Performance of a Closed Recirculating System With Foam Separation, Nitrification and Denitrification Units for Intensive Culture of Eel. Towards Zero Emission

8/6/2019 Performance of a Closed Recirculating System With Foam Separation, Nitrification and Denitrification Units for Inten

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foam separation, nitrication and denitrication units

The development of a closed recirculating aquaculture system that does not discharge efuents

closed recirculating system, which consisted of a rearing tank, a foam separation unit, a nitricationunit and a denitrication unit. The foam separation unit has an inhalation-type aerator and supplies air

rearing water at about 80%. Furthermore, ne colloidal substances were absorbed on the stable foam

nitrication unit. The ammonia concentration and turbidity were kept at less than 1.2 mg of N per litreand 2.5 units, respectively. When the denitrication process was operated, nitrate that accumulated in

recovered from the nitrication and denitrication tanks, and the components were found suitableas compost. Based on these results, the intensive aquaculture of freshwater sh such as eel can be


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Recently, the technology of a recirculating aquaculture system with a high sh density

productivity and energy efciency of such a system have become possible (

was found that the type of sh being cultivated made minimal difference. On average, the

load per unit of cultured sh was 0.8 kg of N per tonne sh per day and 0.1 kg of P per tonne sh per day ( persons per tonne sh assuming that the human nitrogen load is equivalent to 11 g N per person per day. The total sh production of inland aquaculture in 1999 in Japan is 63,000 t.Hence, pollutant discharge from aquaculture corresponds to the waste generated by ve

sh production. In many cases, however, some closed recirculation systems require the

addition, the sludgeand waterused to wash lter media are also directly discharged in many

system are as follows: water use is minimised, drainage water is puried to the same

producedduring sh culture should be made as close to zero as possible. degradable organic

actual aquaculture farm has not yet been developed. However, if intensive sh culture in

With the combined aim of increased sh production and reduced nutrient load in aquatic

foam separation, nitrication and denitrication units. Culture trials of Japanese ounder

was very high, that is, more than 3 months despite the high sh density. The advantage

main purication process. Oxygen supply, removal of suspended substancesand deaeration


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An ideal aquaculture system is one which puries the rearing water while obtaining

A closed recirculating system with foam separation, nitrication and denitrication units . This system consisted of a sh-rearing tank (0.5 m

inhalation-type aerator (200 V, 0.2 kW), a nitrication tank (0.16 m ) and a denitrication

water was then introduced into the nitrication tank with an up-ow style, and the treated

Fig. 1. Schematic diagram (not to scale) of the closed recirculating system with foam separation, nitrication anddenitrication units.


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water and oxygen was efciently dissolved in the rearing water until it passes through the

diameter, 11 mm inside diameter, 14 mm length, 0.93 specic gravity) was used to ll thenitrication tank up to the 0.16 m immobilised onto the medium prior to the sh-rearing experiment.

In the denitrication process, a portion of the rearing water was made to ow into thedenitrication tank using another line via a circulating pump.Thesame medium as that usedin the nitrication process was used as the denitrication medium. The methanol dose tube

was established at the midpoint of the inow line to the denitrication tank and methanol

methanol was introduced into the denitrication tank. Methanol injection was adjusted

water that passed through the denitrication tank was returned to the foam separation tank.

After the water supply to the nitrication tank was stopped by a by-pass pipe, the sludgethat accumulated in the nitrication tank was drained from the bottom and then transferredto another tank. All medium was also removed from the denitrication tank and washed

with sludge water. After washing, the media were returned to the nitrication tank and thesludge was allowed to settle for 2 h. The supernatant was returned to the system and sh

At the end of the experiment, the denitrication tank was also washed in the same way.


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Carbon and nitrogen in the solid samples, such as feed, sh tissue and dried sludge,

in Japan. The sh densityin the rearingtank became 2.6%, which is about four times higher

about 1/3 of the population. This conrmed that the gross weight of eel increased over three


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(244 days), the gross weight reached 33 kg (in a rearing sh density of 7.6%), and about


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with sh feeding or observation.

the sludge supernatant that was used in washing the nitrication tank was returned to the


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systems nitrication process functions well. In contrast, NO oxidation in the absence of denitrication, and NO water. However, when the denitrication process was initiated on the 42nd day, NO


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the stoichiometric methanol quantity needs for denitrication reaction, so that the quantity

not be observed with denitrication. It seemed that residual methanol that passed throughthe denitrication tank was biodegraded under aerobic condition until circulation in the

In the period without denitrication, the cumulative amount of feed intake (

in the rearing water. If the denitrication process did not operate throughout the rearing


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rearing water. However, because of denitrication, the nitrate residue in rearing water wasonly 43 g N at the end of the study period. This showed that denitrication removed 90%


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It has been reported that foam generation of sh mucus is dependent on the concentrations

such as sh mucus, and EC in rearing water.

In studies on the function of secretions from sh skin, the isolation of mucus glycopro-tein from sh skin was performed using a Sepharose CL-4B column (


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The suspended solids were signicantly concentrated in the separated foam water and


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period. Moreover, a brown material was signicantly concentrated in the foam water. The

difcult to remove by biological treatment or physical ltration. While an analysis of the

-N, highly efcient removal was

efciency of phosphorus by foam separation was higher than that of nitrogen.

