Page 148 - Materials Chemistry, Second Edition

Environmental Sustainability Assessment of Ethanol 135

Feedstock processing entails the use of various chemicals and energy carriers
(boiler fuels, electricity, etc.). These data are usually primary data collected from
plant records through production data of chemicals and energy carriers, which are
usually from literature or national databases. This stage usually involves the
production of co-products, which play an important role in the assessment and
must be carefully noted. As environmental burdens must be shared between the co-
products, additional information must be collected for this based on the method-
ology to be used for allocation. For example, if mass or energy allocation is to be
used, data on the mass and energy content of the co-products should be assessed. If
economic allocation is to be used, then data on the economic value of all the
outputs must be collected; this is done either at the company level or a more
average level, depending on the scope of the study. Usually, an average over
several years is considered because economic values can vary substantially over
time. Wastewater emissions are particularly critical as they usually have high
organic content; the type of treatment can significantly affect environmental
emissions. Treatment of wastewater in ponds can result in high methane emissions,
whereas high-rate anaerobic processes could result in the collection and sub-
sequent utilization of the generated methane for energy. These data are usually
based on standard calculations.
Emissions from the use of biofuels in vehicles are usually measured based on
chassis dynamometer tests where specific engine types are operated using a par-
ticular fuel under standardized driving conditions.
Data required for transportation of intermediate and final products are either
directly the fuel used or data on vehicle type, capacity, loading, and transportation
distances. These are usually primary data collected from the transportation com-
panies except for transportation distances which may be estimated from secondary
sources if the source and destination of the transported product are known.
In all the steps, information should be collected on the data uncertainty to
ensure the meaningfulness of the interpretation of results, especially for compar-
ative purposes.

5 Environmental Sustainability Assessment

To illustrate the use of the tools for biofuels environmental sustainability assess-
ment introduced in the preceding section, the cases of ethanol from cassava and
sugarcane molasses in Thailand are used (Silalertruksa and Gheewala 2009).
Energy balances, renewability, and various environmental impact categories will
be evaluated using LCA. The system boundaries are ‘‘cradle-to-gate’’ ending at
ethanol production as the ethanol produced is then blended with gasoline before
use in vehicles (a 10 % blend of ethanol with 90 % gasoline is most commonly
used in Thailand); thus, the study was limited to neat ethanol to facilitate direct
comparison with gasoline. For the impact assessment, the CML2 methdology, a
problem-oriented (midpoint) approach, has been used (Guinée et al. 2002). Thus,