2.3.2. Filtration
A filter membrane module (MD 015 TP 2 N, Microdyn-Nadir,
Germany) made of polyethylene with a polypropylene housing
was used in a cross-flow microfiltration, which is filtration through
the micropores in the filter module in a perpendicular direction to
the flow inside. The filter module had an inner diameter of 5.5 mm,
pore size of 0.2 lm, an effective filtration area of 0.025 m2 and a
free flow area of 0.24 cm2. The membrane was hydrophilazed with
ethanol before use. A peristaltic pump (405U/L2 Watson-Marlow,
Sweden) was used to pump the enzyme–slurry mixture (hereafter
referred to as concentrate pump) from the hydrolysis reactor into
the filter module at flow rate of 0.8 L/min. Another peristaltic
pump (120 S/DM2 Watson-Marlow, Sweden) was used to pump
the permeate out of the filter module (hereafter referred to as permeate
pump) to the fermentation part initially at a flow rate of
1.1 mL/min and gradually increased up to 2.9 mL/min (which corresponds
to a dilution rate of 0.2–0.6 h1) in order to balance efficient
uptake in the fermentation vessel. The retentate was
circulated back to the hydrolysis reactor. Periodic chemical backwash,
in reverse flow direction to the cross-flow microfiltration
using 0.5 M NaOH was used on the membrane after each experimental
run to regenerate the pores of the filter membrane module.