Clara’s research is focused on the achievement of an energy-neutral or even energy-positive wastewater treatment plant (WWTP) through the implementation of autotrophic biological nitrogen removal (BNR) in the main water line. Autotrophic BNR is a two-step process. Firstly, half of the supplied ammonium is oxidized to nitrite under aerobic conditions; and secondly, ammonium and nitrite are directly converted to dinitrogen gas through the anammox process without oxygen and organic matter. To carry out the implementation in the mainstream of an urban WWTP Clara’s project is focused in a two-stage system operated in continuous. It consists of a first airlift granular reactor where ammonium is partially oxidized, and a second anoxic granular reactor where anammox process takes place. The final objective of the project is to achieve a stable operation of both reactors at long-term treating real urban wastewater at low temperature.

The research stay in TU-Delft will be focused on the first stage of the two-stage system: the partial nitritation step. The objective of the stay will be the study of the influence of hydroxylamine concentrations on the N2O emissions in this reactor. During the stay, the N2O emissions and the hydroxylamine concentrations would be determined in the granular sludge performing nitritation for a low strength ammonium wastewater at low temperature. The goal of this research is investigate the mechanisms related to N2O emissions by granular sludge enriched in ammonium oxidizing bacteria (AOB).