Environmental Engineering Reference
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biofuel production process, such as biogas, animal feed, fertilizers, industrial enzymes and chem-
icals, bioplastics, and surfactants. It will also require finding creative new applications for these
“co-products” as needed. Glycerol, a byproduct of transesterification, is still cited as a valuable
co-product for the cosmetics and chemical industries, but at a practical level, the market has
become saturated due to the increasing manufacture of biodiesel (Yazdani and Gonzalez, 2007).
Since the creation of glycerol is intrinsic to the process, newuses will have to be found for glycerol,
such asmicrobial fermentation into fuels andmarketable chemicals (Yazdani andGonzalez, 2007).
Jatropha press-cake has hemicelluloses, cellulose and lignin, which can be converted through
anaerobic digestion into biogas (Demirbas, 2011) or through pyrolysis into bio-oils, gas and char.
Its biomass can be used as animal feed (with appropriate detoxification), or as fertilizer. For a
detailed description of jatropha fruit, shell, husks and wood that could be used to produce energy,
see Jingura et al. (2010).
For algae, there are three major components of biomass: lipids, carbohydrates and proteins.
Lipids and carbohydrates can be converted into fuel, while the proteins can become co-products,
such as animal feed. Another option: anaerobic digestion of algal biomass and cellulose can be
used as a means of H 2 production (Carver et al. , 2011). For other sorts of co-products from
algae, see Cardozo et al. (2007). The remediation of wastewater (Aresta et al. , 2005; Park and
Craggs, 2011; Park, Craggs and Shilton, 2011) or toxic compounds (Petroutsos et al. , 2007) or
sequestration of CO 2 (Aresta et al. , 2005; Sayre, 2010) can be considered co-products for the
purposes of calculating environmental impact in life cycle analysis.
11.6 LIFE CYCLE ASSESSMENT
In general terms, sustainability requires that our activities do no harm to the planet or the life that
depends upon it. This means that people take priority in the competition for food and water. Balat
passionately argues that there is a direct link between using edible oils for biofuel and starvation
(Balat, 2011a,b). Thus, the search for energy production should avoid the use of food crops, arable
land, or fresh water. The huge preponderance of scientific evidence indicates that we are foolhardy
to continue recklessly pumping greenhouse gases (GHG) into the earth's atmosphere. As a result,
we seek energy production techniques that are at least carbon-neutral, i.e., the net effect of all parts
of the process maintains the same level of GHG as currently exists. However, the smarter strategies
will result in a net reduction of GHG in the atmosphere. In considering environmental impact, it is
not sufficient to consider only the emissions resulting from fuel burn. The environmental cost of
materials, energy and changes in land use that are required to produce the fuel must also be part of
the equation. Particularly for the aviation industry, noise and particulate emissions are of concern
for public health and safety and could legitimately be considered a criterion for sustainability. To
quantify the net impact of any particular process or set of processes, a relatively new field of Life
Cycle Assessment has emerged to provide solid guidance for determining which processes are in
fact sustainable.
The heart of sustainability evaluations resides in the Life Cycle Assessment, which is a means
of quantitatively evaluating a process system from start to finish for the purposes of comparing a
number of options. The goal of an LCA may be to evaluate environmental impact, inform market
strategies, and/or analyze socioeconomic impact of a particular set of choices. As an example,
we will consider the outline of an LCA for the environmental impact of conventional versus
alternative aviation fuels.
The first task is to decide on the purpose of the LCA and thereby decide on the “functional
units” that will be used in the analysis. Conversion factors will be used to relate everything in
the analysis to this functional unit, which could be almost anything - but it has to relate to the
problem of interest. If we would like to analyze how much you could save over the next five years
by changing from incandescent light bulbs to compact fluorescent light bulbs in your living room,
your functional unit might be related to the amount of light that is needed to read the paper at
night. In this case, we might choose “lumens per square foot per Euro” as a functional unit.
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