of R1 was fed to reactor R2, where the decolorized effluent
was mineralized further. HRT was maintained at 7.79 h and
0.5614 kg COD m3 per day loading and COD reduction was
41.90%. Interestingly, nitrification was observed in reactor
R2. Ammonia decreased to 3 mg/l with no detectable nitrite
and nitrate. Sulphate remained unaffected. When the HRT
was decreased further to 5.73 h, COD removed remained
more or less constant (44.06%). When the influent load to
reactor R2 was increased to 2.9070 kg COD m3 per day, it
has also affected COD removal (Table 5).
When the overall COD reduction was compared in simulated
wastewater treated in microaerophilic–aerobic reactors,
the initial COD was reduced to 85.30% at 7.72 h
HRT and 2.239 kg COD m3 per day loading. In the first
phase of treatment, the azo dye molecule was cleaved at
the nitrogen-nitrogen bond by biochemical reduction which
leads to formation of amines. This was performed under
microaerophilic conditions where the facultative organisms
cleaved the azo bond which may be serving as an electron
acceptor.