bottles incubated in air). This was much superior to the
strictly anaerobic conditions. Microaerophilic conditions
(static conditions) resulted in cleavage of azo bonds from
dye mixture and the formation of aromatic amines. Consortia
grown on static and static–aeration conditions in the
presence of the mixture of dyes were harvested and enzymes
were extracted. Azoreductase and aromatic amine degradation
assays (Table 4) showed that maximal decolorization
was obtained with static conditions than static-shaking
conditions and exactly reversed for aromatic amine degradation
assay. This shows that the switch on-off mechanism
exists in microorganisms for azoreductase and aromatic
amine degradation. The enzymic study fully supported decolorization
and biodegradation flask experiments. Based
on the above flask experiments the laboratory reactors were
operated.
3.1. Reactor operating principal
The method for the purification of simulated wastewater
was developed on the basis of research on the cleavage of
N=N bonds under microeraphilic condition followed by aerobic
mineralization of simulated wastewater. Haug et al. [26]
have worked on anoxic cleavage and aerobic mineralization
of sulphonated azo dyes Mordent Yellow 3 by a bacterial
consortium. The principle of switching between anaerobic
and aerobic conditions in a bioreactor was used for the treatment
of concentrated reactive dye and the sequence of degradation
of dye molecules during the microaerophlie-aerobic
process is presented in Fig. 3. Accordingly, an investigation
has been made on laboratory scale reactors for decolorization
and degradation of simulated wastewater. Initially the
reactor was loaded several times with fresh media until suffi-
cient growth was achieved. Variation in COD concentration
was determined during the course of experiments. The color
removal efficiency increases with time, indicating that the
reactor was becoming sufficiently mature to decolorize and
degrade the wastewater. Starch was selected as co-substrate
for providing the electrons for the reduction of the wastewater.
The effect of hydraulic retention time for simulated
wastewater was studied by increasing the flow rate and decolorization
and degradation were monitored for R1 and R2
reactors and results are given in Tables 5 and 6, respectively.
In the case of reactor R, decreasing HRT (hydraulic retention
time) from 7.72 to 4.67 h, resulted in a decrease in COD
removal and decolorization. Initial COD (721.76 mg/l) was
decreased to 74.67% at 7.72 h HRT. Ammonia, nitrite, nitrate
and sulphate was also present in the effluent. The outlet