Over the last couple of weeks, we have talked about the different management techniques developed to produce a more sustainable shrimp aquaculture. As we’ve seen, there are two main issues towards achieving this objective: better use of water (a.k.a. reducing the hydric footprint) and better feeding performance, reducing pressure on reduction fisheries, improving food safety, and reducing production costs.
The first method developed to improve the performance, productivity, and profitability per unit of area was the clear water RAS or RAS, which we discussed two weeks ago. As we mentioned, the energy used to treat water to recycle it is too high on occasions. Furthermore, this technique tackles the issue of the hydric footprint but does not look into the feeding efficiency problems.
The second management technique developed that we discussed was the biofloc technology systems (BTS or biofloc). As we mentioned, this technique tackles both hydric footprint by reducing the amount of water discharged and the feed efficiency by promoting the growth of floccules which function as an additional source of protein obtained when treating the organic matter.
To understand the idea behind the bio-RAS it’s crucial to understand the way biofloc works, so we invite you to check out our BTS paper. Let us remember that the idea behind biofloc is to promote the growth of specific bacteria that use ammonia and nitrates to grow in the pond, cleaning the water and producing protein. But there is a catch, the biological characteristics of the different bacteria involved in the process are different between themselves and, more importantly, different from shrimp. That means that the optimal oxygenation, mixing, and total suspended solids for bacterial growth can be other than that of shrimp. When we “improve” water quality in our ponds, we’ll always do it to promote shrimp’s growth, but this could be to the detriment of bacterial growth and water treatment, meaning less protein production and worst ammonia reduction, less bacterial growth and higher risk of diseases and mortalities.
Furthermore, the growth of bioflocs in the pond increases the possibility of producing sludges which, if poorly managed, can produce toxic metabolites, increasing water toxicity and fastly deteriorating water quality.
In a RAS, we can compartmentalize water treatment. Water is treated in different modules through different processes (biofiltration, degasification, oxygenation, filtration, etc.). We can modify water quality parameters in each of the modules and then recirculate it through the system until it reaches this module again. Each water treatment process requires equipment, increasing energy consumption, and initial investment, allowing a more biosecure production with a small hydric footprint.
The idea behind Bio-RAS is to combine both systems looking to gather the benefits of each system tackling their problems.
What is a Bio-RAS
A Bio-Ras is then a hybrid technology that combines the principles of BTS with those of a RAS. As opposed to classic BTS, where the processes are all developed in the pond, Bio-RAS uses a separate module (a biofilter) to capture and decompose the sludges generated by fostering specific microbes, obtaining floccules that are then reintroduced to the rearing ponds recirculating the water. In this system, the separate biofilter allows better control of the water turbulence and oxygenation, which optimizes bacterial metabolic rate, creating floccules and improving the recirculated water.
By only adding an extra recirculation module, water treatment costs, energy consumption, and initial investment are significantly reduced. This biofilter includes several RAS modules at once; here, we eliminate the ammonia resulting from shrimp metabolic processes by promoting the growth of nitrifying and denitrifying bacteria, increasing oxygen, and degasification by increasing water mixing and aeration. Furthermore, due to the probiotic bacteria and exclusive competition, there is no need to sterilize the water, and mechanical filtration is reduced to the water inlet instead of being a component of the recirculation system.
At the same time, we include an essential component of the BTS lacking in RAS, the feed efficiency improvement. The FCR is severely improved by creating high protein bioflocs of bacteria, yeasts, and other microorganisms that are beneficial for shrimp growth, even achieving FCRs lower than 1.
Finally, by separating the sludges promptly, the risks of unbalance and collapse of the BTS are reduced, making management more manageable and improving the farm’s profitability, reducing some of the difficulties presented by the original biofloc system.
Bio-RAS and sustainability
The benefits of the bio-RAS in terms of environmental impact combine those of a clear water RAS and a BTS, significantly reducing the hydric footprint, minimizing the pollutant effluents, and allowing for water treatment previous to discharge minimizing ecosystem disruptions. Furthermore, this technique is better suited for tanks instead of ponds, which means this activity and be developed indoors or inland, provided that water quality standards are met. The use of tanks discourages the implementation of earthen ponds, reducing the risk of earth eutrophication and potentially reducing the impacts on mangrove forests and coastal ecosystems.
The main downside of the Bio-RAS is the space needed for biofiltration. According to the limited amount of information on this technology, a 1:1 ratio needs of biofiltration is required (or recommended); this means that for each m3 of rearing tanks, there is a need for an additional m3 of biofilter, significantly reducing the space used for production and the productivity per unit of area. A 3:1 ratio has been tested in nile tilapia providing good results; hence there is a need to calibrate and study the optimal space of biofiltration needed per ton of biomass in shrimp production to evaluate the feasibility of this technique.
In economic terms, Boi-RAS is supposed to have better FCRs and specific growth rates than any of the previous management systems described, which can make a more profitable farm, but the investment required for a biofilter means that there is a need to double the infrastructure (in terms of tanks). Since the performance is not doubled when compared to a classic BTS, the profitability still opts for the traditional BTS
Bio-RAS does not represent a viable option compared to BTS at this point, but this can change in the future if biofilter requirements are optimized, and infrastructure develops. The fact that separate sludge treatment enhances productivity per tank and reduces risk is an exciting window of research to improve the process and obtain a new management system that can rival the current techniques, improving the sustainability of the industry.