Nitrite removal by a fixed culture in a submerged granular biofilter

The present investigation was carried out in the aim of developing a new fixed-culture nitrification-denitrification scheme short-circuiting the production of nitrate ion. The analysis of the behaviour of a submerged biofilter is reported for the development of a denitritation process. The results obtained show that the denitritation reaction takes place in the submerged biofilter according to apparently zero-order kinetics with a maximum nitrite removal rate of 2.1 kg NO−2---N m−3 of liquid phase • d−1, corresponding to a maximum volumic loading of 1.1 kg NO−2---N m−3 of reactor • d−1. The critical volumic loading applied (above which the denitritation yield fell) was 0.8 kg NO−2---N m−3 of reactor • d−1. The carbon requirement in the form of acetate was estimated for denitritation as 0.84 kg soluble TOC • kg−1 NO−2---N eliminated. Biological sludge was produced at a rate of 0.69 kg dry solids • kg−1 NO−2---N removed. Finally, it was shown that the denitrifying microorganisms adapted very well to a sudden input of nitrate into the denitritation biofilter.