Page 46 - Energy from Toxic Organic Waste for Heat and Power Generation

34 Energy from Toxic Organic Waste for Heat and Power Generation

Particle Size of Feedstock
Although the particle size is not as much an important parameter as the
temperature and pH of the digester, it still has some influence on the biogas
production. The particle size of the feedstock should not be too large; oth-
erwise, it would result in the clogging of the digester, and also it would be
difficult for microbes to carry out its digestion. On the other hand, smaller
particles would provide a larger surface area for adsorbing the substrate,
which would result in increased microbial activity, and hence, increased gas
production.
Gollakota and Meher [61] experimentally investigated the particle size,
temperature, loading rate, and stirring on the biogas production potential
from castor seed cakes. They reported that five particle sizes of 0.088, 0.40,
1.0, 6.0, and 30.0 mm gave the maximum quantity of biogas. They also
documented that a physical treatment of feedstock like grinding may sig-
nificantly enhance biogas production.
Use of Additives
Gunaseelan [62] and Vervaeren et al. [63] have made attempts to increase the
biogas production from cattle manure and maize by stimulating the micro-
bial activity using various biological and chemical additives under different
operating conditions. Gunaseelan [62] has used Parthenium hysterophorus, a
wild grass weed, as an additive in a batch reactor. 10% Parthenium hystero-
phorus was mixed with cattle manure and allowed for anaerobic digestion
at room temperature of 30 ± 1°C in 3-L batch digesters. The chemical
changes during the course of digestion and the effect of the digested slurry
on biogas production were investigated. He observed that the methane
content in the biogas increased from 60% to 70% with the addition of an
additive. Some of the commonly available biological additives are green
plants, weeds crop residues, and microbial cultures. According to a study by
Vervaeren et al. [63], methane production was increased to almost 11% by
adding biological ensilage as additives to maize.

Microbial Strains
Strains of some bacteria and fungi have also been found to enhance gas
production by stimulating the activity of particular enzymes. Tirumale and
Nand [64] have investigated the addition of cellulolytic strains of bacteria
like actinomycetes and mixed consortia for enhanced biogas production
in a floating dome digester. They observed that the biogas production was
increased in the range of 8.4%–44% from cattle dung. Also, they reported