Nitrite production in a granular sequencing batch reactor

The main objective of this research was focussed on the production of an effluent containing nitrite in an aerobic granular sequencing batch reactor (SBR) for heterotrophic carbon removal and combined nitrification-denitrification processes. For this purpose a granular SBR was operated at different carbon to nitrogen (COD/N) ratios in the feeding. The feeding flow was a synthetic medium, which contained acetate as carbon source (0.5 g COD/L) and ammonium as N source (100-200 mg N-NH4+/L). Different COD/N ratios of 15, 5 and 2.5 g/g in the feeding were tested. The COD removal percentage was around 90% during the whole operational period. When, the reactor was operated with a COD/N ratio of 15 g/g no nitrite production was observed in the effluent and nitrate was the only oxidized compound. During the periods fed with COD/N ratios of 5 and 2.5 g/g, nitrite was measured in the effluent at values of 7-20 mg NO2--N/L. Changes on the COD/N ratio provoked the presence of different concentrations of nitrogen compounds in the effluent. The N removal percentages obtained in the reactor decreased with the increase of NH4+ concentration in the feeding from 80% to 40%.