super intensive culture of white leg shrimp (litopenaeus vannamei), in recirculating tank system at different stocking densities

CAN THO UNIVERSITY
COLLEGE OF AQUACULTURE AND FISHERIES






SUPER INTENSIVE CULTURE OF WHITE LEG SHRIMP
(Litopenaeus vannamei), IN RECIRCULATING TANK SYSTEM AT
DIFFERENT STOCKING DENSITIES





BY
LE PHUOC DAI








A thesis submitted in partial fulfillment of the requirements for
The degree of Bachelor of Aquaculture

Can Tho, 12/ 2013


CAN THO UNIVERSITY
COLLEGE OF AQUACULTURE AND FISHERIES






SUPER INTENSIVE CULTURE OF WHITE LEG SHRIMP
(Litopenaeus vannamei), IN RECIRCULATING TANK SYSTEM AT
DIFFERENT STOCKING DENSITIES




BY
LE PHUOC DAI

A thesis submitted in partial fulfillment of the requirements for
The degree of Bachelor of Aquaculture



Supervisor
Assoc. Prof. Dr. TRUONG QUOC PHU





Can Tho, 12/ 2013



APPROVEMENT

The thesis Super intensive culture of white leg shrimp (Litopenaeus
vannamei), in recirculating tank system at different stocking densities
defended by Le Phuoc Dai, which was edited and passed by committee on
12-27-2013
Sign of Supervisor Sign of Student


Assoc. Prof. Dr Truong Quoc Phu Le Phuoc Dai

i


Acknowledgements
First of all, I would like to express my honest thanks to the Rectorate of
Cantho University and the lecturers of College of Aquaculture and Fisheries for
supporting me to study after 4.5 years.
I would like to thank Assoc. Prof. Dr. Truong Quoc Phu and Mr. Huynh
Truong Giang who have enthusiastically instructed me to finish the graduating
thesis. For other valuable help and guidance, many thanks are also extended to
Tran Trung Giang, Phan Thi Cam Tu, and Tran Thi Be Gam.
I also send my gratefulness to my advisor Dr. Pham Minh Duc for his
constant support and my beloved classmates in Advanced Aquaculture Program
for great encouragement during 4.5 years in College of Aquacuture and
Fisheries.
Finally, I want to express my sincere love to my family, my friends who
have encouraged and supported me during the AAP course.

ii

Abstract
This study aimed to evaluate the effects of different stocking densities on
growth and survival rate of white leg shrimp (Litopenaeus vannamei). A
triplicated experiment was conducted with differrent treatments of stocking
densities: 1000 shrimp m
-3
, 800 shrimp m
-3
, 600 shrimp m
-3

, 400 shrimp m
-3
.
The experiment was conducted in 500-L tanks with recirculating system, and
supplied aeration continuously. Brackish water of 15ppt was used for the
experiment. The shrimp were fed four times per day with commercial feed
which 40% of protein. Water was unchanged but circulated continuously
according to recirculating system. Water quality sample was took every week
and analyzed at water quality study lab. After eight weeks of culturing, the
shrimp reached the body length of 5.84±0.21, 6.48±0.55, 6.26±0.30,
5.98±0.39cm/species at the densities 1000, 800, 600, 400 shrimp m
-3
.The
survival rates ranged from 50.2 to 62.8%. There were not significant differences
in both growth rate and survival rate among treatments (p>0.05). The results
indicated that white leg shrimp can be growth at wide range of densities of 400 –
1000 shrimp m
-3
. Further study is a need to examine growth of white shrimp at
higher stocking densities.

iii

Table content
Acknowledgements i
Abstract ii
Table content iii
List of tables vi
List of figure vii
List of abbreviation viii
Chapter 1 1
INTRODUCTION 1
1.1 Introduction 1
1.2 Objectives 2
1.3 Research contents 2
Chapter 2 3
LITERATURE REVIEW 3
2.1. Biological characteristics of white leg shrimp (Litopenaeus vannamei) 3
2.1.1. Classification 3
2.1.2. Life cycle 4
2.1.3. Growth characteristics 4
2.1.4 Distribution 4
2.2.White leg shrimp (Litopenaeus vannamei) production in the world 4
2.3.White leg shrimp (Litopenaeus vannamei) production in Viet Nam 5
2.4.Application of recirculating water system in white shrimp culture 5
2.5. Recirculating aquaculture systems (RAS) 6
2.5.1Principle of RAS 8
iv

