BIOREMOVAL OF A MODEL SYNTHETIC AZO DYE FROM AQUATIC MEDIUM BY Zostera marina L.: BIOSORPTION SYSTEM MODELING STUDIES ABSTRACT In this study, the biosorption of a model synthetic azo dye (basic red 46) from aquatic medium by the residual biomass of Zostera marina L. was first investigated. The experimental data revealed that the removal of dye significantly depended on pH, quantity of biosorbent, dye concentration and contact time. The optimal biosorption conditions were determined as pH of 8, biosorbent dosage of 10 mg, dye concentration of 30 mg L-1 and contact time of 360 min. The biosorption kinetic data were analyzed using the pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion models. Freundlich, Langmuir and Dubinin-Radushkevich models were used to model the experimental isotherm data. The results of modeling studies showed that Elovich and Freundlich models provided the best conformity to the biosorption kinetic and isotherm data. The maximum dye biosorption capacity of biosorbent based on Langmuir equilibrium model was predicted as 160.882 mg g-1 . Thermodynamic studies were performed to clarify the nature of biosorption process and the obtained results revealed that this biosorption system has a spontaneous and physical nature (ΔG° = -8.604 - -5.926 kJ mol-1 ). All obtained findings showed that this natural biowaste could be effectively employed as a low-cost biosorbent material for the removal of such pollutant agents from water medium.