Phytotechnology and Photosynthesis - Environmental Biotechnology: Theory and Application - page 165

various attempts have also been made to turn the algal crop into a number of
different products, including animal feed and insulating material.
Carbon sequestration
Their use as a carbon sink is a simpler process, only requiring the algae them-
selves. However, even as a functional algal monoculture, just as with the joint
algal/bacterial bioprocessing for effluents, without external intervention to limit
the standing burden of biomass within the bioreactor, reduced efficiency and,
ultimately, system collapse is inevitable.
In nature, huge amounts of many elements are held in global reservoirs, reg-
ulated by biogeochemical cycles, driven by various interrelated biological and
chemical systems. For carbon, a considerable mass is held in organic and inor-
ganic oceanic stores, with the seas themselves being dynamic and important
component parts of the planetary carbon cycle. Marine phytoplankton utilise car-
bon dissolved in the water during photosynthesis, incorporating it into biomass
and simultaneously increasing the inflow gradient from the atmosphere. When
these organisms die, they sink, locking up this transient carbon and taking it
out of the upper oceanic 'fast' cycle into the 'slow' cycle, which is bounded by
long-term activities within the deep ocean sediments. In this respect, the system
may be likened to a biological sequestration pump, effectively removing atmo-
spheric CO 2 from circulation within the biosphere on an extended basis. The
number, mass and extent of phytoplankton throughout the world's seas thus pro-
vide a carbon-buffering capacity on a truly enormous scale, the full size of which
has only really become apparent within the last 10-15 years, with the benefit of
satellite observation.
In the century since its effectiveness as a means of trapping heat in the atmo-
sphere was first demonstrated by the Swedish scientist, Svante Arrhenius, the
importance of reducing the global carbon dioxide emissions has come to be
widely appreciated. The increasing quantities of coal, oil and gas that are burnt
for energy has led to CO 2 emissions worldwide becoming more than 10 times
higher than they were in 1900 and there is over 30% more CO 2 in the air, cur-
rently around 370 parts per million (ppm), than before the Industrial Revolution.
Carbon dioxide is responsible for over 80% of global warming and according
to analysis of samples of the Antarctic ice, the world today has higher levels of
greenhouse gases than at any time in the past 400 000 years. The UN Intergov-
ernmental Panel on Climate Change has warned that immediate action is required
to prevent further atmospheric increases above today's level. In the absence of
swift and effective measures to control the situation, by 2100 they predict that
carbon dioxide concentrations will rise to 550 ppm on the basis of their lowest
emission model, or over 830 ppm in the highest.
In 1990, over 95% of the western industrialised nations' emissions resulted
from burning fossil fuels for energy, with the 25% of the world's population who
live in these countries consuming nearly 80% of the energy produced globally.