This paper presents experimental results for the simultaneous removal of formaldehyde (CH2O) and ammonia nitrogen using three bioreactors: a sequencing batch reactor (SBR), a sequencing continuous-inflow reactor (SCR), and a novel modified moving-bed SCR (MSCR). The performance of these bioreactors was first investigated in terms of removal of CH2O and COD. The MSCR achieved the highest removal capacity: 100% of the CH2O and 97% of the COD at an inlet loading rate of 1.25 kg CH2O/m(3) d (1.8 kg COD/m(3) d) over a 24-h cycle time. The SCR was the next most efficient bioreactor. The nitrogen removal performance of the SCR and the MSCR was also studied. Results indicated that the MSCR removed approximately 99.9% of the nitrogen at a loading rate of 1.25 kg N/m(3) d in the presence of 1.25 kg CH2O/m(3) d. This work showed the MSCR to be an efficient modification of the activated sludge process for concurrently obtaining CH2O and nitrogen removal. (C) 2010 Elsevier B.V. All rights reserved.