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Photo Bio-reactor Technical Information 6

I have tested a PBR design and it works success fully. Now i am creating it with technical details. Surely i will launch this commercially in the near...

PBRs are complex systems composed of several subsystems.
1. Light source
2. Optical transmission system
3. Reaction area
4. Gas exchange system
5. Filtration system (remove algal biomass)
6. Sensing system

Several of the subsystems of a PBR interact. The optical transmission system and gas
exchange system interact via the mixing that takes place in the reaction area. Algae are
moved into and out of lit areas by mixing. Assuming that the algae require time to
complete the photosynthetic process once sufficient energy is absorbed to initiate
photosynthesis, energy efficiency may be increased by moving algae into a dark area after
it has absorbed sufficient energy. state that 1ms is the time required to
complete a single cycle of the light reaction in photosynthesis. Moving algal cells into a
dark region of the reactor for a millisecond would likely not affect photosynthesis. Energy
absorbed by the algal cell once it has initiated photosynthesis most like is converted to
thermal energy. The thermal energy is then lost as heat or raises the temperature of the
algae cell.

A general design for a 500gal PBR will be presented. The design of the
below listed subsystems and the interaction of the subsystems will be discussed.
1. Light source
2. Reactor volume
3. Optical transmission system
4. Gas transfer/mixing system

Technical Informations:

The optical system chosen is generally described as a flat plate system. It is
desirable to provide a large lit surface area-to-volume ratio for the reactor. High density
algae cultures are relatively impervious to light transmission. Ogbonna and Tanaka (1997)
give the light extinction coefficient as 200 meters squared per kilogram. A 10g/l algae
concentration would yield an 86% loss of light energy at 1mm depth,
ln(I/Io)=200xCxd 1
where,
I-light intensity at depth of penetration d
Io-initial light intensity
C-algae concentration, kg/cubic meter or g/l

d=60/C 2
A 10g/l algae concentration would yield a penetration depth of 6mm from equation 2. Both
light penetration equation show how light penetration limits algal biomass production by
limiting light penetration.

photosynthesis can be maintained with a light intensity of 7.3 μmol/m2/s. They also state that a better
measure of light supply is the product of the light distribution coefficient defined as the
algal concentration at which 50% of the reactor volume receives sufficient light to
maintain photosynthesis and the energy per unit volume. Given a target algal production of
10g/l algal biomass production and a 6? (152mm) reactor depth lit on both sides yields a
desired light input of 7.4x1033mmol/m2/s. This light intensity is impractical. PBR design
must include mixing effects to move algae into and out of the light area of the reactor. Also
other techniques need to be explored for increasing lit volume of the reactor volume. Light
guides were developed for this purpose and will be discussed latter.

A lab scale PBR was built and tested at . The PBR was 10.67?x10.67? (271mmx271mm)
with a depth of 2? (50mm). The volume of the reactor
area was 3.7l and an algal biomass of 7.1g/l was produced in 14d. Light was provided by
650nm LED on circuit boards provided by DAKTROICS, Inc on each side of the PBR..
The boards provided 14.1W per board yielding a light intensity of 6.04x1014mmol/m2/s
(0.073m2 surface area). We estimate a potential algal biomass of 8.4g/l (light
distribution factor) indicating that the full potential of the PBR was not met. The light
supply for the PBR was 7.7kJ/s/m3.Combining the light distribution factor and the light
supply results in a light supply coefficient of 64.7kJ?kg/m6/s. The PBR had staggered
acrylic light guides 3/8? (9.5mm) in diameter that may have enhanced light distribution.

The 500gal PBR will be composed of 21- 48?x 19? (1220mmx483mm)
compartments with a depth of 6? (152mm) lit on both sides. Light will be provided by
fluorescent lights (1, 2, 5, or 8-40W bulbs on each side), 625nm LED (1536, 3072, and
6144 LEDs per side), grow lights, and metal halide lights. Light supply coefficients will be
determined for all lighting systems used. The light supply coefficients will be based on the
usable wavelengths of light in a spectrum. Usable wavelengths for algae are generally
assumed to be the red and blue visible regions around 436nm, 460nm, and 680nm.

Power Based on Algae Growth: The power required changes as the algal biomass
changes; grows. Kleinjan (1999) provides the following equation for energy demand of
algae.
E=2500xCxVxe0.03t
where,
E-energy required, J
2500-J/g of algae mass

V-reactor volume, l
0.03=ln2/24h-doubling time for algae culture
t-time, h
The integral of equation 3 yields the power (P, W) required by algae at any given time.

P=750xCxVe0.03t
Assuming that the desired doubling time is 24h,
P=1541xCxV
Kleinjan (1999) reported an energy efficiency of the algae of 22% which compares well
with the 23% obtained by Javanmardian and Palsson (1991). Adjusting for algae efficiency
gives:
P=7000xCxV 6
A PBR design must satisfy the energy/power needed for algal production.

Required Algal Biomass Production: Assuming the PBR is being designed to remove air
contaminates from livestock units, the algal biomass production must be sufficient to
remove the contaminants. Javanmardian and Palsson (1991) give equation 7 as the
photosynthesis equation for ammonia as the nitrogen source.
0.89CO2 0.6H2O 0.127NH3?0.89C(mol biomass) O2
The mole biomass is assumed to have the formula of C1.0H1.8O0.432N0.143 with a formula
weight of 22.7. Equation 7 shows that 0.11g of ammonia will be required to produce a
gram of algae biomass ((0.127molx17g/mol)/(0.89mol biomass x 22.7g/mol)). Similarly,
the oxygen produced per gram of algae biomass is 1.58g and the carbon dioxide used is
1.93g. ASAE D384.1 shows the ammonia in swine waste to be 290g /-16g per 1000kg of
pig per day. Data from Table 1 of Gallmann et. al. (2002) can be used to derive an
ammonia emission rate of 307g per 1000kg of pig per day for an 42kg pig ((6.0 /-0.37g
NH3/h-LU)x (2LU/1000kg pig)x(24h/d)). The algae required to remove the ammonia from
air is then 27911g/d per 1000kg pig ((307g/1000kg pig/d) /(0.11gammonia/g biomass)). If
the ammonia in the waste is to be used too, the algae production would need to be 5709g/d
per 1000kg ((307 306)/0.11).
Thu May 06 2010 12:49:03 PM by Kumar Photo Bio-reacto 2820 views

Comments - 4

  • Thu May 06 2010 01:11:25 PM

    Looks like good info, thank you Kumar!

    Vote Up! 0 Vote Down! 0

  • Jivatma wrote:
    Fri May 07 2010 07:12:11 PM

    is the amount of algae you get out of a cycle worth the cost of running one?

    Vote Up! 0 Vote Down! 0

  • Kumar wrote:
    Sat May 08 2010 10:02:28 AM

    We need to select a particular algae strain, perfect PBR , pakka oil extraction , and oil to bio-diesel methods. Then it is very profitable.

    Vote Up! 0 Vote Down! 0

  • Kmichau01 wrote:
    Sat May 08 2010 12:10:05 PM

    Do u have any photos.

    Vote Up! 0 Vote Down! 0

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