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Aquacultural Engineering 1 (1982) 239-244

C O N S T R U C T I O N A N D U S E O F F R E E - S T A N D I N G S O L A R S I L O SA S C O M B I N E D M A S S A L G A L / F I S H C U L T U R E U N I T S

BARRY A . COSTA-PIERCE*Goddard College, Plainfield, Verm ont 05667, USA

A B S T R A C TC o n s t r u c t i o n o f s o la r s i lo s or'or c o m b i n e d m a s s a l g a l/ fi s h c u l t u r e i s d e t a i l e d a n d t h e i rs p e c i a l i t y u s e o u t l h T e d f o r n z i x e d c u l t u r e o f ' u n i c e l lu l a r g r e e n a l ga e a n d b l u e t il a pi a( S a r o t h e r o d o n a u r e u s ) .

INTRODUCTIONThe ma in goa l o f any un i ce l l u l a r mass a lgal p rod uc t io n un i t i s t o ma x im ize pho to -syn th e t i c co nve r s ion e f f ic i enc i e s ( a s s imi l a ti on r a t i o s ) and ne t p rod uc t io n o f p l an to rgan i c m a t t e r t h roug h e f f i c i en t u se o f ava i lab l e so l a r ene rgy . Phy top l an k to n r equ i r eun l im i t ed quan t i t i e s o f pho spho rus , n i t r ogen , i r on , t r a ce me ta l s and ca rbo n d iox ideto a t t a in h igh ne t p roduc t iv i t i e s . H ighes t y i e ld s r epo r t ed fo r f r e shw a te r mass a lgalcu l t u r e o f ove r 30 g d ry w t m -2 day -1 have been r ea l iz ed w hen a ll nu t r i en t s , pa r t i cu -l a r l y h igh phosp horu s , i r on and ca rbon d iox ide , a r e p r e sen t i n exces s , f o r c ing l i gh ta n d t e m p e r a t u r e t o b e c o m e g r o w t h li m i ti n g f a c t o r s ( B r o w n , 1 9 7 1 ; G o l d m a n ,1979 a ,b ) . I n t h i s rega rd , op t imiz ing l igh t and t em pe ra tu r e sho u ld ac tua t e even h ighe ry i e ld s i n a lga l mass cu l t u r e due t o i nc r ea sed pho tosyn the t i c r a t e s concomi t an t w i th t heonse t o f op t ima l l igh t and t em pe r a tu r e r eg imes (Aruga , 1965 ) . Eng inee r ing con cep t ssuch a s sha l low l amina r - f low p ond s o r t r ans lucen t , f r e e - s t and ing s i lo s t ha t expo se ag rea t e r vo lume o f wa te r t o i nc iden t so l a r r ad i a t i on and h ighe r t empe ra tu r e s cou ldconce ivab ly i nc r ea se a lgal y i e ld s d r am a t i ca l l y .* Present address: Department of O ceanography, University of tlawaii, ftonolulu, H awaii 96822,USA.

239Aquacu ltural Engineering 0144-8609 182/0001-023 9/$02.75 Applied Science Publishers Ltd,England, 1982Printed in Grea t Britain

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2 40 B A R R Y A . C O S T A - P I E R C EMuch wo rk ha s been accom pl i shed u s ing the l amina r - f l ow r acew ay des igns ( s ee

