improves denitrification. The OCI does not change signifi-
cantly although it can be seen that this is a combination of
different effects brought about by the volume changes: lower
sludge production, lower aeration energy, higher mixing
energy (due to larger anoxic volumes), higher pumping
energy and less methane production. Especially the reduced
percentage of SNH violations opens perspectives for control.
Time series of DO in the 4th tank and the effluent
ammonia are illustrated in Figure 2 for the new OL. It
shows that the oxygen concentration in the bioreactor is not
adequate, poor during daytime when the plant is highly
loaded (with DO decreasing below 1 g.m23
) and excessive
at night (DO reaching concentration of almost 4 g.m23
).
Moreover, it is highly inefficient in nitrification