Interesting considerations can be formulated if the trends
recorded during a typical treatment cycle are observed (Fig. 3):
while the removal of COD, TSS and total surfactants was
nearly completed in 2.5 h, the removal of nitrogen and colour
continued to occur till the end of the cycle. The analysis of
COD and TSS removal shows that the system could afford
even lower HRT values, as constant COD and TSS values as
low as 50 and 5 mg/l were measured after only about 2.5 h.
However, as ammonia continued to be removed throughout
the whole cycle duration, nitrogen removal is the limiting step
that influences the choice of the maximum OLR and minimum
HRT to be adopted, as a further reduction of the HRT
below 11 h would not allow the removal of ammonia to be
satisfactor