Alkaline-treated sawdust as an effective material for cationic dye removal from textile effluents under dynamic conditions: breakthrough curve prediction and mechanism exploration

This paper deals with the methylene blue molecule (MB) removal from synthetic and real textile wastewaters by alkali-treated orange tree sawdust (ATOS) under different dynamic conditions. Experimental results showed that MB removal efficiencies by ATOS increased when increasing initial dye concentrations and bed depths but decreased with the increase of the applied flow rates with a maximum adsorption capacity of about 110 mg g⁻¹. Moreover, various empirical models were applied to predict the experimental breakthrough curves (BTCs) and to determine the characteristic adsorption parameters. The applied models successfully fitted data in the following order: Thomas (R2−Th = 0.969), dose response (R2−D−R = 0.949), and Clark (R2−Clark = 0.874). ATOS was also found to efficiently remove dyes and other mineral pollutants such as chlorides, nitrates, and phosphates from real wastewaters. MB removal by ATOS involved not only cationic exchange but also complexation with acidic and basic functional groups. Moreover, important MB desorption yields from ATOS (more than 93%) were obtained when using saline solutions. All these results confirmed that NaOH-treated orange tree sawdust can be considered as a promising material for the removal of cationic dyes from industrial wastewaters.