Kinetic modeling of azo dye adsorption on non-living cells of Nannochloropsis oceanica

The presence of toxic dyes in aquatic environments has become an issue of increasing concern worldwide. In this paper we investigate the adsorption behavior of azo dyes on non-living cells of Nannochloropsis oceanica. Nannochloropsis is a marine microalga widely used in aquaculture facilities as a feed material due to its valuable nutritional properties. Reactive Violet 5 (RV5) was selected as a model dye because of its widespread use in textile dyeing. The kinetics and equilibrium of RV5 adsorption on the biomass were studied at 10, 25 and 40 °C. Equilibrium data were found to be well described by the Temkin equation, with an apparent enthalpy change of 41.8 kJ mol-1. A kinetic model assuming local equilibrium and a linear driving force (LDF) mass-transfer mechanism was developed. The estimated LDF mass-transfer coefficient varied between 1.18 10-3 and 1.31 10-3 min-1. The model fitted the experimental data well and was used to simulate a treatment for the removal of RV5 from dyeing wastewater. Overall, the results obtained indicate that non-living cells of Nannochloropsis oceanica can be an effective adsorbent for the treatment of textile effluents containing azo dyes. The kinetic model developed can help evaluate the effect of the main treatment conditions on dye removal.