CA2069414A1 - Photobioreactor - Google Patents

Abstract

A photobioreactor for the cultivation of photosynthetic microorganisms is disclosed wherein a plurality of baffles are mounted in the photobioreactor tank forming hollow cavities which enable the insertion of light sources through openings in the tank wall.
The baffles shield the light sources housed therein from the liquid photosynthetic culture contained in the tank thus facilitating electrical connections with the light sources and the maintenance thereof as well.

Description

20~41~
I
.

E'llO'rO~IOnE7~CTOn Backqround oL Invention ~lgae have ~ee,n cul~ivated artj.icially ~or su~
diverse purposes as the productioll of food for animnls and humans, the treatment of sewage and waste waters, and the accumulation of radioactive wastes. More recently, algal cultures have been used for th~ -production oE en~ymes having industrial and researcll applications and for producing oils and other materials having nutritional value. Modern biotechnology o~ers an opportunity or the gelle~ic modi~3.ca~ion o~ Dlgnr- ~o yield cultures cnpaL]o oL produci.ng a wLde val Lel:y ~r useful materials.
Various methods and equipment have been employed for the artiicial culturing of algae. Perhaps the simplest procedures have involved the ùse of shallow open ponds exposed to sunlight. Such ponds are subject.
to contamination by dust, other microorgani~ms, insects and environmental pollutants and provide minimal ability to control the degree of exposure to light, temperature, respiration and other important factors.
A more sophisticated approach has involved growing algal cultures in plastic-covered trencl-es and ponds, optionally having electrically powered pumps and agitators. ~I'hese con{igurations reduce the ch.llces l-r contamination o~ the culture and permit more accurate control o~ temperature, respiration and other , ::
:.- : .

....
~ . .... .....
":. '',, ' ' ' ~

I'CT/~S9~ l6,~' 2069~1~

p~rameters. Such configurations are still quiLs ine~icient in terms or provi.cling .~dequate and ~nlirorm amounts o~ light to ~he algal cells, p~rticulatly when sunlight is the sole source ot light.
Unlike other microorg~nisms, the nutrient requirements of algas are very inexpensive, carbon dio~ide being the pri.ncipal source o carbon. On tlle other hand, the photosylltlletic process requires thal the algae be exposed to a reIatively constant all(l uniform source o~ light. A primary design factor modern photobioreactors involves providing a means uniformly exposillg tlle cells in tlle algal culture tll the optimum amount of visible light. Like m~ny p~an~s, algae are qui~e sens.iti.ve ~o ~he Dnount and kincl ot light. Excessive lighl~ sensity can damage alld kill ..
algal cells. Too little iight results in low levels o~ -photosynthesis and consequently reduces growth.
~ number oL design factors are affected by the means selected for supylying light to the cells. For example, light sources, ~ncluding nat~ral sunlight, o~ten emit substantial amounts of heat. Algal cultures -:
are sensitive to heat and many of them grow most efficiently at temperatures of 20-35C. Thus, means must o~ten be provided for cooling the algal culture Dnd dissipating heat g~nt?lnl:e~l hy the light sollrce.
Two desi~n Cactors closely related Lo the requirement fo~ a uniform and constant supply of ligllL
are the cell density and the light path length. Like conventional fermentati.on processes, it is usually desirable to use as high a cell density as possib~e.
Many of the same considerations apply to algal cu1l:llre.q as to bacterial cultures. For example, in addi~i.on ~-~
the light requirements, one must take into account L~le competition for nutrients, respiratory demands, -.;:- . -: ' ' - :: . ' :

