Phytotechnology and Photosynthesis - Environmental Biotechnology: Theory and Application - page 166

Unsurprisingly, energy industries account for the greatest share (36%) of carbon
dioxide emissions, a large 1000 Megawatt coal-fired power station releases some-
thing in the region of 5 2 million tonnes of CO 2 annually. Clearly, the current
focus on reducing fossil fuel usage, and on minimising the emissions of car-
bon dioxide to atmosphere, is important. In one sense, the most straightforward
solution to the problem is simply to stop using fossil fuels altogether. However,
this is a rather simplistic view and just too impractical. While great advances
have been made in the field of renewable energy, a wholesale substitution for
gas, coal and oil is not possible at this time if energy usage is to continue at an
unabated rate. The potential role of existing nonfossil fuel technology to bridge
the gap between the current status quo and a future time, when renewables meet
the needs of mankind, is a vital one. However, it is ridiculous to pretend that this
can be achieved overnight, unless the 'global village' really is to consist of just
so many mud huts.
In many respects, here is another case where, if we cannot do the most good,
then perhaps we must settle for doing the least harm and the application of
phytotechnology stands as one very promising means by which to achieve this
goal. The natural contribution of algal photosynthesis to carbon sequestration has
already been alluded to and the use of these organisms in an engineered system
to reduce CO 2 releases, simply capitalises on this same inherent potential in an
unaltered way.
There have been attempts to commercialise the benefits of algae as carbon
sinks. In the early 1990s, two prototype systems were developed in the UK,
aimed at the reduction of CO 2 emissions from various forms of existing combus-
tion processes. The BioCoil was a particularly interesting integrated approach,
removing carbon dioxide from generator emissions and deriving an alternative
fuel source in the process. The process centred on the use of unicellular algal
species in a narrow, water-containing, spiral tube made of translucent polymer,
through which the exhaust gases from the generator was passed. The carbon
dioxide rich waters provided the resident algal with optimised conditions for
photosynthesis which were further enhanced by the use of additional artificial
light. The algal biomass recovered from the BioCoil reactor was dried, and being
unicellular, the effective individual particle size tended to the dimensions of
diesel injection droplets, which, coupled with an energy value roughly equiva-
lent to medium grade bituminous coal at 25MJ/kg, makes it ideal for use in a
suitable engine without further modification. Despite early interest, the system
does not appear to have been commercially adopted or developed further.
Around the same time, another method was also suggested by one of the
authors. In this case, it was his intent specifically to deal with the carbon diox-
ide produced when biogas, made either at landfill sites or anaerobic digestion
plants, was flared or used for electricity generation. Termed the algal cultiva-
tion system and carbon sink (ACSACS), it used filamentous algae, growing as
attached biofilter elements on a polymeric lattice support. CO 2 rich exhaust gas