Comparison of the performances and mechanisms of anammox bacteria in-situ self-enrichment under heterotrophic and autotrophic conditions by inoculating ordinary activated sludge

Abstract

The in-situ self-enrichment of anammox bacteria (AnAOB) was a pivotal facet of anammox in mainstream wastewaters treatment with low ammonia strength. This study explored the performances and mechanisms of AnAOB in-situ self-enrichment under heterotrophic and autotrophic conditions. The absolute abundances of AnAOB increased from 1.7 × 10⁵ to 1.6 × 10⁹ copies/g dry sludge in the partial denitrification/anammox (PD/A) system and 4.6 × 10⁸ copies/g dry sludge in the single anammox system, and the corresponding anammox activities reached 42.7 and 6.5 mg NH₄⁺-N/g VSS/d. In the PD/A system, denitrifying bacteria secreted abundant signal molecules to communicate with AnAOB, thereby promoting the high self-enrichment of AnAOB. Accordingly, the PD/A system showed significant advantages on AnAOB self-enrichment compared with the single anammox system. This study provided new insights into the mechanism of cooperative and competitive interactions between PD bacteria and AnAOB during the AnAOB self-enrichment, promoting the application of anammox process in low-ammonia wastewaters treatment.