Candidatus Accumulibacter phosphatis- the nitrite oxidizer -em class="EmphasisTypeItalic">Candidatus Nitrospira defluvii-or the anammox bacterium -em class="EmphasisTypeItalic">Candidatus Kuenenia stuttgartiensis-are now available through metagenomic studies. Metagenomics allows to genetically characterize full-scale WWTP and provides information on the lifestyles and physiology of key microorganisms for wastewater treatment. Integrating metagenomic data of microorganisms with metatranscriptomic, metaproteomic and metabolomic information provides a better understanding of the microbial responses to perturbations or environmental variations. Data integration may allow the creation of predictive behavior models of wastewater ecosystems, which could help in an improved exploitation of microbial processes. This review discusses the impact of meta-omic approaches on the understanding of wastewater treatment processes, and the implications of these methods for the optimization and design of wastewater treatment bioreactors." />