Miller 1983 Aquacultural-Engineering

7/28/2019 Miller 1983 Aquacultural-Engineering

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Aqu acu l t u ra l E ng i neer i ng 2 ( 1 9 8 3 ) 2 6 3 - 2 7 7

O x y g e n R e c h a r g e a n d A m m o n i a S t r i p p in g C a p a b i l i t ie so f V a r i o u s C l o s e d C u l t u r e C o n f i g u r a t i o n s *

G .E . M iller and G .S . L ibeyDe pa r t m en t o f Fo r e s t r y and Na t u r a l R esour ce s , Pu r due Un i ve r s i ty , Wes t La f aye t t e ,

I n d ia n a 4 7 9 0 7 , U S A

A B S T R A C TA p a c k e d t o w e r ( tr i ck l in g f il te r ) , e m p t y , h a l f f u l l a n d f u l l o f a m e d i u m( s t y ro f oam pack i ng m a t e r ia l ) and a ro t a t i ng b io l og ica l con t a c t or ( RBC ,rota t ing d i sc) w ere t es ted a t var ious rec i rcula ting f lo w rates, w i th andw i t ho u t sup p l em e n t a l aera ti on , t o de t e rm i ne oxyg en r echarge and am m o ni astripp ing capabil it ies . O xyg en recharge capabi l i t ies increased with increasingf lo w rates , b ut a t d i f f eren t ra tes fo r each f i lt er . O xyg en recharge e f fi c ienc iesdecreased as f l o w rate s i nc reased in t he h a l f f u l l an d em p t y t owers , w erea b o u t c o n s t a n t f o r t h e f u l l t o w e r a n d i n cr e as e d in t h e R B C . O x y g e nrecharge capabi li ties wer e s igni f icant ly increa sed w ith the ad di t io n o fsur face ag i ta t i on ; g rea t e r than t he sum o f the com po nen t con t r i bu ti ons .W i t h supp l em en t a l ae ra t ion , t he f u l l t ow er w i t h a rec i rcu l a ti on f l o w o f45 . 4 l i t e r s / m i n was m os t e f f i c i en t and capab l e o f supp l y i ng t he m os toxyge n . A m m on i a s t r ipp i ng was f o un d t o be i n s ign i fi can t i n a l l s y s t em stes ted .

C aC* - C .q

N O M E N C L A T U R Es a t u r a t i o n c o n c e n t r a t i o n ( m g / l i t e r )c o n c e n t r a t i o n d e f ic i t a t c o n c e n t r a t i o n x ( m g / l i t e r )c o n c e n t r a t i o n a t t i m e t ( m g / l i t e r )

* Pu r due Un i ve r s i ty Agr i cu l tu r a l Expe r i m en t S t a t i on j ou r na l pape r num ber 8 880 .263Aquacu l t u ra l Eng i neer i ng 0 1 4 4 - 8 6 0 9 / 8 3 / $ 0 3 . 0 0 A p p l ie d S c i e n ce P u b li sh e rs L t d :Eng l and , 1983 . P r i n t ed i n Gr ea t Br i t a in


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264 G. E. Mil ler , G. S. LibeyC t + TCoEEffxKLa

V

c o n c e n t r a t i o n a t a u n i f o r m t i m e i n t e r v al T a f t e r t i m e t ( m g / l i t e r)s p e c i a l c a s e o f Ct w h e r e t = 0 ; i n i ti a l c o n c e n t r a t i o n ( m g / l i t e r )p o w e r ( k W h )m a s s t r a n s f e r e f f i c i e n c y a t c o n c e n t r a t i o n x ( k g / k W h )m a s s t r a n s f e r c o e f f i c ie n t ; a m e a s u r e o f t h e m o v e m e n t o f g asa c r o s s a u n i t a r e a o f g a s / l i q u i d i n t e r f a c e , K L , ti m e s t h e t o t a lg a s / l i q u i d i n t e r f a c i a l a r e a , am a s s tr a n s f e r r a te a t c o n c e n t r a t i o n x ( k g / h )v o l u m e o f th e s y s t e m

I N T R O D U C T I O NT h e p r o s p e c t o f t h e c o m m e r c i a l u s e o f re c i r c u la t i n g f is h c u l t u r e s y s t e m sb e c o m e s i n c re a s i n g ly a t t r a c t i v e a s t h e d e m a n d f o r fi sh a n d s e a f o o di n c r e a se s ( S t e ll m a c h e r , 1 9 8 1 ) a n d a v a i l a b il i ty o f hi g h q u a l i t y w a t e rd e c r e a s e s. I n a d d i t i o n t o a d v a n t a g e s o f w a t e r r e- u se a n d c o n s e r v a t i o n ,r e c i r c u l a t i o n s y s t e m s o f f e r h e a t c o n s e r v a t i o n , d i se a s e c o n t r o l , s t o c km a n a g e m e n t a n d f r e e d o m f r o m n o r m a l s it e l i m i t a t i o n s (M u i r , 1 9 8 1) .

