Biomass is the plant material derived from the reaction
between CO2 in the air, water and sunlight, via
photosynthesis, to produce carbohydrates that form the
building blocks of biomass. Typically photosynthesis
converts less than 1% of the available sunlight to stored,
chemical energy. The solar energy driving photosynthesis
is stored in the chemical bonds of the structural
components of biomass. If biomass is processed effi-
ciently, either chemically or biologically, by extracting
the energy stored in the chemical bonds and the subsequent
‘energy’ product combined with oxygen, the carbon
is oxidised to produce CO2 and water. The process
is cyclical, as the CO2 is then available to produce new
biomass.
Bioresource Technology 83 (2002) 37–46
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The value of a particular type of biomass depends on
the chemical and physical properties of the large molecules
from which it is made. Man for millennia has exploited
the energy stored in these chemical bonds, by
burning biomass as a fuel and by eating plants for the
nutritional content of their sugar and starch. More recently,
fossilised biomass has been exploited as coal and
oil. However, since it takes millions of years to convert
biomass into fossil fuels, these are not renewable within
a time-scale mankind can use. Burning fossil fuels uses
‘‘old’’ biomass and converts it into ‘‘new’’ CO2; which
contributes to the ‘‘greenhouse’’ effect and depletes a
non-renewable resource. Burning new biomass contributes
no new carbon dioxide to the atmosphere, because
replanting harvested biomass ensures that CO2 is absorbed
and returned for a cycle of new growth.
One important factor which is often overlooked when
considering the use of biomass to assist alleviate global
warming, is the time lag between the instantaneous release
of CO2 from burning fossil fuels and its eventual
uptake as biomass, which can take many years. One of
the dilemmas facing the developed word is the need to
recognize this time delay and take appropriate action to
mitigate against the lag period. An equal dilemma faces
the developing world as it consumes its biomass resources
for fuel but does not implement a programme of
replacement planting