' ~ 1) I'CT~(~9(1/~
20~94~4 viscosity and pumpability o~ the culture medium., an-l the like. 11owever, an ex~remely high cell denslty results in cells more than a lew millimeters trom ~he light source being et~ectively shiel~e~ from t~le liyl-l Simply increasing l.ighL intellsity will not ove~com~
this problem, because higllly intense ligllt will danl.ge o. kill cells near ~lle ligh~ source.
The only effective way of increasing cell densitie.s while main~inin~ a uniform amounl of li~
0 i5 to employ a rela~ively shor~ ligllt.patll lenytll. 0~
course, ~he requiremen~ ~hat Lhe photobioreacior have a relatively short light path leng~h in~roduces a new sel.
of design problems. For industrial applications, i~ i~
usually desirable ~o employ high-volume microbial cultures. Large cul~ure volumes are amenable ~o continuous or large-scale batch recovery op~rations a~
generally resul~ in economies of scale. Sstisfying -:lle requirements for large culture volumes and shor~ ligll~
path lengths has required that the photobioreac~or llave large, txansparellt walls wlli.cll are closely spaced ~n deine a light path and a 1uid chamber within whicll the algal culture is contained. T~le transparellt wal~.s are illumi~na~ed wi~h an appropriate light source to su~tain the growth and photosynthetic reactions Or ~he cells. ~.
Various designs of such photobioreactors have beall .:
employed. A relatively simple design which has been successfully used in laboratory and pilot plant :-:
operations is simply a glass chamber having large, flat, parallel side walls and a narrow bottom and ~?n~l walls. A gas sparging tube is placed in the bottom oi the chamber to allow caxbon dioxide o~ carbon-di.oxi li~?-enriched air to be sparged througll a rulture medium contained in the chamber, and banks of fluorescent , . ~ - , '.

\~ 0 '~ I'CI / ~ S~

q ~0~94~4 light tubes are arrange~ adj.cen~ ~o the si~ wall~. el the chamber. Inocula, nn~rien~s, bn~f~rs, and the lik~
can be introduce~ into ~:h~ cl~ambe~ ongl) ~h~ l.o~-which m~ op~.o~l]y b~ c~v~r~l wi.~l~ o lid. 'I'hi~
design has been very s~lcces~ul and useful or sma]]
scale operations.
~n alternative embodiment of a ~ioreactor employi~g a 1uoreseent ~ube in~olves a cylindricnl culture chamber having glas.s wall~ whicll surronlld a single r~ uorescent ~u~e. 'I'he cul~ure chamber may al~.(.
be surrounded by a concen~ric cylindrical wa~er jacl~l for controlli.ng the temperature oE the eulture. Sue photobioreactor is described by ~admer, R., Behrens, P., and Arnett, L., in a paper titled "~n Analysis of the Productivity of a Continuous ~lgal Culture Systelll", published in Bio~echnolo~Y and Bioenqineerina, 29 (19~), pp. 48~-492. ~rhis design has also proven very valuable for laboratory-scale algal culturing operations, but, for many of the reasons described above, hafi not proven particularly useful for large-scale operations.
Various photobioreactors designs are reviewed in an article by Yuam-Kum Lee, ~Enclosed Bioreactors for the Mass Cultivatlon of Photosynthetic Microorganismfi:
The Future l'rend', Tlu~rEcll~ July 1986, pgs. 186-189.
Furthermore, several problems have resulted from photobioresctor designs which have utilized ligltt bank~c and light compartments immersed in the liquid microllia~
culture. Firstly, it is difficult to fiafely and effectively make the necessary electrical connectiolls w1th the light tubes. Secondly, access to the ligh~
tubes for maintenance is made more difficult.
A significant need still exists for large-scaJe photobioreactors which are ctpable of uslng high ,... . . .
: . , . ;: ~
.
, :, .

': , , .

