Brief information about biofloc technology

Flocs (aggregates) are suspended growth in ponds consists of phytoplankton, algae, bacteria, proto­zoans, and other kinds of particulate organic matter such as feces and uneaten feed. Typical flocs are irregular by shape, have a broad distribution of particle size (0,1-2 mm), are fine, easily compressible, highly porous (up to more than 99% porosity) and are permeable to fluids.

Bioflocs technology (BFT) is the technique of enhancing water quality through the addition of extra carbon to the pond, through an external carbon source or elevated carbon content of the feed. Few types of biofloc systems have been used in commercial aquaculture. The two basic types are those that are exposed to natural light and those that are not.

First, biofloc systems exposed to natural light include outdoor, lined ponds or tanks for the culture of shrimp or tilapia and lined raceways for shrimp culture in greenhouses. A complex mixture of algal and bacterial processes control water quality in such “greenwater” biofloc systems. Most biofloc systems in commercial use are greenwater.

Second, biofloc systems (raceways and tanks) have been installed in closed buildings with no exposure to natural light. These systems are operated as “brown- water” biofloc systems, where only bacterial processes control water quality.

Figure 1. Overview of possible parameters of bioflocs technology and their probable effects. 

The conditions of bioflocs technology system are:

1. Limited the water exchange
2. Organic residues accumulate
3. Mix and aerate are typical features of biotechnological industry.
4. Ideal conditions for bacteria
5. Bacteria control water quality and improve disease protection
6. Fish/shrimp eat bacteria
7. Feed is recycled

Heterotrophic bacteria feed on organic matter. Basically as this flow:

C₆H₁₂O₆ + 6O₂ –> 6 CO₂ + energy

But bacteria are made of protein so they need nitrogen. They use the chemicals energy in organic substrates and consume oxygen (though there are anaerobic bacteria). Then heterotrophic bacterial growth is stimulated and nitrogen uptake through the production of microbial proteins takes place. If carbon and nitrogen are well balanced in the solution, ammonium in addition to organic nitrogenous waste will be converted into bacterial biomass.

The bacteria now take the nitrogen from the water and control water quality. The microbial activity degrade the waste, part of it to CO₂ and about 59% to microbial biomass. Normally, there is no enough nitrogen in ponds for new cell production. However, we can add carbon rich and protein poor material (carbohydrate, CH compound) such as starch or cellulose (flour, molasses, and cassava). The additional purpose for keep C/N ratio higher than 10.

The bacteria makes an important part of food chain. We can manipulate the microbial activity toward the control of nitrogen in the pond. They seem to improve disease protection.

Reference:

Avnimelech, Y. 2009. Biofloc Technology – A practical guide book. The World Aquaculture Society, Baton Rouge, Louisiana, United States. 182 pp.

Crab, R. 2010. Bioflocs technology: an integrated system for the removal of nutrients and simultaneous production of feed in aquaculture. PhD thesis, Ghent University, Belgium.

Hargreaves, J. A. 2013. Biofloc production system for aquaculture. Southern regional aquaculture center Publication No. 4503.