production

Researchers Evaluate Low-Energy

Recirculating System for Inland

Production of Marine Finfish Juveniles

Dual-drain tank systems with airlift and moving-bed torus filters were used for fingerling production.

ery network initiative to evaluate intensive tank production of

juvenile red drum. The design and performance data collected

Timothy Pfeiffer, Ph.D.

for the system will be utilized to design the recirculating aqua-

USDA Agricultural Research Service

culture systems that the commission plans for new hatcheries

Sustainable Marine Aquaculture Systems

throughout the U.S. state of Florida.

5600 U.S. Highway 1 North

Copyright 2009, Global Aquaculture Alliance. Do not reproduce without permission.

Fort Pierce, Florida 34946 USA The recirculating system design described below has been

abqavl@r.postjobfree.com

used in the production of Phase I juvenile red drum, Sciaenops

ocellatus, of 25- to 45-mm standard length and Phase II fish

Paul S. Wills, Ph.D.

with standards lengths of 60-100 mm. Future objectives are to

Harbor Branch/Florida Atlantic University

Center for Aquaculture and Stock Enhancement evaluate the system for the year-round production of juvenile

Fort Pierce, Florida, USA

Florida pompano, cobia and other potential high-value marine

finfish species.

System Design

Summary: The low-energy hybrid recirculating aquaculture system

Several U.S. institutions are collaborating to evaluate consists of nine separate modules that utilize a commercial dou-

low-energy, low-head recirculating aquaculture system ble-drain fish culture tank paired to a moving-bed biofilter. The

designs to intensively produce marine finfish in a low- nine fiberglass tanks are 1.5 m in diameter. Normal water depth

salinity environment. The design and performance data is about 0.9 m for a total tank volume of approximately 1.6 m3.

collected for an intensive tank production system The double drain of each tank has a central sump to purge the

for juvenile red drum will be utilized to design new accumulated solids.

hatcheries for pompano, cobia and other marine species A slotted 5.1-cm-diameter center standpipe transports mid-

throughout the state of Florida. column water from the tank to the moving-bed torus filter. The

standpipe fits into a bulkhead at the bottom of the sump, which

is plumbed to the biofilter. Shallow fins on opposing sides of the

The United States Department of Agriculture Agricultural center standpipe act as a vortex breaker for water and aid the in-

Research Service and the Center for Aquaculture and Stock tank solids transport to the center drain. Water is airlifted into

Enhancement at Harbor Branch Oceanographic Institute-Flor- the biofilter through a 7.6-cm-diameter pipe by flowing air sup-

ida Atlantic University are collaborating to evaluate low-energy, plied by a 3.5-hp regenerative blower. All piping and fittings are

low-head recirculating aquaculture system designs to intensively polyvinyl chloride.

produce marine finfish in a low-salinity environment. Each torus filter is filled with approximately 0.11 m3 of

This growout work is being conducted as part of the Florida commercial floating polyethylene media. A flexible-diaphragm

Fish and Wildlife Conservation Commission s saltwater hatch- bubble diffuser below the media aerates the media to create

56 global aquaculture advocate

May/June 2009

1. Baffled sump

2. Vortex filters for preliminary solids removal

2

3. Foam fractionator with air/liquid oxygen input

4. Ultraviolet sterilizer

2 5. Incoming water with float valves and water meters

6. Dual-drain tanks with vortex breakers, surface drains, paired torus biofilters and influent cones

7. Airlift moving-bed biofilters

The low-energy recirculating aquaculture system is designed for inland juvenile marine finfish production.

toroidal movement within the filter with media rising from the spray nozzle and pressure washer unit. Brushing of the tank and

center splashed to the outside and back down to the bottom. sump sidewalls is kept to a minimum when fish are in the system

Water flows by gravity back into the tank at 15-90 lpm, depend- so as not to stress the fish and cause them to cease feeding.

