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Optimizing tilapia biofloc technology systems, part 1

Published: February 8, 2018
By: Ramon M. Kourie / Chief Technical Officer, SustAqua Fish Farm.
Engineering design at Chambo Fisheries, the world’s largest biofloc tank farm for tilapia
Optimizing tilapia biofloc technology systems, part 1 - Image 1
Battery of eight multi-cohort sequential continuous culture BFT tanks at Chambo Fisheries.
Experience raising tilapia in biofloc technology (BFT), where aerial feeding rates are at least four to five orders of magnitude greater than in shrimp BFT systems, is limited. Areas that are particularly limited are knowledge systems centered on BFT engineering economics, tilapia feeding systems and bioenergetics, cost factors and the economics of this new technology relative to conventional tilapia aquaculture systems. Insightful experience gained at Chambo Fisheries in Malawi, Africa, and described here has helped fill many of these knowledge gaps.
Chambo Fisheries is purportedly the world’s largest tilapia BFT tank farm and the largest tank farm in Africa, located on the outskirts of Blantyre, Malawi. The farm became operational in 2013 based upon the mandatory production of Mozambique tilapia (O. mossambicus) and Shiranus tilapia (O. shiranus) due to restrictions that forbid the importation and culture of farmed breeds of Nile tilapia (O. niloticus) into the country.
Despite the slow growth in feral genes of O. mossambicus and O. shiranus compared to best farmed breeds of O. niloticus, several factors – including good flavor quality without purging, low Feed Conversion Ratios (FCRs), year-round production potential (on completion of the Shallow Solar Pond supplemental heating system) and favorable market factors in Malawi and regionally – make Chambo Fisheries potentially well poised for expansion.
The system architecture was originated by the author as the Chief Technical Officer of SustAqua Fish Farms (Pty) Ltd., which developed the farm blueprints, production schedules, management systems and executed start-up, monitoring and management training.
Vertically integrated farm design
Chambo Fisheries operates a vertically integrated farming operation that carries a quarantine facility, broodstock pairing tanks, an artificial incubation room for hatching eggs removed from female brooders, a dedicated nursery system, purging tanks, a moist feed milling plant and an ice plant and cold-storage facilities apart from the BFT grow-out tanks. Fig. 1 illustrates the farmed lifecycle of O. shiranus tilapia at Chambo Fisheries.
Optimizing tilapia biofloc technology systems, part 1 - Image 2
Fig. 1: Farmed production life cycle of Shiranus tilapia (Oreochromis shiranus) from a four-tank, BFT module producing up to 400 tons per year of 218-gram fish year-round.
Shiranus tilapia reaches an average marketable weight of 218 grams in 189 days from hatching within a temperature range of 27 to 29 degrees-C. Although purging fish to improve flavor quality is practiced, it is unnecessary in well-managed BFT systems as the fish carry no objectionable flavor taints. Fish are sold whole on ice and no form of processing takes place on site.
The farm boasts eight large, Round-ended (R-ended) grow-out tanks having an effective rearing volume of 766,000 liters capable of producing up to 100 tons of tilapia per tank in a year, or up to 130 kilograms per cubic meter (kg/m3) per year via a multi-cohort, sequential, continuous production schedule, although rearing densities average only around 20 kg/m3 (Fig. 1). Management at Chambo Fisheries is presently targeting 80 tons per grow-out tank per year on the completion of the heating system hardware.
Due to the cooler climate at 1,130 meters above sea level in Blantyre, all production facilities required placement beneath greenhouse enclosures in addition to the need for supplemental heat sourced from Shallow Solar Ponds (SSP) coupled to a hydronic heating system, which includes stainless steel heat exchangers built into the tank floor and regulated by thermostatically actuated, heat exchanger pumps for heat transport.
Enhanced efficiency and productivity through engineering design and adopted stock management philosophy
The farm design is tailored to take advantage of the benefits of continuous sequential production where each grow-out tank is stocked and harvested every three weeks. This stock management philosophy is enabled by the use of screened compartments (Fig. 3) in which fish are moved in a conveyor fashion every three week to a larger compartment via simple crowding screens and custom-developed seine nets.
Optimizing tilapia biofloc technology systems, part 1 - Image 3
Indoor view of one of the 766-cubic-meter (effective volume) BFT grow-out tanks at Chambo Fisheries showing the screened compartments enabling the use of a continuous sequential production schedule.
