**1. Introduction**

Industrialization is a main source of water pollution. The negative impact of polluted water is more severe in developing countries as compare to developed nations [1]. Textile wastewaters contain dyes, and these dyes are one of the worst polluters of our environment [2]. Almost 17% to 20% of industrial water pollution is due to textile dyeing and finishing treatments given to fabrics [3]. Many dyes are derived from heavy metals such as copper (Cu), lead (Pb) and cadmium (Cd). The uses of these metal-complex dyes is a source of heavy metals contamination in water bodies [4]. The release of textile wastewater into open waters causes oxygen level depletion. Dyes block the sunlight in water bodies, thus stopping photosynthesis [5]. These textile contaminants are also carcinogenic and mutagenic for all life forms [3].

Some plants have the capacity to take up pollutants from the environment into themselves [6]. In the past, many plant species have proved to remove or degrade dyes, such as *Sesuvium portulacastrum* that removed Green HE4B, *Portulaca grandiflora* that removed Navy blue HD2R, *Brassica juncea* that removed methyl orange and *Glandularia pulchella* that removed green HE4B [7–9]. Bacteria has the potential to remove dyes from wastewater [10]. Bacteria can also degrade synthetic dyes and use them as a sole source of carbon and energy [11]. There are many examples like degradation of crystal violet by *Enterobacter sp. CV-S1* [12].

Wetland technology has emerged as a sustainable approach for wastewater treatment as compared to conventional treatment processes [13–15]. Floating treatment wetland (FTW) is a variant of pond and wetland land technology (Figure 1), that has been proven as an innovative tool for wastewater treatment [16]. In FTWs, plants are vegetated on an artificial floating mat, such that their roots are submerged in the contaminated water and the aerial parts of the plants remain above the water [13]. The mat can be made of PVC pipes, polyethylene or any other suitable material that can support plants on a water surface [13,17]. Roots play an integral role in and provide space for biofilm formation [16]. Organic matter and other pollutants like heavy metals are taken up by the plants' roots and eventually degraded by bacteria inside the plants and on the roots' surface [11,18]. The roots of plants also act as biological filters as they help in filtration, sedimentation and adsorption of organic matter and suspended particles, as well as other pollutants [19]. In contrast to conventional wetlands, floating wetlands can be installed on any aquatic pond without digging, earth moving and additional land acquisition [13].

The application of specific microorganisms in combination with macrophytes in FTW systems is a recent approach to enhance the pollutant removal e fficiency of the system [20,21]. Naturally occurring bacteria and fungi reside inside and outside the plant roots and water, and contribute to pollutants removal process [22]. However, these microorganisms may have limited potential to degrade and remove toxic pollutants [23]. To overcome this concern, FTWs can be restorative by appropriate plant–microbe partnerships [24,25]. This plant–bacteria association may be plant–rhizospheric and or plant–endophytic, depending upon the nature of the bacteria and macrophytes [26,27].

**Figure 1.** Schematic representation of floating treatment wetland and associated pollutant removal process.

Floating wetlands have been widely used for the treatment of wastewater from different sources [28,29]. However, the potential of FTWs composed of *Phragmites australis* in combination with inoculated bacteria has not been fully explored for the treatment of dye-enriched textile effluent. This study was carried out to analyze the potential of *P. australis* and selected bacteria in the degradation of dyes, pollutants reduction and the ultimate alleviation of toxicity of dye enriched water. Further, the focus of this study was on the persistence and survival of inoculated bacteria within the floating wetland system.

#### **2. Materials and Methods**

#### *2.1. Synthesis of Textile E*ffl*uent*

Three different types of textile effluent were synthesized in the laboratory by mixing three different dyes (500 g) in tap water separately. The first type of effluent contained Bemaplex Navy Blue DRD (D1), the second type of effluent contained Bemaplex Rubine DB (D2) and third one contained Bemaplex Black DRKP Bezma (D3). The concentration of these dyes was 500 mg L−<sup>1</sup> in each type of synthetic textile effluent. These dyes were selected because of their common use in the textile industry and the high concentration of these toxic dyes and associated degraded products in textile effluent [30]. The experiments were performed individually on each type of effluent.
