higher biomass adherence to the disc. The inoculum flow rate was
maintained at 1 L/h. The MLSS concentration of the re-circulating
liquid phase was 1.3 g/L. After 15 days of operation, a thin layer
of bio-film was observed on the discs. At this stage the thickness
of the bio-film was less than 1 mm and was uniform in all the discs.
The thickness of the biofilm was measured with a simple phase
contrast microscope (Radical instruments, India). The outlet air
was devoid of any VOC although liquid outlet concentration of
these VOCs was in the order of 4–9 mg/L which is about 14.8–
33.3% of the total incoming VOC on a per hour basis, during these
initial days. The relatively high solubility of the VOCs might have
been the reason of complete transfer of VOCs from gas phase to
liquid phase in the start-up phase. High elimination capacity of
VOCs was observed in this phase even with a thin biofilm on the
discs. This may be due to the high biodegradation rate of VOCs in
the liquid phase probably aided by the low food to micro-organism
ratio. The wet weight of biomass in the reactor was 152 g at the
end of start-up phase. The biofilm grown on the discs was of pale
yellow color. Non-uniform thickness of the biofilm was observed
during the last 10 days of this phase. The disc nearest to the gas
inlet showed maximum growth of biomass. This non-uniform
thickness of biofilm indicated that the biodegradation was taking
place with the help of microbes on the surface of the discs. The