Engineering a Core-Shell Chitosan Aerogel Microbial Reactor for Efficient Treatment of Oil-Contaminated Wastewater

As global industrialization accelerates, crude-oil extraction, refining, and transportation have generated increasing volumes of oily wastewater, posing serious risks to aquatic environments. In this study, porous chitosan aerogels were prepared from chitosan and citric acid via a sol-gel/freeze-drying strategy, and oil-degrading microorganisms were immobilized through a repeated enrichment process to construct a microbial reactor (CS-CA) for oily wastewater treatment. Silane-modified kaolinite was further assembled onto the CS-CA surface to obtain a hydrophobic kaolinite/chitosan aerogel core-shell microbial reactor (CS-CA@HKPS). The resulting reactor exhibited selective oil adsorption, strong hydrophobicity (water contact angle: 135.5°), and improved mechanical stability. CS-CA@HKPS achieved a 0 diesel removal efficiency of 86.7% for 1 wt % 0 diesel. When integrated into a self-designed vertical oily wastewater treatment unit, the reactor formed a stratified biological treatment system comprising aerobic, anoxic, and anaerobic functional zones. Under continuous-flow operation, the system enabled efficient microbial degradation and further purification of organic pollutants in simulated oily wastewater. The optimal process conditions are achieved when the water temperature is controlled at 37 °C, the pH value is maintained between 6.5 and 7.5, and the water aeration rate is set at 200 mL/min. Under these conditions, the removal rate of 1 wt % 0 diesel in simulated contaminated water by CS-CA@HKPS reaches 69.2%, and the chemical oxygen demand (COD) concentration is reduced to only 17.467 mg/L, representing a reduction of 64.43%. This work demonstrates a scalable and operationally stable bioreactor design that integrates material modification with reactor engineering, providing a promising biological route for the treatment of oil-contaminated wastewater.