Rhizoclonium hieroglypicum, a novel biosorbent in the removal of Reactive Orange 107; Optimization, Equilibrium adsorption, Spectral and Toxicity assessment

Abstract

Blooming of textile industries has created environmental pollution due to the discharge of untreated dyeing effluent. Direct discharge of the textile dyeing effluent without proper treatment harms the environment by changing the eutrophication level and causes perturbation in the ecosystem due to their toxicity, mutagenicity and carcinogenicity [1, 2]. Various physico-chemical methods have been employed in the effluent treatment process, but these methods proves to be cost expensive, highly coupled with the formation of sludge and emission of toxic substances [3,4]. In recent years, decolourisation using biologicals such as algae, yeast, bacteria, fungi and adsorbents has gained attention among the environmentalists due to its cost effective and ecofriendly nature [5, 6]. Among them algae have been extensively used as a biosorbent to remove numerous hazardous  elements because of their cheap availability, high surface area and binding affinity [7]. In the present study, Rhizoclonium hieroglyphicum a fresh water macro alga which is rich in cell wall polysaccharides and no reports have been documented in the decolourisation of textile dyes using the candidate alga. Hence, the present study is an attempt to investigate the removal of reactive orange 107 from aqueous solution using Rhizoclonium hieroglyphicum. The surface area of the alga was 3.552m²/g and the moisture content was 29.52%. Optimization of the process variables such as pH, biosorbent and dye concentration and incubation time for dye decolourisation were performed on Response Surface Methodology (RSM) based Box – Behnken Design (BBD) model. The value of predicted R² (0.7276) was in suitable pact with the adjusted R² (0.9054) suggesting the fact that the model could be successfully exploited for modeling the perfect design space. The maximum decolourisation was obtained on 3^rd day at pH 9 in the medium amended with 300mg/l dye with 500mg/l biosorbent concentration under room temperature. The equilibrium adsorption data was performed based on adsorption isotherms (Langmuir and Freundlich isotherm) and the adsorption capacity of the biosorbent was well fitted with the Langmuir isotherm. The kinetic data were adhered well to Pseudo- second order kinetic model. The thermodynamic parameters such as Gibbs free energy (ΔGº), enthalpy (ΔHº) and entropy (ΔSº) were determined and the investigation affirmed the process of adsorption was spontaneous and endothermic in nature. The adsorbate- biosorbent interaction were analysed using Scanning Electron Microscope (SEM) with Energy Dispersive X-Ray Analysis (EDAX), Fourier Transform Infrared Spectroscopy (FT-IR), UV-Visible Spectroscopy and X-Ray Diffractometer (XRD). SEM micrograph revealed that the surface of the biosorbent was occupied by the dye molecules after biosorption. Similarly, FT-IR analysis revealed that the dye loaded on the surface of the biosorbent was evident with the shift in the peak. The disappearance of the peak in dye solution treated with Rhizoclonium hieroglyphicum indicated the process of decolourisation through UV- Vis analysis. XRD revealed the presence of crystalline nature of the biosorbent after biosorption of dye.  Microbial and Phytotoxicity studies substantiated the non-toxic nature of the dye. Thus, the findings of the present study reveals that Rhizoclonium hieroglyphicum could be proposed as an alternative ecofriendly biosorbent with an outstanding performance for reactive orange 107 removal.

Keywords: Rhizoclonium hieroglyphicum, Reactive orange 107, Equilibrium adsorption, Optimization, Microbial and Phytotoxicity studies.