B y k n o w i n g t h e o x y g e n r e c h a r g e r a t e o f a c u l t u r e s y s t e m a t a g i ve nd i s s o l v e d o x y g e n ( D O ) l e ve l , i t is p o s s i b l e t o p r e d i c t t h e c a r r y i n gc a p a c i t y o f t h e s y s t e m p r o v id e d t h e o x y g e n c o n s u m p t i o n r a te s o f t h ec u l t u r e d s p e c i e s a n d t h e f i l tr a t i o n s y s t e m a r e k n o w n . T h i s p a p e r d is -c u s s es t h e a b i l i t y o f s e v e ra l d i f f e r e n t f i lt e r c o n f i g u r a t i o n s t o s u p p l yo x y g e n a n d s t r ip a m m o n i a a t d i ff e r e n t r e c i r c u l a t i o n r a te s .

M E T H O D S

T h e s y s t e m c o n s i s t e d o f a 1 . 22 m d ia m e t e r , 8 3 0 l i te r , c i rc u l a r t a n k a n dt w o 1 1 5 l i te r s u m p s . T h e t a n k w a s t h e c u l t u r e u n it a n d t h e s u m p sp r o v i d e d s e t tl in g o f p a r t i c u l a t e s ; o n e c o n t a i n e d a t u b e c l a ri fi e r, th eo t h e r a s u b m e r g e d p u m p f o r r e c ir c u la t io n . W a t e r f l o w w a s f r o m t h eb o t t o m c e n t e r o f t h e c u l t u r e u n i t t o t h e s u m p c o n t a i n in g t h e t u b ec l a ri f ie r , a n d t h e n t o t h e r e m a i n i n g s u m p .

T h r o u g h o u t t h e s t u d y , n o f is h w e r e in t h e s y s t e m a n d t h e b i o f i l tr a -t i o n m e d i u m w a s n e w ( w i t h o u t m i c r o b i a l c u l tu r e s) . T h i s a l l o w e d t h ed e t e r m i n a t i o n o f t h e m e c h a n i c a l c a p a b i li t ie s o f t h e u n i t s t o d r iv eo x y g e n i n t o , o r a m m o n i a o u t o f , so l u t i o n .


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C l o s e d c u l t u r e c o n f i g u r a t i o n s - o x y g e n r e c h a r ge a n d a m m o n i a s t r i p p i n g 265Two types of filter were used; a packed t ower (trickling filter) and a

rotating biological contactor (RBC, rotating disc). The packed towerconsisted of an aluminum frame, 2-44 m X 42.55 cm X 42.55 cm, parti-tion ed into two baskets made of 0.64 cm plastic mesh, each 0-76 mdeep, separated by a 0.46 m drop space. The remaining 0.46 m was atthe top of the tower to accommodate plumbing and mounting of aperforated splash plate for water distribution. This filter was studiedin three conditions: full tower (FT), half full (bo tto m basket full ofmedia) (HT), and empty (ET). The tower was attached to a frame andset on top of the culture tank so that the water passed from the filterdirectl y into the culture tan k (Fig. 1). Water was pu mpe d to the top of

Fig. 1. Culture system as tested with packed tower (FT) in place. System consistsof an 830 liter culture tank and two 115 liter sumps (one for tube clarification; one

as reservoir with pumping).


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266 G. E. Miller, G. S. Libeyt h e t o w e r in b o t h t h e E T a n d F T ( a g ai n s t a 3 . 0 5 m h e a d ) . I n t h e H T ,w a t e r w a s d i sc h a r g e d d i r e c t l y a b o v e t h e l o w e r b a s k e t ( a 1 -8 3 m h e a d ) .

T h e m e d i u m c h o se n f o r t h e p a c k e d t o w e r s w a s s t y r o f o a m ' p e a n u t 'p a c k i n g m a t e r i a l . I t w a s s e l e c t e d f o r i t s l i g ht w e i g h t , av a i l a bi l it y , a n dl o w c o s t . B r o u s s a r d a n d S i m c o ( 1 9 7 6 ) f o u n d t h a t t h is m a t e r i a l w o r k e ds a t i s f a c t o r i l y i n t h e i r s t u d i e s. G r a p h i c a n a l y s i s s h o w e d t h a t a p p r o x i -m a t e l y 2 2 5 m 2 / m 3 w a s p r o v i d e d f o r m i c r o b i a l h a b i t a t i o n . A f u ll b a s k e to f m e d i a h a d a 5 5 % v o id f r a c t io n .

