Modeling the Effect of Hydroxylamine Addition on Nitrifying Biofilm Communities

<p>The mechanisms of chemically-induced nitritation in biofilm systems were explored using a 1-D model with hydroxylamine (NH₂OH) as a case study. Replacing conventional nitrification in wastewater treatment processes with nitritation and anammox would reduce both O₂ demand and the need for carbon addition. Implementing nitritation in a biofilm system would have further benefits due to the high cell density, high solids retention time, and the presence of microenvironments that foster a wider variety of transformations. This research used modeling to explore the potential of NH₂OH-induced nitritation in co- and counter-diffusional biofilms under mainstream conditions with NH₂OH supplied either from the bulk liquid or the base of the biofilm. The results suggested that achieving full nitritation was possible in both co- and counter-diffusional biofilms. For co-diffusional biofilms, both supply methods (bulk liquid or the base of the biofilm) were effective at inducing nitritation with low concentrations of NH₂OH. However, the retention of a small amount of NOB even at high NH₂OH concentrations suggests that nitritation could be more easily compromised. For counter-diffusional biofilms, NH₂OH supplied from the bulk was unable to induce nitritation, but when supplied from the base it was able to induce nitritation and fully eliminate NOB, even at low NH₂OH concentrations.</p>