X~ ql~ ( 2~

206~41~

intensity, low-cost Jamps which provide uniform distribution of ligh~ ove~ large surface are~s wlli]e utilizing a sae anl les.s complicated me~l)s Eor providing elec~i.cal poweL.
SummarY oL tlle lnvell~ioll The present invention in accorddllce witll one embodiment thereoC, compri~e~ a novel ptlotobioreflct.t)r in which at least one .nd preferably ~ pluraliLy or light transmitting ba~les are mounted side by side i a tank containing a liquid microbial culture. Ea~h baf1e is fo~med witll a hollow cavi~y and is mountetJ s-~that the cavity i5 accessible Lrom outside the tank the insertion o a ligh~ source. ~he sides ot the - ba~fles are constructed of optically transparent lS material to transmit the light from the light source t-~the liquid which is ln con'act witl the outsicle surfaces of the baffles. Each light source is made up of a plurality of light tubes, preCerably 1uoresce lamps, supported by braces or similar supporting structures and mounted in the baffles. Electrical leads are extended Lrom tlle tubes to al~ow connec~i with an external power source.
In another embodimen~, a single higll intenslty light source is mounted in a light compartment l~aving walls made of in~ernally reflective prismatic sheet material to p~ovlde unlrorm li~ht of ~ suitable intensity to tl~e microbial liquid culture.
The invention thus provides lor sreatly simplirie-3 electrical circuitry and connections, and reduces maintenance costs. Enabling access to the liglt - sources from outside the tank and shielding tl~e liglm sources from actual contac~ Wittl the mlcrobial cul-ule makes it easier to identify and replace burned bulbs :
and it reduces the risks oC short circuits as well.

. -- , ' : ' . :
... . .

G 20~;9~

Furthermore, as the ligl)t transmitting ba~Lle~ ~r~
surrounded on its major light emit.ting surfaces by ll-~
liquid microbial culture the spacing between adjac~l~t tubes as well D5 betweell a~ljacellt barLles is such ar. ~n optimize absorption o ~he emitted ligh~ by ~he algne and to assure virtually complete ~bsorpLio~l oI tlle emitted light.
In addition tlle light ~ransmitting bafles a~o perform a structural Iurlction in Ihat their ex1.ernnl surfaces serve a5 walls or drDrt spaces to deIille circulation paths through which the algae is movecl b~
means such as air liIt agitation. The baffles also form basic building blocks or mo~ules which can be In~ed in combination in any ~esiretl number for large sca]e photobioreflc~or systems of any selected capaci~y.
Orief DescriDtion of the Drawin~s Figu~e 1 is a perspective view of the photobioreactor illustrating an embodiment of the present invention;
Figure 2 i5 perspective view oL a bafile and fluorescent tube arrangement forming part of the photobioreactor of Figure l;
Figures 3-5 are top, side, and bottom views respectively of the photobioreactor illustrating the present invention;
.Figure 6 is a perspective view o an alternate light source for the photobioreactor illustrating another embodiment o~ the present inventi.on;
Figure 7 is a perspective view of the photobioreactor illustrating the present inven~ion utilizing the light source oI Figure 6.

- . :. . - , , . - .
.. . . ~ .
'' ' ' ~' ' " :
. , .

~ Ç~ t.l 7~

7 20~9~

~etailed DescriDtioll o~ the ~oventioll Referring now to tl~e drawings Figure 1 is .
perspective view o~ a photobiorenctor 10 embodyjllg ll present inventiol1 to bo used in B~ ou]~uril~g ot dispersed cells or cell ~ggregate.s Ol multice].llllal-organisms having a liglll. reqllirelllel~ s an exnln~
this photobioreactor ma~ be used to grow unicellula algae wllicll carry on photosynthesis. ~rhe exterior the photobioreactor 10 i9 in the Lorm of a tank 11 capable of containing a liquid culture medium as illustrated by numeral 12. 'I~he liqui~ culture me~j.lll-l is sometimes referred to as an "algal" culture, but i-will be appreciated ~ha~ the photobioreactor 10 may l)e employed for tlle cull:ivation of any type of ~ :
photosynthetlc microorganism.
The basic unit o the photobiol-eactor is a rectangular tank 11 as shown in Figu~e 1 with nllmerolls internal baf1es 14 WhiCIl extend from one end o[ the tank to the other and whose ends are sealed to the tank's inside walls Eacl~ baffle 1~ is ormed with n hollow cavity which is accessible through openings in the wall of the tank. Tank end walls 13 can be cut nul.
or molded in any conventional manner to enable access to the baffle c.~vities trom o~lLsicle tlle tank~s encl w.

