Aerobic Granulation Technology-Based Cresol Degradation: A Comparative Evaluation of Reactor Studies

Cresols (ortho-, meta-, and para-isomers), potent xenobiotic compounds prevalent in industrial wastewaters, pose severe environmental and health threats and require effective bioremediation solutions. Aerobic granulation technology was assessed for its degradation efficiency toward a mixed cresol-isomer system in batch and continuous reactors, addressing a key gap in existing research that has focused mainly on individual cresol isomers. The comparative reactor evaluation revealed that continuous operation achieved a 10.21% increase in cresol degradation efficiency compared with batch mode, highlighting its sustained performance. The continuous reactor demonstrated optimal cresol degradation at a flow rate of 120 mL h⁻¹ (HRT, 8.33 h), supported by elevated volumetric and specific degradation rates. Enzyme analysis confirmed elevated activities of catechol 1,2-dioxygenase and phenol hydroxylase, supporting oxidative metabolism. The biodegradation mechanism was supported by enzyme activity assays and FT-IR spectral analysis, which demonstrated the absence of characteristic peaks associated with cresol functional groups and the emergence of oxygenated functional groups, thereby confirming structural changes during aerobic granular degradation. The significant degradation efficiency and enzyme-assisted structural transformation of cresol validate aerobic granular sludge as an effective treatment system for cresol-contaminated wastewater.