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The merits of novel partial nitrification inhibitors: Enhancing nitrogen removal performance while suppressing the spread of resistance genes in partial nitrification-anammox system
Summary
This study evaluated two novel inhibitors—hexadecyl trimethyl ammonium chloride (ATMAC) and acetaminophen (APAP)—for controlling nitrite-oxidizing bacteria in a partial nitrification-anammox wastewater treatment system over 150 days, achieving 81.74% total nitrogen removal. The inhibitors selectively suppressed unwanted bacterial genes without significantly enriching antibiotic resistance genes in biofilms, though resistance gene leakage into the water phase remained a concern, particularly on polyethylene and polyurethane microplastic carriers.
Hexadecyl trimethyl ammonium chloride (ATMAC) and acetaminophen (APAP) were two novel partial nitrification (PN) inhibitors that effectively suppressed the activity of nitrite-oxidizing bacteria (NOB). However, ATMAC and APAP were considered emerging contaminants, their long-term use as inhibitors may pose environmental risks that requires attention. This study investigated the long-term (150 days) effects of ATMAC and APAP on the nitrogen removal capacity of the partial nitrification-anammox (PNA) system. Microbial community succession and resistance genes (RGs) propagation were also examined on three carriers: polyethylene (PE) carriers of K1 (PEK1), PE microplastics (PE MPs), and polyurethane (PU) MPs. The optimal condition was observed with 0.5 mg/L ATMAC and 2 mg/L APAP, under which the system achieved 81.74% total nitrogen removal. This combination selectively suppressed NOB-associated genes while enriching those of ammonia-oxidizing bacteria and anaerobic ammonium-oxidizing bacteria. Notably, stress induced by 0.5 ATMAC and 2 APAP did not result in significant enrichment of RGs on the biofilm, suggesting a favorable trade-off between performance enhancement and resistance risk. However, the high abundance of RGs in the water phase of the PNA system indicated a potential risk of environmental leakage. Furthermore, among the detected RGs, mexF and qacH-02 (efflux pump genes) consistently maintained high abundance across all samples, representing the primary manifestation of microbial resistance to the inhibitors. In addition, the increase in mobile genetic elements alerted to the risk associated with RGs propagation when using inhibitors.