Treatment of Municipal Organic Waste Leachates by Nitrification: Analysis of the Diversity and Abundance of Canonical and Comammox Microorganisms

Leachates from municipal organic waste contain high concentrations of ammonium and organic matter, making their treatment a top priority. The present study addressed leachate treatment under nitrification and focused on the diversity and abundance of comammox bacteria and their interaction with other canonical microorganisms. Batch reactors (1L) were fed with synthetic (100 mg HN4+-N/L) or leachate ammonium and operated at 150 rpm, 3 mg DO/L, pH 7, and 30 °C. Reactor performance was evaluated using metabolic response variables and the microbial community by shotgun metagenomic sequencing. The results showed ammonium and organic matter (5200 mg COD/L) consumption efficiencies above 95%. The abundance and richness of the microbial community decreased in the presence of leachates. Sequences of the genus Nitrosomonas predominated with the synthetic medium, while the genus Nitrospira was the most abundant when fed with leachates. Archaea and anammox sequences were also detected. Comammox sequences of Candidatus Nitrospira inopinata, C. N. nitrificants, C. N. kreftii, C. N. neomarina, C. N. nitrosa, and C. N. allomarina were also detected, with the first species being predominant in the presence of leachates. These findings demonstrate that comammox and canonical microorganisms coexist during ammonium removal from leachates.