Comparison of oxygen transfer and uptake between an integrated fixed-film activate sludge (IFAS) process and a conventional activated sludge process (ASP)

Integrated fixed-film activated sludge (IFAS) processes are a combination of biofilm reactors and activated sludge processes, achieved by introducing and retaining biofilm carrier media in activated sludge processes. We tested a full-scale IFAS process equipped with AnoxKaldnes media and coarsebubble aeration. This process operated independently in parallel with an existing full-scale activated sludge process. Both processes achieved the same percent removal of COD and ammonia, despite the double hydraulic load and double oxygen demand on the IFAS process. In order to prevent kinetic limitations associated with dissolved oxygen (DO) diffusional gradients through the IFAS biofilm and to avoid media coalescence on the reactor surface and promote biofilm contact with the substrate, high DO and high mixing requirements are specified for the IFAS system. These require an elevated air flux in the IFAS process, which was much higher than that of the parallel activated sludge process. Even though the air used per unit load removed should be the same for both processes, the IFAS reactors were characterized by higher air flux and air use per unit load treated due to the high DO and mixing requirements. This directly affected the energy footprint for aeration, which in this case was much higher for the IFAS system than activated sludge.