. Roots of plants provide a base for periphytic microorganisms which enhance the breakdown of organic pollutants and nitrogen removal from water (Hu et al. 2010; Zhao et al. 2012).

In this study, although the phosphorus concentration was low (2.5 mg/L) in the water, the average removal efficiency was about 67% to 76% in the vegetated FTWs, which is much higher than those reported previously (Stewart et al. 2008; Tanner & Headley 2011). In FTWs, phosphorus removal may depend upon the sorbent/substrate surrounding the roots (Yang et al. 2008; Lijuan et al. 2017), surface area and aeration (Stewart et al. 2008). Plants and microbial populations that colonize plant tissues and the rhizosphere are the major factors responsible for the removal of phosphorus (Stewart et al. 2008). In this study, FTWs inoculated with a bacterial consortium have shown a high percentage of P removal as compared with non-inoculated treatments, which may be due to the enhanced activity of bacteria. Moreover, the P removal efficiency of T. domingensis was better than that of L. fusca, which might be the result of the vigorous growth of its roots (Table 2). In addition to microbial activity in the rhizosphere, physical processes also play a key role in P removal (Zhu et al. 2011).

In this study, a significant amount of heavy metals was removed from the polluted river water. Adsorption, direct uptake by plants, entrapment by bacterial biofilms and metal sulphide formation can be the major processes involved in removal of heavy metals from contaminated waters (Kadlec & Wallace 2008). Other factors which may contribute in the removal of metal ions from water entail pH, redox potential, hydrated oxides and carbonates of metals and biofilm development on the rhizoplane (Hansel et al. 2001). Sequestration of metal ions and iron plaque development around the roots of submerged macrophytes are common processes of heavy metal removal (King & Garey 1999; Hansel et al. 2001; Ashraf et al. 2018b). Oxidation by bacteria may also enhance iron plaque formation (Li et al. 2011).

In this study, heavy metal removal was increased by the inoculation of bacteria to the plants. The enhanced performance due to bacterial inoculation can be attributed to the ability of bacteria to sorb metals on their cell walls (Ijaz et al. 2015; Ashraf et al. 2018c). Bacterial inoculation also helps in the uptake of heavy metals by plants because their bioavailability is increased with microbes (Sessitsch et al. 2013; Khan et al. 2015; Ijaz et al. 2016b).

The survival of fish in treated water indicated detoxification and pollutant reduction in the river water (Table 6). Moreover, bacterial augmentation in FTWs further improved water quality and reduced the toxicity of the water. Many earlier studies also demonstrated that plant–bacteria synergism is a more effective approach in the detoxification of polluted water (Shehzadi et al. 2014; Ijaz et al. 2015).

Table 6

Fish toxicity assay of polluted river water detoxified by FTWs

TreatmentFish death over time
Total death
24 h48 h72 h96 h
T1 2/10 
T2 1/10 
T3 1/10 
T4 2/10 
T5 4/10 
7/10 
TreatmentFish death over time
Total death
24 h48 h72 h96 h
T1 2/10 
T2 1/10 
T3 1/10 
T4 2/10 
T5 4/10 
7/10 

T1 (Typha domingensis), T2 (T. domingensis and bacteria), T3 (Leptochloa fusca), T4 (L. fusca and bacteria), T5 (only bacteria), and C (without bacteria and vegetation).

CONCLUSIONS

The aim of this study was to evaluate the effect of bacterial inoculation in FTWs on the remediation of polluted river water. The developed FTW system efficiently decreased COD, BOD, TOC, TN, NO3, TP and heavy metals in the polluted river water. The performance of T. domingensis was better than L. fusca in the removal of most of the pollutants. Therefore, Typha domingensis is a better choice for developing FTWs for the treatment of polluted river water. The inoculation of FTWs with bacteria further boosted the efficiency of the plants in removing the pollutants from the water. The FTW-treated water complies with the national standards of water for irrigation and aquatic life. These results suggest that FTWs with bacterial inoculation are a simple and efficient technology for the treatment of polluted river water and for the natural ecosystem of river to flourish. Floating treatment wetlands augmented with bacteria can be applied on wastewater collection drains to mitigate their pollutant load prior to discharging it into rivers or other water systems. Additional research is needed to explore the practical application of the developed FTW system at a commercial scale.

