In the present study the influence of hydraulic retention time (HRT) in SBR and sludge age (SRT) on the effectiveness of nitrogen removal from leachate was investigated. Two series were performed. In each series, experiments were carried out in four SBR operated in parallel at HRT 12, 6, 3 and 2d, respectively. Each series differed in sludge age. In series 1, SRT decreased from 51 to 17d with shortening of HRT, while in series 2 it was about 2 times shorter.
In each series the amount of nitrogen used on biomass synthesis, removal of nitrogen in denitrification and losses of ammonium during the aeration phase were estimated on the basis of material balance for all nitrogen forms in SBR cycle. It was shown that nitrogen consumption on biosynthesis was decreased linearly to the HRT increase. In series 1, the rate of ammonium nitrogen removal increased from 5.38 mgN_NH4/g VSS·h to 7.36 mg N_NH4/g VSS·h with HRT shortening from 12 to 3d, respectively. In series 2 the rate of ammonium nitrogen removal was nearly constant, regardless of HRT and on average it was 1.74 mg N_NH4/g VSS·h. The losses of ammonium nitrogen in series 1 increased from 8.2 mg N/dm^3.cycle in SBR 1 to 33.4 mg N/dm³.cycle in SBR 4, while in series 2 it was almost 2 times lower.