Fig. 2 depicts the colour removal efficiencies throughout
the 9 days of the incubation period under anaerobic,
aerobic and microaerophilic conditions for azo dye DB
38. More than 72% of the colour was removed within 3
days under anaerobic conditions while at the same time
24 and 63% decolorization was observed under aerobic
and microaerophilic incubations, respectively. In other
words, the efficiency of colour removal with E. coli in
anaerobic incubations was faster than that obtained in
aerobic incubations. A maximum of 75% colour removal
efficiency was obtained under microaerophilic conditions
while a maximum of 80% decolorization efficiency
was achieved after incubation with E. coli under
anaerobic conditions. It has been observed that very
high decolorization efficiencies were achieved under
anaerobic incubation, although the MLSS concentration
of E. coli was comparably lower (MLSS/637 mg/
l) than those obtained under aerobic conditions
(MLSS/1000 mg/l). The results of this study showed
that the rate and the efficiency of decolorization did not
sharply increase with increases of anaerobic cell mass
concentration of E. coli . Dye removal rate (E/80%) of
20 mg/(l day) was observed at a MLSS concentration of