Two strategies (run 1 and run 2) were tested for biological nitrogen removal (BNR) of the digester supernatant of a plant treating municipal solid wastes (MSW) using a laboratory-scale sequencing batch reactor (SBR) with control of temperature. External chemical oxygen demand (COD) was added for denitrification, as not enough biodegradable COD was present. A Monod model was used to fit the NH4+-N removal. In run 1, temperature was fixed at 30 degrees C, and pH was fixed between 7.4 and 8.6 by the addition of NaHCO3. The hydraulic retention time (HRT) was set to 3 days, and the sludge retention time (SRT) was kept at 12 days. The cycle length was set to 8 h. Nitrate formation was avoided by temperature, pH, and limited aeration flow rate. In run 2, alkalinity was recovered with an intermediate denitrification period, thus avoiding the use of NaHCO3. The strategy consisted of alternating different aerobic-anoxic subcycles inside the operating cycle. The second strategy was found to be effective, with improved kinetics and without addition of chemicals. NH4+-N concentrations of around 360 mg L-1 day were removed with this strategy. The behavior of the SBR was modeled with a modification of Activated Sludge Model No. 1, using kinetic constants obtained in previous experiments. The model was used to predict the profiles of an optimal cycle of 6 h.