ACKNOWLEDGEMENTS

The authors would like to thank the Higher Education Commission, Pakistan (grant numbers 1-52/ILS-UITSP/HEC/2014 and 20-3854/R&D/HEC/14), and the International Foundation of Science, Sweden, and the Organization for the Prohibition of Chemical Weapons (grant number W/5104-2).

REFERENCES

REFERENCES
Allan
J. D.
&
Castillo
M. M.
2007
Stream Ecology: Structure and Function of Running Waters
.
Springer
,
New York, USA
, pp.
317
344
.
APHA (American Public Health Association)
2012
Standard Methods for the Examination of Water and Wastewater
, 20th edn.
American Public Health Association
,
Washington, DC, USA
.
Arslan
M.
,
Imran
A.
,
Khan
Q. M.
&
Afzal
M.
2017
Plant–bacteria partnerships for the remediation of persistent organic pollutants
.
Environmental Science and Pollution Research
24
(
5
),
4322
4336
.
Ashraf
S.
,
Afzal
M.
,
Rehman
K.
,
Naveed
M.
&
Zahir
Z. A.
2018a
Plant-endophyte synergism in constructed wetlands enhances the remediation of tannery effluent
.
Water Science and Technology
77
(
5
),
1262
1270
.
Ashraf
S.
,
Afzal
M.
,
Naveed
M.
,
Shahid
M.
&
Zahir
Z. A.
2018b
Endophytic bacteria enhance remediation of tannery effluent in constructed wetlands vegetated with Leptochloa fusca
.
International Journal of Phytoremediation
20
(
2
),
121
128
.
Ashraf
S.
,
Afzal
M.
,
Rehman
K.
,
Tahseen
R.
,
Naveed
M.
&
Zahir
Z. A.
2018c
Enhanced remediation of tannery effluent in constructed wetlands augmented with endophytic bacteria
.
Desalination and Water Treatment
102
,
93
100
.
Azfar
K. R. W.
,
Shahzad
N.
&
Mumtaz
S.
2018
Lowering of groundwater table around River Ravi in Lahore: aggravated by Indus Water Treaty
.
Australia and New Zealand Journal of Social Business, Environment and Sustainability
4
(
2
),
65
72
.
Fang
T.
,
Bao
S.
,
Sima
X.
,
Jiang
H.
,
Zhu
W.
&
Tang
W.
2016
Study on the application of integrated eco-engineering in purifying eutrophic river waters
.
Ecological Engineering
94
,
320
328
.
Fatima
K.
,
Afzal
M.
,
Imran
A.
&
Khan
Q. M.
2015
Bacterial rhizosphere and endosphere populations associated with grasses and trees to be used for phytoremediation of crude oil contaminated soil
.
Bulletin of Environmental Contamination and Toxicology
94
(
3
),
314
320
.
Faulwetter
J. L.
,
Burr
M. D.
,
Cunningham
A. B.
,
Stewart
F. M.
,
Camper
A. K.
&
Stein
O. R.
2011
Floating treatment wetlands for domestic wastewater treatment
.
Water Science and Technology
64
(
10
),
2089
2095
.
Hansel
C. M.
,
Fendorf
S.
,
Sutton
S.
&
Newville
M.
2001
Characterization of Fe plaque and associated metals on the roots of mine-waste impacted aquatic plants
.
Environmental Science and Technology
35
(
19
),
3863
3868
.
Headley
T. R.
&
Tanner
C. C.
2008a
Floating treatment wetlands: an innovative option for stormwater quality applications
. In:
11th International Conference on Wetland Systems for Water Pollution Control
,
Indore, India
.
Headley
T. R.