T h e R B C ( F ig . 2 ) c o n s i s t e d o f 3 0 p l a te s , 1 .0 9 m i n d i a m e t e r , m o u n t e do n a 2 - 5 4 c m s h a f t , a n d s u s p e n d e d i n a t a n k t o a d e p t h o f 0 . 4 5 m . T h es h a f t w a s r o t a t e d b y a 0 . 1 9 k W , 6 r p m g e a r m o t o r . T h e s e m i - c yl i n d ri c a lR B C t a n k c o n t a i n e d 2 1 0 l it er s o f w a te r . T o e q u a t e m o r e c l o se l y t h ev o l u m e o f t h e R B C s y s t e m w i t h t h e p a c k e d t o w e r c o n fi g u r a t i o n , th ep u m p w a s p l a c e d i n t h e c l a r if y in g s u m p a n d t h e r e m a i n i n g s u m p w a sb y p a s s e d .

S i n c e s u p p l e m e n t a l a e r a t i o n is r o u t i n e l y a d d e d t o c u l t u re u n it s , t e s tsw e r e c o n d u c t e d t o d e t e r m i n e o x y g e n r e ch a rg e r a te s w i t h s u p p l e m e n t a l

Fig . 2 . Rotat ing b iological c ontac tor (RBC). Unit tes ted contained 210li te rs .Con tact area was provided by 3 0 plates, 1.09 m in diameter, rota ted by a 0.19 kW,6 RPM gear m otor .


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C l o s e d c u l t u r e c o n f i g u r a t i o n s - o x y g e n r e c h a rg e a n d a m m o n i a s t r i p p i n g 267

6

a bFig. 3. Supplemental aeration was supplied by a 0-037 kW surface agitator (a) or anairlift pump (b) (3-81 cm, 5.08 cm, or 7.62 cm ID) with an air flow of 0.28 m3/min.

aeration. An airlift pump or a 0.037 kW surface agit ator was used invarious combinations with the filters (Fig. 3). The outlet of the airliftpump was just at the wate r's surface (essentially no lifting involved) andwas tested with either 3.81 cm, 5.08 cm, or 7.62 cm ID pipe of equallength, and an air flow of 0.28 m3/min. The effect of recirculation flowrate on oxygen recharge was also investigated. Flows studied rangedfrom 11.4 to 56.8 liters/min.

Oxygen was measured with a Yellow Springs Instrument Co. (YSI)model 54 dissolved oxygen meter. To assure that the DO reading wasnot influenced by oxygen consumption of the probe, the probe wassuspended above the outlet of a small submersible pump located on thebot tom of the culture tank. The oxygen conce ntratio n was recordedon a Hone ywel l Elec troni k 19 stripchart recorder.

Ten mg sodium sulfite per ppm DO was added in combination with0.05 rag/liter cobalt chloride to drive the initial concentration of dis-solved oxyge n to zero. This amo un t allowed sufficient time to mix the


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268 G. E. Mil ler , G. S. Libeys o l u t io n t h r o u g h o u t t h e s y s t e m a n d t o z e r o t h e s t r i p c h a rt r e c o r d e rb e f o r e t h e o x y g e n c o n c e n t r a t i o n b e g a n to r is e.

A q u e o u s a m m o n i a d i ss o c ia t es in t o i o n iz e d a n d u n i o n i z e d f o r m s(N I-F 4 a n d N H a r e s p e c t i v e l y ) . T h e s e f o r m s w e r e e x p r e s s e d a s n i t r o g e n( N H ] - N a n d N H a - N ) w i t h to t a l a m m o n i a n i t ro g e n ( a m m o n i a - N ) r e p re -s e n t i n g t h e i r s u m .

S e p a r a t e t e s ts w e r e p e r f o r m e d t o o b s e r v e t h e a b i l it y o f th e s y s t e m t os tr ip a m m o n i a f r o m s o l u t io n . T h e s e t e st s w e r e o n l y c o n d u c t e d o n t h ep a c k e d t o w e r w i t h b o t h b a s k e t s f ul l ( F T ) , a f lo w r a te o f 4 5 . 4 li te r s / m i n ,w i t h a n d w i t h o u t s u r fa c e a gi ta t io n . A m m o n i u m c h l o r i d e ( a p p r o x i m a t e l y4 0 g ) w a s a d d e d t o o b t a i n a c o n c e n t r a t i o n g r e a t e r t h a n l 0 m g / l i t e rN H r N . S o d i u m h y d r o x i d e w a s a dd e d t o t h e s y s t em t o a c hi ev e a n dm a i n t a i n p H 1 1.0 s o t h a t e s s e n ti a l ly all o f t h e a m m o n i a w a s i n t h eu n i o n i z e d f o r m . T h u s a l l o f t h e a m m o n i a w a s a v a il a bl e f o r v o l a t il i z a ti o na n d e r r o r a s s o c i a t e d w i t h c a l c u l a t i o n o f t h e p e r c e n t u n i o n i z e d d u e t ot e m p e r a t u r e , p H , o r o t h e r f a c t o rs w a s e l im i n a t e d . M e a s u r e m e n t s o fa m m o n i a c o n c e n t r a t i o n w e r e m a d e w i th a n O r i o n m o d e l 9 5 - 10 a m m o n i ae l e c t ro d e , a n O r i o n m o d e l 8 1 1 p H / m i l l iv o l t m e t e r , a n d an O r i o n m o d e l4 0 7 A I o n a l y z e r .

