Continuous fixed-bed adsorption of Congo red dye by dual adsorbent (Neurospora crassa dead fungal biomass and wheat bran): experimental and theoretical breakthrough curves, immobilization and reusability studies

Abstract

A continuous study in a fixed-bed adsorption column was carried out by using dead fungal biomass of Neurospora crassa with wheat bran as a dual adsorbent for the removal of Congo red (CR) from aqueous solutions. Adsorption experiments were conducted at 303 K and at pH 6. The effect of operating parameters such as bed height (2–4 cm), flow rate (1–5 mL min–1), and influent dye concentrations (10–50 mg L–1) on the breakthrough characteristics of the CR adsorption system were determined using free dual adsorbent. Data confirmed that the total amount of adsorbed dye decreased with increasing flow rate and increased with increasing bed height and inlet adsorbate concentration. The highest column adsorption capacity of 5.71 mg g–1 was obtained using 50 mg L–1 inlet adsorbate concentration, 2 cm bed height, and 1 mL min–1 flow rate. The dual adsorbent was immobilized in various polymeric matrices such as calcium alginate, polyvinyl alcohol, polysulfone and sodium silicate. Batch experiments were conducted to select a suitable matrix for immobilization of the dual adsorbent. The maximum percentage of CR adsorption (84.72%) occurred using the polymeric matrix sodium silicate. Desorption studies were conducted in batch mode to desorb the CR dye from free and immobilized dual adsorbents using the desorbing agent methanol. Reusability studies of free and immobilized dual adsorbents for the adsorption of CR dye were carried out in three cycles in continuous mode. The equilibrium dye uptake and percentage adsorption of the regenerated free and immobilized dual adsorbents were decreased significantly after the first cycle. The percentage adsorption and equilibrium dye uptake using immobilized dual adsorbent in all three runs were lower than when free dual adsorbent was used. The percentages of dye adsorption were 57.75% and 41.70%; equilibrium dye uptakes were 0.696 mg g–1 and 0.35 mg g–1 in the third run of operation with free and immobilized dual adsorbent, respectively. Various mathematical models such as Adams-Bohart, bed depth service time (BDST), Thomas and Yoon-Nelson models were applied to column experimental data to predict the breakthrough curve and to evaluate the column capacity and kinetic constants of the models. The results fitted well to the experimental values in Thomas and Yoon-Nelson models with coefficients of correlation R2 ≥ 0.967 at different operating conditions. The adsorption of solute from textile industrial CR dye effluent was carried out in column studies separately, using free and immobilized dual adsorbents. The percentages of solute adsorption were 82.18% and 67.34%; equilibrium solute uptakes were 10.79 mg g–1 and 8.26 mg g–1 with free and immobilized dual adsorbent, respectively. We concluded that the dead fungal biomass of Neurospora crassa with wheat bran were shown to be suitable dual adsorbent for adsorption of CR using fixed-bed adsorption column and it can be used effectively in wastewater treatment.