Potenciales y Viabilidad del Uso de Bioetanol y Biodiesel para el ...

Potenciales y Viabilidad del Uso de Bioetanol y Biodiesel para el Transporte en México (SENER-BID-GTZ)
Task 6: Potentials in relation to sustainability criteria
weight (in water). Cassava also uses large quantities of water. For sugar cane the average
water withdrawal from the sources (rivers, lakes, underground water) in Brazil 1.8 m 3 / t cane,
but the system can be improved (Chapter 7.2).
Sugar cane (and sorghum): air pollution with bagasse boilers: bagasse boilers are conventional
biomass boilers (relatively low temperatures) and the emissions associated are well known
(PM, NOx, ozone); they can be controlled in all modern boilers (Chapter 5.2).
Stillage disposal / utilization: stillage treatment is required to avoid the discharge of high
organic matter loads in rivers. This concept is still true, but the possibility of profiting with
ferti-irrigation has been demonstrated with the evolution in the last 25 years: the nutrients
(mainly the Potassium) and water in stillage can pay for all application costs with increased
productivity (Chapter 9). Ferti-irrigation must be the first priority in stillage use, whenever
possible; it requires a better management, but this will be needed for all the agricultural
procedures in the near future, approaching a “precision agriculture” for the energy crops.
Some level of concentration (or some process development to reduce stillage volume) may be
economically feasible, to improve the distribution in ferti-irrigation, depending on the
topography.
High concentration (~60 Brix) to allow for burning is a process intensive in capital and
energy, being difficult to justify, except in very special situations.
Anaerobic Digestion is an option to be reserved for situations where full ferti-irrigation is not
possible. It usually is not sufficient to comply with the local requirements set by the
environmental legislation; and an aerobic complementation may be mandatory.
The ethanol end use
Ethanol partial substitution for gasoline helps increasing energy security and reducing gasoline
/ additives imports (economic impacts). Economic impacts are also seen in the relative costs of
ethanol and the (expected) gasoline cost; in the economic development due to equipment and
services suppliers for the new energy sector; and in the strengthening of the rural area, with
job creation.
Bio-ethanol (and co-generated electricity) show positive environmental impacts by reducing
the use of natural resources (fossil fuels) and the corresponding GHG emissions.
Ethanol use in blends with gasoline (and also the use of ETBE) presents different atmospheric
emissions (than those from gasoline). The possibility and consequences of leakage and
contamination of groundwater must be considered.
The main environmental impacts are summarized below.
The biomass and conversion processes proposed, for Mexico conditions (Chapter 2), present
energy ratios (energy output / fossil energy inputs) varying from nearly one (corn: 1.3) to ten
(sugar cane, with co-generation). Sweet sorghum ratio is ~4; wheat and sugar beets ratios are
~2; and cassava is ~1. Impacts in fossil energy utilization are shown below, for 10% blend of
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