Abstract
Wastewater treatment remains a challenging issue in developing countries, particularly due to the difficulty in controlling nitrogenous compounds release. Anaerobic reactors are widely used and effective in removing organic matter, but they are usually insufficient to meet nitrogen discharge criteria. The recirculation of nitrified effluent has become a viable alternative to promote denitrification without major structural changes. The present study evaluated the denitrification occurring in a Upflow Anaerobic Sludge Blanket reactor (UASB) and in a packed-bed reactor (PBR), operating with fixed concentrations of nitrate (50 mgN–NO 3 − L −1 ) and five decreasing levels of organic matter. The results showed similar performance between both systems, with complete denitrification occurring only when the COD/N–NO 3 − ratio was higher than 6. At lower ratios, both systems exhibited partial removal, with a slight advantage for the PBR.