Fig. 1 compares the total amount of reducing sugar from dilute
acid hydrolysis of boiled and steamed water hyacinth samples
(Samples 5x and 6x). Boiling and steaming pretreatment had produced
higher sugar amount than untreated condition, up to 35.9%
and 52.4%, respectively. Resulting shear stress and tensile forces
from the pretreatment process will breakdown the substrate and
subsequently increase the surface area and accessibility to cellulose
(Chen et al., 2010). It is believed that the same mechanism
was responsible for the improved sugar release from boiled and
steamed samples in this work. Similar steaming method (121 C
at neutral pH) was found to improve COD solubilization of water
hyacinth biomass for biomethanation process (Patel et al., 1993).
However, this improvement may not be applicable for different
types of feedstock because of the variation in their lignocellulosic
contents and different process requirements (Rogalinski et al.,2008).
For example, Nlewem and Thrash (2010) found a negligible
enhancement on enzymatic hydrolysis outcome when treating
switchgrass with boiling water (100 C) and recommended higher
temperature to be used.