T h e r a t e o f c h a n g e in t h e c o n c e n t r a t i o n o f a g a s i n s o l u t i o n c a n b ee x p r e s s e d a s :

d C / d t = K L a ( C * - - C t ) ( 1 )w h e r e C * = s a t u r a t i o n c o n c e n t r a t i o n , C t = c o n c e n t r a t i o n a t t i m e t a n dK L a ---- m a s s t r a n s f e r c o e f f i c i e n t .

T h e i n te g r a l f o r m o f e q u a t i o n ( 1 ) is:C t = C * [ 1 - - e x p ( - - K L a t ) ] + C o e x p ( - - K L a t ) ( 2 )

w h e r e C o = c o n c e n t r a t i o n a t t i m e 0 .D u r i n g t h e o x y g e n r e c h ar g e e x p e r i m e n t s , C o w a s z e r o a n d t h e s e c o n dt e r m d r o p p e d o u t l e a v i n g :

C t = C * [1 - - e x p ( - - K L a t ) ] ( 3 )T h e c o n c e n t r a t i o n a f t e r s o m e t i m e i n te r va l T w a s :

C t + T : C * [1 - - e x p ( - - K L a t + T ) ] ( 4 )T h e c h an g e in c o n c e n t r a t i o n ( C t + r - - C t ) , m e a s u r e d a t u n i f o rm t im ei n t e rv a l s , w a s p l o t t e d a g a i n s t C t , r e s u l t i n g i n a l i n e a r r e g r e s s i o n w i t h a


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Closed cu l t u re con f igura t ions - oxy ge n recharge and am mo n ia s t r i pp ing 269slope of --[ 1 -- e x p ( - - K L a t ) ] . Each test (except for airlift pump s) wasrun in triplicate.

K L a was comput ed from:In (slope + 1)K L a = -- (5)T

The K L a value gave an indication of how rapidly change was occurring.However, this value was only representative of the specific test condi-tions from which it was obtained. To be more useful, K L a was incor-porated into the equation:

N x = K L a ( C * - - Cx) V (6)where N x = mass transfer rate at some concent rat ion x, V = volume ofthe system, (C*--Cx)= concentration deficit at concentration x andoxyge n transfer efficiencies obtain ed by the e quation:

N~E f f x = - - ( 7 )Ewhere E l f x = transfer efficiency (kg Oz/kWh) at conc entra tion x andE = power required to produce N x .

Values used for the power requirements were calculated based onflow rates and h ead losses. The rated powe r of the surface agitat or wasused and power calculations for the airlift pump were based on theability of a 0-025 kW pu mp to supply 0-28 m3/min.

When removing a gas, such as ammonia, C* approaches zero and thefirst term of equation (2) is dropped. The equation then becomes:

C t = C o e x p ( - - K L a t ) (8)The natural log of C t was regressed against t, resulting in a linearequation with slope equal to K u a . Ammonia tests were not replicated.

All tests were conducted with dechlorinated tap water at a tempera-ture of 25C. The results were adjusted to st anda rd co ndit ions (Coltand Tch oban oglou s, 1981). Results of the Nx and E f f x calculationswere analyzed using Student-Newman-Keuls (SNK) multiple rangeanalysis (Sokal and Rohlf , 1969). Natur al log tra nsf orma tion s wereused to stabilize the variances among the factor levels.


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270 G. E. Miller, G. S. LibeyRESULTS

There was considerable variation in mass transfer rates ( N x ) among thedif ferent configurations (Table 1). No (mass transfer with 0.0 ppm DO)increased with increasing flow rates and with the addition of aeration,but increases were not proportional among the filters.

In the FT system wi thout aeration, increasing flow rates producedapproximately linear increases in No (doubling of the flow rate pro-ducing a doubling of No). No o the r sys tem was capable of matchingthis performance .

Stude nt-Newma n-Keuls (SNK) multiple range analysis indicated thatwithout aeration the FT and HT values for No were not significantlydiffe rent (P > 0.05) at a flow rate of 22.7 liters/min; the ET and RBCwere not different, but the ET was also similar to the HT and FT(Table 1). Although the HT had the highest No, doubling the flow rateresulted in increasing No by only 36%. The RBC and ET gave betterresponses to increasing the flow rate (51% and 65% respectively), buthad lower No values at 22.7 liters/min. Thus, these th re e systems (ET,HT and RBC) were not significantly diff erent (P > 0.05; SNK) at thehigher flow rate. However, they were significantly different from theFT system.The addition of surface agitation caused a significant increase in Nofor all configurations (9.91-34.66 without agitation, 51.24-79.13 with).The response to aeration was greatest at the lower flow rate, resulting ina 2.99-4.36 fold increase in No; a 2.26-3.01 fold increase at the higherflow rate. However, the increases did not reflect relative performanceswithout aeration and tended to mask variations among the filters.

