Abstract

In single-sludge nitrification-denitrification process biomass is passed periodically through oxic and anoxic reactors. Nitrifying bacteria need oxygen for substrate oxidation. Behavior of these bacteria under anoxic conditions is still not sufficiently known. In this paper influence of retention time in anoxic reactor on nitrifiers has been studied. Optimum retention time for tested biomass was found to be 3 hours. A possible way to set-up this retention time is to increase denitrification rates by addition of support material of fixed-film biomass to anoxic reactor (e.g.polyurethane cubes). Increased denitrification rate results in decrease of necessary volume of anoxic reactor followed by increase of nitrification efficiency. Presence of fixed-film biomass has no influence on clarifier capacity and oxygen concentrations in oxic reactors. Theoretical aspects of this modification were confirmed in laboratory models with synthetic wastewater as substrate.

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