2.5.2 Recirculating System Economics 9
2.6. Biofilters 10

2.6.1. Trickling biofilters 11
2.6.2. Fluidized – beds biofilter 11
Chapter 3 15
METHODOLOGY 15
3.1. Time and location 15
3.2 Materials 15
3.2.1 Equipment 15
3.2.2 Water source 15
3.3 Experiment design 15
3.3.1 RAS preparation 15
3.3.2 Tanks system and biofilter media. 16
3.3.3 Stocking shrimp 18
3.3.4 Monitoring 18
CHAPTER IV 20
RESULTS AND DISCUSSIONS 20
4.1 Water quality parameters 20
4.1.1. pH 20
4.1.2 TDS (Total Dissolve Solid) 21
4.1.3: EC (Electricity Conductivity) 21
4.1.4 DO (Dissolve Oxygen) 22
4.1.5 TAN (Total Ammonia Nitrogen) 23
4.1.6 NO
2-
23
v

4.1.7 NO
3-
24
4.1.8 TSS (Total solid suspended) 24

4.2 Growth rate 25
4.2.1 Survival rate 25
4.2.2 Weigh and length 26
CHAPTER V 27
CONCLUSIONS AND RECOMMENDATIONS 28
5.1 Conclusion 28
5.2 Recommendations 28
REFERENCES 29
Appendixes Error! Bookmark not defined.

vi

List of tables
Table 1: Production of white shrimp in North, Central and South of
Viet Nam in 2009 5
Table 2. Advantages and disadvantages of commonly used biofilter
(Wilton, 2001) 14
Table 3: Method for water quality analysis. 19
Table 4: DLG, DWG and SGR in length and weigh of the shrimp 26
vii

List of figure
Figure 1: White shrimp (Litopenaeus vannamei) 3
Figure 2. Required unit processes and typical components used in recirculating 9
Figure 3: RAS schema 16
Figure 4: Settling tanks 16
Figure 5: Moving bed Bio-reactor 17
Figure 6: Plastic beds 17
Figure 7: Trickling biofilter. 18
Figure 8: pH in the experiment 20

Figure 9: Variation of TDS in the experiment over culture period 21
Figure 10: Variation of EC in the experiment over culture period 22
Figure 11: Variation of DO in the experiment over culture period 22
Figure 12: Variation of TAN in the experiment over culture period 23
Figure 13: Variation of NO
2-
in the experiment over culture period 23
Figure 14: Variation of NO
3-
in the experiment over culture period 24
Figure 15: Variation of TSS in the experiment over culture period 25
Figure 16: survival rate of the shrimp after 8 weeks experiment. 26
viii

List of abbreviation
WLS: White Leg Shrimp
RAS: Recirculating Aquaculture System
FAO: World Food and Agriculture Organization
DLG: Daily Length Gain
DWG: Daily Weight Gain
SGR: Specific Growth Rate
SR: Survival Rate
TAN: Total Ammonia-Nitrogen
RBCs: Rotating Biological Contactors
SSA: Specific Surface Area
DO: Dissolve Oxygen
TSS: Total Solid Suspended
TDS: Total Dissolve Solid
EC: Electricity Conductivity

1


Chapter 1
INTRODUCTION
1.1 Introduction:
White leg shrimp (Litopenaeus vannamei), which is naturally distributed
along Pacific coasts of Central and South America, has become a primary
species currently being cultured in Asia. For more than 10 years, commercial
white leg shrimp farming has developed rapidly in China, Thailand, Indonesia
and Vietnam. As the result, there is a great change from the native black tiger
shrimp (Penaeus monodon) to this species in SouthEast Asia. In the year 2010,
global aquaculture for white leg shrimp was about 2.7 million tones (FAO,
2012).
In 2012, Vietnam’s shrimp export reached of 2.25 billion US dollars. White
leg shrimp played an increasing important role, and accounted for 32.8% of total
shrimp export volume and value (Report of shrimp in Viet Nam, 2012)
There are many methods to culture white leg shrimp; such as extensive,
semi-intensive, intensive and super-intensive, which was represented by low,
medium, high and extremely high stocking densities respectively. In many kinds
of farming, super-intensive is more and more popular nowadays. Because of
high density, super-intensive farming bring high profit to the farmers. However,
we have many important factors to care about, such as water quality, suitable
density, growth rate, environment, etc The requirement for shrimp culture
nowadays is a method to get high quality of shrimp without negative impacts on
the environment. The topic “Super intensive culture of white shrimp
(Litopenaeus vannamei), in a water circulation system at different stocking
densities” is needed to determine the sensible density and the growth rate of
shrimp in circulation system. Besides, it show the comparisons about the effect

