Bender 1984 Aquacultural-Engineering

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Aquaculrural Engineer ing 3 I 1984) 141 -152

An Integrated System o f A qua culture , V egetableProd uction and Solar H eating in an UrbanEnvironment

J u d i t h B e n d e r

Associate Professor, Morehouse College, Department o f Biology,Atlanta, Georgia 30314, USA

A B S T R A C TThis s tu dy inves tiga tes the feas ib i l i ty o f an in tegrated sys tem o f f i shcul ture wi th vege table produ c t ion and so lar ho m e heat ing in an urbane nv i ronme n t . Tilapia aurea a n d Ictalurus punctatus are polycul tured in ase mi -c lose d po nd sy s t e m loc a te d ne ar dow n to w n A t lan ta , Ge org ia . F i shcul ture is in tegrated wi th vege table pro du c t ion and com pos t ing in orderto recyc le ~ ,ced n i t rogen and avoM the use o f com merc ia l fer ti li zers . Waterqua l i ty in the greenhouse p on d is main ta ined by se t t l ing processes and bythe use o f s im ple b io logica l and so lar me tho ds . Cos t analys is o f the to ta lp ro je c t i s p re se n te d and re c omm e nda t ions fo r s y s t e m improv e m e n t s a regiven.

I N T R O D U C T I O NT h e s u c c e s s o f s m a l l s ca le a q u a c u l t u r e a n d g a r d e n in g v e n t u r e s t o d a ym a y b e d e p e n d e n t o n t h e a c c e le r a ti n g c o s t s o f w a t e r a n d e n e r g y an d o nt h e i m p a c t o f th e s e r e so u r c es o n p r e s e n t m e t h o d s o f f o o d p r o d u c t i o n .T r a d i t i o n a l, c e n t ra l iz e d m e t h o d s o f f o o d p r o d u c t i o n in t h e U S a ree n e r g y i n te n s iv e p r o c e s s e s w h i c h d e p e n d o n c o n s i s t e n t w e a t h e r p a t t e r n sa n d a d e q u a t e g r o u n d w a t e r s u p p l i es o f t h e m i d w e s t . A l t h o u g h t h e c o ste f f e c t i v e n e s s o f a q u a c u l t u r e is a ls o l i m i t e d b y w a t e r a n d e n e r g ys u p p l i e s , i t l e n d s i t se l f m o r e e a s il y t o s m a l l, d e c e n t r a l i z e d m e t h o d s o ff o o d p r o d u c t i o n . S m a ll a q u a c u l t u r e s y s t e m s in t e g ra t e w e ll i n to s o l a r

141Aquac u l tu ra l Eng ine e r ing 014 4-86 09/8 4/$3 .00 Elsev ie r Applied Sc iencePublishers Ltd, England, 1984. Printed in Great Britain


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142 Z B e n d e rtechnologies (Chervinski and Stickney, 1981; Zweig e t a l . , 1981) andcan be designed to conserve water either by recycling or by multi-useof the water for expanded agricultural applications (Lincoln e t a l . ,1977).

8% of the world's population lives in the urban environment. Thesepopulations are probably most vulnerable to protein shortages andescalating costs of these products. At the same time, even minimallevels of self-sufficiency in food and energy production present themost difficult problems in the city. In urban areas where open landspace is scarce and water is costly, unique methods of intensive culturesystems must be developed. In contrast to traditional systems, thebenefits here are no t measured in marke tabili ty or profits, but rather ina return of basic human needs at the family or neighborhood level.

The economics of small aquaculture systems are presently question-able, if land purchase costs are taken into account. However, multi-purpose systems which produce a number of benefits and make use ofland already available in neighborhoods may be more economicallyfeasible. The experiments discussed in this report involve not only theintensive culture of fish for protein, but also demonstrate methods ofintegrating the fish production with solar heating and vegetable pro-duction. The methods used in this project are based on conservation,recycling and bioconversion using solar power as the primary energysource. Such bio-solar technologies may have broad applications forfood production in the future (Oswald and Golueke, 1960).