&
Tanner
C. C.
2008b
Application of Floating Wetlands for Enhanced Stormwater Treatment: A Review
.
Auckland Regional Council Technical Report TR2008/030
,
Auckland Regional Council
,
Auckland, New Zealand
.
Headley
T. R.
&
Tanner
C. C.
2012
Constructed wetlands with floating emergent macrophytes: an innovative stormwater treatment technology
.
Critical Reviews in Environmental Science and Technology
42
(
21
),
2261
2310
.
Hegazy
A. K.
,
Abdel-Ghani
N. T.
&
El-Chaghaby
G. A.
2011
Phytoremediation of industrial wastewater potentiality by Typha domingensis
.
International Journal of Environmental Science and Technology
8
(
3
),
639
648
.
Hu
M.-H.
,
Yuan
J.-H.
,
Yang
X.-E.
&
He
Z.-L.
2010
Effects of temperature on purification of eutrophic water by floating eco-island system
.
Acta Ecologica Sinica
30
(
6
),
310
318
.
Ijaz
A.
,
Shabir
G.
,
Khan
Q. M.
&
Afzal
M.
2015
Enhanced remediation of sewage effluent by endophyte-assisted floating treatment wetlands
.
Ecological Engineering
84
,
58
66
.
Ijaz
A.
,
Imran
A.
,
ul Haq
M. A.
,
Khan
Q. M.
&
Afzal
M.
2016a
Phytoremediation: recent advances in plant–endophytic synergistic interactions
.
Plant and Soil
405
(
1–2
),
179
195
.
Kadlec
R. H.
&
Wallace
S.
2008
Treatment Wetlands
, 2nd edn.
CRC Press
,
Boca Raton, FL, USA
.
Keizer-Vlek
H. E.
,
Verdonschot
P. F. M.
,
Verdonschot
R. C. M.
&
Dekkers
D.
2014
The contribution of plant uptake to nutrient removal by floating treatment wetlands
.
Ecological Engineering
73
,
684
690
.
Khan
M. U.
,
Sessitsch
A.
,
Harris
M.
,
Fatima
K.
,
Imran
A.
,
Arslan
M.
,
Shabir
G.
,
Khan
Q. M.
&
Afzal
M.
2015
Cr-resistant rhizo- and endophytic bacteria associated with Prosopis juliflora and their potential as phytoremediation enhancing agents in metal-degraded soils
.
Frontiers in Plant Science
5
,
755
.
King
G.
&
Garey
M. A.
1999
Ferric iron reduction by bacteria associated with the roots of freshwater and marine macrophytes
.
Applied and Environmental Microbiology
65
(
10
),
4393
4398
.
Li
H.
,
Zhao
H.-P.
,
Hao
H.-L.
,
Liang
J.
,
Zhao
F.-L.
,
Xiang
L.-C.
,
Yang
X.-E.
,
He
Z.-L.
&
Stoffella
P. J.
2011
Enhancement of nutrient removal from eutrophic water by a plant–microorganisms combined system
.
Environmental Engineering Science
28
(
8
),
543
554
.
Lijuan
C.
,
Wei
L.
,
Jian
Z.
,
Yan
Z.
,
Manyin
Z.
,
Yinru
L.
,
Xiaoming
K.
,
Xinsheng
Z.
&
Xu
P.
2017
Influence of substrate depth and particle size on phosphorus removal in a surface flow constructed wetland
.
Water Science and Technology
75
(
10
),
2291
2298
.
Mietto
A.
,
Borin
M.
,
Salvato
M.
,
Ronco
P.
&
Tadiello
N.
2013
Tech-IA floating system introduced in urban wastewater treatment plants in the Veneto region – Italy
.
Water Science and Technology
68
(
5
),
1144
1150
.
Morrison
G.
,
Fatoki
O. S.
,
Persson
L.
&
Ekberg
A.
2001
Assessment of the impact of point source pollution from the Keiskammahoek Sewage Treatment Plant on the Keiskamma River – pH, electrical conductivity, oxygen-demanding substance (COD) and nutrients