of different densities on water quality , growth rate and survival rate.
Recirculating aquaculture systems (RAS) consist of an organised set of
complementary processes that allow at least a portion of the water leaving a fish
culture tank to be reconditioned and then reused in the same fish culture tank or
other fish culture tanks (Timmons et al.,2002).
Recirculating systems for holding and growing fish have been used by
fisheries researchers for more than three decades. Attempts to advance these
2

systems to commercial scale food fish production have increased dramatically in
the last decade although few large systems are in operation. The renewed
interest in recirculating systems is due to their perceived advantages such as
greatly reduced land and water requirements; reduced production costs by
retaining energy if the culture species require the maintenance of a specific
water temperature, and the feasibility of locating production in close proximity
to prime markets (Dunning et al., 1998).
A key to successful RAS is the use of cost-effective water treatment system
components. Water treatment components must be designed to eliminate the
adverse effects of waste products (Losordo et al. 1998). In recirculating tank
systems, proper water quality is maintained by pumping tank water through
special filtration and aeration and/or oxygenation equipment. Each component
must be designed to work in conjunction with other components of the system.
To provide a suitable environment for intensive fish production, recirculating
systems must maintain uniform flow rates (water and air/oxygen), fixed water
levels, and uninterrupted operation (Masser et al., 1999).
1.2 Objectives:
To determine the effects of stocking density of white leg shrimp on
growth, survival rate, to propose the suitable density for culture shrimp in
recirculating aquaculture system (RAS), which a way to protect environment in
aquaculture.

1.3 Research contents:
To identify the effect of RAS on water quality in intensive system.
Effect of stocking density growth and survival rate of white leg shrimp
rearing in RAS.

3



Chapter 2
LITERATURE REVIEW
2.1. Biological characteristics of white leg shrimp (Litopenaeus vannamei):
2.1.1. Classification
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Family: Penaeidae
Genus: Litopenaeus
Species: Litopenaeus vannamei

Figure 1: White shrimp (Litopenaeus vannamei)
(Source: www.fao.org)



4

2.1.2. Life cycle:
Adult Litopenaeus vannamei spawn in the ocean, releasing their eggs into

the water. The eggs hatch into non-feeding nauplius larvae, which last about two
days, before molting into zoea stage (4-5 days),mysis stage (3-4 days) and post-
larvae (10-15 days) (Barnes 1983; FAO, 2011). Post-larvae and juveniles tend to
migrate into estuaries, while adults return to the sea for spawning (FAO, 2011).
2.1.3. Growth characteristics:
Males become mature from 20 g and females from 28 g onwards at the age
of 6–7 months. L. vannamei weighing 30–45g will spawn 100,000–250,000 eggs
of approximately 0.22 mm in diameter. Hatching occurs about 16 hours after
spawning and fertilization. The first stage larvae, termed nauplii, swim
intermittently and are photopositive. Nauplii do not feed, but live on their yolk
reserves. The next larval stages (protozoea, mysis and early post-larvae
respectively) remain planktonic for some time, eat phytoplankton and
zooplankton, and are carried towards the shore by tidal currents. The post-larvae
change their planktonic habit about 5 days after molting into post-larvae, move
inshore and begin feeding on benthic detritus, worms, bivalves and crustaceans.
(FAO,2011)
2.1.4 Distribution:
The white leg shrimp (WLS) is native to the Eastern Pacific coast from
Sonora, Mexico in the North, through Central and South America as far South as
Tumbes in Peru, in areas where water temperatures are normally >20°C
throughout the year. (FAO,2011)
2.2.White leg shrimp (Litopenaeus vannamei) production in the world
White leg shrimp was introduced in Asia experimentally from 1978-79, but
beginning in 1996, L. vannamei was introduced in Asia on a commercial scale.
This started in Mainland China and Taiwan Province of China and subsequently
spread to the Philippines, Indonesia, Viet Nam, Thailand, Malaysia and India.
(RAP Publication 2004/10)
In 2008, 67% of the world production of cultured penaeid shrimp
(3,399,105 MT) consisted of L. vannamei (2,259,183 MT). Such dominance was
attributed to an 18-fold increase of production in Asia, from 93,648 MT in 2001

to 1,823,531 MT in 2008, which accounts for 82% of the total world production
of L. vannamei. China leads the world cultured L. vannamei production from
5

