‘Swinging ORP’ as operation strategy for stable reject water treatment by nitritation–anammox in sequencing batch reactors

A single stage nitritation–anammox pilot scale SBR was implemented to treat reject water from sludge dewatering. The SBR was operated with a new strategy, a combination of interval feeding with interval aeration using the oxidation–reduction potential (ORP) as the main process indicator parameter. The strategy allowed for optimized treatment of high nitrogen loaded reject water providing stable operation and achieving a nitrogen removal efficiency of more than 90% at a volumetric nitrogen load of 400 g N m−3 d−1. COD removal was also observed with an efficiency of around 70%.The concept of interval feeding monitored by the ORP also allowed for adjustments to changing environmental conditions (i.e., decrease in temperature) by adjusting the number of intervals per cycle and the number of cycles per day. The distinct swing in the ORP signal which showed the largest amplitudes and most distinct pattern of all monitored parameters made the ORP the most favorable control parameter for nitritation–anammox in this type of SBR.

► Our study presents a new operation strategy for nitritation–anammox in SBRs.
► Interval feeding allows for use of the ORP as main monitoring parameter.
► ORP signal has the largest amplitudes (∼80 mV).
► ‘Swinging redox’ operation avoids large substrate variations, hence creating a stable environment for the microorganisms.
► The average volumetric nitrogen load was 400 g N m−3 d−1 (N removal >90%).