2~ surface.
From the outer surface of the tank walls are openings permitting access to the cavity of the baffle for the lnsertion of a ligh~ source. In the embodi.n~
shown in Figure 1 a plurality of light tubes 15 are inserted into the baffle cavity from outside the tank's surface and housed therein. Baffles 14 serve to protect 1.ight tubes 15 rom di.rect con~ct witl~ l.lle liquid culture medium 12. Light is therefore emitte(l;

;'' .', ' : ` . , . ', 59/)/l~h-"

2 ~

substantially uniformally fr.om ~lhes lS and is abso-l-ed by the a~gal culture.
~ltllougil tl~e embodimellt i.llllstrate~l in ri~re ~
shows a rectangularly sl~aped tank 1~ it is recogni~ed that any convenient .shape may l~e l~sed.
The tank and ba[tle .strl~cl.ure Or Ll~e p~ese invention i.s an improvemerlt over ~he pllotobiore.lctt-disclosed in pending in applicaLion S.N. 07/163 ~41 incorporated hereill by reLerence wllich disclose~ n compartment for protecti.ng a light bank again.st flni(l communication with a liquid culture medil1m. rermi~ llg insertion of a light source in~o tlle baLfle cavitie.c through the tank s outer surfaces, as in the presenL
invention, greatly facilitates electrical connecto~s to the light source and maintenance as well.
Located outside the tank 11 is means to control the temperature of the contents. ~ preferred means fol-controlling the temperature include water jackets or internal heat transfer coils which can be connected to refrigeration l~nits (not sllown) or lleating uni~s (IIOt shown). ~lso the dls~olved oxygen an~ pll levels Or the contents are continuou~ly monitored and concrol~e(l by any conventional, well known means.
Figure 2 is a perspec~ive view of a baffle l4 alld 2S the housing of light tubes 15 t)lerein. Side panels 1?
are substantially planar walls forming th0 baffle cavity therebetween. Planar walls 17 are major surfaces on the opposite sides of the cavity Ior the emission of light into said cavity. Side panels l7, top panel l8 and bottom panel l9 are made of a chemically inert and optically transparent material such as glass or acry.lic. lnternal br~ces l6 ar~
mounted to Iacilitate placelllent and to support ligll~ r tubes 15 or a bank oI ]i.ght tubes. Open baffle ends 20 ~:
: :

9 2~69~1~

permit the simple insertion o~ ~ubes ~llrough either end even wl~ile the photobjore,~c~or is in .~ll operational state as shown in Figure 1.
In the embodiment shown in ~igure 2, light tubes 15 are fluorescent tube lamps essentially in their "otl the shelf" condition without any modification or customization. The advan~ages Or such lamps in ~hi~s embodiment are that light is emitted ~rom them substsntially uniformly along the lengtll of the tul)es and in all directions perpendicular to the tube~.
This, along with ~he particular baffle spacing, enable.s optimum absorption o the light by the algal culture.
Because end sec~ions 20 o2 baffle 14 are open, electrical connections can e~sily and safely be made to light tubes 15 at their oppo.si~e ends in Dny conventional, well known way. As shown in Figure 2, individuai connections cre m~de to each fluorescent tube 15 by members 22 whereby leads are brought ou-through wires 23 and 24 which terminste in an electrical plug connectable to a source of electric power (not shown). Suitable ballasts (not sllown) a~e provided as well. These connections could also be made by provldlng a single adapter on each end section o~
the baffle or by grouping the tubes in any number.
In an alternative embodiment of the present invention, only one end of the baffle cavity is opened to the tank's outside surface. Tlris structure would require running the leaG wires connecting the fluorescent tubes at the closed end through the barrle cavity to the open end.
As mentioned above, the tank and bafle dimensiol-~
are selected to optimi~.e light absorption by the algae culture durin~ the photobioreactor'~ operation.
According to one embodiment, as illustrated in Figures :`:.- ' . - ' :
.: ~ ., ` ., .,~ ...

