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This paper summarizes the results obtained using the hybrid aerated submerged fixed-film (HASFF) process. HASFF is an innovative system comprising a four-compartment reactor having an array of fixed ceramic plates maintained under diffused aeration to support attached biomass, with activated sludge recycle to promote suspended growth in the reactor. Wastewater from a municipal treatment plant was fed to the reactor and its activated sludge was used for recycling in the hybrid system. Four pilot units were operated in the plant at various hydraulic retention times, HRTs (2, 4, 6 and 8 h), using primary-settled wastewater under organic loading rates up to 0.7 g BOD/gMLTVS. d. Data obtained showed that the overall BOD percentage removal efficiencies were consistently above 94.0% at all HRTs including the 2 hours while the COD percentage removal efficiencies ranged between 65.7-76%. The effluent's mean filtered BOD concentration ranged between 4.5-7.5 mg/l whereas the mean filtered COD concentration ranged between 70.0-89.6 mg/l. Increasing the hydraulic loading rate by four-folds from 0.08 to 0.32 m3/m2.d had a minor effect on the unit's BOD and COD percentage removal efficiencies indicating a robust biological process that is resilient to hydraulic shock loads, thereby offering a viable upgrading option.