BACKGROUND: Redox potential value (or pE) can be used as a monitoring parameter for deammonification processes treating rejectwater. In this study its use as a control parameter was investigated. Experiments were carried outwith a one-stage partial nitritation/anammox process in a 200 L moving bed biofilm reactor (MBBR) with 40% filled Kaldnes biofilm carriers. RESULTS: Tests on different combinations of nitrogen loads (1.8-3.3 gN m(-2) d(-1)) and pE values (-1, 0, 1) revealed that process performance was stable and nitrogen removal efficiency >80% was achieved at all tested pE values except pE=-1. A value close to pE=0 was the most suitable in terms of process performance at 25 degrees C at all tested pE values. With a fixed redox potential value (pE=0) used in the system, the air supply adjusted automatically under different nitrogen loads and maintained a high nitrogen removal efficiency. Theoretical calculations showed that pE>0.15 (at pH=7) provides conditions for nitrite conversion into nitrate at 25 degrees C. CONCLUSION: Redox control turned out to be a suitable control parameter for operation of a partial nitritation/anammox process. A redox value of 0 was a suitable value under different nitrogen loads in this pilot-scale study. (C) 2015 Society of Chemical Industry