presentation1 biofloc

8/17/2019 Presentation1 biofloc

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Biofoc ProductionSystems orAquaculture


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Composition and nutritional value of bioflocs

Bioflocs are aggregates (flocs) of algae, bacteria,

protozoans, and other kinds of particulate organic

matter such as feces and uneaten feed.The biofloc community also includes animals that are

grazers of flocs, such as some zooplankton and

nematodes. Large bioflocs can be seen with the naked

eye, but most are microscopic. Flocs in a typicalgreenwater biofloc system are rather large, around !

to "!! microns, and will settle easily in calm water .


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The nutritional #uality of biofloc to cultured animalsis good but rather $ariable. The dry%weight protein

content of biofloc ranges from " to ! percent, with

most estimates between &! and ' percent. Fat content

ranges from !. to percent, with most estimates between and percent.

ried bioflocs ha$e been proposed as an ingredient to

replace fishmeal or soybean meal in a#uafeeds. The

nutritional #uality of dried bioflocs is good, and trials

with shrimp fed diets containing up to &! percent dried

bioflocs show promise


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Suitable culture species* basic factor in designing a biofloc system is the species to

be cultured. Biofloc systems work best with species that are able

to deri$e some nutritional benefit from the direct consumption of

floc. Biofloc systems are also most suitable for species that can

tolerate high solids concentration in water and are generally

tolerant of poor water #uality. +pecies such as shrimp and tilapiaha$e physiological adaptations that allow them to consume

biofloc and digest microbial protein, thereby taking ad$antage of

biofloc as a food resource. early all biofloc systems are used to

grow shrimp, tilapia, or carps. Channel catfsh and hybridstriped bass are examples o fsh that are not goodcandidates or biooc systems because they do nottolerate water with very high solids concentrationsand do not have adaptations to flter solids rom

water.


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systems

Few types of biofloc systems ha$e been used in

commercial a#uaculture or e$aluated in research. Biofloc

systems e-posed to natural light include outdoor, a

comple- mi-ture of algal and bacterial processes control

water #uality in such greenwater/ biofloc systems. 0ost

biofloc systems in commercial use are greenwater.

These systems are operated as brown% water/ biofloc

systems, where only bacterial processes control water

#uality.The specifications and performance of $arious biofloc

production systems are discussed in more detail at the end

of this publication.


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Denitrification and sludge treatment

*lkalinity can be reco$ered in denitrification units. itrateaccumulates in most intensi$e biofloc systems because of

ongoing nitrification. 1f unchecked, nitrate concentration

reflects the cumulati$e feed loading to the system. itrate

accumulation can be tempered by dilution through water

e-change, but this defeats the purpose of intensi$e water use

and reduces biosecurity.

enitrification units are used as part of a water conser$ation

and biosecurity strategy where it is also a cost issue to

conser$e salts. This is an acute need in superintensi$esaltwater systems for shrimp, especially those located inland.

Furthermore, the discharge of saline effluent is restricted or

regulated in many areas, especially inland.


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enitrification units are operated under generally

#uiescent and ano-ic conditions. +olids can beshunted to a side%stream tank and allowed to

accumulate. * low flow of culture water, sufficient to

pro$ide a detention time of to " days, is ade#uate to

control nitrate concentration. +olids accumulation will

reach a steady state.


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Problems+uspended solids are central to the function of biofloc systems.

The capacity to control solids concentration depends on system

configuration. 2-cessi$e solids concentration is counter%

producti$e because solids can log gills of fish or shrimp.

1t also increases the energy re#uired for mi-ing to keep solids in

suspension and aeration to meet the o-ygen demand of ele$atedwater respiration. 2-cessi$e solids concentration also means that

the response time in the e$ent of system failure is $ery short,

often less than hour. 3ccasionally and unpredictably bioflocs

will de$elop that include large numbers of filamentous bacteria.This so%called filamentous bulking/ effect makes flocs slow to

settle and makes it difficult to control solids concentration.

Filamentous bacteria can also clog shrimp gills and cause

mortality.


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*s in most recirculating a#uaculture systems,

nutrients and minerals (especially metals) accumulatein the water of intensi$ely managed biofloc systems.

1n shrimp raceways with low water e-change rates,

nitrate can accumulate to se$eral hundred mg4L, a

le$el that reduces shrimp feed consumption. 1ncludingthe capacity for denitrification in intensi$ely managed

biofloc systems is recommended. 1n marine systems,

maintaining a nitrate concentration of about ! mg4L

is an effecti$e way to minimize the production ofhighly to-ic hydrogen sulfide.

presentation1 biofloc

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