G o l d m a n , 1 9 7 9 a ) . C o m p a r a t i v e l y l it tl e o r n o w o r k h a s b e e n d o n e w i t h f r e e -s t a n di n gs i l o s f o r mass a lga l cu l t u r e o r f i sh r ea r i ng even t hough p r ev ious r e sea r che r s haved o c u m e n t e d h i g he r a l ga l p ro d u c t i v i ti e s ( T a m i y a , 1 9 5 7 ) a n d g re a t e r p h o t o s y n t h e t i ce f f ic i enc i e s (Co ok , 1950 ) w i th cy l i nde r s o r t an ks w i th tr ansp a ren t s ide wa l ls ove rl amina r - f l ow r aceway des igns . Recen t l y Zwe ig e t a l . ( 198 1 ) and P i e rce (1980 ) haveused f r ee - s tand ing , t r ans luc en t f i berg l as s cy l i nde r s f o r t he m ass cu l tu r e o f mixedspec i es o f f r e shw a te r a l gae com bined w i th t he r ea r ing o f he rb iv o rous f ish , S a r o t h e r o d o na u r e u s (M cLarne y and T odd , 1977 ; Tod d , 1976 , 1977 ; Zwe ig , 1977 ) . Th i s pap e rde t a il s t he s imp le con t ru c t i on and u se o f t he se so l a r s il o s and t he i r p r imaryp roduc t i v i t y and f i sh y i e ld a s combined a lgae / f i sh p roduc t i on un i t s .

S I L O C O N S T R U C T I O N

Al though so l a r s i l o s may be cons t ruc t ed i n a w ide va r i e ty o f shapes and s i ze s t hes t anda rd s iz e appea r s t o be 1 .52 m (5 f t ) i n d i am e te r and he igh t , ho ld ing 238 0 l i tr e(630 ga l lons ) o f w a t e r . F o r i ndoo r a r ea s o r g r eenhouses o f l i t t le f l oo r space , t a ll , t h i ns i l o s m a y b e m o r e a p p r o p r i a t e . I n g r e e n h o u s e s t h e s e t r a n s l u c e n t t a n k s m a y s e r v e t h edua l pu rpo se o f hea t s t o r age ( t he rma l mass ) and aq uacu l t u r e un i t s . Ge ne ra l l y t he si zeo f t he cy l i nde r w i ll be a f unc t i on o f t he spec i a l needs o f the aqu acu l t u r i s t f o r po r t ab l et anks t ha t may p roduce a lgae , ho ld f i sh , e t c . On t h i s occa s ion cy l i nde r s we re neededfo r a l ga l cu l t u r e i n a pa s s ive so l a r g r eenhouse o f l im i t ed f l oo r space (7 .2 m x 7 .2 m ) .The re fo r e i t was dec ided t ha t t a l l , t h i n t anks (1 .98 m h igh , 0 . 46 m in d i ame te r ) shou ldb e c o n s t r u c t e d ; d e ta i ls o f c o n s t r u c t i o n a r e g i ve n h e r e . T h e a u t h o r a n d c o w o r k e r s h a v ea lso success fu l ly c on s t ruc ted nu m ero us fu l l s ize (1 .52 m 1-52 m ) si los us ing ident ica lme thods (F ig . 1 ) .

The s ilo s a r e cons t ruc t ed o f Ka lwa l l (Ka lwa l l So l ar Corp . , PO Box 23 7 , M anches t e r ,New Ha mp sh i r e , USA ) , a fi be rg l a ss - li ke ma te r i a l ava i lab l e in r o l l s 15 .24 m 1 -52 m x0 . 1 0 c m h a v in g a p u r p o r t e d a b i l it y t o t r a n s m i t 9 0 % o f i n c id e n t s o la r ra d i a t io n w h e nnew. The ma te r i a l i s expec t ed t o l a s t 20 yea r s . The cy l i nde r s a r e e a s il y cons t ruc t edin to w a t e r t i gh t t anks by s ea ling s t ri p s t oge th e r w th an epo xy and a ca t a ly s t . F ir s t ame asu red r ec t ang l e ( he igh t o f de s ir ed s il o m u l t i p l i ed by t he c i r cum fe rence p lu s 5 .2 cm )i s cu t f r om the ro ll . A s imp le j ig is con s t ruc t ed t o ho ld t he p i ece i n p l ace wh i le t her e s in and ca t a ly s t a r e p r epa red (F ig . 2 ) . The epoxy , Arcon 2795 , and t he ca t a ly s t ,Ve r samid 140 , a r e mixed i n a 3 :1 r a t i o f o r app l i c a t i on t o t he ove r l app ing s eam ( t he5 .2 c ln a l l owed fo r ove r l ap above ) , mak ing a cy l i nde r . (Bo th epo xy and ca t a ly s t we ref r o m t h e M l i e d R e s i n C o r p ., W e y m o u t h I n d u s t r ia l P a r k , E a s t W e y m o u t h , M a ss a-chuse t t s , USA. ) The Ka lwa l l su r f ace con t a in s a s ea l i ng ( r e l ea se coa t ) wh ich mus t besanded sho r t l y be fo r e ap p ly ing t he r e s in t o t he s eam to ensu re p rop e r adhes ion .A 1 . 9 8 m x 0 . 4 6 m c y l i n d e r r eq u i re s a b o u t 2 0 0 m l o f m i x e d r es in t o s ea l t h e s e am .Af t e r app l i c a t i on , t he s imp le j i g and ' C ' c l am ps ho ld t he K a lwa l l i n p l ace wh i l e t he

