International Council forthe Exploration of the Sea

C.M. 1985/ F:57Mariculture CommitteeSession W

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A COMPARISON OF TRICKLING FILTER AND SUBMERGED UPFLOW FILTERPERFORMANCES WITH FISH TANK EFFLUENT

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by

V. Hilge1), U. V. Rakelmann 2) and K. Chiba3)

1) Bundesforschungsanstalt für FischereiInstitut für Küsten- und Binnenfischerei

,Außenstelle, Wulfsdorfer Weg2070 Ahrensburg

2) Technische Universität Hamburg-HarburgArbeitsbereich GewässerreinigungstechnikEißendorfer Straße 382100 Hamburg 90

3) Fisheries LaboratoryTokyo University2971 Maisaka, Maisaka-cho, Hamana-gunShizuoka-ken, 431 -02 Japan

ABSTRACT

A trickling filter (2.7 mfilter bed depth; 1.5 m diameter; 4.77 m3 volume;954 m2 totalsurface) packed wi~h a plastic material, an~ a submerged fixedfilm bed reactor (1.3 m bed depth; 1 m diameter; 1 m3 volume; 340 m2 totalsurface) filled with 8-16 mm diameterexpanded clay, both aerated, wereintegrated into a small closed warm water sytem. Theywereboth suppliedwith the same fish tank effluent at identical flow rates of 3 and 4 m3/h.At low ammonium load the nitrification rate was good in both filters,

but decreased earlier in the trickling filter with higher inlet

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concentrations. The maximum oxidation velocities observed amounted to2.7 mg N/m2h in thetrickling filter and to 15.1 mg N/m2h in the sub­merged filter. The results are discussed with regard to the specificproperties of each filter type.

RESUME

Les performances d'un lit bacterien (2,7 m de profondeur; 1,5 m dediametre; 4,77 m3 de volume; 954 m2 de surface) avec du plastique commemateriau filtrant, et un filtre bacterien a passage ascendant de l'eau(1,3 m de profondeur; 1 m de diametre; 1 m3 de volume; 340 m2 de surface)rempli d'argile expanse de 8-16 mm de diametre, tous les deux a ventilation ~

forcee, ont ete etudiees dans un circuit ferme de 6 m3 de volume et •250 kg de poissons environ. Les filtres ont ete alimente avec de l'eauusee aux debits de 3 et 4 m3/h. A fabile charge l~ taux de nitrificationetant bon pour les deux filtres, le lit bacterien a montre une oxidationincomplete acharge elevee. La vitesse maximum de l'oxidation de l'ammoniaqueetait de l'ordre de 2,7 (lit bacterien) et de 15,1 mg N/m2 h (filtrebacterien). Les resultats sont discutes sous l'aspect des proprietesspecifiques de ces filtres.

1. Introduction

Closed system technology remains an interesting tool in fisheries biologydespite all constraints and failures. There are at least three fields ~

to use such a technique; a) quarantine of imported fish, b) rearing offry and fingerlings for stocking purpose, c) ecologicalresearch.The production of fish wastes - in particulate or dissolved form - mayvary over a wide range of concentrations according to biomass and foodsupply, as do the performances of the differe'nt treatment systems usedfor the degradation of these metabolie wastes. Besides the'filtration of

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suspended solids the elimination of nitrogenuous compounds is another major

task of recycllng water reconditioning. This'is often done by nitrifying

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1-

\

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bacteria in biological filters eithei kept in suspension (~ctivated

sludge) or attached as a fixed film on an artificial medium. Sand; .. gravel or plastics of varying geometry are generally used withthe'filters especially designed for nitrification. The three biofilter .types at work most frequently are trickling filters, rotating disc contactorsor fixed film bed reactors.

Recently we have evaluated the performances of a'small fixed film bedreactor model in order to find out whether it would be suitable fo~

the treatment of fish tank effluent (HILGE and RAKELMANN 1984f. Specialattention had been paid to the fact that rapid changes in the inletconcentrations of e.g. ammonium have to be digested by the filter in

4It order to avoid·a break -·through, which would lead to an steadily-increasing level of this me~abolite in the whole system. As theresultswere encouraging we were interested to construct afi1ter that cou1d beintegrated into anexisting closed system. Thepossibility to compareit directly with a working·trickling filter was considered to be anadvantage.

