Microbubbles and their generation are of utmost importance in many scientific fields and have a wide array of practical applications from waste treatment and engineering to this article’s subject, aquaculture. Microbubble aeration has been shown to have profound positive effects on the growth of biofloc cultures and farmed shrimp, and with the right type of generator, it can be applied to other forms of aquaculture.
Microbubbles are bubbles that are smaller than one hundredth of a millimetre in diameter, but larger than one micrometre.
They have a wide range of practical applications such as wastewater treatment, disinfection, engineering, medical uses and in this case, aquaculture.
There is a potential to greatly increase an aquafarm’s production through the application of microbubble generators that increase the dissolved oxygen in the tanks, improving the aquatic life’s metabolism.
Biofloc technology systems, in particular, can greatly benefit from this. Biofloc is an alternative fish farming system where recycling and reuse of waste nutrients as fish food is employed. First developed in the 1970s, this system’s principal approach is to culture suitable microorganisms along with aquatic life (fish or shellfish) to create a sustainable ecosystem.
As such, biofloc systems utilize the nitrogen cycle in order to encourage the growth of beneficial bacteria colonies, who feed on organic waste (faeces, excess feeds and dead matter) and produce nutritional aggregates that can be fed upon by fish or crustaceans.
Whiteleg shrimp (Litopenaues vannamei) can greatly benefit from biofloc systems, given that it is the single most popular commercial crustacean species in the world but has many concerns attached to its intensive rearing such as water quality control, environmental and ecological sustainability, cost-effectiveness and disease-free production. Concerns that can be addressed by the use of bioflocs.
Bioflocs require extensive and efficient oxygenation in order to maintain the nitrogen cycle and generate sufficient mixing intensity to keep bioflocs in active suspension for good water quality control, something that microbubble generators can provide.
A group of researchers, which includes University of Malaya’s Assoc. Prof. Dr. Poo Balan Ganesan, sought to prove this idea by investigating the effects of microbubble aeration on biofloc formation, water quality and the growth of whiteleg shrimps.
“Doing something related to living stock makes me feel excited,” says Dr. Poo, “On top of that, this is a society impact orientated work for food security and sustainability.”
Based on the results, shrimps cultured in tanks utilising microbubble aeration grew larger and faster than shrimps without. Additionally, microbubble aeration has significantly enhanced the growth of bioflocs and heterotrophic bacteria.
The design of the microbubble generator is equally in ensuring the highest level of effectiveness and efficiency. Indeed, factors such as the throat length/diameter of the generator’s nozzle have effects on the size of the bubbles produced.
The simplest and most practical design utilizes air injection combined with a Venturi-type geometry system (a system that speeds up the flow of water by constricting it in a cone-shaped tube) to produce large amounts of microbubbles at a rapid rate.
Dr. Poo Balan believes that the data from his studies can help encourage aquafarmers to adopt an intensive/super-intensive-nursery-culture integrated with a microbubble aeration system and biofloc technology for better productivity.
Wilson, D.A., Pun, K., Ganesan, P.B., Hamad, F. (2020) Geometrical Optimization of a Venturi-Type Microbubble Generator Using CFD Simulation and Experimental Measurements. Designs, 5(1), 4.
Yan, S.L., Ganesan, P.B., Varman, M., Hamad, F.A., Krishnasamy, S. (2020) Effects of microbubble aeration on water quality and growth performance of Litopenaeus vannamei in biofloc system. Aquacultural Engineering, 93(2021), 102159.