Biological nutrients removal via nitrite from the supernatant of anaerobic co-digestion using a pilot-scale sequencing batch reactor operating under transient conditions

The short-cut nitrogen removal (SCNR) and denitrifying phosphorus removal via nitrite (DPRN) were studied using a pilot-scale sequencing batch reactor (SBR) for the treatment of the supernatant produced from the anaerobic co-digestion of waste activated sludge (WAS) and the organic fraction of municipal solid waste (OFMSW). The stability and behaviour of the biological via-nitrite processes were examined under transient conditions, imposed from the ordinary and extraordinary operation of the full-scale anaerobic digestion plant and the dewatering process of the anaerobic digestate. Nutrients removal was tested at low volumetric nitrogen loading rates (vNLR = 0.2 kgN m(-3) d(-1)), at the vNLR of the system's nitrifying capacity (0.8 kgN m(-3) d(-1)) and above its nitrifying capacity (1.1 kgN m(-3) d(-1)). Complete absence of nitrite oxidizing bacteria (NOB) activity was accomplished, even when the free ammonia (FA) concentration in the reactor was very low (