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2. Materials and Methods

The'fixed film bed reactor was included into a closed freshwater systemparallel to,an existing trickling filter. Both units were fed by onepump from a sump with the same water at equa1 flow rates. From the bio­filter the water run by gravity to troughs from which a total of 8 tanksof 360 1 vo1ume each were supplied. During the whole course of theexperiments the totalfish biomass in the tanks, consisting of adultmirror'carp(Cyprinus carpio L.) and .channe1 catfish (Ictalurus. .

punctatus Raf.,) varied between 230-270 kg. From the fish tanks the water. ,- .

was drained into a sedimentation tank and fina11y arrived at the pumpsump again~ The total system water volume was approx. 6 m3. It wasmaintained at rather constant temperatures in the range of 23-240C.Total dailywater losses by sludge removal etc. amounted to 1/3 of thetotal water vo1ume. They were ab1e to compensate for the loss ofalkalinity.due to the various oxidative processes generating free hydrogen

ions, thus keeping the pH rather stab1e throughout the who1e experimentalperiod.

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.1.;,

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The trickling filter hada height of 4 m, a diameter of 1.5 m and wasfilled with a plastic medium (Hydropak' foil, 200 m2/m3) of 2.7 m depth.The water was distributedover the plastic foil with an electric motordriven sprinkler. The total surface' area was 954 m2 in a 4.77 m3 filtervolume (void space 96 %)~ The trickling filter was force aerated frombottom to top in a countercurrent to the water.

thefixed film bed reactor consisted of a 1.8 m high zylindrical glassfiber tank of 1 mdiameter with a 1 m3 filter bed volume of,l.3 m depth.The filter bed material was placed on a support, that was fixed 0.3 mabove the tank bott,om. Below this support the water inlet and the ",aerationpipes were situated as well as a drain in the bottom .for completeevacuation of the ~ilter. Aeration was achieved through.a series of 12 mm ~

dia~eterinterconnected PVC pipes at 10 cm distance over the whole bottomwith 1.5 mm holes at 4 cm distance. The filter bed consisted of a8-16 mm diameter expanded clay with a specific surface area of approx.340 m2 and a porosity ~f 0.43. The filtered water was drained fromthetop into a trough (for comparison of data see Table 1).

,Water samples were taken at the inlet to and at the outlets from thefilters. The samples were analysed for pH, ammonium, nitrite,. BOD (asBOD 2) and TOC according t~ the German Standard Methods(N.N. 1983). Alldeter~inations,were made after filtering the water through a prewashedpaper filter (S&S 595 1/2) except for TOC, that were measured afterfiltration on a 0.45 Nm.glass fiber filter.

, .Table 1: Data of trickling filte~ and fixed film bed reactor •

Trickling filterPVC plasticMaterial

Specific'surface area (m2m-3)Surface area' (m2) .

Filt~r diametei (m) . 'Fi 1ter depth (m) -,

Filter'volume(m3) ,

Filter ~oid spac~'(%)

Filter total surface (m2)Hydraulic load (m3m-3 d-1 )

Hydraulic surface loading(m3m-2 h-1)

2001.771.52.74,77

96954

15.1 - 20.1

1.7 - 2.3

Fixed film bed reactor ­expanded clay

340 '

0 ..79LO1.31,0

43340

72 - 96 .

3.8 - 5.1

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3. Results

The ex'periments were performed. several months' after st'art'in.9 the' newsubmerged fi lter: Duri ng the'acc1i~at ion phase the system' were 'run underconditions similar to those of the'experiments.·Usual concentration levels of the parameters measured of'an unfed systemare shown in Fig. 1. There ,are rather little variations in all observedparameters throughout the whole day. The effluent pH are somewhat, higherthan the inlet ,levels t being a little higher in the water leaving the 'trickling filter. This holds generally for all observations. ,The,effieiencyof nitrification seems to be somewhat lower in thetrickling filter ascompared to the submerged filter with eoneentrationsnear to the deteetionlevel. (It should be noted here t that ammonium values are obtained aftersubtraetions of the blanks). The influenee of a small amount of food givenin three portions on the observed parameters reveals almost noehanges inthe pH t but the other inlet conentrations vary, clearly (Fig. 2). With,ammonium aslight reaction ean be detected' in the triekling f'ilter while theo'xidation in ~,he ~ixed film r,ea'etor is almost' eompJete. There is a more,pronouneed deerease,of the removalrate of nitrite in the triekling filter.

