70 Introduction to Renewable Biomaterials
Partial decomposition*
Fossil fuels
Combustion Combustion
Respiration
Photosynthesis
Heat + light
CO 2 + H 2 O
Heat + light
CO 2 + H 2 O
Potential energy
Biomass + O 2
Figure 3.3Biomass and fossil fuels – origins and energy content. Biomass is an important element of
carbon cycle. In the process of photosynthesis, carbon dioxide and water are converted into
carbohydrates and other structures called biomass. Biomass can be then digested or combusted to
recover stored chemical energy and release oxidised compounds: carbon dioxide and water. Fossil
fuels are biomass that underwent fossilisation process, that is, slow partial decomposition in the
absence of oxygen powered by heat and pressure from geological sources. In a process of fossilisation,
biomass lost significant content of oxygen and became composed of hydrocarbons having higher
energy content than original biomass. Bentley 2002 [4]. Reproduced with permission of Elsevier.
atmosphere and mere 250 years to disrupt it. In principle, carbon fixation by photosyn-
thetic organisms could deal with the excessive CO 2 concentration due to the inherent
features of carbon cycle (Figure 3.3).
In reality, however, the ability of photosynthetic organisms to mitigate the effects of
anthropogenic release of CO 2 is limited. It is estimated that no more than about a half
of current anthropogenic emissions (15 of 33 billion tons CO 2 annually [11]) can be
mitigated by photosynthetic activity; clearly not sufficient to stop CO 2 accumulation in
the atmosphere and prevent anthropogenic climate change. This problem is aggravated
by other anthropogenic activities such as deforestation, soil erosion and other processes
that decrease primary productivity. Another major carbon sink is ocean. It is estimated
that about a third of all anthropogenic emissions has been dissolved in the oceans. It
may help to alleviate the effects of global warming but results in the acidification of the
oceans. Since the beginning of industrial revolution the pH level dropped by 0.1 unit. It
is expected that continued release of CO 2 to atmosphere will lower the pH by another
0.2–0.3 units having profound effects on marine organisms such as corals and plankton
[12]. The excessive accumulation of dissolved CO 2 in the oceans will also shift the future
absorption pattern towards the atmosphere, and it is expected that the capacity of the
oceans to absorb more CO 2 will be about 60% lower in the year 2100 than it is today,
aggravating the effects of climate change [12].
It remains to be seen how non-conventional resources impact the environment
but the initial findings are not promising. Non-conventional fossil resources have
lower EROI than traditional resources and as such require much larger investment,
infrastructure and volume of production to deliver an equal content of usable energy.
Since all these values change exponentially so does the environmental impact of these
processes. Emissions of carbon dioxide from non-conventional resources are larger