20~9~
IU

3-5, baffles 14 are constr~cted to he ~ inclles widn l.o enable the insertion of a fluorescent tube. Tlle overall height Or the ha~fles is determi.ned by the number of 1uorescent tubes Lo be inserLe~ hi~
embodiment, the height is approximately 2~ inches which, as shown in Figure 2, allows for l~ rluorescellt.
tubes and three brace.s 16. I`he outer surfaces of ad~acent baffles are separated by a distance of l illCh, and one-half inch separates a baffle's outer surface and the tank wall. Baffles 14 will generally extend along the entire 48 inch tank length as .illustrated in Figure 5. The overall height and width of the tank in this embodiment are 31 inches and 1~ inches as shown in Figures 4 and 3 respectively. Vsing high output, cool white fluorescent tubes, this spacing provides a near optimal light source for micro algae.
Furthermore, as illustrated in Flgures 2-5, planar walls l7 form a major portion of the light emitting surfaces of the baffle. In accordance with the baf[le dimensions set forth in tl~e preferred embodiment described above, approximately 90~ of the liqht emitted by the 1uorescent tui~es 15 is transmitted through planar walls i7. These figuses are not intended to i~e limitations but are provided only to illustrate thaL
plannr walls are ma~or surfaces forming a major portion ~.
o the bafle l.ight emitting surfaces.
The particular tank and baff 1Q dimensions shown in Figures 3-5 are for illustrative purpose~ only. It is to be recognized that the baffle widths and spacing between adjacent baf1es will depend upon the photon flux of the light source, the optical properties o~ the baffle walls and the cell density of the culture being .
used. Furthermore, the photobioreactor can easily t)s constructed in any volume due ~o the tank~s in~ernal ' ' . .

o ~ n~) Pcr/~ 7' 1l 2069414 symmetry of the light-transmitting baffles. 1he photobior.~acl:o~ in ~i gtlre 1 l~a~ rk i ng vol~lm~ Or 110-130 lil~ers. 1'hi~ vol~lm~ cao ~ily be illcr~.~s~
widening tlle ~ank increasillg ~he ll~igll~ arld increasirly S the numbe~ o~ ~aff~es. SIICII n cllnrly~ i~l tlle photobioreactor dssign does not a~[ec~ the operatioll or performance ot ~he pllo~o~ioreactor in arly way.
~ s mentioned above, ~he ligllt Lransmitting barrles also perform a structural function in that their external surfaces serve as walls or draft spaces ~o define circulation patlls Lor the a19A1 culture. ~s shown in Figure 1, bafrles 1~ are mounted in tlle tank to form passages 21 therebetween to enable the culture circulation and to enhance the growth process. In order to promote circulation and agitation within tlle tank, a series of hollow tubes or cylinders 20 preferably formed of a metal or ceramic material or inert material are placed in the preferred embodiment, between alternate pairs of baffles as illustrated in Figure 1. Tlle cylinders 20 can also be positioned between any adjacent baffles at any vertical position or between tl~e baf[le an~ the tank wall.
Furthermore cylinders 20 can be placed just below l.he baffles such that substantially all the gas flows there-between as illustrated in Figure 7.
The cylinders 20 contain small perforations or ~ :
apertures extending ~hrouqh the walls tllereof for~ning gas sparging tubes througll WhiC11 a pressurized gas ~e.g. carbon dioxide) is supplied for ~he photosynthesis requirements of the algal culture. rlle gas may be air or nitrogen or another inert gas elther singly or enriched with carbon dioxide. ~s gas is bubbled into the culture, it forces the medium to rise creating a circulation up one channel and down ano~l-er ,. . - . . ' :. .
: . . ,, . , . :
.,' : ~ , ~
- :: . . .

~l) qll~)-O~ I'Cl/~91~/1)(,,"

