Biotic and abiotic removal of acetaminophen during sidestream partial nitritation processes: Underlying mechanisms and transformation pathways

Pharmaceutical residues in sidestream wastewater pose the hazardous threats to ecosystem and human health. In this work, the biotic and abiotic degradation of acetaminophen were investigated during the sidestream partial nitritation process. Results demonstrated that the abiotic removal efficiency of acetaminophen was positively correlated with nitrite concentration, whereas the biotransformation of acetaminophen was mainly dependent on metabolic types and free nitrous acid (FNA) concentrations. 91.6 % of acetaminophen, acting as the sole carbon and/or energy source to support the growth of ammonia-oxidizing bacteria (AOB) and heterotrophs, was removed by adsorption (6.2 %) and biotransformation (consisting of 49.4 % AOB-induced metabolism and 36.0 % heterotrophs-induced metabolism) when lacking nitrite and FNA. Increasing FNA from 0.03 mg N L−1 to 0.15 mg L−1 led to decrease in acetaminophen removal (from 78.8 % to 60.1 %) and ammonia oxidation, ascribed to the inhibitory effect of FNA on AOB activity. Nitro substitution occurred under AOB-induced cometabolism, while hydroxylation was conducted by heterotrophs. N-deacetylation, ring cleavage, hydroxylation, nitro-reduction, and deamination at lower FNA levels (0.03 mg N L−1) contributed to the formation of small molecular products, supporting the feasibility of sidestream partial nitritation in the effective elimination of acetaminophen. This work provides strategies for optimizing anti-inflammatory drugs removal via the regulation of FNA in the sidestream wastewater treatment process. [Display omitted] •Acetaminophen could act as the sole carbon/energy source for AOB and heterotrophs.•Abiotic transformation was positively correlated with nitrite concentration.•Regulating FNA level favors the simultaneous removal of nitrogen and acetaminophen.•Biotransformation pathways correlate with FNA levels and microbial metabolic types.