Elucidation of microbial nitrogen-transformation mechanisms in activated sludge by comprehensive evaluation of nitrogen-transformation activity

•It developed a simple and reliable method to differentiate various N-transformation activities.•Optimization of S0/X0 ratios reduced N-transformation activity determination errors.•The oxygen environment and assay media effectively differentiate N-transformation activities.•ATU addition can differentiate chemolithotrophic from heterotrophic ammonia oxidization.•Comprehensive activity evaluation elucidated major microbial N-transformation mechanisms.

Using prepared nitrifying sludge, anaerobic ammonia oxidization (anammox) sludge and two heterotrophic ammonia oxidization bacterial (AOB) species as inocula, this study elucidated the effect of oxygen conditions, assay media, and selective metabolic inhibitors on various microbial nitrogen (N)-transformation activities including aerobic chemolithotrophic ammonia and nitrite oxidization, aerobic heterotrophic ammonia oxidization, anammox, and aerobic and anoxic denitrification. The oxygen conditions and assay media effectively differentiated among almost all ammonia removal pathways except for separating aerobic chemolithotrophic ammonia oxidization from aerobic heterotrophic ammonia oxidization. A final allylthiourea concentration of 10 mg·L−1 was optimal for accurate determination of aerobic heterotrophic ammonia oxidization activity in the presence of aerobic chemolithotrophic AOB. Finally, this study developed a simple and reliable method to individually determine and compare the comprehensive N-transformation activity characteristics of several activated sludge samples from different origins, and to elucidate the major microbial N-transformation mechanisms for ammonia removal and N2 production.

Graphical abstractBased on the classic nitrification and denitrification activity tests, this study developed a simple, rapid and reliable method to individually determine and compare the comprehensive N-transformation activity characteristics of activated sludge by a combination of oxic/anaerobic conditions, assay media, and inhibitor addition (only ATU).Download high-res image (149KB)Download full-size image