The airlift pumps were not as effective as the surface agitator. Infact, the 3.81 cm ID unit produced no increase in No. Increases in dia-meter improved No; however the 7.62 cm ID unit provided only 68%No of the surface agitator at the flow rate tested.

Oxygen transfer efficiencies ( E f f o ) ranged from 0.72-2.45 kg O:/kWh(Table 2). Comparable systems without aeration (except for the ET)were more efficient than those with aeration.

Without aeration, both the ET and HT had a loss of efficiency as theflow rate increased. The efficiencies of the RBC (both with and withoutaeration) improved at the higher flow rate. The efficiency of the FT(without aeration) was about constant from 22.7-45.41iters/min,somewhat bet ter at 11-4 liters/min, and less at 56.8 liters/rain. How-


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272 G. E. Miller, G. S. LibeyT AB LE 3Am monia Stripping Capabilities o f a Full To we r at 45.4 liters/min. Tem perature ---

25C, volu m e = 1060 liters, pH ~ 11.0Supp leme ntal In i tia l Mass t ransfer Coef f icient o f A m m on ia

aeration con centration coe ff icient dete rm ination stripping(mg NH3-N/ l it er ) KL a r 2 capacity aCo No.1

No 10.30 0 .041 0 .9969 - -4 . 35Yes 11-48 0 .059 0 .9956 - - 6 .25

a Mass transfer rate ( N x ) a t concen t ra tion x (mg NH rN/h ) .

e v e r , r e g r e s s i o n a n a l y s i s o f E f f o v e r s u s f l o w r a te f o r t h e F T ( w i t h o u ta e r a t i o n ) f o u n d t h e s l o p e n o t s i g n i f ic a n t ly d i f f e r e n t f r o m z e r o (P > 0 . 0 5 ) .T h u s , t h r o u g h o u t t h e r a n g e o f f l o w r a te s te s t e d , t h e F T ( w i t h o u ta e r a t io n ) p r o d u c e d a b o u t t h e s a m e a m o u n t o f o x y g e n p e r k W h . W i ths u r f a c e a g i t a t i o n , a s t h e f l o w r a t e i n c re a s e d t h e F T e f f i c i e n c y im p r o v e d ,t h e H T e f f i c i e n c y w a s c o n s t a n t , a n d t h e E T h a d a l o ss o f e f fi c i e n c y .T h e 3 . 8 1 c m I D a ir li f t p u m p w a s e s p e c i a l l y i n e f f i c i e n t s i n c e th ea d d e d p o w e r r e q u i r e d d i d n o t i m p r o v e N o . T h e 5 - 0 8 a n d 7 . 6 2 c m I Da i rl if t p u m p s h a d e f f ic i e n c i e s l es s t h a n t h e s u r f a c e a g i t a t o r u n d e r t h es a m e t e s t c o n d i t i o n s .

T h e a m m o n i a s t r ip p i n g c a p a c i t y ( N o .l ) o f t h e F T ( w i t h a f l o w r a teo f 4 5 - 4 l i te r s / m i n ) w i t h o u t a e r a t i o n w a s - - 4 . 3 5 m g N H 3 - N / h . T h e a d d i-t i o n o f s u r f a c e a g i t a t io n r e s u l t e d i n a n N o.1 o f - - 6 . 2 5 m g N H r N / h( T a b l e 3 ) .

D I S C U S S I O NT h e r e a l i t y o f w a t e r r e - u s e i n f is h c u l t u r e is a s s u r e d a s t h e a v a i l a b i l i tyo f l a rg e r e s e r v es o f h i g h q u a l i t y w a t e r b e c o m e i n c re a s i n g ly s c a rc e . W i thr e- us e c o m e s t h e n e e d t o r e c o n d i t i o n t h e w a t e r , b u t o n c e t h e r e c o n d i-t i o n i n g p r o c e s s h a s b e e n d e v e l o p e d s u f fi c i e n tl y , t h e n u m b e r o f r e -u s ec y c l e s a v a i la b l e t o t h e c u l t u r i s t b e c o m e s v e r y l a rg e , a n d e f f ic i e n c i e s o fp r o d u c t i o n i m p r o v e e x p o n e n t i a l l y ( M u i r, 1 9 81 ).