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S O L A R S IL O S F O R M A S S A L G A L / F I S H C U L T U R E 2 4 1

Fig. 1 . (a) Ind oor so la r s i lo (1 .52 m X 1 .52 m) in a pass ive so la r greenh ouse prod uc ing vege tables .The ' ha t ' i s used as added insula t ion in winte r , (b) Ou tdo or so la r si los in a re f lec t ive marb lecou r tya rd . (Photos taken a t the New Alchem y Ins t i tu te , Ha tchvi l le , Massachuse tt s, US A.)

r e si n s e ts f o r 4 8 h ( F i g . 2 ) . W e i g h t s ar e a d d e d a l o n g t h e t o p o f t h e s e a m t o a p p l yp r e s s u r e a ll a l o n g i ts le n g t h . A f t e r d r y i n g , t h e t o p a n d b o t t o m e d g e s a r e r e i n f o r c e dw i t h 5 .2 c m w i d e s t r ip s o f K a l w a ll a r o u n d t h e c i r c u m f e r e n c e a n d a l lo w e d t o d r y4 8 h b e f o r e t h e b o t t o m is c o n s t r u c t e d . F o r t h e b o t t o m , t h e c y li n d e r is p l a c e du p r i g h t , i ts d i a m e t e r m e a s u r e d a n d t w o i d e n t i c a l c i r c u l a r p i e c e s a r e c u t , l e a v in g a

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2 4 2 BARRY A. COST A- PI E RCE/ / 5 1 c m 5 . 1 c m

F ig . 2 . A c o ns t ru c t io n j ig f o r 1 . 9 8 m 0 . 4 6 m s ilo s. A 1 . 2 n l l - 2 n l 2 0 . 3 c m b o x c u t i n h a l fserves to hold the precut p iece o f Kalwal l. A circ le wi th the desi red radius is marked on the end o fthe hal f box wi th a compass and cut wi th a jigsaw. The Kalwal l p iece i s p laced in the j ig and thecut ou t , w ooden ci rcles are pushed back in to the c yl inder to g ive s t ructural in tegr i ty .