33% in 2001 to 47% in 2008 (1,062,765 MT), among which 51% (542,632 MT)
were produced in inland freshwater pond (Liao and Chin, 2011). Thailand
produced 299,000 MT, Vietnam 100,000 MT, Indonesia 103,874 MT of
L.vanamei I 2005 (Kongkeo, 2007).

2.3.White leg shrimp (Litopenaeus vannamei) production in Viet Nam:
In Viet Nam, white shrimp were cultured from 2000 but low production,
reached 84,320 tones (MARD, 2009).
Production of white shrimp in North, Central and South of Viet Nam in
2009 as the table below
Table 1: Production of white shrimp in North, Central and South of Viet Nam in
2009 (MARD, 2009)
Area
Yield (tones)
Percentage
North
6,058
7.2%
Central
63,554
75.4%
South
14,708
17.4%
Total
84,320

2.4.Application of recirculating water system in white shrimp culture:
Shrimp culture can help reducing pressure on overexploiting wild stocks, in
terms of natural resources protection. However, due to poor planning and
management as well as lack of appropriate regulations, shrimp aquaculture itself
may have several adverse environmental impacts. Since the effluents from
shrimp aquaculture typically are enriched in suspended solids, nutrients,
chlorophyll a and biochemical oxygen demand (BOD), the effluents often
contribute to eutrophication of waters nearby (Dierberg and Kiattisimkul, 1996;
Paez-Osuna et al., 1998). Diseases are also recognized as the biggest obstacle to
the future of shrimp aquaculture. Therefore, some methods have been developed
to help to improve the water quality in discharge water, such as recirculating
systems (Rosati and Respicio, 1999), constructed wetlands (LaSalle et al.,
1999), and better feeds and feeding practices (Cho and Bureau, 1997). These
6

innovations can reduce the load of organic matter and bio-solid in aquaculture
effluent (McIntosh & Fitzsimmons, 2003).
Recirculating systems have been used successfully in fish aquaculture for
the past 20 years, and now application in shrimp culture. RAS as more
sustainable shrimp culture: (1) Water circulates throughout the system lead to
the reduction of total water consumption; (2) RAS requires much less land than
a conventional aquaculture system; (3) RAS enables climate control and allows
year-round production with consistent volumes of product, giving RAS a
competitive advantage over outdoor systems; (4) Recirculating shrimp systems
are usually located inland and use municipal water for artificial preparation, so
risk of disease is reduced. Reduced water exchange also reduces disease
introduction. (5) Because water quality can always maintain at appropriate level,
shrimp can be grown in recirculating systems at very high densities. (Wenting
Sun, 2009). In Sam Courtland’s experiment, he demonstrated: 1) in a traditional

flow-through system, about 4% of females spawn per night, while in
recirculating systems, 6-8% spawn per night. In addition, females mature more
completely in recirculating systems, and produce more viable eggs per spawn. 2)
reduced cost of nauplii production. 3) reduced mortality of broodstock. 4)
Production based on low water exchange systems
2.5. Recirculating aquaculture systems (RAS)
Aquaculture has been on the frontline of public concerns regarding
sustainability. Different issues are raised, such as the use of fish meal and oil as
feed ingredients (Naylor et al., 2000), escapees of farmed fish from sea cages
into the wild and the discharge of waste into the environment (Buschmann et al.,
2006). Recirculation aquaculture systems (RAS) are systems in which water is
(partially) reused after undergoing treatment (Rosenthal et al., 1986). Each
treatment step reduces the system water exchange to the needs of the next
limiting waste component. Based on system water exchange it is possible to
distinguish between flow through (>50 m
3
/kg feed), reuse (1-50m
3
/kg feed),
conventional recirculation (0.1-1 m
3
/kg feed) and ‘next generation’ or
‘innovative’ RAS (<0.1 m
3
/kg feed). RAS have been developed to respond to
the increasing environmental restrictions in countries with limited access to land
and water. Furthermore, the new EU water management directive calls for sound
environmental friendly aquaculture production systems. RAS offer advantages
in terms of reduced water consumption (Verdegem et al., 2006), improved
opportunities for waste management and nutrient recycling (Piedrahita, 2003)