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C l o s e d c u l t u r e c o n f i g u r a t i o n s - o x y g e n r e ch a r g e a n d a m m o n i a s t r i p p in g 273Foremost in system design criteria are the abilities to maintain high

concentrations of DO and to remove or detoxify metabolic wasteseconomically. Pilot studies are a must, for no two production locationswill be alike. Water chemistry, environmental conditions, and even feedingredients will affect the performance of the water reconditioningsystem.One should not base the choice of filtration system on its ability tomaintain DO. Rather, the primary purpose of such a system is toremove/detoxify metabolic wastes. Each treatment process has itsdesign criteria that must be met to per form properly. However, withinthe range of acceptable operating conditions, the system's ability tosupply DO can have an impact on costs of production. Although thecapital cost and the operating costs of the FT configuration were some-what higher than the other packed tower configurations, it provided atremendous range of flexibility which did not add cost. That is, withinthe range of flow rates tested, the cost per kg O2/kWh remained aboutconstant (without supplemental aeration) or improved (with aeration).With pumping properly selected and installed to provide maximumflexibility, the flow rate could be adjusted to meet loading requirements(i.e. engaging additional pumps as needed) thus reducing operating costsunder low load conditions when oxygen demand is low. If the produc-tion unit is designed without operating flexibility, the producer is fixedat one operating condi tion that approaches peak efficiency near peakloading conditions.

As the flow rate was increased through the RBC, the oxygen costdecreased. This is because most of the power requirements were associ-ated with the RBC drive system. A doubling o f flow on the short headassociated with an RBC (here 0-15 m) has a less significant effect onkW requirements than does a doubling of flow against the large headassociated with a packed tower (3.05 m). It may be that an RBC canprovide better waste treatment than a packed tower in aquaculturalapplications. If so, with comparable DO recharge efficiencies at higherflow rates, the higher capital costs may be overshadowed. It could alsobe that an RBC driven by low pressure air (Antonie, 1974) would beeven more economical due to increased DO recharge capabilities andreduced operating costs.

Colt and Tchobanog lous (1981) provided a listing of typica l oxygenmass transfer efficiencies of various aeration systems used in aquaculture.Except for U-tube aeration, all devices ranged from 0.6-2 .4 kg O2/kWh


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274 G. E. Miller, G. S. Libeyunder standard conditions, with the major ity being from 1.2-2.0 kgOz/kWh. The systems evaluated in our study (Table 2), were comparable;emphasizing the importance of the contribu tion by the filtration system.Also important is the contribution of supplemental aeration. Thesurface agitator used in this study had a lower mass transfer efficiencythan the filters; reducing the system efficiencies (except for the ET).However, the rate of oxygen transfer was greater when the agitatorwas used in conjunction with the filter than the sum of the filter andagitator transfer rates when operated separately. Thus, 2.28-4-37 timesas much oxygen was provided for a minor increase in the cost ofoxygen. Therefore, production could be increased with substantiallyless additional cost than the construction of an additional facility.To predict the carrying capacity of a recirculating system, it is firstnecessary to know how much oxygen is consumed by the culturespecies and within the filtration system. Andrews and Matsuda (1975)found that at 26C with 6.0-7.0 ppm DO, channel catfish (Ictaluruspunctatus) consumed oxygen according to the equation:

y = 1.35X -'2 (9)where y = Oz consumption 1 h post feeding (g O2/kg fish/h) andX = weight of individual fish (g).Gigger and Speece (1970) found tha t a nitrifying filter consumesabout 150% of the nitrification oxygen demand. Since 4.5 g 02 arerequired to oxidize 1.0 g ammonia-N to NOS-N, and approximately 20 gammonia-N are produced per kg of feed by channel catfish at 28C(Page and Andrews, 1974), this suggests tha t approximate ly 135 g Ozare required by a nitrifying filter per kg feed supplied to the fish at26-28C. From this, the equation:

g 02 required/h = Tw t( 1. 35X -'2 + 5.63R) (10)where Twt = total weight of fish in the system (kg), X = average weightof the fish (g) and R = daily feeding ratio (as a fraction of Twt) , can bederived to predict the amount of oxygen required by channel catfishunder the above culture conditions.

The rate at which oxygen is supplied by a culture system with a givenambient DO concentration can be determined, as in this study. Substi-tuting this available supply for the 02 required in equation (10) allowsprediction of the total weight of a specific fish size that can be sup-ported. If the FT configuration was used to produce 0.45 kg channel


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C l o s e d c u l t u r e c o n f i g u r a t i o n s - o x y g e n r e c ha r g e a n d a m m o n i a s t r i p p i n g 275c a t f is h ( w i t h a 4 5 . 4 l i t e r /m i n f l o w r a t e , s u r f a c e a g it a t io n , 6 -0 p p m D O ,2 6 C , 1 .5 % f e e d i n g r a t i o ) i t s h o u l d b e a b l e t o s u p p o r t 4 7 . 8 k g a t h a r v e s t.S i m i l a rl y , t h e H T w i t h a 2 2 . 7 l i t e r / m i n f l o w r a t e a n d s u r f a c e a g i t a t i o ns h o u l d b e a b l e t o s u p p o r t 3 0 . 3 k g a t h a r ve s t. E x p e r i m e n t a t i o n is c o n -t i n u in g t o c o n f i r m t h e s e p r e d ic t i o n s .