m a r g i n o f 2 -5 c m g r e a t e r t h a n t h e m e a s u r e d d i a m e t e r . A l t e r n a t i v e l y t h e c y l i n d e ri s p u t u p r i g h t a n d a l in e is t r a c e d a r o u n d i t s c i r c u m f e r e n c e , l e a v i n g a 2 .5 c m m a r g i n .A f t e r t h e p i e c e s a r e c u t , t h e a d j o i n i n g s i d es a r e s a n d e d , g lu e d t o g e t h e r , a n d a l l o w e dt o d r y f o r 4 8 h w i t h w e i g h t o n t o p . L a s t l y t h e c y l i n d e r i s p u t u p r i g h t o n t o t h isb o t t o m p i e c e , a l in e i s t r a c e d a r o u n d t h e c i r c u m f e r e n c e a n d a s m a l l b e a d o f m i x e dr e s in ( a b o u t 5 0 m l ) t h e n a d d e d a r o u n d t h e l i n e. T h e c y l i n d e r is p u t o n t o p o f t h eb o t t o m p i e c e a n d w e i g h t a d d e d t o t h e t o p t o h o l d i t in p l a c e f o r 4 8 h . A f t e r d r y i n g ,5 0 m l o f m i x e d r e si n a r e a d d e d i n t o t h e t o p o f t h e c y l i n d e r a n d t h e w h o l e c y l i n d e rr o t a t e d o n i t s b o t t o m e d g e to i n s u r e t h e s e a li n g o f t h e i n t e r i o r b o t t o m w a l l s e a m .T h e c y l i n d e r i s a ll o w e d t o d r y f o r 4 8 h , f i ll e d a n d c h e c k e d f o r l e a k s . I f a n y a r e f o u n dt h e y a r e p a t c h e d w i t h l i g h t a p p l i c a t i o n s o f th e m i x e d r e s i n ( 1 0 m l ) .C o s t o f c o n s t r u c t i n g t h e t a l l, t h i n s i lo s w a s j u s t $ 1 9 . 0 0 w h i l e c o s t o f t h e l a r g e r1 . 5 2 m x 1 . 5 2 m u n i ts w a s ju s t $ 6 5 . 0 0 , o r l e ss t h a n o n e - h a l f t h e c o st o f i d e n t ic a lu n i t s p u r c h a s e d in 1 9 8 2 ( $ 1 6 3 . 0 0 ) .

B e f o r e t h e s i l o s a r e u s e d f o r a l ga e o r fi s h c u l t u r e t h e y m u s t b e c o n d i t i o n e d t op r e v e n t t h e l e a c h in g o f d i o c t y l p h t h a l a t e s f r o m t h e r e si n i n t o t h e w a t e r ( C o r m i g n a n ia n d B e n n e t t , 1 9 7 6 ) . E a c h s i lo i s w a s h e d w i t h w a r m , s a l t y w a t e r (3 6 - 3 8 0 /0 0 ) a n d t h es id e s a n d b o t t o m s c r u b b e d w i t h a b r u s h . T h e y a r e t h e n f i ll e d w i t h w a t e r a n d a l lo w e dt o s t a n d f o r 7 - 1 0 d a y s . T h i s w a t e r i s d i s c a r d e d , fr e s h w a t e r r e a d d e d , a n d t h e s y s t e mr e a d i e d f o r s t o c k i n g .

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SOLAR SILOS FOR MASS ALGAL/FISH CULTURE 243

SILO USE

S i lo s h a v e n u m e r o u s s p e c i a l i ty u s es b u t m o s t l y h a v e b e e n u s e d f o r c o m b i n a t i o n m a s sa lg al c u l t u r e / f i s h c u l t u r e . Up t o 1 6 a lg al sp e c i e s m a y c o e x i s t i n t h e n u t r i e n t - s a tu r a t e ds y s t e m s ( T a b l e 1 ). P h o t o s y n t h e t i c r a t e s i n t h e m i x e d a lg a l c o m m u n i t y , m e a s u r e d b yo x y g e n l i g h t / d a r k b o t t l e m e t h o d s , r e a c h 3 - 0 g C m - 3 d - 1, a m o n g t h e h i g h e s t r a t e sr e c o r d e d f o r e u t r o p h i c s y s t e m s ( W e t z e l, 1 9 7 5 ) , o r a t r a t es c o m p a r a b l e t o t h e m o s tp r o d u c t i v e m a s s al ga e p r o d u c t i o n s y s te m s ( G o l d m a n , 1 9 7 9 a ) .

