SUMMARY
Low cost cellulosic wastes like paper sludge, municipal wastes, solid wastes from food,
packing etc. contain a high amount of cellulose which can be converted to bioethanol by
two steps: (1) solubilization of cellulosic fibers to monosaccharides (2) conversion of
monosachharides to bioethanol via fermentation. At present the implementation of this
technology has been deterred by high cost for enzymes. Enzymatic hydrolysis of
cellulosic fibers shows a biphasic behavior with an initial fast step followed by a slow
step leading to low cellulose conversion rates. Low hydrolytic conversion rates
necessitate the use of a high enzyme dosage to obtain meaningful cellulose conversion
rates which make the implementation of this entire technology economically infeasible.
The objective of this study is to get a better understanding of the mechanism of
enzymatic hydrolysis of fibers to glucose and to investigate the effect of cationic
polymers on enzymatic hydrolysis rates. To achieve the first objective, we performed
experiments so as to study changes in morphological and physiochemical properties like
fiber length, percentage of fines, crystallinity index, kink angle, kink index, mean curl,
total organic carbon and glucose production with time. We used bleached kraft softwood,
hardwood, and unbleached softwood fiber as cellulosic substrate and pergalase as
cellulase enzyme. All of the experiments were carried out at experimental conditions of a
temperature of 50 .C and a pH of 5.0 which maximize enzymatic activity. We studied the
impact of recycling and refining on hydrolysis rates by measuring total organic carbon
and glucose production. We found that refining increases enzymatic conversion rates by
about as much as 20 %, however refining being energy intensive makes implementation economically unfavorable. We found a novel way of enhancing
hydrolysis rates by the use of cationic polyacrylamides. The effect of cationic
polacrylamides was studied on both hardwood and softwood fibers at similar
experimental conditions. Cationic polyacrylamides produced a maximum rate increase of
20 % in hydrolytic conversion rates for hardwood fibers. Even though, the increase in
hydrolysis rates for softwood fibers was smaller than hardwood fibers, it was still
significant. We further studied the effect of parameters like polymer concentration,
cationicity and molecular weight to find a relation between properties of polymers and
the increase in enzymatic hydrolysis.