utilizable residues are cane trash in sugar cane
production, bagasse in sugar production and stillage in
ethanol conversion.
In sugar cane production, burning cane trash prior to or
after harvesting is commonly practiced to favour manual
harvesting and land preparation for new growth. Worldwide,
there is increased interest in utilizing cane trash as a
fuel instead of open burning in fields. Research has shown
that up to 50% trash can be removed without leaving
behind any negative effect on soil quality (Gabra 1995).
However, such a utilization scheme needs to take into
account energy and environmental costs associated with
collecting, hauling and preparing trash for off-season use.
In sugar production, bagasse is being utilized as the
major fuel to generate both process steam and electricity.
The surplus electricity sold to the grid is counted for both
energy and environmental credits.
The distillation residue from the production of ethanol,
called stillage or spent wash, can be refined into biogas via
advanced anaerobic digestion systems, e.g. UASB reactors
(Fig. 1). This has been considered a good measure to secure
Table 1 Scenarios of molasses-based ethanol case study
Case Process energy source % cane trash burning in fields
Scenario 1: E10-a, MoE-a (base case) Coal, rice husk and biogas recovered from 12% spent wash
(the remaining 88% sent to an anaerobic pond)
40
Scenario 2: E10-b, MoE-b Rice husk and biogas recovered from 100% spent wash 40
Scenario 3: E10-c, MoE-c Cane trash and biogas recovered from 100% spent wash 0
Scenario 4: E10-a(nb) Same as E10-a but cane trash burning outside system boundary 0
Scenario 5: E10-ahl Same as E10-a but including human labour in farming stage 40