Screening of Plant Species for Phytoremediation of Synthetic Textile Dye Wastewater

Most of the dyes are carcinogenic and mutagenic in nature. Plants are potential candidates to remediate textile dye wastewater from contaminated sites. The present study aimed to design an ecient hydroponic system to screen potential ornamental plant species for removal of synthetic dye solution of triarylmethane dye Methylene Blue (MB) and diazo dye Congo Red (CR). The six plants selected for screening are Trachyspermum ammi, Tagetes erecta, Hibiscus rosa-sinensis, Chrysanthemum indicum, Bryophyllum fedtschenkoi, and Catharanthus roseus. The phytotreatment of dyes was done up to 40 h for two different concentrations of dyes, i.e., 10 and 20 mg L − 1 . Among screened plant species, the maximum decolorization was obtained from T. ammi followed by B. fedtschenkoi. Both plant species showed active growth in indigenous designed hydroponic system even after the phytoremediation process. T. ammi decolorized the MB dye 99% (10 mg L − 1 ) and 86% (20 mg L − 1 ) while the decolorization of the CR dye solution was up to 95% (10 mg L − 1 ) and 84% (20 mg L − 1 ). T. ammi was found to have maximum potential among screened plants for the removal of MB and CR dye from synthetic dye solution when kept in designed hydroponic system and can be used for phytoremediation of wastewater contaminated with synthetic dyes. The plant B. fedtschenkoi shows signicant decolorization of triarylmethane dye MB having a percentage decolorization of 85% (10 mg L − 1 ) and 69% (20 mg L − 1 ). The response of B. fedtschenkoi plant towards the removal of a toxic azo dye, CR was also observed as signicant for textile wastewater treatment. The B. fedtschenkoi decolorized the CR dye 77 and 70% for 10 and 20 mg L − 1 dye concentrations, respectively. It was observed that plant parts remained active after adsorption of the dye and were able to remove more dye concentration than 20 mg L − 1 . These results proved that B. fedtschenkoi plant has a good tendency to decolorize synthetic wastewater of CR azo dye as well as triarylmethane dye MB.


Introduction
Due to the increasing world population, there is a tremendous growth of various industries, which uses many harmful chemicals for the generation of different commodities for public demands but the side byproducts such as contaminants not only affect water bodies but also the air and soil. Dyes have a major demand and application in the textile industries for the dyeing process. About 10-15% of the azo dyes get lost in the e uent during the dyeing process (Stolz 2001) and 50% of other reactive dyes are reported for use in the textile industry which is discharged into water (Chen 2002). Azo dyes are extensively used in the dyeing process. The e uent containing dyes released into the surrounding seriously affects the environment by destroying the ecosystem, causing water pollution, and reducing light penetration for aquatic life (Imron et al. 2019). Due to textile dye wastewater, the biological oxygen demand, chemical oxygen demand, and suspended solids increase in the nearest river located beside the textile industry (Ekanayake et al. 2021). So, there is a big challenge to treat textile dyes e uent before released into water bodies.
There are many physical and chemical methods, for example, adsorption, coagulation, sedimentation, occulation, ltration, photo degradation, and chemical oxidation, for managing contamination produced by textile dyes ; Khandare and Govindwar 2015). These methods relate to the high expense, low productivity, require huge space and undependable to work. Because of these issues, there is a requirement for the advancement of productive and cost-effective methods for the treatment of textile dyes. Biological methods are more effective than physical and chemical methods to treat the textile dye wastewater. Biological

Chemicals and plant material
The triarylmethane dye, MB and a diazo dye, CR dye were used for experimentation. MB is a heterocyclic aromatic chemical compound with molecular formula C 16 H 18 N 3 SCl. The molecular weight of MB dye is 320 g mol -1 . CR dye is a diazo dye that can be synthesized by a coupling reaction containing hydroxyl, amino or other groups with an aromatic diazotized base. The chemical formula of CR dye is C 32 H 22 N 6 Na 2 O 6 S 2 and its molecular weight is 696 g mol -1 . The chemical structure of MB and CR is given in Fig. 1. MB dye and CR dyes were purchased from Sanjay lab Amritsar, India. All the chemicals used were of the highest purity and of an analytical grade. The synthetic dye wastewater was prepared at two different concentrations of 10 and 20 mg L − 1 . The entire apparatus was sterilized before experimentation. Screened ornamental plants T. ammi, T. erecta, H. rosa-sinensis, C. indicum, B. fedtschenkoi, C. roseus were harvested from the Botanical garden of Guru Nanak Dev University campus, Sathiala and Government High School, Sathiala (Punjab), India. The plants were washed completely to remove mud, dirt, and particulate matter and acclimatized for three days in distilled water. Table 1 shows the description of screened plants used for the research study.

