2.3. Algal biomass
Ash, lignin, cellulose and hemicellulose contents of algal
biomass were determined as follows: four samples of air
dried, ground (0.5 mm) algal biomass (0.7 g each) were
boiled with 5 mL of 72% w/w H2SO4 solution for 4.5 h in
order to hydrolyse the cellulose and hemicellulose. The suspension
remaining after the above treatment was filtered
through a crucible and the solid residue dried at 105 C
for 24 h and weighed (W1). The residue was then transferred
to a pre-weighed dry porcelain crucible and heated
at 600 C for 5 h. After cooling down, it was weighed
(W2) and ash content (%) was determined. Acid insoluble
lignin was then calculated by the difference (W1 W2).
The filtrate from the H2SO4 treatment that contained
the sugars released from cellulose and hemicellulose was
thoroughly stirred and homogenized. Glucose (C1) and
reducing sugar (C2) concentrations in the filtrate were
determined according to a glucose oxidase–peroxidase
assay kit (Biosis TM, Athens, Greece) and the DNS method
(Miller, 1959), respectively. Following these measurements,
the cellulose content in the starting material was calculated
using the following equation: