Page 47 - Energy from Toxic Organic Waste for Heat and Power Generation

Energy Extraction From Toxic Waste Originating From Food Processing Industries 35

that all the strains exhibited a range of activity of all the enzymes involved
in cellulose degradation, viz., C 1 enzyme, exoglycanase, endoglucanase, and
β-glucosidase. It seemed that the endoglucanase activity was of central im-
portance for the hydrolysis of cellulose. The improvement of CH 4 yield
from thickened activated sludge ranged from 8.1% to 86.4%, while in the
case of a mixture of thickened activated sludge, and primary sludge, it was
found to vary from 0% to 24% [65].

Green Biomass Addition With Feedstock
Sichuan and SPOBD [66] and Chowdhry et al. [67] investigated the biogas
production potential of tree leaves. They observed that the powdered leaves
of plants and legumes like Gulmohar, Leucacena leucocephala, Acacia auriculi-
formis, Dalbergia sisoo, and Eucalyptus tereticonius have been found to stimulate
biogas production ranging from 18% to 40%. The additives were useful to
maintain favorable conditions for rapid gas production in the reactor, such
as pH, inhibition/promotion of acetogenesis and methanogenesis for the
best yield, etc. Alkali-treated (1% NaOH for 7 days) plant residues such as
lantana, wheat straw, apple leaf litter, and peach leaf litter, when used as a
supplement to cattle dung, resulted in almost twofold increase in biogas
quantity and methane production [51]. Kalia et al. [68] experimentally in-
vestigated the addition of green biomass for an enhanced biogas production
from ageratum. They observed that partially decomposed ageratum pro-
duced 43% and Euphorbia tirucalli L. produced 14% more gas as compared
to pure cattle dung.

Digested Slurry Recycling: The recirculation of the digested slurry
back into the reactor can improve the gas production marginally, since the
microbes that were washed away are reintroduced into the reactor, thereby
providing an additional microbial population. Malik et al. [69] and Kanwar
et al. [70] recycled the digested slurry along with the feedstock to con-
serve water and to increase biogas production. They observed that about
60%–65% more biogas can be obtained by simply recycling the digested
3
slurry in 1 m plug flow type pilot plants. The liquefaction of cellulose
and hemicellulose that are present in the feedstocks was low at the start of
recirculation (3%–20%) and was not affected by carrying out digestion in a
3
plant of 1 cm capacity. Santosh et al. [71] investigated water conservation
during the anaerobic digestion of a feedstock in a large-scale biogas digester.
They observed that the recycling of the digested slurry into the digester
saved about 50% of water consumption. They also reported that recycling of