Occurrence and fate of nitrosamines and their precursors in municipal sludge and anaerobic digestion systems

The fate of six nitrosamines and their secondary amine precursors and total precursors in three municipal wastewater treatment plants' primary sludge (PS), waste-activated sludge (WAS), and anaerobic digester mixed liquor (ADML) was investigated. N-Nitrosodimethylamine was detected at significant concentrations, with mean concentrations at 678 ± 302, 394 ± 322, and 271 ± 100 ng/L in PS, WAS, and ADML samples, respectively. N-Nitrosopyrrolidine was the other nitrosamine detected in sludge samples but at about an order of magnitude lower concentrations. PS samples also contained the highest concentrations of second a ryamines (mostly dimethylamine (DMA) and pyrrolidine) followed by WAS and ADML samples, with mean DMA concentrations at 1280 ± 689, 210 ± 266, and 6.2 ± 3.9 μ g/L, respectively. Secondary amines in ADML and some WAS samples accounted for only 20-30% of total nitrosamine precursors underlining the significance of as of yet uncharacterized precursors. Overall, anaerobic sludge digestion was a sink for nitrosamines and secondary amines on the basis of the decreasing trends of these compounds from PS to WAS to ADML after taking mass balances into account. An anaerobic bioassay conducted with ADML showed complete degradation of secondary amines even without additional carbon sources, while nitrosamine removal required carbon addition and was directly related to the chemical oxygen demand consumption.