TABLE 1Sixteen com mo n phyto plankton species found in solar s i los(identification according to Prescott (1962))Algal species Cell or colony

A nkistrodesrnus braunii CellChlorella sp. CellDictyosphaerium pulchellum ColonyGloeocystis major ColonyGolenkinia paucispina CellHaematococcus lacustris CellLepocinclis fusiJbrmis CellMicractinium pusillum ColonyNavicula sp. CellPediastrurn integrum ColonyScenedesmus acurninatus ColonyScenedesmus longus ColonyScenedesmus quadricauda ColonySphaeorocystis schroeteri ColonyTetraederon duospinum CellTrachelomonas sp. Cell

G e n e r a l l y a s e a s o n a l p r o d u c t i o n c y c l e o p e r a t e s a s f o l l o w s ( T o d d et al., 1 9 7 9 ; P i e r c e ,1 9 8 0 ) . T h e s y s t e m s a r e f il le d w i t h f r e sh w e ll w a t e r , s e e d e d w i t h w a t e r f r o m a l o c a le u t r o p h i c p o n d ( o r n o t s e e d e d ) , a n d f e r t il i z ed o n c e w i t h s o l u b le n u t r i e n t s d e r iv e df r o m m a n u r e , a m a n u r e ' t e a ' ( o r n o t f e r ti l iz e d a t a ll ). A m o n o c u l t u r e o f t il a p ia(Sarotherodon aureus) is s t o c k e d w i t h a n i n i ti a l s t o c k i n g d e n s i t y o f 2 - 4 k g p e r s iloo f f i s h r a n gi n g f r o m 3 0 t o 1 2 0 g si ze c la ss e s. F i s h a r e f e d 3 % o f t h e ir b o d y w e i g h t d a i l yo f c o m m e r c i a l t r o u t d e v e l op e r f e e d a n d a l lo w e d t o g r o w f o r 9 0 - 1 2 0 d a y s. W a t e rq u a l i t y m a n a g e m e n t is a c c o m p l i sh e d b y s i m p ly s i p ho n i n g 2 0 % o f t h e w a te r v o l u m ee v e r y w e e k a n d a d d i n g f r e s h w el l w a t e r a s r e p l a c e m e n t . A e r a t i o n is p r o v i d e d o n l y a tn i g h t b y b u b b l i n g f r o m a c o m m e r c i a l a e r a t o r ( S i le n t G i a n t , C o n t 6 , e t c . ). F is h p r o d u c -t i v i ty p e r 9 0 - 1 2 0 d a y s g r o w i n g s e a s o n v a ri e s a r o u n d 2 5 k g p e r y e a r , w i t h o n e p o n d

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2 4 4 B A R R Y A . C O S T A - P I E R C E

f e d i n s e c ts a t a h i g h r a t e ( 1 7 5 g d a y - 1 ) h a v i n g a f is h p r o d u c t i v i t y o f 4 8 k g p e r y e a r( Z w e i g e t a l . , 1 9 8 1 ) .

T h e c o n s t r u c t i o n a n d u s e o f m o d u l a r , s o l a r s il o u n i t s as e x p e r i m e n t a l t a n k s , s p e c ia lh o l d i n g t a n k s, m a s s al ga l p r o d u c t i o n u n i ts , o r as u n i t s f o r a q u a c u l t u r e f o o d p r o d u c t i o nis a s im p l e o p e r a t i o n w h i c h m a y a l l o w t h e s il o d e s i g n t o b e c o m e m o r e r e a d i l y av a i la b l et o a q u a c u l t u r i s t s a n d r e s e a r c h e r s w o r l d w i d e . P r e l i m i n a r y r e s u l t s i n d i c a t e t h a t p r i m a r ya n d s e c o n d a r y p r o d u c t i v i t i e s i n t h e s e s i lo u n i ts a r e a m o n g t h e h i g h e s t r e c o r d e d a n df u r t h e r u s e a n d r e s e a r c h o f f re e - s t a n d i n g s o l a r s il o s is e n c o u r a g e d . S i lo s m a y p r e s e n ta l o w c o s t a l t e r n a t i v e t o t h e h i g h c a p i t a l s ta r t - u p c o s t s i n v o l v e d w i t h l a m i n a r - f l o w r a ce -w a y d e s i g n s fo r a lg a e a n d f i sh c u l t u r e w i t h o u t s a c r if i c in g h ig h p r o d u c t i v i t y .

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