Display omitted •MAIFAS displayed better N and P removal compared to suspended control.•MAIFAS process removed >99% ammonia and 51% P without mechanical aeration.•Localized photo-oxygenation at the biofilm surface was observed using microelectrodes.•Biofilm microprofiles showed no ammonia uptake by algal portion of biofilms.•Candidatus Accumulibacter contributed to 55% of the rRNA in the MAIFAS biofilm. The Integrated Fixed-Film Activated Sludge (IFAS) process is an advanced biological wastewater treatment process that integrates biofilm carriers within conventional activated sludge to uncouple the sludge retention time for nitrifiers and heterotrophic bacteria. In this study, we incorporated microalgae into the IFAS configuration for photo-oxygenation and evaluated the symbiotic reaction between microalgae and bacteria for both suspended solids and IFAS biofilm media. In a sequencing batch mode, the microalgae-IFAS system removed more than 99% ammonia and 51% phosphorous without the need for mechanical aeration. Biofilm microprofiles revealed localized photo-oxygenation by the algal biofilm and nitrification by nitrifiers on the IFAS media. Genetic sequencing showed that the addition of microalgae to the IFAS system promoted significant changes in the bacterial community structure and altered metabolic activity of several bacterial groups. Overall, this research represents a novel strategy for reducing energy consumption while meeting stringent effluent standards using a hybrid symbiotic microalgae-IFAS technology.