Textile processing is one of the largest industrial sectors that produce large quantities of colored wastewater that must be treated before discharge. In developing countries where cotton is a significant feedstock, cellulose-reactive anionic dyes are dominant for textile finishing. For most textile processing units, the treatment of colored wastewater is a significant cost burden. The overarching primary goal of this thesis was to develop and utilize a low-cost and environmentally sustainable water hyacinth root powder (WHRP) bioadsorbent. A secondary goal was to combine the bioadsorbent with phytoremediation using water hyacinth live plants. To achieve the above aims, WHRP bioadsorbents that are neither carbonized nor activated were prepared to remove cellulose-reactive anionic blue dye from an aqueous solution. The WHRP had a high specific surface area of 670 m2/g, suitable for adsorption. The effect of adsorption pH (2 – 8), adsorbent dose (1 g/L – 6 g/L), dye concentration (50 mg/L – 500 mg/L), adsorbent particle sizes (50 μm –1000 μm), adsorption mixing speed (100 rpm – 200 rpm), and adsorption temperatures (22 oC – 60 oC) were systematically studied. It was found that the protonation of the lignin polyphenols was responsible for the adsorption process at low pH. Adsorption of cellulose-reactive blue dye to WHRP was spontaneous as characterized by the negative Gibbs energy (−11 kJ/mol to −24 kJ/mol) and exothermic with negative enthalpy (−13 kJ/mol to −23 kJ/mol). The overall adsorption process was controlled by more than one mechanism since the intraparticle diffusion was not the only rate-limiting step under the experimental conditions. Dye removal by adsorption was effective, but the process is inherently non-destructive and merely concentrates the adsorbate without degrading it, thus generating solid waste. To address this challenge, an in situ heterogeneous oxidative degradation process of the adsorbed dye was developed. A kinetic model of the in situ dye oxidation reaction allowed the determination of the best operating conditions to achieve a high reaction rate and high dye degradation percentage within 20 min. Notwithstanding the adsorption and in situ degradation of cellulose-reactive blue dye, this process does not achieve complete removal when the dye concentration is above 200 mg/L. To this end, the batch adsorption process was coupled with sand column filtration/adsorption and phytoremediation with live water hyacinth plants. This integrated process allowed the complete removal of the dye at concentrations ranging from 200 mg/L to 500 mg/L. Keywords: Adsorption, adsorption kinetics, in situ oxidative degradation, phytoremediation.