Kinetic Comparison of Attached and Suspended Biomass in an IFAS-MBR System Operated Under Intermittent Aeration: Long-Term Monitoring Under SRT Variation

This study presents a thorough investigation of a Membrane BioReactor – Integrated Fixed Film Activated Sludge – Intermittent Aeration (MBR-IFAS-IA) pilot plant operated from a biokinetic point of view. Specifically, respirometric techniques were applied on suspended and attached biomass to evaluate kinetic and stoichiometric parameters. The main aim was to investigate how the simultaneous presence of biofilm and activated sludge could affect the kinetic behaviour and the role of the Sludge Retention Time (SRT) variation in the kinetic behaviour of the system. The results highlighted a specialisation in the IFAS-MBR configuration, with the suspended biomass more affine to organic matter, whilst biofilm in the nitrification process. It was demonstrated that it is possible to operate IFAS-MBR systems at very low SRT without hampering the nitrification ability of the system due to the growth of nitrifiers in the biofilm, and the “seeding” effect would sustain nitrification even in the activated sludge. Respirometry has been confirmed to be an effective tool for evaluating biomass kinetic and stoichiometric parameters. The results of this study can be helpful in applying mathematical models in the design phase and for monitoring biomass viability during plant operations.