Sustainable removal of methylene blue from wastewater using silica sand coated with Al<sub>2</sub>O<sub>3</sub> nanoparticles: a comparative study of batch and fixed bed column reactors.

Abstract

This research addresses the challenge of effectively removing methylene blue (MTB) dye from wastewater, given its high solubility and stubborn resistance to biodegradation. Iraqi silica sand coated with synthesized aluminum oxide nanoparticles (SSC-Al₂O₃) was investigated as a novel adsorbent for removing MTB molecules. This study demonstrated the adsorption capacity of SSC-Al₂O₃ in a batch configuration and predicted the breakthrough curves in a fixed-bed column reactor. At the ideal pH (6), under an agitation speed of 200 rpm and 75 minutes, isothermal equilibrium adsorption achieved 95.33% adsorption efficiency. Adsorption isotherms followed the Freundlich isotherm type. Experiments were carried out applying fixed bed columns with bed heights of 4 cm (78.5 g), 7 cm (137.4 g), and 10 cm (196.3 g) with a flow rate of 10 L h^-1. The bed height of (10 cm) offered the longest breakthrough time and the least steep breakthrough curve. Higher flow rates decreased the adsorption capacity and yielded steeper breakthrough curves. FTIR analysis of SSC-Al₂O₃ showed that the hydroxyl, carboxyl, and amine functional groups were involved in bonding between MTB dye and the sorbent. This shows that SSC-Al₂O₃ has excellent ability in batch and continuous flow systems to treat industrial wastewater containing MTB dye.