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With ~ bigger amount of food these differences become clearer (Fig. 3).The increasing metabolie load redu~es the differenees between inlet andout let levels of the pH in the submerged filter although aeration was not.' ~ , . .

ehanged. There is a eontinuous inerease of the ammonium and nitrite levels. during the whole observation period t a slight deereaseof ammonium removal. - . . .' .in the triekling.filter and a more than 90% effieieney in the submerged

~ .. . . .filter. Clear differenees ean be observed with.the oxidationofnitrite.. '.. . '.

Both filters adapt to the inereasing amounts, but in quite different manners.While all these experiments were performed at a flow rate of 3'm3/h for

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eaeh of the two filters, an even more severe shoek load was attempted.at aflow of 4'm3/h using ~mmonium chl~ride (F'ig~ 4). It was cont'inuously added to

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the sump water at ~hree different increasing quantities. AS.a.result the pH.. . .of the outlet water from thesubmerged filter dropped below the inlet level.With the ammonium concentrations the three different levels at the inlet. . .ean be distinguished. The reactions of the filters demonstrate that the

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submerged filter can easier withstand these changes. Its outlet level is. . .'

always fairly below that of the trickling filter. The nitrite outletconcentration of this'filter is even higher than at the inlet, i.e. the. . . . .

trickling filter is not longer able to oxidize the amount of nitrite,, . ,

which is equivalent to that being formed within the biofilter fr~m ammonium.

Although the BaD is not a real problem in fishtank effluent (asa matterdifficult to be treated), that·needs special attention,its degradation wasobserved in both filters (Fig. 5)~ The BaD 2 values. from filtered waterdemonstrate that both biofilters are able to r~move the easily biodegradabledissolved organic load in a sufficient manner. No data are available to havean estimation of the TOC removal in the submerged filter, but Fig. 6 givesan idea onits removal in the trickling filter. The efficiency is not highand the fluctuations during the.day are rather small.

4. Discussion

The evaluation of the performances of the two biofilters gave some clear. ,

results on thecapabilities of both systems. It is difficult to compare themdirectly by other means than the effluent qualities, becaJse'they arediffer~~t in s~ze and mode of o~e~ation. This mean~ on the ~th~r ~and, thatas 'a'rough estimation a tricklingfilter as it was used is at least,thr~etimes as expensiv~.as the'fixed film bed re~ct;on by investment cost~.

Furthermore ~s it is'about 4 m in height and consid~reing that. it ~i~l feedthe fish tanks bygravity flow in order to avoid the costs of'a second'pump,such abiofilter 'probably has to 'be installed outdoors. This requires specialisolation when working with warm water in temperaturmclimates. Otherwise the 4Itcooling of the water during night or the cool season will result inelevated heating expenses. A' submerged filter will have smaller dimensionsin order to'meet the same'waterquality standards. The ratio of filter bedheight to diameter should be much in'favour of the height. This is opportuneto achieve goodremoval efficiencies (MILLER and LIBEY 1984). In this'case

'a submerged fi Her can be divided into two parts without a second pump,but with a little additional head loss. On the other hand with changing biomassand wat~r'flow rates there remairis the possibility to ta~e one filter out ofuse. '

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Besides these attractive v~ews there are some disadvantages with the fixedfilm bed reactor related to the suspended'soli~s in fi~~ tank ~fflu~nts.

The:y may "partially o~ completely clog the filter, form azone of"anilxiccondit~ons in the lower part of the biofilter and decrease the nitrificationrate. With a medium size of 8 - 16 mm backwash veloci'ties of probably about500 - 600 m/h would be nec~ssary, which is extremely hi'gh. As a con~eque~ce

car~ must' be taken to almost completely eliminate the suspe~ded solids'fromthe water before entering the biofilter. This has for example be~n attemptedin ,the c.ase of pres'surized submerged filters (MAUREL 1983), which were filledwith very small granules.

As we could not backwash, the filter was emptied through the bottom drainand then washed in a downflow mode. Thismode of "cleaningl~.. happenspermanently in a trickling,filte~filledwith pl,astic mater,ial ~~such a highrate of, void space as used in our experiments. Long-term observations neverrevealed any problem with respect to clogging in such a filter (ROSENTHALet al., 1979). Another possibility to at least partially overcome the problem-- '. • '. <

of clogging in ,a submerged filter is the alternate flooding arid draining ofthe biofilter at regular, shourt intervals. PALLER'and LEWI~ (1982) reportedon 'higher carrying cäpacities of the recycling system and better ammoniumremoval as compared to a conventional ,submerged filter.

