maximum applied MEK ILR of 720 g/m3/h the residual ammonium
ion concentration in the effluent was 107 mg/L. The biofilm samples
from the disc D1 was collected after each phase for elemental
analysis using CHNS analyzer (Table 2). Nevertheless, a decrease in
nitrogen content of the biofilm in the present study indicates a
decrease in protein content of the biomass [43–45]. This decrease
in nitrogen content may be correlated to a decrease in enzyme
activity. The biofilm samples when observed under a fluorescent
microscope (Nikkon, Japan) at 100 with blue filter, without adding
any external dye showed high degree of natural green color
fluorescence (Fig. S2) which may be indicative of NADPH/NADH
activity. To further investigate the changes in enzyme activity,
dehydrogenase activity of biofilm sample scrapped from disc D1
was measured for all the sub-phases (Table 3). The experimental
results showed a decrease in dehydrogenase activity from
2.75 lmol/g to 2.62 lmol/g corresponding to a decrease in
nitrogen content from 10.72% to 10.03% of the disc biofilm. The
thickness of the biofilm increased in subsequent sub-phases of
phase-1 with increasing MEK inlet loading rate.
3.3. Performance of the RBC during the treatment of MIBK
MIBK was applied as the sole carbon source to the RBC reactor
from day 91 to day 135 day of operation. It is reported that same
microbial species can degrade both MEK and MIBK due to their
similar chemical nature [40,46]. This may be the reason for the
high removal efficiency of 92% for an ILR of 90 g/m3/h on the very
first day of phase-II. High removal efficiency was observed
throughout this phase at different ILRs. However, 100% removal
efficiency could be achieved only up to an ILR of 240 g/m3/h
(Fig. 2). The concentration of MIBK in the liquid outlet was always
below detectable limit for first 5 sub-phases. However, occasionally
very low concentrations of MIBK was observed in the liquid
phase (maximum concentration observed was 4.3 mg/L which
was about 0.6% of the inlet load) particularly during the higher
ILRs, immediately after the increase in loading, for a few days.
The presence of MIBK in the liquid effluent clearly indicates reaction
limitation. The change in the EBRT and simultaneous increase
in ILR in the II-6 sub-phase marked the reaction limiting phase
maximum applied MEK ILR of 720 g/m3/h the residual ammonium
ion concentration in the effluent was 107 mg/L. The biofilm samples
from the disc D1 was collected after each phase for elemental
analysis using CHNS analyzer (Table 2). Nevertheless, a decrease in
nitrogen content of the biofilm in the present study indicates a
decrease in protein content of the biomass [43–45]. This decrease
in nitrogen content may be correlated to a decrease in enzyme
activity. The biofilm samples when observed under a fluorescent
microscope (Nikkon, Japan) at 100 with blue filter, without adding
any external dye showed high degree of natural green color
fluorescence (Fig. S2) which may be indicative of NADPH/NADH
activity. To further investigate the changes in enzyme activity,
dehydrogenase activity of biofilm sample scrapped from disc D1
was measured for all the sub-phases (Table 3). The experimental
results showed a decrease in dehydrogenase activity from
2.75 lmol/g to 2.62 lmol/g corresponding to a decrease in
nitrogen content from 10.72% to 10.03% of the disc biofilm. The
thickness of the biofilm increased in subsequent sub-phases of
phase-1 with increasing MEK inlet loading rate.
3.3. Performance of the RBC during the treatment of MIBK
MIBK was applied as the sole carbon source to the RBC reactor
from day 91 to day 135 day of operation. It is reported that same
microbial species can degrade both MEK and MIBK due to their
similar chemical nature [40,46]. This may be the reason for the
high removal efficiency of 92% for an ILR of 90 g/m3/h on the very
first day of phase-II. High removal efficiency was observed
throughout this phase at different ILRs. However, 100% removal
efficiency could be achieved only up to an ILR of 240 g/m3/h
(Fig. 2). The concentration of MIBK in the liquid outlet was always
below detectable limit for first 5 sub-phases. However, occasionally
very low concentrations of MIBK was observed in the liquid
phase (maximum concentration observed was 4.3 mg/L which
was about 0.6% of the inlet load) particularly during the higher
ILRs, immediately after the increase in loading, for a few days.
The presence of MIBK in the liquid effluent clearly indicates reaction
limitation. The change in the EBRT and simultaneous increase
in ILR in the II-6 sub-phase marked the reaction limiting phase
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