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

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

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 NO2- 23

v

4.1.7 NO3- 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 NO2- in the experiment over culture period 23

Figure 14: Variation of NO3- 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):

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

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

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 m3/kg feed), reuse (1-50m3/kg feed), conventional recirculation (0.1-1 m3/kg feed) and ‘next generation’ or

‘innovative’ RAS (<0.1 m3

/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

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

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 m2/m3) 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 250m3/day per m2; media depth of 1 – 5m; media specific surface area of 100 – 300m2/m3; and TAN removal rate of 0.1 to 0.9g/m2 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 (15m3/min to 150m3/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 45000m2/m3 for sand versus 100 to 800m2/m3 for trickling biofilter media and 1050m2/m3 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,

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 CO2

removal concurrent with biofiltration

Media and design assistance is

currently available from reputable

commercial vendor facilitating the

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 CO2

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)