Phytotechnology and Photosynthesis - Environmental Biotechnology: Theory and Application - page 167

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 combustion pro-
cesses. 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 equivalent 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 dioxide
produced when biogas, made either at landfill sites or anaerobic digestion plants,
was flared or used for electricity generation. Termed the algal cultivation system
and carbon sink (ACSACS), it used filamentous algae, growing as attached biofil-
ter elements on a polymeric lattice support. CO 2 rich exhaust gas was passed into
the bottom of a bioreactor vessel, containing the plastic filter elements in water,
and allowed to bubble up to the surface through the algal strands as shown in
the following Figure 7.6.
Again, this approach to carbon sequestration was based on enhanced intra-
reactor photosynthesis, the excess algal biomass being harvested to ensure the
Figure7.6 SchematicACSACS