Surfactant-assisted biodegradation of nitrobenzene in groundwater by sulfided nano-zero valent iron activated persulfate: Synergistic effect, mechanism, and application.

Groundwater contamination by dense non-aqueous phase liquids (DNAPLs), particularly nitrobenzene, represents a significant environmental challenge due to their chemical stability, persistence, and low solubility. This study aims to develop a synergistic approach for the biodegradation of nitrobenzene in groundwater, leveraging a combined system of Tween 80-assisted solubilization, sulfidized nano-zero valent iron (S-nZVI), and persulfate (PS) activation. The reduction process is facilitated by S-nZVI, while PS activation generates strong oxidizing radicals, and Tween 80 enhances nitrobenzene solubilization, thus improving the overall treatment efficacy. Laboratory experiments, including both batch and column studies, were conducted to evaluate the performance of this approach. Furthermore, a persulfate slow-release gel system was introduced to provide sustained activation, leading to improved long-term degradation efficiency. The results demonstrated that the synergistic combination of S-nZVI, PS, and Tween 80 led to significantly enhanced degradation of nitrobenzene and its byproduct aniline, achieving degradation rates of up to 96.74% for nitrobenzene and 100% for aniline after 6 h under optimal conditions. Additionally, the oxidation rate of aniline reached 91.53% within 5 min when the optimal dosage of 1.2 mM PS was used. The Tween-80/S-nZVI/PS slow-release gel system further achieved cumulative degradation rates of 87.49% for nitrobenzene over 14 pore volumes in a column study, demonstrating its potential for practical applications in groundwater remediation. These findings provide a promising new direction for the remediation of contaminated groundwater.