Enhanced Degradation of Nitrosamines from Water Using Zero-Valent Iron-Assisted Biological Activated Carbon

Nitrosamines have become a focus of considerable research because of their carcinogenicity and environmental universality. In this study, to effectively remove nitrosamines, biological activated carbon (BAC) was acclimatized by a nitrosamine-reducing bacterial strain, and zero-valent iron (${\mathrm{Fe}}^0$)-assisted BAC was used to degrade nitrosamines from aqueous solution. The influencing factors and degradation mechanism were investigated. Compared with activated carbon (AC), the removal efficiency of more strongly polar nitrosamines by BAC and $\mathrm{BAC}\_{\mathrm{Fe}}^0$ increased prominently (21.0%–32.3%), yet there was no change between BAC and $\mathrm{BAC}\_{\mathrm{Fe}}^0$. The highest ratios of nitrosamine degradation by $\mathrm{BAC}\_{\mathrm{Fe}}^0$ were 49.8%–99.0%, and degradation reaction kinetics conformed best to a pseudo-second-order model ($R^2>0.9269$). The rate constants $k_{\mathrm{obs}}$ for six nitrosamines ranged from $3.4\times {10}^3$ to 6.9 × 10⁵ (M · s)⁻¹. Additionally, the removal ratios and $k_2$ of the linear nitrosamines partially scaled with their molecular weight, $\mathrm{Log}{K}_H$, and $\mathrm{Log}{K}_{ow}$ ($R^2=0.5661-0.952$). All nitrosamines were degraded within $30\min$ under strong acidic conditions; the removal ratios increased by 11.2%−23.1% under anaerobic conditions, but were decreased by $\sim 10\%$ in the presence of humic acid. The primary degradation products were secondary amines, methylamine, formic acid, nitrate, and nitrite resulting from the reduction of ${\mathrm{Fe}}^0$ and biodegradation by the nitrosamine-reducing bacteria.