Acute Effect of Acetaminophen and Chloramphenicol on Hydrogenotrophic Denitrification Driven by Anaerobic Granular Sludge

Hydrogenotrophic denitrification (H2Den) is a promising strategy for NO3− removal from a supply water with low or negligible organic carbon content. However, its performance may be affected by emerging contaminants (ECs), which pose increasing risks to the environment and human health. This study investigates the acute effect of two widely detected ECs, acetaminophen (ACN) and chloramphenicol (CHP), at a 200 mg/L concentration, on H2Den using anaerobic granular sludge (AnGS) as inoculum. Acute exposure to ACN enhanced NO3− removal, likely due to the formation of oxidizable metabolites serving as electron donors through the heterotrophic pathway. On day 3, the residual NO3− concentration had already dropped below the regulatory limit of 50 mg/L, reaching 4.3 mg NO3−/L. In contrast, CHP initially inhibited the denitrification process, resulting in limited NO3− removal, i.e., a residual concentration of 145.4 mg NO3−/L on day 3. Nevertheless, short-term microbial adaptation likely enabled performance recovery under CHP exposure. On day 6, both EC exposure tests allowed a NO3− removal above 97%, although CHP resulted in residual NO2−, i.e., 37 mg NO2−/L. In the presence of ACN, the accumulation of gaseous denitrification intermediates was observed, with NO concentration in the headspace peaking at 9.5% (i.e., 16.2 × 10−2 µg NO/min/g VS) on day 6. Thus, in terms of either the production of gaseous intermediates or the presence of residual nitrogen in the liquid phase, ACN and CHP significantly influenced the denitrification performance, highlighting the importance of considering their presence in the operation of the denitrification process.