This management technique elevates Production: Capacity ratios (P:C ratios) greatly from around 2.9 in a batch system to within a range of 5.5 to 6.2:1 yielding around 4.6-5.8 tons of market-ready fish every three weeks, or around 17 times a year, and greatly increases the crop turnover rate using O. niloticus for this illustration (Table 1 and Fig. 2).
The use of a sequential multi-cohort production system essentially increases production output by a factor of 2.5 and reduces input power costs by 60 percent when gauged against a batch production system yielding an effective P:C ratio of only 2.9:1. Viability is greatly enhanced due to the more than doubling of production output based upon the same investment in equipment and infrastructure compared to a batch production system. This unique innovation by SustAqua Fish Farms (SAFF) was first pioneered by the company in the Middle East on two RAS farms and a third RAS farm in Malawi and is called the SAFF One-Tank Husbandry Approach.
Kourie, BFT, Table 1
Optimizing tilapia biofloc technology systems, part 1 - Image 4
Production performance metrics: Batch vs. Continuous Multi-Sequential Production in the SAFF Biofloc Technology SAFF grow-out tank of 766 cubic meters (effective rearing volume) raising all-male O. niloticus (Xibaha strain).
Optimizing tilapia biofloc technology systems, part 1 - Image 5
Fig. 2: Biofloc grow-out tanks at Chambo Fisheries operated on a continuous sequential production system (GS = Growth Stanzas 3-8) increases production output by 150 percent over a batch-production system.
Every aspect of the BFT R-ended tank design aims to minimize both capital and operating costs taking full advantage of the superior hydraulic environment created by SAFF’s integrated R-ended tank design. The R-ended BFT grow-out tanks include a built-in lamella separator for solids capture and removal. Control over the concentration of floc in the water column and the retention time of fecal and organic material (dead material) is achieved by regulating the run-time and water flow rate through a lamella separator from a full width floor drain in the main tank. Water is pulled through the lamella separator by causing a head differential at the far end of the central channel by a multiple pod airlift pump, allowing for infinite control over the pumping rate.
One of the important provisos for the success of the continuous BFT culture tanks at Chambo Fisheries is ascribed to careful engineering design to prevent solid waste accumulation anywhere in the system, as well as the effective twice daily discharge of solids from the tanks at capacity.
Horizontal water velocity control in the range 15 to 30 centimetres per second creates a beneficial streaming effect by adjusting the depth of the paddles on the paddlewheel aerators to regulate horizontal trust to overcome frictional drag forces of the moving water mass in the tanks and through segmented screened compartments. This improves the driving concentration gradient for oxygen transfer of carefully selected and positioned aeration devices, consisting of four, full-width floor diffusers at strategic intervals along the length axis of the tanks as well as the two 10-Hp paddlewheel aerators.
Forced moderate exercise has been shown to induce muscle hypertrophy, improve growth rates and reduce the energetic costs of protein accretion. Here fed fish, even described in tilapias, under continuous moderate exercise conditions exhibit a shift in their metabolisms to derive energy for swimming activity and protein accretion largely from carbohydrates and lipids rather than protein (a survival mechanism to spare protein loss from the muscle). This results in fish at harvest which carry a lower fat content while Feed Conversion Ratios (FCRs) are reduced, growth is enhanced, meat texture is improved (firmer), and fillet yields are elevated marginally (more plump fish relative to their body lengths).
One of the concerns of BFT is the higher energy demands for mixing, aeration and horizontal water movement for solids transport to the waste drains. Regardless of the stock management philosophy, whether production originates from batch culture or sequential multi-cohort culture, both modes of operation require continuous mixing and aeration. The advantage of sequential multi-cohort production, apart from the increased crop turnover relative to carrying capacity, is the greatly improved energy efficiency. Table 1 indicates a power demand of 4.24 kWh/kg of biomass gain in a batch system versus just 1.7 kWh/kg under a sequential multi-cohort production system at sea-level. This result is quite comparable to unit power consumption in more efficient RAS systems raising tilapias.
In part 2 of this article, I will continue discussing the benefits of BFT as a competitive and sustainable alternative, low-cost, intensive feedlot technology for tilapia aquaculture.
This article was originally published in Global Aquaculture Advocate (https://www.aquaculturealliance.org/advocate/optimizing-tilapia-biofloc-technology-systems-part-1/)