T h e a m m o n i a r e m o v a l r a te w a s v e ry lo w . T h e 4 5 . 4 l i te r / m i n F Ts y s t e m w i t h s u r fa c e a g it a t i o n p r o d u c e d a n N 0 q o f o n ly - - 6 - 2 5 m gN H 3 - N / h . F o r e x a m p l e , i f t h e w a t e r i n t h e 1 0 6 0 l i te r s y s t e m h a d at e m p e r a t u r e o f 2 5 C a n d a p H o f 7- 5, t h e p e r c e n t u n i o n i z e d a m m o n i aw o u l d b e e q u a l to 1 .7 7 (E m e r s o n e t a l . , 1 9 7 5 ) . I n o r d e r t o h a v e ac o n c e n t r a t i o n o f 0 . 1 0 0 0 m g / l i te r N H s - N , t h e r e w o u l d b e a n a m m o n i a - Nc o n c e n t r a t i o n o f 5 . 6 5 r a g /l i te r ( 5 . 6 5 m g / l i te r X 0 . 0 1 7 7 = 0 - 1 0 0 0 m g /l it e r) . A s q u i c k l y a s N H s - N i s r e m o v e d , N H ] - N w i ll s h if t t o t h e u n i o n i z e df o r m , m a i n t a i n i n g e q u i l i b ri u m . O p e r a t i n g f o r o n e h o u r w o u l d r e d u c et h e a m m o n i a - N f r o m 5 9 8 9 ( 5 . 6 5 m g / l i t e r X 1 0 6 0 l it e rs = 5 9 8 9 m g ) to5 9 8 3 m g ( 5 . 6 4 m g / l i t e r) , r e s u lt i ng i n a N H 3 - N r e d u c t i o n t o 0 . 0 9 9 8r a g / l i te r ( 5 . 6 4 m g / l i t e r X 0 . 0 1 7 7 = 0 . 0 9 9 8 r a g / li t e r) . A s n o t e d b yB u r r o w s a n d C o m b s ( 1 9 6 8 ) t h e a m m o n i a r e m o v a l b y a e r a t io n i s i ns ig ni-f i c a n t b y c o m p a r i s o n t o t h a t r e m o v e d b y m i c r o b i a l a c t i o n i n t h e f i lt e ru n i t. C o n s e q u e n t l y , a m m o n i a l o ss e s d u e to st r ip p i n g s h o u l d b e c o n -s i d e r e d a n i c e p lu s , b u t n o t s i g n i f i c a n t e n o u g h t o i n f l u e n c e f i lt r a t i o nd e s i g n c o n s i d e r a t i o n s .

C O N C L U S I O NT h e i n f l u e n c e o f f l o w ra t e , m e d i a d e p t h i n a p a c k e d t o w e r a n d su p p l e -m e n t a l a e r a t i o n o n o x y g e n t r a n s f e r r a t es an d e f f ic i e n c ie s , a n d t h ei m p o r t a n c e o f a m m o n i a s t r i p p i n g w e r e i n v e s t ig a t e d w i t h re s p e c t t ov a r i o u s c l o s e d s y s t e m a q u a c u l t u r a l d e s ig n s ( i n c lu d i n g R B C s ) . O f t h es y s t e m s t e s t e d , i t w a s d e t e r m i n e d :

( 1 ) t h e b i o f i l t e r i s a s e f f i c i e n t ( i n a n e w c o n d i t i o n ) a s m a n y a e r a t i o nd e v i c e s u s e d i n a q u a c u l t u r e ,

( 2 ) i n c r e a s e d f l o w r a t e s t h r o u g h a fi lt e r i n c r e a s e d o x y g e n m a s st r a n s f e r r a t es , b u t b y d i f fe r e n t a m o u n t s a m o n g t h e d es i gn s t e s t e d ,

( 3 ) t h e R B C w a s n o t a s c a p a b l e a s t h e p a c k e d t o w e r s in p r o v id i n go x y g e n a t i o n a t t h e f l o w r a te s t e s t e d w i t h o u t s u p p l e m e n t a la e r a t i o n ,


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276( 4 )

(5)(6)(7)( 8 )(9)

( l O )

