The biggest issue when producing hydrogen through photosynthetic
microorganisms is the matter of supplying light efficiently. Since light is
absorbed and scattered by photosynthetic microorganisms, light intensity
rapidly declines at the receiving service in culturing solution, resulting in a
relatively irregular distribution of light intensity within the PBR. Hydrogen
production by photosynthetic microorganisms is reliant on light intensity;
reactions become saturated and inhibited under high light intensity conditions, resulting in a marked drop in light-to-hydrogen conversion efficiency.
These two-issues, the irregularity of light intensity distribution in PBRs,
and the existence of a photo-saturation point, will be need to be addressed
to produce hydrogen efficiently with PBRs (Pulz 2001).
(5) Closed Photobioreactors
A closed PBR must be used to make efficient use of solar energies when
applying factory or power plant waste gas containing large concentrations
of CO 2 for hydrogen production by photosynthetic microorganisms or mass
culturing of those microorganisms.
The biggest advantage of closed PBRs is that it is possible to build
three-dimensional systems for efficient usage of solar energy. At the same
time, consideration should also be given to cleaning of the PBR interior, as
the capital expenditures (CAPEX) and operating expenses (OPEX) are
greater than with an open PBR. Tube, flat, and bag types are currently used,
depending on the purpose.
(6) Open Photobioreactors
An open photobioreactor can be used when there is no contamination risk
during mass culturing of photosynthetic microorganisms or when
mass-cultured algal body biomass is used for hydrogen production. The
biggest advantage of an open PBR is the low capital expenditure. At the
same time, the culturing area is directly proportional to the installation area,
which means that a vast space is needed. Among the photosynthetic
microorganisms that can be mass-cultured with open PBRS in raceways or
open and round ponds are Chlorella, which exhibits a fast growth rate;
Spirulina platensis (when the medium is strongly alkaline); Euglena gracilis (when the medium is strongly acidic); and Donaliela salina (when the
medium has a high saline concentration)
Cynatonech, which mass-cultures Donaliela in Hawaii, uses an affordable
PBR created by digging a ditch in a lava plateau and installing vinyl
sheeting (Wakayama 2011).
9.4.4 Hydrogen Production from Algal Biomass
During harvesting season, kelp has a component ratio of 79% water, 4% ash, 1%
protein, 1% cellulose, 7% alginic acid, and 8% mannitol. Of the 17% organic
324
9 Marine Bioenergy Production
microorganisms is the matter of supplying light efficiently. Since light is
absorbed and scattered by photosynthetic microorganisms, light intensity
rapidly declines at the receiving service in culturing solution, resulting in a
relatively irregular distribution of light intensity within the PBR. Hydrogen
production by photosynthetic microorganisms is reliant on light intensity;
reactions become saturated and inhibited under high light intensity conditions, resulting in a marked drop in light-to-hydrogen conversion efficiency.
These two-issues, the irregularity of light intensity distribution in PBRs,
and the existence of a photo-saturation point, will be need to be addressed
to produce hydrogen efficiently with PBRs (Pulz 2001).
(5) Closed Photobioreactors
A closed PBR must be used to make efficient use of solar energies when
applying factory or power plant waste gas containing large concentrations
of CO 2 for hydrogen production by photosynthetic microorganisms or mass
culturing of those microorganisms.
The biggest advantage of closed PBRs is that it is possible to build
three-dimensional systems for efficient usage of solar energy. At the same
time, consideration should also be given to cleaning of the PBR interior, as
the capital expenditures (CAPEX) and operating expenses (OPEX) are
greater than with an open PBR. Tube, flat, and bag types are currently used,
depending on the purpose.
(6) Open Photobioreactors
An open photobioreactor can be used when there is no contamination risk
during mass culturing of photosynthetic microorganisms or when
mass-cultured algal body biomass is used for hydrogen production. The
biggest advantage of an open PBR is the low capital expenditure. At the
same time, the culturing area is directly proportional to the installation area,
which means that a vast space is needed. Among the photosynthetic
microorganisms that can be mass-cultured with open PBRS in raceways or
open and round ponds are Chlorella, which exhibits a fast growth rate;
Spirulina platensis (when the medium is strongly alkaline); Euglena gracilis (when the medium is strongly acidic); and Donaliela salina (when the
medium has a high saline concentration)
Cynatonech, which mass-cultures Donaliela in Hawaii, uses an affordable
PBR created by digging a ditch in a lava plateau and installing vinyl
sheeting (Wakayama 2011).
9.4.4 Hydrogen Production from Algal Biomass
During harvesting season, kelp has a component ratio of 79% water, 4% ash, 1%
protein, 1% cellulose, 7% alginic acid, and 8% mannitol. Of the 17% organic
324
9 Marine Bioenergy Production