12 2~9~14 in the directions show1\ hy the arrows in rigurq 1. 1 is recognized, however, that the up an~l down circulation as illustrate~ is not necessary ~o acllinve mixing. Yositioning the sp.~Jging ~ube~ between adjacent bafLles and betwee~ af[le and t~nk wall will also acllieve this desired result. Other means [or supplying nutrient source gases and ~or circulating tl-~
culture m~y also be used.
~ecause the baffles exte!ld througll the entire length of the tank and the hollow cavities ormed therein are accessible from the outer surface of the tank walls on either side, supplying electrical connections to the fluorescetlt tubes housed therein is great~y simplified. Providing maintenance for the ~;
tubes is simplified as well. ~lectrical leads connected to the ends of the tubes are made in th~ simple conventional manner and are completely .shielded ~rom the liquid culture 12. necogni~ion and replacemen~ or burned light tubes is greatly facilitated by this nove~ ~
structure. Furthermore, by selecting the proper ligll~
path lengths as described above, virtually 100~ of the emitted light is ~bsorbed by the culture and the lLght absorption is relatively uni~orm and optimized throughout the culture as well.
In accordance with another embodiment of the inventlon, as illu~trated in Figure 6, the light source is a single concentsated high-lntensity light 31 mounted in a light compartment 30 to provide uniform high intensity light to the microbial liquid culture.
3~ Liqht compartment 30 contains means for substantial]~
uniformally distributinq ligllt rom source 31 wi.th reflector 33 across ~he interior surface of transpare walls 34 and 35. Such means maybe in the form of a light guide constructed of internally reflective ~. -. : .

:.:. . - : , - .

13 2~9~

prismatic sheet material (not shown)~ The internally reflective prismatic sheet material is rormed trom highly tran.sparent flexible shee~ mn~erial, sucll ,~
polyacrylate, on the s~lrtn~ o~ wlli~h is inscril~e~ witl.
minute 90 corrugations. ~s a result o~ ~hese corrugations, light strj.kill~ l.he .shee~ wi~ll an c~ngJ-! or incidence o~ about ~7 or less will be reflec~e~ Wi nearly 100~ e~Liciency. Minor imperfe~tions in the prismatic sheets as well ~s light iniringing tlle sh~el.s at angles greater than about 27 result in transmiss of light thro~lgl~ the prismatic shee~ m~terial.
~ s shown in Figure 6, a mirror 32 is located at the bottom of light compartment 30. ~s a result o~ t:he internal reflectDnce of the prismatic sheet material, reflectance of mirror 32 and re~lector 33, light from the light source 31 is, to a large extent, reflecte<l back into the compartment. The net result of this internal reflectance is ~hat the light from the light source is distributed substantially uniformly across the inner surface of wall 33 and thus provides a hiql~ly controlled distribution of light throughout the light paths in the walls 34 and 35. Li~ht from the light source is there~orr? emi.tted and distril~u~ed -~
substantially uniformally from the exterior surface~ or the baffle's planar walls.
Slnce it i.s not desirab]e to hnve light emitte~l from end curfaces 36 and 37, a re~lective cover ~no~
shown) is placed between the compartment wall and ~lle internally re1ective prismatic sheet so that the liqh~.
30 is redirected back into the compartment. Mirrors may be used as end surfaces 36 and 37 as well.
Furthermore, light source 31 could be placed near end surfaces 36 and 37 in vertical arrangement to efiect.
the uniform emittance. Constructing a light .
: .

94~4 compartment utili~in~ a prism.~tic sl1eet material ,lnd the light guides rormed ~herefrom is de~cribed ilt U.~.
Patent Application S.N. 07/33~,53~, Lncorpora~e~ he~Pi by reference.
The electrical power can be supplie~ to the hit111 intensity ligll~ source 31 in any ~:onvelltional manne1.
~s illustrated in this embodimen~, leads connected ~o source 31 are brought ou~ through wire 38 and ~ermina~e in an electrical plug connec~able to a source of electric power (not shown).
Figure 7 shows a perspective view of the photobioreactor utilizi.ng ~he ligh- source 30.
Photobioreactor 40 operates in an identical way as described with reference to photobioreactor 10.
i5 Baffles 41 are formed with hollow cavities extending the entire tank length and are constructed to enable the insertion of the light source from the either or both ends of the tank, througll open ends 42.
Electrical connections to source 30 are very simply --2~ made in any well known, conventional way as de.scribed above.
While it is apparent that the preferred embodimelll.
shown and described provides certain advantages, many of the advantages of the present i.nvention can nevertheless be realized in other conflgurations, and it will be appreciated that various modifications, changes and adaptions can be made, all of WtliC)I are intended to be comprellended within ~he meanlng and range equivalen~s of the appended clnims.

r; r ' ' ' ' ~ ' ' ' `
. ~, .' '. ,' ' ' . ' ~, : :' `

.

