PARTIAL NITRITATION PROCESS ASSESSMENT
In this study, partial nitritation has the aim to oxidise a fraction of ammonium (about 50–60 %) into nitrite without following oxidation to nitrate. Experiments performed during eight months describe partial nitritation of supernatant from dewatering of digested sludge at Himmerfjärden wastewater treatment plant in the south Stockholm region. The process was the first step (reactor R1) and was followed by a second step (reactor R2) for oxidation of ammonium with nitrite to nitrogen gas. The evaluation was based on time series analysis and results from 15 profiles of inorganic nitrogen compounds and different operational parameters. The effluent Nitrite-to-Ammonium Ratio (NAR) depends on the influent supernatant composition (mainly ammonium concentration and alkalinity) and conditions in R1 (mainly dissolved oxygen concentration and drop in pH value). Modified methodology for biofilm was developed to measure Oxygen Uptake Rate (OUR) of ammonium and nitrite oxidisers.