Results And Discussion
The utility of hydroponic system was optimized by using two sets of plants-one set in upper pipe where treatment of synthetic water was screened by different plants and in lower pipe, growth of roots of screened plant were observed in treated water after treatment (Fig. 3). The decolorization results of each plant were compared with the abiotic and biotic control dye solution. The roots of plants were found to have dye pigmentation in comparison to biotic control via physical examination (Fig. 4).  Table  2.  and 70% for 10 and 20 mg L − 1 dye concentrations, respectively. It was observed that plant parts remained active after adsorption of the dye and were able to remove more dye concentration than 20 mg L − 1 . These results proved that B. fedtschenkoi plant has a good tendency to decolorize synthetic wastewater of CR azo dye as well as triarylmethane dye MB. Figure 5e and 5f show the decolorization of MB and CR respectively by using C. indicum. The percentage decolorization obtained for 10 and 20 mg L − 1 MB dye concentrations were 87 and 70% respectively. Initially plant leaves became dried, later stems and roots of the plant also showed dryness after the removal of dyes. The plant becomes died after treatment with higher dye concentrations. However, the MB color removal by this plant was acceptable yet plant endurance was not signi cant for the treatment of triarylmethane dye, MB. The results with CR dye synthetic wastewater revealed only 44 and 42% decolorization at 10 and 20 mg L − 1 concentrations, respectively. Wilting of the plant takes place after treatment of CR dye. The plant was not able to treat dye concentration higher than 20 mg L − 1 . Hence, C. indicum is not suitable for the phytotreatment of CR synthetic dye wastewater.
T. erecta plant was also used for a screening test to remove MB dye from synthetic wastewater. It was observed that plant had the more capacity to decolorize the triarylmethane dye, MB in comparison to CR dye. Figure 5g and 5h show the decolorization of MB and CR dye, respectively. The decolorization for 10 and 20 mg L − 1 MB dye wastewater was 84 and 68% respectively. After decolorization, the MB dye plant shows withering. Initially, the leaves become dry then subsequently stems and roots. Due to these conditions, the plant was no more active for treatment with more MB dye concentrations than 20 mg L − 1 .
The percentage decolorization was observed 67 and 66% for 10 and 20 mg L − 1 CR dye concentrations, respectively. Though the plant can decolorize the azo dye, CR and MB but T. erecta plant dryness after removal of the toxic dye makes it unsuitable for the treatment of synthetic dye wastewater.  Hence, the results obtained from the screening experiments clearly indicate that the maximum percentage decolorization obtained from the T. ammi plant followed by B. fedtschenkoi and both plants also remain active after removal both MB and CR dyes. C. indicum and T. erecta plants also show their potential for decolorization of synthetic dye wastewater however, their survival rate makes them insigni cant for phytoremediation process. H. rosa-sinensis plant was also not considerable for survival because owers wither after dye removal. The plant C. roseus is able to bear the toxic impact of dyes but the rate of decolorization is quite slow for both MB and CR dyes.
In the literature, the removal of MB and CR was reported by a few researchers by using the phytoremediation technique as shown in at 10 and 20 mg L − 1 CR dye concentrations respectively and remained active after the decolorization process. However, it has been observed that the dye was found to be adsorbed on the roots of T. ammi plant possibly due to the rhizo ltration process, and hence plant could be able to provide maximum decolorization. Therefore, T. ammi plant acts as a potential candidate for future research where it can be used as a phytoremediator for decolorization of dye wastewater.

Conclusion
The design of hydroponics system shows the e cient utilization of system for screening the plants and developing the growth of the root system of plants in optimum time by using alternative two pipe system.
The results from the present research support the ability of six screened plants for the removal of MB and CR dyes. T. ammi and B. fedtschenkoi are the most e cient plants for the removal of both dyes. Moreover, the survival of both plants seems to be signi cant. Maximum percentages of decolorization obtained from the T. ammi plant are 99 (10 mg L − 1 ) and 86% (20 mg L − 1 ) for MB dye, and 95 (10 mg L − 1 ) and 84% (20 mg L − 1 ) for CR dye due to its adsorption on the roots of the plant. Therefore, further research work can be focused on dye removal by using T. ammi plant based on the adsorption mechanism. In the future, adsorption mechanism explored by using different instrumental techniques such as Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy, and statistical analysis can also be done with different operational parameters such as plant weights, the relative growth rate of plants, the effect of pH, etc.

Declarations
Competing interests: The authors declare that there are no competing interests.
Ethics approval and consent to participate: "Not applicable", as research does not report on or involve the use of any animal or human data or tissue.
Consent for publication: Not Applicable.

Funding
This research work did not receive any funding.

Availability of data and materials
The data used to support the ndings of this study are available from corresponding authors upon request as the relevant data will be used by PhD scholar for her future works in continuation.  Image depicting growth of (a) B. fedtschenkoi and (b) T. ammi before and after 2-step treatment in hydroponic system. Red circles showed the growth of roots enhanced after treatment. See the Supplemental Files section for the complete gure caption.

Supplementary Files
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