7

and for a better hygiene and disease management biological pollution control
(no escapees, Zohar et al., 2005), and reduction of visual impact of the farm.
These systems are sometimes referred to as ’indoor‘ or ’urban’ aquaculture
reflecting its independency of surface water to produce aquatic organisms. In
addition, the application of RAS technology enables the production of a diverse
range of (also exotic) seafood products in close proximity to markets (Masser et
al., 1999; Schneider et al. 2010), thereby reducing carbon dioxide (CO2)
emissions associated with food transport and the negative trade deficits related
to EU imports of seafood.
Despite its environmentally friendly characteristics and the increasing
number of European countries applying RAS technology, its contribution to
production is still small compared to (sea) cages, flow-through systems or
ponds. The slow adoption of RAS technology is in part due to the high initial
capital investments required by RAS (Schneider et al., 2006). High stocking
densities and productions are required to be able to cover investment costs. As a
consequence welfare concerns may arise (Martins et al., 2005). However, due to
the possibility to maintain a constant water quality, RAS may also contribute to
an improved welfare (Roque d’Orbcastel et al., 2009).
Managing disease outbreaks pose specific challenges in RAS in which a
healthy microbial community contributes to water purification and water quality.
Minerals, drug residues, hazardous feed compounds and metabolites may
accumulate in the system (Martins et al. 2009) and affect the health, quality and
safety of the farmed animal. How these different factors interact and influence
the fish and the various purification reactors is still poorly understood.
Furthermore, RAS historically developed producing freshwater fish species that
are rather tolerant to poor water quality. The expansion of RAS being used for
the production of marine and brackish water species often focuses on hatchery
operations which pose extra requirements on water quality and require further

innovations in RAS technology.
Taken together, these examples reflect environmental, economic and
social challenges to the sustainability of RAS. Considering these challenges, an
European effort was made (e.g. CONSENSUS, www.euraquaculture.info/,
SUSTAINAQUA, www.sustainaqua.com; SUSTAINAQ www.sustainaq.net;
AQUAETREAT www.aquaetreat.org) to identify the most relevant
sustainability issues for RAS, to quantify sustainability in RAS and to develop
new technologies to improve sustainability of RAS. This review summarizes
recent developments that contributed to the environmental sustainability of the
8

aquaculture production in RAS in Europe. These developments are either
technology (e.g. incorporation of new water treatment units that reduce water
exchange rates and reduce/concentrate waste) or ecology driven (e.g. biological
re-utilisation of wastes).
2.5.1Principle of RAS:
According to Sustain Aqua ( 2006), recirculating aquaculture systems
(RAS) are systems in which aquatic organisms are cultured in water which is
serially reconditioned and reused
Recirculation Aquaculture Systems (RAS) are land-based systems in
which water is re-used after mechanical and biological treatment so as to reduce
the need for water and energy and the discharge of nutrients to the environment.
These systems present several advantages, such as: water saving, a rigorous
control of water quality, low environmental impacts, high biosecurity levels and
an easier control of waste production as compared to other production systems.
The main disadvantages are high capital costs, high operational costs,
requirements for very careful management (and thus highly skilled labour
forces) and difficulties in treating disease. RAS is still a small fraction of
Europe’s aquaculture production and is most significant in the Netherlands and
Denmark.

Based on Rowan University (2006), the most important consideration in
recirculating systems design is the development of an efficient water treatment
system. Recirculating production systems must be designed with a number of
fundamental waste treatment processes. These processes, referred to as "unit
processes," include the removal of waste solids (both feces and uneaten feed),
the conversion of ammonia and nitrite-nitrogen (a non-toxic form of dissolved
nitrogen), the addition of dissolved oxygen to the water, and the removal of
carbon dioxide from the water. With less robust species, and depending upon the
volume of new water used, a process to remove fine and dissolved solids, as
well as a process to control bacterial populations, may need to be applied. Figure
2.1 shows these unit processes and some common components used to perform
these operations.
9


