Biomedical Engineering Reference
In-Depth Information
Assimilation
Plant:
Lignocellulosics
Carbohydrates
Proteins, Fats
Animal:
Carbohydrates
Proteins, Fats
Death
Death
Nonliving
Organic matter
Excretion
Oxygen gas
Fossilization
hv
O
2
Sequestered carbon
Peat, coal, oil, gas
Urea
H
2
NCONH
2
Carbon dioxide
CO
2
and Water
O
H
2
with Oceans
and Soil
Carbonate CO
2
3
Bicarbonate HCO
3
-
FIGURE 15.1
A simplified schematic of biological H
2
O, CO
2
, and O
2
cycle in nature.
Water vapor is the dominant greenhouse gas (GHG), followed by carbon dioxide with less
than half the effect of water vapor, in the atmosphere, absorbing radiant heat from the sun.
Life is supported by water, O
2
, and CO
2
with energy from the radiant heat of the sun. There-
fore, the sustainable or steady levels of these agents are of the critical concern for the intel-
ligent life form on earth. While continuity or longevity is a universal concern: every process,
every product, and every raw material we use, water and CO
2
, are two key substances in
the cycle of life.
In this chapter, we shall focus on the narrow perceptions of sustainability based on
humanity, especially in regards to the basic ingredient for life: water and CO
2
. As such,
energy, chemical and material source and/or energy carrier forms part of the discussion in
this chapter. However, more fundamental understanding of bioprocess sustainability is dis-
cussed in Chapter 16.
15.1. WHAT IS SUSTAINABILITY?
Sustainability is the capacity to endure. In a more general scientific sense, sustainability is
equivalent to continuum or ability to continue the course without termination. Therefore,
sustainability is compatible with the existence of universe and it is the ability to maintain
a definite “stable” outcome. The evolution to a sustainable state is predictable. However,
the form or state that is sustainable can be changed with intelligence or systematic interven-
tion during the course of evolution.
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