Page 155 - Materials Chemistry, Second Edition

142 S. H. Gheewala

whereas the latter in high-efficiency UASB systems results in a higher eutrophi-
cation potential for the former.
Human toxicity potential is mainly related to the emissions of NOx, SO 2 , and
particulates, which are almost the same as the acidifying substances. Hence, the
contributing stages of human toxicity potential are also similar to acidification as is
the trend of comparison between molasses and cassava ethanol.
One important issue that was mentioned in the earlier sections, but not covered
in the impact assessment, is that of land use. Land use change was not considered
because all the current plantations of cassava and sugarcane are quite old and there
is no plan in the near future by the government to increase the plantation area. The
policy focus is on increasing the yield of both cassava and sugarcane. Neverthe-
less, land is a scarce resource and it is interesting to evaluate its utilization in terms
of land occupation. The evaluation shows that to produce 1,000 L of cassava
ethanol, 0.37 ha.y of land is required, which is almost the same for molasses
ethanol at 0.39 ha.y (after accounting for sugar based on energy allocation).
Increasing the yields of cassava and sugarcane as well as better utilization of co-
products would help reduce this.

6 Key Messages

The energy balance and LCA studies helped evaluate the environmental sustain-
ability of biofuel systems as illustrated for the examples of ethanol production
from cassava and sugarcane molasses. A combination of NER and renewability
was useful for evaluating the energy performance and utility of using renewable
energy sources to replace fossil energy. LCA was useful for evaluating the envi-
ronmental and health impacts. For the studied cases, the following improvement
options were identified:

(a) Optimum utilization of the land resource could be achieved by improving the
yields of sugarcane as well as cassava. This could be obtained by improving
soil fertility through utilization of organic fertilizers or animal waste and
reducing chemical fertilizer use. This would also result in reduced eutrophi-
cation, which originates mainly from the use of chemical fertilizers.
(b) Air emissions from the sugarcane cultivation stage can be reduced by avoiding
the burning of cane trash. This would result in the reduction in all the potential
environmental impacts too.
(c) Effective waste management would go a long way in enhancing the efficiency
of the system. Thus, biogas recovery from wastewater, organic fertilizer, and
distiller’s dried grains with solubles (DDGS) production would yield valuable
products and reduce the environmental burdens.
(d) Use of renewable energy sources especially in the ethanol conversion stage
would reduce the emission of greenhouse gases as well as improve the
renewability of the system.