Figure 2. Required unit processes and typical components used in recirculating
aquaculture production systems (Source: Losordo, et al., 1998).
2.5.2 Recirculating System Economics
While considerable resources have been expended on recirculating
systems in the private sector, there is very little data available on the economics
of fish production in commercial recirculating systems. The North Carolina Fish
Barn project has provided a non-biased look at some of the capital and
operational costs of these production systems. This section takes a brief look at
some of the important areas to be considered when evaluating recirculating fish
production technology for commercial operation.
From a variable cost (feed, fingerling, electricity, and labor cost)
standpoint, the cost of producing fish in recirculating systems is not that much
different from other production methods. Where pond culture methods require a
great deal of electricity (at least 1 kW / acre of pond) for aeration during the
summer months, recirculating systems have more even and steady electrical

loads over the entire year. While it may appear that recirculating systems require
more labor than ponds (in system upkeep and maintenance), the difference
would be minimal if the long hours of nightly labor for checking oxygen in
10

ponds, moving emergency aerators around, and harvest effort are taken into
account.
Feed cost is an area in which recirculating systems can actually have an
advantage. Tank production systems generally can produce a better feed
conversion ratio than pond systems. This is mainly due to the fact that the
producer can monitor the fish population and feed consumption more accurately
in tank systems. Using the particle trap technology that has been used in the
North Carolina Fish Barn system, feeding can be even more precisely
controlled. Given that feed is the largest single variable cost item in fish
production, close attention to feeding can yield a major economic advantage for
the recirculating production system. The problem with recirculating technology
is that the capital cost of these systems is higher (Rowan University, 2006)
2.6. Biofilters
In the aquaculture environment, nitrogen is of primary concern as a
component of the waste products generated by rearing fish. In particular, fish
expel various nitrogenous waste products through gill diffusion, gill cation
exchange, urine, and feces. The decomposition of these nitrogenous compound
is particularly important in intensive recirculating aquaculture systems (RAS)
because of the toxicity of ammonia, nitrite, and to some extent, nitrate. The
process of ammonia removal by a biological filter is called nitrification, and
consists of the successive oxidation of ammonia to nitrite and finally to nitrate.
The reverse process is called denitrification and is an anaerobic process where
nitrate is converted to nitrogen gas. Although not normally employed in
commercial aquaculture facilities today, the denitrification process is becoming
increasingly important as stocking densities increase and water exchange rate

are reduced, resulting is in excessive level of nitrite in the culture system.
There is considerable debate as to the most appropriate biological filter
technology for intensive aquaculture applications. An ideal biofilter would
remove 100% of the inlet ammonia concentration, produce no nitrite, require a
relatively small footprint, use inexpensive media, require no water pressure or
maintenance to operate, and would not capture solids. Unfortunately, there is no
one biofilter type that meet all of these ideals, each biofilter has it own strength
weaknesses and areas of best application. Large scale commercial recirculating
systems have been moving towards using granular filters (expanded beds,
fluidized beds and floating bead beds). However, there are many type of biofilter
that are commonly used in intensive RAS: submerged biofilter, trickling
11

biofilter, rotating biological contactors (RBC), floating bead biofilter, dynamic
bead biofilter, and fluidized bebiofilter.
2.6.1. Trickling biofilters:
Trickling biofilter operate in the same way at submerged biofilters, except
the waste water flows downward over the media and keeps the bacteria wet, but
never completely submerged (Wheaton et al, 1991). Since the void spaces are
filled with air rather than water, the bacteria never become oxygen – starved.
Trickling filter have been widely used in aquaculture, because they are easy to
constructs and operate, are self-aerating and very effective at off gassing carbon
dioxide, and have a moderate capital cost. In municipal waste water treatment
systems, trickling filter were traditionally constructed of rock, but today most
filter use plastic media, because of its low weight, high specific surface area
(100 – 300 m
2
/m
3
) and high void ratio (>90%). A range of trickling filter design

criteria has been reported. Typical design values for warm water systems are
hydraulic loading rates of 100 to 250m
3
/day per m
2
; media depth of 1 – 5m;
media specific surface area of 100 – 300m
2
/m
3
; and TAN removal rate of 0.1 to
0.9g/m
2
per day surface area. Trickling biofilters have not been used in large
scale cold water system, probably due to the decrease in nitrification rates that
occurs at the lower water temperatures and the relatively low specific surface
area of the media. They have found a use in smaller hatchery systems where
loads tend to be low and variable (Wilton, 2001).
2.6.2. Fluidized – beds biofilter
Fluidized – beds biofilter have been used in several large scale
commercial aquaculture system (15m
3
/min to 150m
3
/min or 400 to 4000 gpm).
Their chief advantage is the very high specific surface area of the media, usually
graded sand or very small plastic beads. Specific surface areas range from 4000
to 45000m
2
/m

