Nonylphenol (NP), one of the priority hazardous substances, is in fact a mixture of
numerous isomers. It is inconclusive whether or not biodegradation during wastewater
treatment process is isomer-specific, leading to the environmental release of NP in
different isomer profiles. In this study, we evaluated the isomer selectivity of 19 NP isomers
in a laboratory-scale continuous flow conventional activated sludge bioreactor under
various operational conditions. The removal efficiency of NP isomers ranged from 90 to
99%, depending on the operational conditions and isomer structures. Isomer selective
biodegradation resulted in the increase of composition of recalcitrant isomers, such as,
NP193a/b, NP110a and NP194 in the effluent. Moreover, biodegradability was related to the
bulkiness of a-substituents and followed a-dimethyl > a-ethyl-a-methyl > a-methyl-a-npropyl
> a-iso-propyl-a-methyl. Steric effect index, a quantitative descriptor of steric hindrance,
was linearly correlated with residues of NP isomers in the effluent (R2 ¼ 0.76).
Decrease of temperature to 10 C decreased the overall biodegradability and also enhanced
the relative enrichment of recalcitrant isomers. These findings suggest that isomer compositions
of NP entering the environment may be different from those in technical mixtures
and that isomeric selectivity should be taken into account to better understand the
occurrence, fate, and ecological risks of NP.
Nonylphenol (NP), one of the priority hazardous substances, is in fact a mixture of
numerous isomers. It is inconclusive whether or not biodegradation during wastewater
treatment process is isomer-specific, leading to the environmental release of NP in
different isomer profiles. In this study, we evaluated the isomer selectivity of 19 NP isomers
in a laboratory-scale continuous flow conventional activated sludge bioreactor under
various operational conditions. The removal efficiency of NP isomers ranged from 90 to
99%, depending on the operational conditions and isomer structures. Isomer selective
biodegradation resulted in the increase of composition of recalcitrant isomers, such as,
NP193a/b, NP110a and NP194 in the effluent. Moreover, biodegradability was related to the
bulkiness of a-substituents and followed a-dimethyl > a-ethyl-a-methyl > a-methyl-a-npropyl
> a-iso-propyl-a-methyl. Steric effect index, a quantitative descriptor of steric hindrance,
was linearly correlated with residues of NP isomers in the effluent (R2 ¼ 0.76).
Decrease of temperature to 10 C decreased the overall biodegradability and also enhanced
the relative enrichment of recalcitrant isomers. These findings suggest that isomer compositions
of NP entering the environment may be different from those in technical mixtures
and that isomeric selectivity should be taken into account to better understand the
occurrence, fate, and ecological risks of NP.
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