Impact of bioaugmentation with nitrifying biomass in a CAS and in an MBR pilot plants

A Conventional Activated Sludge (CAS) system and a Membrane Bioreactor (MBR) were bioaugmented with a same nitrifying biomass selected in a side-stream MBR fed with a high nitrogen-loaded influent. Microbial communities evolution was monitored and comparatively analysed through bio-molecular investigation (FISH and T-RFLP techniques) followed by statistical analyses. The bioaugmentation process caused, indeed, a conspicuous increase of nitrifying bacteria of the genera Nitrosomonas and Nitrobacter in both the inoculated CAS and MBR reactors. The overall structure of the microbial community was actually changed in these reactors, although not evolving toward an overlapping with that of the side-stream community. Finally, the effect of bioaugmentation was significantly more pronounced on the biomass of the MBR reactor with respect to the CAS