Abstract

Copper (Cu) is a heavy metal found in waters from regions impacted by mining. This type of contamination can present a significant challenge to the efficiency of biological nitrogen removal processes. This study investigated the impact of Cu on two anaerobic ammonium oxidation pathways: Feammox (ammonium oxidation coupled to iron reduction) and Anammox (anaerobic ammonium oxidation). Batch experiments using enriched cultures from both processes were conducted under controlled Cu concentrations (0, 4, 8, and 10 mg/L), and Feammox was analyzed under two carbon sources (acetate and bicarbonate). Anammox showed stable NH4+ removal (similar to 50%) at all Cu concentrations, although NO2- accumulation at higher Cu levels indicated potential stress. In contrast, Feammox was more sensitive to Cu, particularly in terms of Fe3+ reduction and Fe2+ accumulation, where acetate promoted greater activity than bicarbonate. Molecular analyses revealed the presence of key microorganisms associated with Feammox processes, such as Albidiferax ferrireducens, Acidimicrobium, Geobacter spp., Shewanella spp., as well as Anammox bacteria. Similarly, nitrogen cycle-related genes also remained detectable under moderate copper concentrations. These results indicate that while both processes can operate under moderate copper concentrations, Feammox was more susceptible to inhibition. These findings contribute to understanding the resistance and limitations of biological N removal in Cu-contaminated wastewater, allowing for the development of more robust and efficient treatment strategies.