G. E. Miller, G. S. Libeyw i t h o u t s u r f a c e a g i ta t i o n , t h e r e w a s a g e n e r al i n c r ea s e i n o x y g e nt r a n s f e r a s f l o w r a t e a n d f i l te r h e i g h t a l s o in c r e a s e d ,i n m o s t s y s t e m s , t h e a d d i t i o n o f s u r fa c e a g i t a ti o n r e m o v e d s ig ni -f i c a n t d i f f e r e n c e s i n o x y g e n t r a n s fe r ,s u r f a c e a g i t a ti o n h a d a s y n e rg i s ti c e f f e c t o n t h e o x y g e n m a s st r a n s f e r ra t e w h e n a d d e d t o a s y s t e m ,a i rl if t p u m p s w e r e l es s e f f e c t i v e t h a n s u r f a c e a g i t a ti o n , b u t p er -f o r m a n c e i m p r o v e d a s t h e p u m p d i a m e t e r i n c re a s e d,t h e b i o f i l te r s t e s t e d w e r e i n e f f i c i e n t f o r s t r i p p i n g a m m o n i a ,o x y g e n a t i o n a c r o s s a f i lt e r r e p r e s e n t s a n i m p o r t a n t c o n t r i b u t i o nt o o v e ra ll s y s t e m p e r f o r m a n c e ,o x y g e n a t i o n p e r f o r m a n c e o f a s y s t e m c a n b e u se d t o p r e d i c tc a r r y i n g c a p a c i t i e s .

A C K N O W L E D G M E N T ST h e a u t h o r s w i s h t o e x p r e s s t h e i r s in c e r e a p p r e c i a t i o n t o D r G e o r g eP . M c C a b e o f t h e D e p a r t m e n t o f S ta t is ti c s, D r J o h n C . N y e o f t h eD e p a r t m e n t o f A g r i c u l t u r a l E n g in e e r in g , D r A n n e S p a c i e o f t h e D e p a r t -m e n t o f F o r e s t r y a n d N a t u ra l R e s o u r c e s , a n d D r R o n a l d F . W u k a s c h o ft h e S c h o o l o f C iv il E n g in e e r in g , P u r d u e U n i v e r s it y , fo r t h e i r r e v ie w o ft h e m a n u s c r i p t a n d v a l u a b l e c r i t i c i s m .

R E F E R E N C E SAndrews, J. W. & Matsuda, Y. (1975). The influence of various culture conditionson the oxygen consumption of channel catf ish . Trans. A m . Fish. Soc., 104,

3 2 2 - 7 .An tonie, R. L. (1974). Nitr if ication of activated sludge efflue nt: BIO-SURF process,part II . Water & Sewage Works, 121 (12) , 54-5 .Broussard, M. C. Jr . & S imco, B. A. (1976). H igh den sity cultu re of channel ca tf ishin a recirculating system. The Progressive Fish-Culturist, 38 , 138-41 .Burrows, R . E. & Com bs, B. D. (I 968 ). ControUed environments for salmon propa-gat ion . The Progressive Fish-Oulturist, 30 , 123-36 .Colt, J . E. & Tchobanoglous, G. (198 1). D esign of aeration system s for aquacultu re.In : Proceedings o f the b io-engineering sym posiu m fo r f i sh cul ture, eds L. J. Allenand E. C. Kinney. Fish Culture Section of the American Fisheries Society,W ashington, District o f Columbia, pp. 1 38 -48 .


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Closed culture configurations - oxygen recharge and ammonia stripping 277Emerson , K . , Russo , R . C . , Lund , R . E . & Thurs ton , R . V . (1975) . Aqueous am-

mon ia equ i l ib r ium ca lcu la t ions : e f fec t o f pH and t emp e ra tu re . J . Fish. Res.Board of Canada, 3 2 , 2 3 7 9 - 8 3 .

Gigger , R. P . & Speece, R. E . (1970) . T rea tm ent o f f i sh ha tche ry e ff l uen t for recyc le .Eng inee r ing Expe r imen t S ta t ion , Technical Report Number 67, New MexicoState Un iversi ty, I_as Cruces, New M exico, 119 p p.

Muir , J . F . (1981 ) . M anagem ent and cost imp l ica t ions in rec i rcula t ing wa ter sys-tems. In : Proceedings of the bio-engineering symposium for fish culture, edsL. J . A l len and E . C . K inney , F i sh C u l tu re Sec t ion o f the Am er ican F i she r ie sSoc ie ty , W ash ing ton , D i s t ri c t o f C o lumbia , pp . 116-27 .

Page , J . W. & Andrews , J . W. (1974) . Chemica l compo s i t ion o f e f f luen t f rom h ighdens i ty cu l tu re o f channe l c a t f i sh . Water, Air, and Soil Pollution, 3 , 3 6 5 - 9 .

Soka l , R . R . & Roh l f , F . J . (1969) . Biometry. W. H. F reeman and Com pany , SanFranc isco , Cal i forn ia , 776 pp .SteUmacher, M. (1981). Aquaculture outlook and situation. United States Depart-ment of Agricul ture , Economics and Sta t i s t ics Service , Nat iona l Economics Divi -

s ion , AS-1 Apri l 1981, Washing ton, Dist r ic t of Colum bia , 22 pp .

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Miller 1983 Aquacultural-Engineering

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