An experimental study investigating the nitrogen removal efficiency from the recycle stream generated in the dewatering facility of the anaerobically digested sludge at the Deer Island wastewater treatment plant (WWTP) in Boston was conducted using a single submerged attached growth bioreactor (SAGB), designed for simultaneous nitrification and denitrification. The applied nitrogen loading to the reactor ranged from 0.7 to 2.27 kg-N/m3xd, and the corresponding total nitrogen (TN) removal rate ranged from 0.38 to 1.8 kg-N/m(3)xd. The observed nitrification rates varied from 0.42 kg-N/m3-d to 1.45 kg-N/m(3) xd with an ammonia load of 0.5 kg-N/m3-d and 1.8 kg-N/m(3)xd, respectively. An average nitrification efficiency of 91% was achieved throughout the experiment. Denitrification efficiency varied from 55%/o, obtained without any addition of carbon source, to 95% when methanol was added in order to obtain a methanol/nitrate ratio of about 3 kg methanol/kg NO3- -N.