Synergistic microbubble ozonation and CaO₂ activation for refinery sludge valorization: Organic carbon liberation and...

Petroleum-containing waste sludge (PWS) accumulation and internal carbon scarcity are major hurdles in oily wastewater treatment. This study develops a cleaner production strategy using microbubble ozonation (MB-O₃) coupled with calcium peroxide (CaO₂) activation to simultaneously valorize PWS and remediate hydrocarbons. The MB-O₃/CaO₂ treatment (initial pH 7.0, CaO₂ dosage of 0.25 g/gTS) released 7620 mg/L of soluble chemical oxygen demand (SCOD) and 1163 mg/L of volatile fatty acids (dominated by acetic and propionic acid), improving sludge biodegradability by 6.8-fold. Concurrently, 70.3% total petroleum hydrocarbon (TPH) removal was achieved following pseudo-first-order kinetics, demonstrating broad-spectrum degradation across C₁₀-C₄₀ hydrocarbons. Mechanistic insights reveal that the synergistic effect hinges on the microbubble-enhanced ozone mass transfer and the dual-functional role of CaO₂ in sustained H₂O₂ liberation and self-driven pH modulation. The transition from •O₂^- dominated alkaline micro-zones to a persistent •OH oxidation regime ensures the synchronous mobilization of entrapped organic carbon and the oxidative cracking of hydrocarbons. Correlation analysis confirms that carbon liberation and TPH removal are mutually reinforcing processes. This strategy facilitates simultaneous waste remediation and carbon liberation, aligning with circular economy principles.