The limited ability of the tricklingfilter, as demonstrated with the,experiments,:to easily a~apt to higher a~monium and nitrite loads, hasalreadY,been noticed by KRONER and ROSENTHAL (1983), who found that variations

~ in the filter performances were mainly due to fluctuations of ammonium andnitrite at the filter inlet. Biofilters of a higher removal efficiency wouldbe advan~ageous to avoid the recirculation of increasing amounts of wastes.Other~ise it can be 'possi~le ~o detect ammonium concentrations at the bio­filter inlet, that are several times higher than those being actually producedin the fish tank. This also holds for nitrite as the final product of thefirsi itep of nitrification. Ozonation hassucces~fully been employed tooxidiz~ ,it (OTTE and ROSENTHAL 1979).

From data not presented here in detail, but belonging to the experiment shownin Fig. 4,'the oxidation speed'of both steps of nitrifica~ion (mg N oxi­

dized/m2 filter medium surface x h) can be calculat'ed to 2.7 (tricklingfilter) and 15.1. (fixed film bed reactor), expressed as N - N03,

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At the filters were fed the same water, the differences between bothcannot be attri~uted.~o any co~pounds in the w~ter, that can large~~ ~:.

influence the nitrification processes (KHIET and KLONTZ, undated).Poss~ble explanations are related to the aeration. We could already showwith the small filter model, that bubbling increased the nitrificationrate by 1/3. Ammonia stripping could not beresponsible due ~o,the ,"low" pH and the big bubble size of several, millimeters. As a side effectan increase in pH during the passage through the biofilter is observeddue to stripping ?f CO2. With str~nglY increasing nitrificati~n ~at'e's th'eproduction of, hydrogen ions and their reaction with hydrogen carbonateions'to form carbon dioxi~e will lower the pHat the outlet of the s~b~'

merged filter (Fig. 4). This was not observed with,the trickling filter.The thin water film above the bacterial populations and the enormous aeratedvoid space support the rapid transfer of CO2 from the liquid into thegasous phase. But this will lead,to an accelerated loss of hydrogen carbonateand a faster drop in alkalinity.

With regard to the lower nitrification rate of the trickling filter theoccurrence'of strong ,competitio~ for ,space between heterotrophs and'nitrifiers seems to be an appropriate explanation (WILDERER and NAHRGANG1982).'This is particularly, important for thesecond step of nitrification,as the high nitrite levels at the outlet of the filter demonstrate. In anupflow filter a clear,zonation can easier be maintained,'because thedistribution of particulate organics is restricted to a small filter area.

5. Literature •

,Hilge, V. and U.V. Rakelmann: Laboratory scale experiments on the nitri-1984 fication of fish tank effluent in a fixed film'bed reactor.

In: Research on Aquaculture (eds.: H. Rosenthal and S. Sarig,p. 55-66). Speical Publication No. 8, European MaricultureSociety .

Knlet, V. and G.W. Klontz: Evaluation of environmental and nutritionalUndated factors influencing the performance of biofilters in fish

rearing systems: Final Report. Contract DACW 68 - 77 - C -0118,Walla Walla, Washington

Krüner, G. and H. Rosenthal: Efficiency cf Nitrification in Trickling Filters1983 Us ing Different Substrates.'

Aquacultural Engineering 2 (1): 49-68

Maurel, P.:1983

Miller, G.E. and1984

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Les circuits fermes·en aquaculture: Technologie etdomaines d1application. .La Pisciculture francaise 71 (1): 6-18

•G.S. Libey: Evaluation of a Trickling Biofilter'in aRecirculating Aquaculture System Containing ChannelCatfish.Aquacultural Engineering 3: 39-57

N.N.1983

Otte, G. and H.1979

German Standard Methods for Aanlysis of Water, WasteWater and Sludge.Verlag Chemie. Weinheim

Rosenthal: Management of a closed brackish water system forhigh density fish culture by biological and chemical watertreatment.Aquaculturale 18: 169-181

Paller, M.H. and W.M. Lewis: Reciprocating Biofilter for Water Lense in1982 Aquaculture.

Aquacultural Engineering 1: 139-151, . ,

Rosenthal, H., G. Otte and G. Krüner: Lang-term operation of a brackish water1979 recycling system: Progress report 1978.

ICES C.M. 1979/F:12, Mariculture Committee

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Wilderer, P.1982

and Th. Nahrgang: Biotechnologische Grundlagen derNitrifikation im Tropfkörper. ' ..Stuttgarter Berichte zur Siedlungswasserwirtschaft, Nr. 77.p. 30-47, Verlag R. Oldenbourg, München

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Explanations to Figuresl ~ 5:

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inlet concentrationoutlet concentrations of the trickling filter

outlet concentrations of the fixed film bed reactor

Figures 1 - 4 show variations in pH, ammonium and nitrite during theday course. Arrows indicate time of feeding. All flow rates are perfilter.

