Fig. 1 shows the main components of the aerobic reactor. It
comprises a glass flask of 2 L operating volume, the reactor
Fig. 1 – Schematic diagram of an experimental setup used
for aerobic pretreatment experiments.
contents of which were homogenized using a magnetic stirrer.
Air from a compressor was injected from the bottom of
the reactor at a flow rate of 0.65 L air per litre of reactor and
per minute. The temperature of the fermentation was not regulated.
The aeration process was conducted in discontinuous
mode (in batch) without adding any specific aerobic bacterium,
given that air injection activates the growth of aerobic
microorganisms already present in the OMWW samples.
2.2. Experimental setup for anaerobic digestion
The anaerobic digestion experiments were carried out in a
digester operating in semicontinuous mode; that is, a given
volume of digested sludge was extracted daily from the reactor
with a syringe and immediately the same volume of substrate
was introduced, so that digestion at constant-volume configuration
was guaranteed.
A scheme of the experimental setup is shown in Fig. 2,
which essentially consists of a 2 L capacity glass flask, whose
rim is attached to a central tube immersed in the reaction
medium, and which has an input hole to introduce the substrate
and an output hole to collect the biogas generated in the
process. The digestion unit was submerged in a water tank and
maintained at 38 ◦C by a thermostat equipped with a heating
resistor. The substrate inside the reactor was homogenized
by the continuous action of a magnetic stirrer, allowing for
complete mixing.
A 5 L tank assembled to the biodigester was used to determine
the volume of methane generated during the AD process.
A squeeze bottle containing a sodium hydroxide solution (20%
by weight) was placed between the digester and the gas tank,
aimed at retaining the carbon dioxide generated during the
digestion process. The methane volumes generated during the
experiment displaced water in the tank, which was collected
in a measuring cylinder. This way, the volume of displaced
water allowed for the determination ofthe volume of methane
generated in each experiment.