98 Introduction to Renewable Biomaterials
3.5.3.2 Impacts of Feedstock Cultivation
Cultivation of bioenergy feedstocks is considered as one of the most important con-
tributors to the overall impact of the process. First, agricultural practices such as soil
preparation, biomass harvesting and transportation require significant energy inputs
that usually come from fossil fuels [45]. Second, many feedstocks for bioenergy use
require numerous agricultural inputs such as fertilisers, pesticides and insecticides.
Especially high yielding food crops that produce abundance of easily accessible pools
of starch and triglycerides, like corn or rapeseed, are particularly intensive to cultivate.
Among these inputs, nitrogen fertilisers can contribute significantly to the overall
sustainability of the process. Vast majority of nitrogen fertilisers used in agriculture
are direct result of Haber–Bosch process, a revolutionary technology of synthetic
production of ammonia from nitrogen and hydrogen. Although production of synthetic
fertilisers allowed human population to grow to an unprecedented scale, it comes with
significant environmental impact. First, fertilisers are produced using both energy and
hydrogen derived from fossil fuels; second, the process of conversion is very energy
intensive; and third, nitrogen fertilisers are usually supplied in excess that results in
the release of sewage effluents and agricultural run-off carrying fertilisers into natural
waters resulting in eutrophication, algal blooms and formation of anoxic zones in
water bodies. Utilisation of bioenergy feedstocks that can acquire nitrogen form waste
streams like microalgae or have very efficient nitrogen cycle through its remobilisation
likeMiscanthuscan significantly reduce the impact of cultivation on the processes of
bioenergy and biomaterial production.
3.5.3.3 Impacts of Conversion Process
Conversion of biomass to renewable fuels and materials allows introducing new func-
tionalities to the biomass. It can enhance its utility for customer, increase energy density
of the fuel and its storability and transportability. There are, however, different routes
to obtain these new functionalities and broadly thermochemical routes and biochemi-
cal routes can be distinguished, as well as an emerging field of hybrid technologies. In
general, thermochemical conversion processes of biomass conversion often use higher
energy inputs, usually from fossil sources, more aggressive chemicals and produce waste
that may be more difficult to dispose or remediate than those of biochemical processes.
The advantages of thermochemical processes are their higher compatibility with current
chemical industry and shorter conversion times. Biochemical processes on the other
hand are generally much longer as they require cultivation of microorganisms before
desired metabolites can be used. Very often they produce chemicals that are not fully
compatible with current infrastructure designed for fossil fuels. Most of the side prod-
ucts of biochemical processes are not hazardous and often have commercial utility as
food or feed components or can be relatively easily converted to methane and/or energy
through anaerobic digestion technology.
3.5.3.4 Impacts of Product Use
The products resulting from conversion of biomass can have various impacts on the
environment depending on their chemical properties. Their toxicity and environmental
impacts could be due to the leakage or combustion. Many bio-fuels that are a direct
result of microbial metabolism, that is, lower alcohols or fatty acids can be relatively eas-
ily decomposed by bacteria or fungi [31, 46]. This does not mean however that the usage
