INFLUENCE OF SEEDING CONDITIONS ON NITRITE ACCUMULATION IN A DENITRIFYING FLUIDIZED-BED REACTOR

The factors influencing the nitrite accumulation during denitrificatio n have been studied in a laboratory scale fluidized bed biofilm reacto r. The nitrate and nitrite removal activity of two different biofilms were compared. A high residual nitrite accumulation (up to 30% of the initial nitrate feed) was observed in the biofilm generated with Ps. a eruginosa as preponderant organism. In the biofilm with a preponderanc e of Ps. stutzeri the residual nitrite appeared only at very low hydra ulic residence times below 0.25 h. The environmental factors (oxygen c oncentration) and the operating conditions (C/N ratio, nitrate loading , biofilm thickness) did not significantly influence the nitrite accum ulation. The residual nitrite in the biofilm of Ps. stutzeri remained lower than that in the biofilm of Ps. aeruginosa, even under condition s of carbon source limitation, oxygen saturation and high nitrate load ing up to 8.3 kg N-NO3- m(-3) d(-1). The more active biofilm was chara cterized by higher protein concentration and protein/polysaccharides r atio.