In parallel with the ex situ experiments, the normal operation of the SBR process was monitored. The results obtained with the use of the two different carbon source are summarised in Table 2. In Period I, OFMSW FL was added and in Period II combined PS & OFMSW FL was added. Fig. 3a shows the evolution of the influent ammonium concentration and the ammonium and nitrite concentration
in the treated effluent during the scSBR operation.
In the first seven days of the SBR operation ammonium removal was relatively low (67.6 ± 14.3%) and the treated effluent contained 18.5 ± 9.5 mgNH4-N L1. Consequently, during days 1–7 the treated effluent did not meet the limit of 10 mgN L1 in terms of the nitrogen concentration required for the discharge of treated effluent into sensitive water recipients for municipal WWTPs serving a population equivalent higher than 100,000 (Directive 91/271/EEC).
Since only some of the ammonium was oxidised to nitrite, there was enough PHA stored to completely remove them. The low nitritation was attributed to the addition of carbon source and the low DO (1.5 mg L1) resulting in a lag phase of nitritation at the beginning of the aerobic phase.