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 in physical examination. The results of different batch experiments for decolorization of dyes with respect to time were shown in Fig. 3. It has been observed from Fig. 3 that the decolorization percentage of dye increases with increase in the time. The same pattern of dye decolorization has been reported in literature by various researchers [12-15, 19-20, 24]. For instance, the different dye concentrations green HE4B decolorize to varying extent during 48 h of contact period by Glandularia pulchella and maximum decolorization was observed at 48 h in each concentration [24]. All these decolorization results and impact of synthetic dye wastewater on growth of plant used for screening were summarized in Table 2.
Fig. 3 (a) and (b) shows the decolorization pattern of MB and CR dye by utilizing T. ammi plant. Out of six screened plants, excellent decolorization of MB was observed in the case of T. ammi plant. The decolorization of 10 and 20 mg L−1 MB was 99 and 86% respectively. Plant growth was normal after adsorption of the dye into the roots. The decolorization (%) of CR dye by T. ammi shown in Fig. 3 (b) clearly indicates the admirable efficiency of T. ammi to decolorize the CR. The percentage decolorization of 10 and 20 mg L−1 of CR dye were 95 and 84% respectively. The plant remains survived after adsorption of dye into the roots. However, percentage decolorization decreases with increase in the concentration. These outcomes showed that T. ammi plant is an outstanding plant to decolorize the azo dye CR and triarylmethane dye MB at lower concentration. The decolorization graph of MB and CR dye by using B. fedtschenkoiplant was shown in the Fig. 3 (c) and (d) respectively. The plant B. fedtschenkoi shows significant decolorization of triarylmethane dye MB having 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 significant 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 the dye and plant was able to remove more dye concentration than 20 mg L−1. These results proved that B. fedtschenkoi plant has good tendency to decolorize synthetic wastewater of CR azo dye as well as MB, triaryl methane dye.
Fig. 3 (e) and (f) showed the decolorization (%) graph 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 become dried, later stems and roots of the plant also showed the dryness with the removal of dyes. The plant becomes died after treatment with more dye concentrations. However, the MB color expulsion by this plant was acceptable yet plant endurance was not significant for treatment of triarylmethane dye, MB. The results with CR dye synthetic wastewater revealed only 44 and 42% decolorization with the 10 and 20 mg L−1 concentration respectively. Wilting of the plant takes place after treatment of CR dye. The plant was not able to treat with more dye concentration than 20 mg L−1. Hence, C. indicum is not suitable for the phytotreatment of CR dye synthetic 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. Fig. 3 (g) and (h) shows 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, 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, plant was able to 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.
Fig. 3 (i) and (j) shows the decolorization of MB and CR respectively by H. rosa-sinensis plant. The decolorization obtained were 86 and 71% from the 10 and 20 mg L−1 MB concentrations respectively and 41 and 39 % decolorization obtained from the 10 and 20 mg L−1 CR dye solution. It indicated the potential of H. rosa-sinensis for MB synthetic dye wastewater decolorization. But the toxicity of dye effects on plant’s growth and plant was unable to remove dye concentrations than 20 mg L−1.
Fig. 3 (k) and (l) shows the percentage decolorization of MB and CR dye respectively by C. roseus. The decolorization percentage obtained for MB 10 and 20 mg L−1 was 35 and 34% respectively and 48 and 43% for CR 10 and 20 mg L−1 respectively. In case of C. roseus plant, it was found that plant remain active after dye removal however plant removal rate is quite slow for both the dyes. It was observed that plant could not effectively decolorize the synthetic wastewater up to 40 h.
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 the plant also remained active after removal the both MB and CR dyes. C. indicum and T. erecta plants also showed their potential for decolorization of synthetic dye wastewater however, their survival rate makes them insignificant for phytoremediation process. H. rosa-sinensis plant was also not considerable for survival because flowers withered after dye removal. The plant C. roseus can 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 phytoremediation technique as shown in Table 3. Eichhornia crassipes successfully removed MB dye (50 mg L−1) in 20 days experiment up to 98.4% [18] while Lemna minor (2 g) was exposed into 50 mg L−1 of MB dyes for 24 h decolorize up to was 80.5% [3]. In another study, 98% decolorization has been reported for Lemna minor in 144 h for 10% concentration and claimed it as a phytoremediation agent to remove MB dye from wastewater [19]. Another aquatic species Azolla piñata also reported in literature for removal of MB dye [20]. In literature, MB remediation reported by using aquatic plant species mostly. In the present research work, ornamental plant T. ammi plant showed the decolorization up to 99 (10 mg L−1) and 86% (20 mg L−1) for MB dye in 40 h experiment only. Hence, T. ammi plant proven to be more effective than Eichhornia crassipes and Lemna minor. Again, for phytoremediation of CR dye, Chara vulgaris [15] and Pistia stratiotes [21] aquatic species are reported for maximum decolorization 95 and 90% respectively. In present study, T. ammi reported for maximum decolorization up to 95 and 84% from the 10 and 20 mg L−1 CR dye concentrations respectively and remain active after decolorization process. However, it has been observed that the maximum dye was found to adsorb on the roots of T. ammi plant and it is possibly due to rhizofiltration process, plant could able to give maximum decolorization. Therefore, T. ammi plant acts as potential candidate for future research where it can be used as phytoremediator for decolorization of dye wastewater.