Claims (18)

What is Claimed Is

1. A photobioreactor comprising:
(a) a tank for containing a liquid photosynthetic culture at a preselected operating level within said tank;
(b) a plurality of baffles each extending from one tank wall to an opposite tank wall, each of said baffles comprising optically transparent and generally planar walls having exterior light emitting surfaces and forming a liquid impervious hollow cavity therebetween;
(c) means for mounting said baffles within said tank such that the hollow cavity in each of said baffles is accessible from outside the tank wall which enables the insertion of an array of light sources in said hollow cavity in each of said baffles; and (d) means for positioning said baffles in said tank spaced apart with said planar walls in generally parallel relation with each other.

2. The photobioreactor as set forth in claim 1 wherein substantially all light emitted into said liquid photosynthetic culture is emitted through said light emitting surfaces of said planar walls.

3. The photobioreactor as set forth in claim 1 wherein said means for positioning comprises means for spacing apart said baffles such that substantially all the light emitted from the exterior surfaces is absorbed in the culture.

4. The photobioreactor as set forth in claim 1 wherein said means for mounting comprises sealing ends of said baffles to the tank walls and wherein said cavities are accessible through an opening in at least said one tank wall.

5. The photobioreactor as set forth in claim 1 wherein said light source is a plurality of fluorescent tubes.

6. The photobioreactor as set forth in claim l including means for introducing a sparging gas to flow between at least some of said baffles.

7. The photobioreactor as set forth in claim 6 wherein said means for introducing a sparging gas is positioned between at least some of said baffles.

8. The photobioreactor as set forth in claim 5 including means for connecting said fluorescent tubes with an electrical power supply.

9. The photobioreactor as set forth in claim 5 wherein each of said baffles comprises at least one spacer for separating and supporting said fluorescent tubes.

10. The photobioreactor as set forth in claim 4 wherein said light source is insertable into said cavity through an opening in said one tank wall and said opposite tank wall.

11. The photobioreactor as set forth in claim 2 wherein each of said baffles is approximately two inches in width and 24 inches in height.

12. The photobioreactor as set forth in claim 3 wherein outer surfaces of adjacent baffles are separated by a distance of approximately one inch.

13. The photobioreactor as set forth in claim l wherein said light source is a high intensity light source directed into a light compartment;
said light compartment comprising an internally reflective prismatic sheet extending substantially from said light source to an end wall opposite said light source, said compartment further comprising a mirror at an end opposite said light source oriented to reflect light back into said compartment wherein said light source, said reflective prismatic sheet and said mirror are arranged such that light from said light source is distributed and emitted substantially uniformly from the exterior surfaces of said planar walls.

14. The photobioreactor as set forth in claim 1 wherein said tank and said baffles are generally rectangular in shape.

15. A photobioreactor comprising:
(a) a tank for containing a liquid photosynthetic culture;
(b) a plurality of light compartments each containing a high intensity light source;
(c) a plurality of baffles mounted within said tank extending from one tank wall to an opposite tank wall and positioned in generally parallel relation to each other, each said baffle comprising substantially planar and optically transparent surfaces forming a liquid impervious hollow cavity which is accessible through an opening in the tank wall and enables the insertion of said light compartments into said cavity of each of said baffles; and (d) said light compartment comprising means for emitting and distributing light from said high intensity light source substantially uniformly from exterior surfaces of said planar surfaces.

16. The photobioreactor as set forth in claim 15 wherein said means for distributing and emitting light comprises an internally reflective prismatic sheet material extending substantially from said light source to an end wall opposite said light source and a mirror at an end opposite said light source oriented to reflect light back into said compartment.

WO 91/07080 PCT/US90/06?22

17. The photobioreactor as set fourth in claim 15 including means positioned between at least some of said baffles for introducing a sparging gas.

18. The photobioreactor as set forth in claim 15 including means for connecting said high intensity light source with an electrical power supply.