Removal of azo dye from water via adsorption on biochar produced by the gasification of wood wastes.

It was the aim of this work to evaluate the adsorptive performance of the biochar obtained from the gasification of wood residues onto a solution of Indosol Black NF1200 dye. The study was performed by means of factorial design 22, having as control variables: pH and adsorbent's granulometry. Batch tests were carried out at 200 rpm for 3 h (T = 28 °C). As output variable, the percentage removal of dye was determined. The best operating conditions were pH = 2 and 100 mesh granulometry. Also, adsorbent dosage studies were carried out, as well as equilibrium and adsorption kinetics. Both kinetics and equilibrium of adsorption tests were proceeded in basic and acid medium. For a basic pH value (pH = 12), it was concluded the equilibrium was reached in about 3 h of experiment, the experimental qmax value was near 12 mg g-1, and the equilibrium data fitted the Langmuir model. On the other hand, for tests with pH = 2, the equilibrium was reached after 5 min of experiment, the experimental qmax value was over 185 mg g-1, and the equilibrium data fitted both the Langmuir and Freundlich models. Thus, the biochar produced via gasification of wood wastes appears to be a promising adsorbent for the removal of azo dyes from textile wastewater, especially when working at lower pH values. Also, for a 10-kg/h consumption of wood residue, approximately 10 kW of energy is generated and 1 kg of biochar is produced, which represents another advantage from the environmentally friendly point of view. Graphical abstract.