.
Water SA
27
(
4
),
475
480
.
Pan
B.
,
Yuan
J.
,
Zhang
X.
,
Wang
Z.
,
Chen
J.
,
Lu
J.
,
Yang
W.
,
Li
Z.
,
Zhao
N.
&
Xu
M.
2016
A review of ecological restoration techniques in fluvial rivers
.
International Journal of Sediment Research
31
(
2
),
110
119
.
Sessitsch
A.
,
Kuffner
M.
,
Kidd
P.
,
Vangronsveld
J.
,
Wenzel
W. W.
,
Fallmann
K.
&
Puschenreiter
M.
2013
The role of plant-associated bacteria in the mobilization and phytoextraction of trace elements in contaminated soils
.
Soil Biology and Biochemistry
60
,
182
194
.
Stewart
F. M.
,
Muholland
T.
,
Cunningham
A. B.
,
Kania
B. G.
&
Osterlund
M. T.
2008
Floating islands as an alternative to constructed wetlands for treatment of excess nutrients from agricultural and municipal wastes – results of laboratory-scale tests
.
Land Contamination and Reclamation
16
(
1
),
25
33
.
Tanner
C. C.
,
Sukias
J. P. S.
&
Upsdell
M. P.
1999
Substratum phosphorus accumulation during maturation of gravel-bed constructed wetlands
.
Water Science and Technology
40
(
3
),
147
154
.
Weyens
N.
,
Schellingen
K.
,
Beckers
B.
,
Janssen
J.
,
Ceulemans
R.
,
van der Lelie
D.
,
Taghavi
S.
,
Carleer
R.
&
Vangronsveld
J.
2013
Potential of willow and its genetically engineered associated bacteria to remediate mixed Cd and toluene contamination
.
Journal of Soils and Sediments
13
(
1
),
176
188
.
Winston
R. J.
,
Hunt
W. F.
,
Kennedy
S. G.
,
Merriman
L. S.
,
Chandler
J.
&
Brown
D.
2013
Evaluation of floating treatment wetlands as retrofits to existing stormwater retention ponds
.
Ecological Engineering
54
,
254
265
.
WWF (World Wildlife Fund)
2007
National Surface Water Classification Criteria and Irrigation Water Quality Guidelines for Pakistan
.
WWF-Pakistan
,
Lahore
,
Pakistan
.
Yang
Y.
,
Costa
A.
,
Leonhardt
N.
,
Siegel
R. S.
&
Schroeder
J. I.
2008
Isolation of a strong Arabidopsis guard cell promoter and its potential as a research tool
.
Plant Methods
4
(
1
),
6
.
Zhai
X.
,
Piwpuan
N.
,
Arias
C. A.
,
Headley
T.
&
Brix
H.
2013
Can root exudates from emergent wetland plants fuel denitrification in subsurface flow constructed wetland systems?
Ecological Engineering
61
,
555
563
.
Zhang
L.
,
Zhao
J.
,
Cui
N.
,
Dai
Y.
,
Kong
L.
,
Wu
J.
&
Cheng
S.
2016
Enhancing the water purification efficiency of a floating treatment wetland using a biofilm carrier
.
Environmental Science and Pollution Research
23
(
8
),
7437
7443
.
Zhao
F.
,
Xi
S.
,
Yang
X.
,
Yang
W.
,
Li
J.
,
Gu
B.
&
He
Z.
2012
Purifying eutrophic river waters with integrated floating island systems
.
Ecological Engineering
40
,
53
60
.
Zhao
F.
,
Zhang
S.
,
Ding
Z.
,
Aziz
R.
,
Rafiq
M. T.
,
Li
H.
,
He
Z.
,
Stoffella
P. J.
&
Yang
X.
2013
Enhanced purification of eutrophic water by microbe-inoculated stereo floating beds
.
Polish Journal of Environmental Studies
22
(
3
),
557
564
.