METHODSSolar designThe greenhouse/fish pond system is attached to the south side of ahouse near downtown Atlanta, Georgia. This passive solar structure isused for home heating from November through April. The greenhouseis 17-1 x 2-4 m with an L-shaped fish pond (4920 liters) recessed in thefloor of the southeast comer (See Fig. 1). Warm air is transferred to thehouse by a thermostatically controlled fan and returned to the green-house through louvers in the west door of the basement. A wood stove(80 50 45 cm) and a small kerosene hea ter are used for backup heaton cloudy days. Incident radiation is increased in the pond with a


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144 J. Bendersouthfacing aluminum foil reflecting surface angled at approximately50 for op timum reflection (see Fig. 1); azolla and cyanobacteria, usedfor fish grazing, are cultured in reinforced fiberglass tanks. The watertanks and fish pond provide large volumes of water in the greenhouse,which serve as thermal storage mass to prevent night time cool down.

FertiliTation

Figure 2 illustrates the integrated ecosystem involved in the productionand recycling of fertilizer material for the fish and vegetable production.In addition to the organic materials, small amounts of ground rockphosphate are added during prepara tion of the soil (0.3 kg m -3). Noadditional commercial fertilizer is used. Blue-green algae (cyanobacteria)are harvested from the growth tank and applied to the gardening soil.These nitrogen-fixing algal cultures are mainta ined in the beds until thevegetables shade the soil surface. A small bin of compost providesmaterial for pond and soil enr ichment. A rabbit converts rough proteinsources such as weeds, grass and inedible vegetable parts to a concen-trated, microbial-rich manure product. The manure is used to fertilizeboth the fish pond and gardening soil. The concentrated fish wastematerial removed from the pond's bottom provides a constant supplyof nitrogen to the vegetable beds.

Pond purificationWater is pumped to a translucent settling tank (250 liters) from thedeepest end of the pond three times per week. Required pumping timeis 12 min per week. After a day of settling, the nutr ien t rich bottomwater is used for vegetable fertilizer (see Fig. 3). The top half of thetank is drained into a second smaller tank where the sun can penetratethe volume of water. Water is warmed in the tanks by the sun andoxygenated by residual algae in the water. It flows from the tank bygravity across a tray of oyster shells, phosphate rock and water hya-cinths which further conditions the water as it returns to the fishpond. Oxygen levels are increased with two aquarium pumps supplying3.4m3min -t.


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146m l

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L,, 101'i'011 SLANTS TOWAIIDPUlPWater purification of fish pond during winter months.

Summer culture pondAddi tional component of this system is an ellipse-shaped (7-0 X 9-8 mdiameter ) backyard pond with a holding capacity of 76 m 3 water. Ponddepth ranges from 91 to 122 cm. The outdoor pond is used from Juneto October or November, when temperatures are suitable for outdoorgrowth of Tilapia. The water quality of the outdoor pond was main-tained using the following mechanical and biological systems: (1) twoair pumps delivering 3.4 m 3 mAn-t; (2) a small submerged pump locatedin the deepest part o f the pond which removes approximately 379 liters


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Aquaculture/vegetable production~solar heating in urban environment 147h -t from the bottom of the pond (water was passed over a 914 X 15X 15 cm trough filled with oyster shells and pebbles, then drained backinto the pond); (3) algae-photosynthesis oxygenation; and (4) waterhyacinths for removal of NH3, thereby preventing algal blooms.

Once a month the fertile water is used on the adjacent neighborhoodvegetable gardens. In a normal summer season, this water is replaced byrainfall.

The fish are harvested in the autumn by emptying the pond with asump pump. All the nutrient rich material from the pond bottom isapplied to the gardens and greenhouse vegetable beds.Stocking of fishS e a s o n 1A total of 400 unsexed Ti lap ia aurea (19 weeks old) were transferred tothe indoor pond on 19 November 1981. The average body weight andtotal length at stocking time, determined from a random sample of25 fish, were 4.9 g and 66.7 mm. Afte r overwintering in the solar green-house, the fish were transferred to the outdoor pond in May 1982.S e a s o n 2In October 1983, 35 offspring Ti lap ia were harvested from the outsidepond and stocked in the greenhouse for the next season production.In addition 37 small adult Ti lap ia , which were below edible size at thetime of the first harvest, were returned to the greenhouse pond for thewinter. Fifty-two catfish I c t a l u r u s p u n c t a t u s , having an average weightand length of 3.08 g and 7.5 cm, were divided into two groups foroverwintering. Forty-two were stocked in the outside pond and 10 inthe greenhouse.

