Subsequently, the biomass was spiked with ammonium and an external carbon source (OFMSW FL or PS & OFMSW FL) at a fixed concentration determining sAUR and VFA uptake rate.
The duration of the aerobic phase was maintained in the range of 100–180 min, depending on the experiment.
After the aeration reaction, the supply of air ceased and the top part of the flask was covered with aluminium foil to avoid direct contact with air in order to then measure sNUR. The profiles of VFA, ammonium, nitrite and nitrate were recorded during the ex situ tests under aerobic and anoxic conditions. Respirometric tests were also performed in order to determine the effect of the carbon source on the sAUR as well as its contribution to the oxygen requirements.
The oxygen uptake rate (OUR) was recorded with a respirometric device (MARTINA, SPESS Italy).
All batch activity tests were conducted at room temperature and the pH was maintained in the range of 7.8 ± 0.2 using NaOH and HNaCO3 when required.
The reported activities have been corrected to the reference temperature of 20 C using the Arrhenius temperature correction equation and have been normalised to the volatile suspended solids (VSS) of the mixture.