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Authors:
Ramon Kourie
SustAqua Fish Farms Pty Ltd.
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Ramon Kourie
SustAqua Fish Farms Pty Ltd.
16 de enero de 2020
Hi Sanu. Using the same design architecture to that developed at Chambo Fisheries we are busy on a 250 tonne per annum BFT multi-cohort sequential system which will run at 35ppt (seawater) raising Mozambique tilapia (O. mossambicus). The sub-surface aeration system will drive the needed horizontal water movement to achieve 30cm/sec current speed, strip CO2 and add dissolved oxygen very efficiently. Power use will come down to around 1kWh/kg of fish production due to the enhanced effect of increased aeration efficiency under saline conditions where the alpha factor climbs to 2.5 at 35ppt. Once this new system is put into use the results will be in the new book, "A Guide to Tilapia Production in Biofloc Technology (BFT) Systems" which will follow. Best, Ray
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Ramon Kourie
SustAqua Fish Farms Pty Ltd.
16 de enero de 2020
Hi Sanu Thanks for your comments. I believe the need for efficient gas stripping, particularly CO2 levels, from BFT culture water, which requires conventional aeration and possibly the use of a combination nano bubble system may have some merit. This will require elaborate testing in a research environment prior to commercial use. A control will enable the merits (or not) of the use of nano bubble under BFT conditions to be understood. Best, Ray
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Ramon Kourie
SustAqua Fish Farms Pty Ltd.
31 de julio de 2018

Hi Neil

The only way to maximize throughput production relative to maximum carrying capacity is via the management of a single tank system as a multi-cohort sequential stock management system. This we call the Production: Capacity Ratio (P:C ratio). Apart from reduced CAPEX per unit fish production, the benefits filter down to energy costs for aeration, carbon dioxide stripping and horizontal water movement where power costs are basically halved when compared to a batch production system.
As far as water velocities are concerned there are two aspects that require hydraulic calculations 1) the frictional drag forces of the moving water mass which occurs at the wetted surface area (walls and floor) and 2) the frictional drag forces which occur through the screened compartments. The sum of which is called the system hydraulic gradient against which horizontal water movement needs to be balanced to achieve the design water velocity.
Screen selection, number of screens, % open area are all important affecting the final hydraulic gradient. An offset bottom bar raised three inches from the tank floor and the use of a round bar or cable to achieve complete closure of the screen are the tricks of the trade preventing solids collecting at the floor-bottom bar of the screens.

At velocities of 25-30cm/sec, the movement of heavier solids (dead material, fibrous material) the heavier material drifts on the tank floor at velocities around 15-20% slower than the water column velocities - movement is still achieved. Industrial aquaculture involves a significant amount of engineering design, hydraulics, fluid mechanics, thermodynamics, heat transfer etc. The objective being to produce fish sustainably at the lowest possible cost capitalizing on the benefits of scale economies. At 1130m above sea level we opted to run at 4.5mg/L while the added cost to take dO2 levels to 5mg/L was not great but not essential - calls for added floor diffusers. The combination of paddlewheels and floor diffusers greatly improved the driving gradient in R-ended tank systems increasing oxygen transfer efficiencies under field conditions. Our next project using sea-water BFT for O. mossambicus will, in addition, carry a nano-bubble aeration system to pick dO2 levels up into the 75-85% saturation range. Hope the above is satisfactory for now.

Best, Ray.

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Femi Solagbade
30 de noviembre de 2021
Hi My interest is in biofloc tank monitoring. From your experience, what parameters need regular monitoring and at what will be your recommended frequency?
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r.k.singh
16 de octubre de 2020
beautiful discussion
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Sambhaji Shedge
29 de febrero de 2020
I am interested in shrimp farming thru BFT...would like to know about its feasibility and investment part and economics of the project .can anyone guide me or End me details on sbshedge@gmail.com? I am partner in Shantadurga aqua products.Tiger prawns farming has been done in the past now intend to restart with vannmie culture thru BFT . technology
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Ramon Kourie
24 de enero de 2020

