Regarding nitrogen, the plant was able to remove
87.5 5.3% of TKN with a residual concentration in the
effluent of 4.9 2.4 mg/l, indicating that a stable nitrification
process was established, with average concentrations of oxidised
nitrogen in the effluent of 7.6 4.5 mg/l, contrary to
what usually detected in biological systems treating textile
wastewater, where the nitrifying biomass activity is usually
reduced because of the many textile inhibitory compounds
(Rozzi et al., 1999; Bortone et al., 1997). Nitrogen balance also
highlights the existence of a somewhat extended denitrification
process, although no final anoxic phase was included in
the treatment cycle. In fact, less than 1 mg/l of TKN was
required for biomass growth, considering a nitrogen request
of about 4.5 mgN/gCODremoved, calculated by multiplying
sludge production (0.15 gTSS/gCODremoved; see paragraph 3.2)
and measured N biomass content (0.03 gN/gTSS).