Re-use of wasted sludge to treat industrial pollutants

Abstract

The wasted sludge from ferrous ion-dependent nitrate removal (FeNiR) process is potential to be re-used as adsorbent to remove industrial pollutants. After pretreatment, the adsorption efficiency of FeNiR wasted sludge to reactive red X-3B, minocycline hydrochloride and Cr6+ was 88.95%, 90.08%, and 95.97%. The optimal initial pH to adsorb reactive red X-3B, minocycline hydrochloride, and Cr6+ was 2, 4, 2, while the optimal adsorbent dosage was 0.3 g, 0.8 g, and 1.0 g, and the optimal temperature was 50 °C, 30 °C, and 50 °C. The adsorption process follows the pseudo-secondary adsorption kinetics model, indicating the chemical adsorption dominates the adsorption process. The analysis of adsorption thermodynamic shows that all three adsorption reactions proceed spontaneously. From the results of the scanning electron microscope (SEM) and Brunner-Emmett-Teller (BET) analysis, the FeNiR wasted sludge after pretreatment is porous that endows the wasted sludge physical adsorption ability. The Fourier transform infrared (FTIR) analysis shows that the chemical bonds, including the hydroxyl group of Fe3O4, the Fe-O, and the α-FeOOH in the iron encrustation play more important roles in the adsorption process. Being used as adsorbent to treat industrial wastewater is a promising way to re-use the wasted sludge and decreases the cost of FeNiR process.