Removal of triclosan in nitrifying activated sludge: Effects of ammonia amendment and bioaugmentation

• Faster triclosan removal was highly related to higher ammonia oxidation in NAS.
• NAS showed slower triclosan removal when ammonia oxidation was inhibited.
• Bioaugmentation with strain KCY1 did not enhance triclosan removal in NAS.
• This study indicated the important role of unknown triclosan degraders in NAS.

This study investigated two possible strategies, increasing ammonia oxidation activity and bioaugmenting with triclosan-degrader Sphingopyxis strain KCY1, to enhance triclosan removal in nitrifying activated sludge (NAS). Triclosan (2 mg L−1) was removed within 96-h in NAS bioreactors amended with 5, 25 and 75 mg L−1 of ammonium (NH4–N). The fastest triclosan removal was observed in 25 mg NH4–N L−1 amended-bioreactors where high ammonia oxidation occurred. Inhibition of ammonia oxidation and slower triclosan removal were observed in 75 mg NH4–N L−1 amended-bioreactors. Triclosan removal was correlated to the molar ratio of the amount of nitrate produced to the amount of ammonium removed. Bioaugmentation with strain KCY1 did not enhance triclosan removal in the bioreactors with active ammonia oxidation. Approximately 36–42% and 59% of triclosan added were removed within 24-h by ammonia-oxidizing bacteria and unknown triclosan-degrading heterotrophs, respectively. The results suggested that increasing ammonia oxidation activity can be an effective strategy to enhance triclosan removal in NAS.

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