Results of carbon and nitrogen removal by moving bed biological reactors operating in two modes – continuous flow and sequencing batch – are presented. Three hybrid reactors with intermittent aeration were simultaneously operated in laboratory. Real septic tank effluent from a household was treated. The research confirmed satisfactory removal of carbon and nitrogen (up to 88% and 64%, respectively) by the hybrid reactors. The most preferable conditions for carbon and nitrogen removal were: hydraulic retention time = 0.55 d with 15/15 minutes aeration/non-aeration intervals in continuous flow reactors and four-hour cycles in sequencing batch reactors. Higher COD loadings on reactors’ volumes induced higher biomasses of biofilm and lower concentrations of activated sludge, but sludge wastage was negligible. Various groups of organisms were observed in both – activated sludge flocks and biofilm. The highest concentration of filamentous microorganisms was observed in the reactor with the highest COD loading. Rotifers were much more abundant in biofilm than in flocks, due to their relatively long growth time.