ing on the amount of air supplied into the riser pipe. Typical

Water Quality

flow through the filters is approximately 60 lpm, which provides

Variations of this system have been in operation with varying

2 turnovers/hour.

stocking densities and biomass loads since December 2007. Sys-

A small, secondary polishing loop is included in the system

design for fine particulate filtration, oxygen supplementation and tem modifications based on previous culture trials are made in

untraviolet sterilization. A bulkhead fitting in the tanks provides an effort to improve water quality while minimizing capital and

surface water removal and water height regulation. Surface water operating expenses.

from the tanks drains into a manifold which then flows toward the Although initial stocking has varied depending on grading

sump. Plastic mesh netting wrapped around the drainpipe prevents needs, each tank has held over 3,500 red drum with a mean size

fish, feed and media from flowing into the drain manifold. of 4 g. Fish biomass in the tanks has ranged from 5 kg/m3 at ini-

The water from the drain manifold line gravity flows into a tial stocking to a peak of 55 kg/m3 before grading and removal of

265-l wave vortex filter. Matting placed inside the filter improves the larger fish. Feeding rates have been greater than 1 kg feed/

the capture of large solids. In addition to the in-tank sump purg- day of sinking 50% crude-protein pellets.

ing, this vortex filter is the primary solids filtration device in the The water temperature over the course of the year is 25 5 C.

water treatment loop. Outflow from the filter enters a second vor- The range is large because the airlift blower is located outside.

tex filter filled with commercial media. Outflow from the second Salinity for the red drum culture has been maintained at 10-13

vortex filter spills into a 3.2-m3 fiberglass sump. ppt. Total ammonia nitrogen values range 0.2-1.2 mg/l, and

Water from the front end of the sump is recirculated through

nitrite nitrogen is in the 0.1-0.3 mg/l range.

a commercial foam fractionator with a high-efficiency pump at

System pH is usually 7.3 to 7.7, as the air input to the torus

about 210 lpm. The 0.56-m-diameter fractionator stands 2.5 m

filters and the return spill into the sump help keep carbon diox-

tall. Water from the fractionator spills into the back half of the

ide to a minimum in the system. Alkalinity is maintained around

sump, which is separated from the front half by a baffle wall.

200 mg/l calcium carbonate by sodium bicarbonate dosing. A

A 1.0-hp pump returns water to the culture tanks through an

graph of the volumetric nitrification rate for the torus filters at

80-watt ultraviolet sterilizer. Return flow ranges 20-35 lpm,

two daily feed rates is presented in Figure 1.

providing a minimum tank turnover rate of once an hour.

Return water is drawn from the back half of the sump, where

make-up water is added as needed. 250

900 g feed/day

200

Water returned to the tanks is oxygenated by implementing a

Volumetric Nitrification

300 g feed/day

small custom Speece cone whose diameter increases as water flows

through the inlet and into each tank to allow greater contact time 150

and oxygen absorption. Liquid oxygen is metered in at the top

end of the cone in the range of 0.2-1.0 standard feet2/minute and 100

flows out near the tank bottom. Preliminary testing indicated

absorption efficiency of 90%. In case of power outage or pump 50

failure, emergency oxygen is supplied by a simple system of sole-

noids, flow switches and air stones. 0

System Maintenance

The tank sump is purged two or three times daily to remove Mid- 3:00 6:00 9:00 Noon 3:00 6:00 9:00 Mid-

night a.m. a.m. a.m. p.m. p.m. p.m. night

any accumulated solids. The matala filter pads are exchanged

Time of Day

daily. On a weekly basis, the tanks center pipes and drainpipes

are scrubbed to remove accumulated solids and biofilm build-up, Figure 1. Volumetric nitrification rates (g total ammonia nitrogen

which hinder the flow out of the tanks into the drain manifold. converted/m3 media/day) for the torus moving-bed biofilters

The drain line is cleaned on an as-needed basis with a rotary at different daily feeding rates.

57

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