On 27 May 1983, the outside pond was cleaned and refilled, the fishfrom both ponds were weighed and measured and all fish were placedin the outside pond for summer growth until harvest on 27 October1983.FeedingSince the winter temperatures of the indoor pond were rather low,feeding levels were minimal to protect against ammonia increase in thewater. Commercial catfish feed was fed at approximately 1% body-


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148 J. Benderweight from November to April. A total of 4.2 kg feed were fed duringthese 6 months (10-5 g to each fish). Sinking pellets were fed, since thefish did n o t come to the surface to feed until May. At this time feedwas changed to floating type and was increased to the amount that thefish would consume in 10 min (approximately 40 g day- t). This ratewas increased to 160 g feed day -t for the Ju ly -Octob er period (appliedin two feedings per day) . A total of 16-2 kg commercial feed was fedduring the 10 months from November to August (41 g to each fish).No quantitative estimate is made of other types of feed consumedwhich included algae, azolla fern and compost .

RESULTS AND DISCUSSIONH e a t i n gA sample of the solar heating capacity is given in Table 1. In general,with ideal solar conditions, the greenhouse raised the house temperatureby approximately 17C. However, cloudy periods and extreme coldrequired continuous use of the wood stove. Approximately one cord ofwood was burned for space heating during the first year.Water quafityThe water quality of both ponds ( 1981-82 season) is given in Table 2.Values represent the range of samples taken twice per month. Generally

T A B L E 1January 1981 Solar Home HeatingLiving space o f hom e, C Outside C

21 717 314 --916 315 --4

Mean: t6.6 0


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Aquaculture/vegetable production~solar heating in urban environmentT A B L E 2Water Quality, 19 81 -82 Season

149

Test Inside po nd Outside po ndOxygen (pp m ) 8 .0-12.2 3:2-8.2Ammonia (ppm ) 0 .02-2 .0 >0-0 2pH 6.0-7-0 6 .5-7 .0Temperature (C) 16-19 25-3 2Sample taken 15 cm belo w po nd surface. Oxygen and amm oniadeterminations were made with f ie ld water test kid (LaMotte Co.);pH lev els were determined with a battery pow ered pH me ter(Sargent-Welch).

t h e w a t e r q u a l i t y d u r i n g b o t h s e a s o n s r e m a i n e d w i t h i n t i le p a r a m e t e r sr e q u i r e d f o r g o o d f is h p r o d u c t i o n . H o w e v e r , t h e p r e s e n t 1 9 8 4 s e a so n( n o t r e p o r t e d ) d e m o n s t r a t e s t ha t m a i n t e n a n ce o f l o w a m m o n i a an dh ig h o x y g e n in a s m a ll s e m i - c lo s e d s y s t e m c a n b e c o m e a p r o b l e m i f t h eo r g a n i c lo a d is h i gh a n d e n v i r o n m e n t a l c o n d i t i o n s a r e n o t c o n d u c i v et o t h e p r o p e r f u n c t i o n i n g o f t h e b i o p u r i f i c a t i o n s y s t e m s .F i s h p r o d u c t i o nIn a 1 0 - m o n t h g r o w t h p e r i o d t il e f ir st s e a so n ( 1 9 8 1 - 8 2 ) p r o d u c e da p p r o x i m a t e l y 1 0 0 f i sh o f e d i b l e s iz e ( 1 8 0 g p e r f i sh ) a n d a l ar gep o p u l a t i o n o f s m a l l e r f is h a v e ra g i n g 5 3 g p e r f is h. I n t h e s e c o n d s e a so nt h e s t o c k i n g d e n s i t i e s w e r e k e p t l o w e r ; 1 2 4 f is h w e r e s t o c k e d . I na d d i t i o n , a p o l y c u l t u r e s y s t e m o f ca t f i s h a n d Ti lap ia aurea w a s u s e dt h e s e c o n d s e as o n . S p e c i f ic g r o w t h d a t a f r o m t h e s e c o n d se a so n( 1 9 8 2 - 8 3 ) a re gi ve n in T a b l e 3 .

