2. Experimental
2.1. Experimental set-up
2.1.1. Microbial process
First a batch process was performed to determine what substances
were released from the rice husks, if any. This experiment
was performed in 250mL Erlenmayer flasks and two parallel
continuous systems were used. Both systems consist mainly of
cylindrical plexiglass reactors and pumps. In the first continuous
system, two or four reactors (1st and 2nd reactors have 450mL
volume, 3rd and 4th reactors have 430mL volume) connected in
series were used and in the second system just two serial connected
reactors (each reactor has 450mL volume) were used.
2.1.2. Catalytic wet peroxide oxidation
The experimental set-up shown in Fig. 1 mainly consists of a
reactor, a condenser and suitable measuring devices for temperature,
pressure, and air flow rate. The main part of the system was
a 500mL (h = 500mm; D= 35mm) stainless steel reactor equipped
with an electrical wires wrapped around, a temperature controller
(PID-1/32 DIN model), and a pressure indicator. The condenser
mounted at the top of the reactor was used to condense the vapors
formed during the reaction and to send the condensate back to the
reactor. The experimental setup has been explained elsewhere in
detail [14].
2.2. Experimental procedure
2.2.1. Microbial process
The general experimental procedure followed can be summarized
as follows: in the batch experiment 8 g of rice husks and
250mL of 0.9% NaCl solution are mixed in 250mL Erlenmayer
flasks under anaerobic conditions. Samples are taken from the
flasks every two days and then they are scanned with Perkin
Elmer Lambda 35 UV/VIS spectrophotometer. In the continuous
systems the reactors are filled with rice husks. The connection tubes
between the reactors and feed bottles are washed with ethanol for sterilization. A desired synthetic dye mixture is prepared by using
tap water and then put into an autoclave at 121 ◦C for 15 min for
sterilization to ensure that there are not any microorganisms in
the synthetic dye solution. The speed of the pump (C6-MIDI multichannel
pump, Watson Marlow SCI) is changed to provide a flow
rate between 0.351 mL/min and 0.981 mL/min in order to maintain
the required residence time. To determine the dye removal efficiency
of the microorganisms, samples are taken every two days
from each reactor and also from the orginal dye mixture and then analyzed.