Conventional Anaerobic Reactors Applied to Denitrification: a Comparison Between Packed Bed and UASB Reactors Under Low COD Conditions

Anaerobic reactors have been spreading in places with tropical climate and in developing countries. Their association with aerobic reactors provides great removal of carbonaceous matter with lower energy consumption and sludge production, although it does not allow the reduction in the concentration of total nitrogen. An alternative that could provide nitrogen removal without the construction of new reactors would be the nitrified effluent recirculation to the anaerobic reactor, in which denitrification would take place. Therefore, in this study, we sought to perform the nitrified effluent recirculation to the packed bed reactor (PBR) and UASB and concluded the following: (a) due to the presence of filling material, PBR tended to present a better performance in denitrification and removal of organic matter and suspended solids than the UASB reactor; (b) when performing the nitrified effluent recirculation to anaerobic reactors, the COD/NO3−-N ratio must not be less than 6; (c) the concentration of N2O in the biogas of both reactors remained below the detection limit, minimizing the production of greenhouse gases; and (d) the limitation of organic matter promoted partial denitrification, creating conditions for the emergence of anammox bacteria in the sludge.