Degradation and transformation of nitrated nonylphenol isomers in activated sludge under nitrifying and heterotrophic conditions

Abstract Nitrated nonylphenols (2-nitro-nonylphenols, NNPs) are metabolites of the endocrine-disrupter nonylphenols (NPs). While they have been detected in the environment, their fate in activated sludge has yet to be determined. In this study, we used synthesized NNP isomers and a 14C-tracer technique to study the degradation and transformation of four NNP isomers (NNP111, NNP112, NNP38, and NNP65) in nitrifying activated sludge (NAS) and heterotrophic bacteria-enhanced activated sludge (HAS). Our results showed that the degradation of NNPs in both NAS and HAS was isomer-specific. The half-lives of the NNPs decreased in the order: NNP111 > NNP112 > NNP38 > NNP65. After 36 days of incubation, 9.48 % and 4.01 % of the 14C-NNP111 was mineralized in NAS and HAS, respectively. In addition to mineralization, five metabolites of NNPs containing hydroxyl, carbonyl, and carboxyl substituents on the alkyl chains were formed in NAS but not in HAS. The transformation of NNPs differed in NAS and HAS, mainly due to the differences in their microbial communities and the activities thereof in NAS and HAS. This is the first study of the isomer-specific fate of NNP isomers in activated sludge. Future studies should assess the toxicity, stability and potential risks of NNP metabolites in the environment.