T h e f in a l f i sh p r o d u c t i o n w a s a p p r o x i m a t e l y 2 4 k g f is h o f ed i b l e s iz ea t t h e t i m e o f th e 1 9 8 3 h a r v es t ( a p p r o x i m a t e l y 1 3 m o n t h s f r o m st o c k -i n g ) . T h e c a t f i s h p e r f o r m e d b e t t e r u n d e r t h e s e c o n d i t i o n s s h o w i n g aw e i g h t g a in o f 3 1 5 g p e r fi sh a s c o m p a r e d t o 1 6 6 g p e r f is h f o r t h eTilapia ( c a l c u l a t i o n m a d e f r o m t h e Ti lap ia w h i c h w e r e s t o c k e d a s f ry ) .T h e t o t a l b i o m a s s f r o m 4 2 c a t f is h w a s 1 3 . 4 k g w h e r e a s t h e Tilapiap r o d u c e d 11-1 k g f r o m 7 1 f is h. T h e s o m e w h a t l o w e r t h a n e x p e c t e dp r o d u c t i o n o f Tilapia m a y b e a c c o u n t e d f o r b y s e v e r a l f a c t o r s . T h e


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t 5 0 J . B en d erT A B L E 3

G r o w t h o f Tilapia a nd Ca t f i sh 1982 - 83 S e a sonS a m p l e F i s h g r o w t h

Weight, Len gth, To tal f i shg per f i sh cm b iomass , g1 O c tobe r 1982 a t s t oc k ing aTilapia 26.6 I 1 .0 1 917

Catf ish 3.8 6.7 1982 t Ma y 1983 e nd o f ove r w in t e r ingaTilapia 42 .5 15 -2 2 80 4

Ca t f i sh b 342Gro up A 8 .2 10 .7Gro up B 18 .8 13-6

27 O c to ber 1983 f ina l ha rves t cTilapia 173.7 a 7.8 1 t 071Ca t f i sh 319-0 32 .0 13 398

a P o p u l a t i o n o f 7 2 Tilapia w e r e s toc ke d . T h i r ty - five w e r e p r oge ny f r om f ir s t ye a r ' sp r od uc t io n ( a ve ra ge s iz e : 6 -7 g , 7 c m ) a nd 37 w e r e sma ll, p r e d om ina n t ly f e ma lef ish re turne d to the greenho use for second season growth (ave rage s ize : 41 .7 g ,13 . 3 c m) . T e n c a t f i sh w e r e s toc ke d w i th t he Tilapia i n g r e e nhouse pond a nd 42 inouts ide pon d . (Average s ize , bo th groups : 3 .8 g , 6 -7 cm ) .b G r oup A : ou t s ide ove r w in t e r ; G r o up B : g r e e nhouse ove r w in t e r .c Surv iva l: g reenh ouse po nd - 92% Tilapia and 100% ca t fi sh ; ou ts id e po nd - 81%winter ca tf ish, 100% summer survival of a l l f ish.a Weight rep resen ts the average o f f ish co nsid ered to be edible s ize (12 5 g) ; 22%po pu la t io n was be low th is we ight ( ave rag ing 95 g pe r f i sh).

3 5 a d u l t f is h , s t o c k e d w i t h t h e fr y , w e r e p r e d o m i n a n t l y f e m a l es , w h i c ha re k n o w n t o g r o w m o r e s l o w l y t h a n t h e m a l e s o f t h i s sp e c i es . T i l a p i ar e p r o d u c t i o n in t h e o u t s i d e p o n d r e s u l t e d in a n o v e r a b u n d a n c e o fs m a ll f is h , c o m p e t i n g f o r f o o d a n d d e g r a d i n g t h e w a t e r q u a l i t y . T h e s ef a c t o r s , h o w e v e r , d i d n o t s e e m t o h a v e a m a j o r i m p a c t o n t h e c a t f i s h ,a s m i g h t b e e x p e c t e d . I t m a y b e t h a t t h e m a t u r i n g c a t f i s h w e r e p r e d a -t o r y o n t h e T i l a p i a f ry , r e s u l t in g in a c o m p e n s a t o r y e f f e c t f o r t h ec a t f i s h .