3
for sand versus 100 to 800m
2
/m
3
for trickling biofilter media and
1050m
2
/m
3
for bead filter media. The fluidized – bed biofilter can easily be
scaled to large size, and are relatively inexpensive to construct per unit treatment
capacity (Sumerfelt and Wade, 1998, Timmons et al, 2000). Since the capital
cost of the biofilter is roughly proportional to its surface area, fluidized – beds
biofilter are very cost competitive and are relatively small in size compare to
other types of biofilters (Summerfelt, 1999). Fluidized – beds biofilter are
efficient at removing ammonia; typically removing 50 – 90% of the ammonia
during each pass in cold and cool – water aquaculture system (Summerfelt et al,
12

2001). Nitrification rate for cold water system range from 0.2 to 0.4kg TAN per
day per cubic meter of expended bed volum (Timmons and Summerfelt, 1998).
In warm water system, TAN removal rate range from 0.6 to 1kg per day per
cubic meter expanded bed volum (Timmons and Summerfelt, 1998). The main
disadvantages of fluidized – beds biofilters are the high cost of pumping water
through the biofilter and that a fluidized – beds biofilter does not aerate the
water, as do trickling towers and RBC’s. Additional disadvantages are that they
can be more difficult to operate and can have serious maintenance problems,
usually due to poor suspended solids control and biofouling.

Pro’s
Con’s
Trickling biofilter

Very simple design and construction
requirements
Currently a very popular method of
biofiltration in the waste water
industry, which should improve
material availability and cost
Allow for passive aeration and CO
2

removal concurrent with biofiltration.
Media and design assistance is
currently available from reputable
commercial vendor facilitating the
design effort.
System using these types of filters tend
to be extremely stable
Some biofilm sheared off is large
enough to be problematic and many
systems integrate post-biofiltration
mechanical filtration for this reason.
Filter using this media type tend to be
very large in high feed load coldwater
systems.
Media itself can be costly due to low
specific surface area.

Rotating Biological Contactors
(RBCs)

Low energy to move fluid across
media.
Provides passive aeration for
nitrification process and limited CO
2

control.
Can allow for efficient facility layout
and combination of several processes
Can be expensive due to low specific
surface area for large scale facilities.
Mechanically more complex than most
other biofilter.
Subject to rotational wear on bearing
surfaces.

13

(mechanical filtration, biofiltration,
aeration and pumping in one common
sump.
Amenable to modularization, which
can be useful for development of
scalable facilities.
Bead filters

Well developed product available from

reputable commercial vendors. Can
simplify system design and
construction.
Can be combined with other filter
types in interesting hybrid system as
alternative design method.
Can in some case improve fine particle
removal rate in well design system.
Amenable to modularization, which
can be useful for development of
scalable facilities.
Can be expensive due to low specific
surface area for large scale facilities.
Relatively high head loss across filter
can be an operational cost
consideration.
Variable head loss across system can
be problematic in system without
variable speed pumps.
Has potential to leach nutrients into
system or to fuel heterotrophic bacteria
growth if not installed with-filtration
system or is backflushed infrequency.
Fluidized – Bed Biofilter

Very economical to build from
commercially available materials.
Large amount of design effort specific
to coldwater systems using these types
of filters.

Raw filter media has very high specific
surface area at low cost, which allows
for very conservative design allowing
for inherent capacity for expansion or
load fluctuation.
Widest installed base of coldwater
biofilter offers large operational and
design experience base to draw form.
Can be field built using a variety of
proven methods or purchased from
established and reputable vendors
Can have problem with media
carryover (initial fines) on system
start-up.
There are historical anecdotal reports
of intermittent bed motility and system
crashes.
Can have problems with restarting if
not designed to account for bed re-
fluidization and distribution
manifold/lateral flushing.
Media density changes over time with
biofilm accumulation in fine sand filter
typical of coldwater systems, which
necessitates a bed growth management
strategy.
Some systems can require relatively
14

opening many design and construction

options for facility designers or
operator.
expensive plumping to ensure that
media is not back-siphoned on pump
shut-down or power failure.
Table 2. Advantages and disadvantages of commonly used biofilter (Wilton,
2001)