Fig. 1:

Fig. 2:

Fig. 3:

Fig. 4:

Flow rate 3 m3/h; no food given; water temperature 23.0 - 23.70 C;fish biomass 255 kg

Flow rate 3'm3/h; 450 9 food, water temperature 23.0 - 23.50 C;fish biomass 255 kg .

Flow rate 3 m3/h; 1 500 9 food; water temperature 23.0 - 23.50 C;fish biomass 255 kg

Flow rate 4 m3/h; continuous addition of NH4Cl at three levels;Water temperature 23.90 C;fish biomass 255 kg

·.... --...--....._-",;- .-.-.',pH '

-11-Eg.1 :

8.0x--- x--_ x

X X ---x---x------x-2.'.:.- .' x-.~.x.--e-.;...x_ e - eX- e- eX-::- .-eX

, M k

)

•

Q05 .......x --_ x,," "

-~ ......X-- ......"-K- --- - ~-. -- - --- x

__ .X-';';'e_ x x . _ e"X-.-.XX_ e ., ", e -.-. -e-ex_e "

X-e_ ex_ e _ e x- e_ eX_e _eX- e -.c-e_ex., -' ' '... - {

X- - - x

I.

-)t-)f-

X- x" . x-- ..... 'x--- ---..... .-. x --- -,~

N02-Nmg/l

Q1

8'" .,-,

12 16 h

~------- ~~.-

pH .Eig.2 :'l

•

x":"_-x -- -x__ x.--ee_eX_-- eX_ e_

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M M "N M K

..1_, ,L , ._ ~_~ _.L __,,_.L___J~, __._:r.... '

1 1

x- '.... -x __x-_ - x _ - - _x - - - x - - - x - - - x-,e X '

-e)fo _'ex_e_ex_e_ex-e-ex_e-.xM " '.,

x_.". - - x_

.". --.".

x- - - x""

1

..__....... , ------'-----=---(NH3 +NHZ)-N

mgll

~_.. -- --. .._-- .. "--' --

N°i-Nmg/l

1 1 1

__ X---x_x- ---~__ -x

--__x-x--

16 h12·

,.-e- eX-.-.X-.-·X- .-«-.- .x-,_, .,',' e-:--.x

fJn tJ.g,,j:

x-_ --x

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x_-x-x__ • - - x-----. .)C . x- - --' )(- -

'15 ~-·-.x- __-'~x~-·~.==~.~~;=:~.~~'.x~'_==~.==~,,==_Ir . . ~ --0.--'-~~'~Zi'~~==~:::-::r:::=--,c=:=!:==::r==~=.-::.~(. NH

3+ NH +-)--N-- ._! -!- L_, I1. _, ," ._- _i__ L.~_..L,---!..- )

mg/l

8.

.',

, ~__ - x--- ",,- ' ' .-.__x---~ ,

/~"

1 1 1

Q2

• -N02-N

mg/l

1 ! 1__ x

x-

8 ' 12 16" h

7,5

- 14 .-

X"iC-" .-x~~-X_' . '.

.... ' '...:;-.~~ .:~ - :_ ,- --Xe--x . k

e_"",_~_e_e-X

.Fi g. 4·'•

. " '

//

"XX \

\\

x- _X/ /X \/ ~/. '. \

. )<- -X / '\. \x' . I e

.....__. X._ ---"_.;....l( " X

N02 ~N-"----' 'Xmg/I

0.3

0,5

rTN-H-~:; N-~[Y=-'N--O. -

mg/l

0.2

0.1

8 12 h

...------ -- - -..

ass 2

T

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_x­x-/

/~~/ ~_ X..--. ..... .... .....]IC .......x-.-x - x --, /." -·--.....c-·-_x-·--x

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Tx T

8 12 h

Fig. 5: nOD 2 concentrations at flow rates of 3 m3/ h; 900 g food;temperature 2~.5° ~ 24.50 c ( aSB 2 means BOD 2 in og / 1)

TQemg/l

16 h

...... .._w.-

12

.--./ --/ .Ir __ ..

,-- , ,, -.-

•8

10~

15

Fig. 6 Concentrations of TOC at the inlet and the outlet of thetrickling filter. ?low rate 5.6 m3 / h; water tem~erature

23.5 - 23.6 0 C: fish biomass 240 kg