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A q u a c u l t u r e ~ v e g e t a b l e p r o d u c t i o n ~ s o l a r h e a t i n g i n u r b a n e n v i r o n m e n t 15 1Catfish over-wintered in the outside pond showed only a two-fold

gain, whereas over-wintering in the greenhouse resulted in a five-foldgain. The feed conversion ratio (calculated as the amount of commercialfeed per unit weight gain of first season Ti lap ia ) was 0.84. Early massmatings of these fish produced about 1000 first generation offspring;later matings produced several thousand fry by harvest time.E c o n o m i c s o f th e integrated systemThe system produced good returns in both energy and food product ion.An estimated US$85 broccoli, carrots, lettuce and kale were raised,using only cyanobacteria and recycled wastes for fertilizer. Heating costbenefits were US$700 in 1982-83 and fish production totaled US$85for the season (cost benefits are based on present local market prices).Total cost input for construction materials and maintenance of thesystem was US$6290. The cost return time is approximately 7 years.*

Proper evaluation of this experiment must include projections offuture costs and shortages. Since the price of commercia l fertilizer istied to dwindling fossil fuel supplies, it has a major impact on theeconomics of any agricultural operation. This demonstration projectshows that microbes can be effectively employed to add fixed nitrogento a small system which is then conserved by recycling through severalstages of food production. An aquaculture component (particularly onewhich includes algae-filtering Ti lap ia ) has a central niche tbr the ferti-lizer economy of this integrated system.

The cost effectiveness of the total system can be improved by lower-ing the maintenance costs and increasing fish production. Severalchanges are suggested for such improvements.

A multipond system might solve several problems and increase theeconomic advantages enough to warrant expansion of this system to theneighborhood or community level. Two factors which have a majorimpact on maintenance costs and fish production are (1) the pumpingof water for purification o f the outside pond (US$48 in 1981-82season) and (2) prolific reproduction of Tilapia causing limited growthin the outside pond. If three ponds were developed, one could be used* Estimates exclude costs of land, as backyard space was available. No estimate wasmade of labor costs, because the system is designed as a family or neighborhoodproject.


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iS3 f. Benderto harvest water from house rooftops. This water could be stored andused to flush out the pond bottom during the summer when the highlevel of organic build-up requires uater pumping. A second pond couldserve as a spawning area to provide only male Ti lup ia to the third,grow-out pond, thereby preventing overproduction.

Small systems are labor rather than energy intensive and a multiponds>,stem would substantially increase the man-hours required for vege-table and fish production. However. this factor may also indicate thatthe integrated system may be most appropriate for concentratedpopulations where unemployment is highest.

ACKNOWLEDGEMENTSThis work was supported by two grants from the US Department ofEnergy, Appropriate Technology Program (Grants GA1 17, 1044 and13-O 181). The Georgia Solar Coalition is acknowledged for its contri-bution in nlonitoring the grants and for organizing the use of thisproject as a demonstration urban home. The author would especiallylike to thank Dr K. Bondari of the University of Georgia and Dr R.Schmittou of Auburn University for their kind assistance in the aqua-culture phase of this project.

REFERENCES

Chervinski. J. & Stickney, R. R. (1981). Overwintering facilitieS for Tifapia inTexas, Prog. Fish Cul t ., 43, 20-I .Lincoln, E. P., Hill. D. J. & Nordstedt. R. A. (1977). Microalgae as a means of

recycling animal wastes, Sot. Agri c. Ety Pup. IVO. 77-3026, pp. 26-9.Oswald, W. J. & Golueke, C. G. (1960). Biological transformation of solar energy,

Adv . Appl , M i crobial ., 2, 223-64.Zweig, R. D., Wolfe, J. R., Todd, J. H., Engstrom, D. G. & Doolittle, A. M. (1981).

Solar aquaculture: An ecological approach to human food production. Bio-Etlgheering Symposium for Fi sh Cl rl rure (FC5 Publ. I), pp. 210-26.

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Bender 1984 Aquacultural-Engineering