Nitrogen, VFA and PHA profiles during one representative SBR cycle are presented in Fig. 3b. The sAUR increased when VFAs were depleted. A 10-min lag phase of nitritation was observed due to the presence of VFA.
After VFA depletion, the sAUR was 3.3 mgNH4-N (gVSS h)1. Aerobic conditions were maintained for 160 min in order to achieve almost complete ammonium oxidation to nitrite.
PHA were accumulated to a maximum of 5.5% coinciding with the depletion of VFA. The PHA level decreased during nitritation due to the lack of available COD. However, after complete nitritation, there was enough PHA to carry out the denitritation process with a sNUR of 9.36 mgNO2-N (gVSS h)1.
The overall nitrogen removal in this cycle was 98% resulting in an effluent with only 0.8 mgNH4-
N L1. Similar results were obtained by Morgan-Sagastume et al. (2010) who reached a 4% of PHA storage using fermented sludge as carbon source.