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

Abstract

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 (Fe0)-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 BAC_Fe0 increased prominently (21.0%–32.3%), yet there was no change between BAC and BAC_Fe0. The highest ratios of nitrosamine degradation by BAC_Fe0 were 49.8%–99.0%, and degradation reaction kinetics conformed best to a pseudo-second-order model (R2>0.9269). The rate constants kobs for six nitrosamines ranged from 3.4×103 to 6.9 × 105 (M · s)−1. Additionally, the removal ratios and k2 of the linear nitrosamines partially scaled with their molecular weight, LogKH, and LogKow (R2=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 ∼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 Fe0 and biodegradation by the nitrosamine-reducing bacteria.