Hi Sanu

Last comment. It is often erroneously believed that ALL solids require to be kept in suspension in BFT systems raising tilapias. Our BFT design is selective allowing heavier solids (10-20min settlement time in an Imhoff Cone) to drift on the tank floor which enabled their easy removal from the tank system once a day. While floc was less dense at required 30-35min to achieve a terminal reading using an Imhoff Cone. The objective in BFT is NOT to lose the valuable floc but rather to enable the removal of heavier solids which includes fibrous material and has little more to add in terms of benefits in a BFT system. Proper BFT system design would require careful selection and matching tank hydrodynamics with aeration system selection such that floc is continuously suspended while the heavier unwanted material remains easily removable without impacting on floc volumes. We were able to routinely achieve FCR's of 1:1 on a 20% protein diet under large scale conditions (766m^3 rearing volume) BFT tanks using the system architecture set-up for Chambo Fisheries which applied the above design philosophy.

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Ramon Kourie
24 de enero de 2020

Hi Sanu

Further to my comments above.

It would appear that moderate training actually reorganizes metabolism so as to spare the muscle [against muscle loss] in many teleost's including tilapias (Belal, 2015) with the result that protein growth is promoted over lipid growth in fish that are both fed and continually swum (Christiansen et al., 1989; Lauff and Wood, 1997). The Belal (2015) study indicated reduced body lipid proximate analysis at velocities of 25-35cm/sec. which supports the below hypothesis. In view of a great deal of convincing literature that net protein accretion rates, protein conversion efficiency from the diet, and overall growth rates are all improved if fish are continually swimming (Houlihan and Laurent, 1987; Christiansen et al., 1989; Davison, 1989, 1997), it seems likely that the exogenous fraction of nitrogen excretion will be lower if fish swim aerobically while feeding; that is, amino acids from the free pool will be funneled preferentially toward protein synthesis, rather than toward deamination and oxidation. Because feeding seems to preferentially elevate the concentrations of essential amino acids in the blood plasma (Brown and Cameron, 1991; Espe et al., 1993), whereas swimming preferentially elevates nonessential amino acids (Barton et al., 1995), it may be that the combination is most effective in stimulating protein synthesis. Interestingly, the Specific Dynamic Action (SDA, a measure of protein accretion) effect of feeding continues unabated (Beamish, 1974; Alsop and Wood, 1997) or may even increase (Muir and Niimi, 1972; Blaikie and Kerr, 1996) during sub maximal exercise. Because SDA mainly represents the cost of elevated protein synthesis, this indicates that carbohydrate or lipids are used to a greater extent, not only to power exercise itself, but to power protein synthesis during exercise. This hypothesis then explains the results of the Belal (2015) study.

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Ramon Kourie
24 de enero de 2020
Hi Sanu. A recent study entitled, “Effect of Water Velocity on Tilapia, Oreochromis niloticus Fingerlings Growth Parameters and Body Composition” (Belal, 2015) looked at horizontal water velocities in fingerling Nile tilapia production. A velocity range of 20-35cm/sec was considered optimal, although lower FCR’s were recorded at a velocity of 25cm/sec as opposed to 35cm/sec where the higher velocity resulted in larger weight gain at the expense of FCR’s. A number of studies have indicated that smaller fish benefit from higher water velocities relative to their body length and smaller fish due to their higher metabolic rates are capable of 1.5-2 BL/sec while larger fish require a reduction in water speed (0.4 to 0.8BL/sec) due to their slower metabolic rates. It seems as though a water velocity of around 30-35cm/sec would optimal for grow-out operations raising fish over 20g to harvest (>500g). Swimming energetics and the Cost of Transport (COT) is a fascinating avenue of study. In a follow-up commentary I'll explain the the merits of reduced FCR's and enhanced growth under moderate water velocities (as above).
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Ramon Kourie
17 de enero de 2020
Hi Sanu.We wont try to enhance density as there is a correlation between density and FCR's that was apparent in the Chambo Fisheries BFT tank systems operating at 16-22kg/m^3 (as a function of fish size. Rather through further design optimization the aims are to use less power via a more efficient sub-surface diffused aeration system and elevated horizontal water movement from 20cm/sec to 30cm/sec at reduced power input and larger scale and deeper tank systems using seawater and O. mossambicus targeting 1kWh/kg of fish production. best, Ray
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