Suspended solids accumulated in the nitrication tank as the rearing period progressed.Therefore, in order to prevent plugging of the nitrication tank, cleaning of the medium and

the study, the sludge that accumulated in the nitrication and denitrication tanks were also

accumulated in the nitrication tank. The polypropylene cylindricalmediumwas very light,such that taking them out fromthe nitrication tank was very easy. The sludge immediately

The components of the recovered sludge from the nitrication tank on the end were

the calculated C/N ratio was 5.9. The C/N ratio and N content satised the organic fertilizer

The eel production was 2669 g dry weight. The N and P contents in the sh body were 8.2


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tion and 3.9% was accumulated in the nitrication and denitrication tanks as sediment ). Regarding mass balances in the culture, the assimilation of nitrogen in the sh

in sh species (

) and 5% in the owing system for carp (

denitrication. Denitricationcould have removedtheresidual nitrate in the rearing water if


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the operation was continued for a few days after the sh was harvested. Since the recovered

nitrication and denitrication tanks as sediment (

than that of nitrogen. The decrease in the phosphorus content in the sh (1728% of the

in the nitrication tank. Sludge recovery and effective sludge utilisation are important in

Oxygen was efciently supplied to the rearing water by a foam separation unit and oxygen

separation process removed the brown colloidal substances generated by sh mucus. Thenitrication tank removed suspended solids and likewise rapidly nitried NH nitrate accumulated in therearing water in theabsenceof denitrication, after it was initiated

of the study. About 90% of the total nitrogen in the system was removed by denitrication.Sludge was easily recovered from the nitrication and denitrication tanks and proved to

at zero emission. The next step is to evaluate its economic feasibility while considering sh

the skin mucus of an Antarctic sh,

Blancheton, J.P., 2000. Developments in recirculation systems for Mediterranean sh species. Aquaculture Eng.


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high-density culture of the African catsh,

Geiner, A.D., Timmous, M.B., 1998. Evaluation of the nitrication rates of microbead and trickling lter in an

Hall, P.O.F., Holby, O., Kollberg, S., Samuelsson, M., 1992. Chemical uxes and mass balances in a marine sh

Holby, O., Hall, P.O., 1991. Chemical uxes and mass balances in a marine sh cage farm. II. Phosphorus Mar.

rearing of Japanese ounder,a denitrication unit. Suisanzoushoku 41, 1926 (in Japanese, with English abstract).

Knosche, R., 1994. An effective biolter type for eel culture in recriculating system. Aquaculture Eng. 13, 7182.Maruyama, T., Okuzumi, M., Saheki, A., Shimamura, S., 1991. The purication effect of the foam separating

system in living sh transportation and preservation. Nippon Suisan Gakkaishi 57, 219225 (n Japanese, with

Maruyama, T., Okuzumi, M., Satoh, Y., 1996. The purication of rearing seawater of Japanese ounder with theclosed foam separation-ltration system. Nippon Suisan Gakkaishi 62, 578585 (in Japanese, with English

Maruyama,T.,Suzuki, Y., 1998. Thepresent stage of efuentcontrolin Japan andpollutant loadfromsh culturetoenvironment.-Possibility of intensive recircutating sh culturesystems. Nippon Suisan Gakkaishi 64, 216226

withfoam-separation and nitricationunits for intensivecultureof Japanese ounder. NipponSuisan Gakkaishi

a recirculating system for tropical ornamental sh culture. Aquaculture 103, 123134.

van Rijn, J., 1996. The potential for integratedbiological treatment systems in recirculating sh cultureA review.

van Rijn, J., Rivera, G., 1990. Aerobic and anaerobic bioltration in aquaculture unitnitrate accumulation as aresults of nitrication and denitrication. Aquaculture Eng. 9, 217234.

Skjlstrup, J., Nielsen, P.H., Frier, F.O., McLean, E., 1998. Performance characteristics of uidized bed bioltersin a novel laboratory scale recirculation system for rainbow trout: nitrication rates, oxygen consumption and

Sumi, T., Hama, Y., Maruyama, D., Asakawa, M., Nakagawa, H., 1997. Purication and characterization

Suzuki, Y., Maruyama, T., 1999. Performance of a closed recirculating system with foam separation, nitrication

and denitrication units for the intensive culture of Japanese eel. In: Hino, A., Maruyama, T., Kurokura, H.

sh mucus. J. Jpn. Soc. Water Environ. 23, 181186 (in Japanese, with English abstract).

separation, nitrication and denitrication units for the intensive culture of eel. J. Jpn. Soc. Water Environ. 22,

of Japanese ounder using a closed recirculation system with foam-separation and nitrication units. Nippon


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Tambo, N., Kamei, T., 1998. Coagulation and occulation on water quality matrix. Water Sci. Technol. 37, 31

Uchida, Y., Tsukada, Y., Sugimori, T., 1977. Distribution of neuraminidase in Arthrobacter and its purication by

afnity chromatography. J. Biochem. 82, 14251433.

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Performance of a Closed Recirculating System With Foam Separation, Nitrification and Denitrification Units for Intensive Culture of Eel. Towards Zero Emission