RAS discharge treatment is obligatory

Aquaculture is an important food source for meeting present and future global consumption demands.

Today, one billion people worldwide rely on fish as their primary source of animal protein.

The aquaculture sector supplies more than half of the fish consumed by humans today by providing farm-raised fish to replace diminishing wild species.

When we settle a fish farm it’s important to realize that every production facility has its wastes, so the recirculating aquaculture systems are here to accomplish this mission.

Thanks to RAS, aquatic living is on the safe side.

What is RAS? How does it work? We will talk about its amazing technology in the coming Lines.

The aquaculture boom paves way for the water treatment market

Water treatment is critical to effective aquaculture, according to new Lux Research (LR) studies, and demand for water treatment is predicted to nearly double from $7.2 billion in 2014 to $13.3 billion by 2030.

Without water treatment, fish populations swim in a nasty cocktail of dead fish, feed, feces and nutrients, breeding illness and threatening entire harvests; modern treatment systems are required for the market to flourish.

At the moment, advanced reuse systems account for only 4.5 percent of the whole aquaculture market, with pond culture dominating production.

According to this study, the United Kingdom added 25 RAS facilities between 2000 and 2013, while Norway’s Nofima, Europe’s largest aquaculture research facility, has installed over 1,000 tanks and hatcheries and Denmark expects 90 percent of its aquaculture production to come from recirculating systems.

Aquaculture wastewater

Aquaculture effluent contains suspended particles, nitrogen compounds, and phosphorus compounds.

Wastewater treatment is critical in aquaculture systems to maintain a healthy fish culture while also avoiding negative environmental effects.

Traditional wastewater treatments have several limitations in aquaculture systems due to the economic and energy burden they impose.

Furthermore, existing treatment methods for aquaculture wastewater, such as aerobic and anaerobic treatment methods, emit greenhouse gases such as CO2 and CH4, and the nutrient resources in wastewater cannot be reused efficiently.

Aquaculture and water treatment for sustainability

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According to much research, the amount of total energy and water utilized in the seafood supply chain with the least environmental impact is critical to maintaining sustainability.

Traditional treatment procedures must be improved for the aquaculture business to remain sustainable.

The aquaculture industry, a key contributor to the global food supply, is facing considerable challenges, with the availability and accessibility of quality water being a major issue.

Maintaining sufficient water quality for good marketable products and limiting the negative effects of aquaculture effluent are critical requirements for long-term sustainability.

The replacement of wastewater, which requires a huge amount of fresh water, is a critical challenge for conventional wastewater treatment systems.

Recirculating aquaculture systems (RAS) address the constraints of traditional systems by reusing wastewater and so decreasing the use of fresh water.

The RAS system employs 10% of the total volume of water as additional fresh water for large-scale fish production, making it more sustainable than traditional techniques.

Furthermore, it lowers environmental contamination caused by wastewater, which is a sustainable method of aquaculture development.

What are recirculating aquaculture systems?

Recirculating aquaculture systems (RAS) are used for fish production where water exchange is limited and the use of biofiltration is necessary to decrease ammonia toxicity.

Other types of filtration and environmental control are often also mandatory to keep the water clean and provide a suitable habitat for fish.

The main benefit of RAS is that it’s capable of decreasing the need for fresh, clean water while still maintaining a healthy environment for fish.

Advantages of RAS 

When compared to pond aquaculture methods, it requires less water, reduced the volume of wastewater effluent and reduces land requirements owing to high stocking density.

In addition to flexibility in site selection, independence from a large, clean water source, and Improved biosecurity and disease outbreak treatment.

To maximize production efficiency, the ability to closely monitor and manage environmental conditions is required.

Similarly, freedom from changing weather and environmental factors.

Disadvantages of RAS 

High operational expenses, mostly owing to electricity and system maintenance; and the requirement for highly skilled personnel to monitor and operate the system.

Greenhouse gas emissions are higher than in non-recirculating aquaculture.

Special types of RAS


Aquaponics is the practice of growing both plants and fish in a RAS.

In this kind of system, the plants also purge the water of ammonia created by the fish by converting it to nitrate.

Fish in an aquaponics system successfully fertilize the plants, resulting in a closed-looped system with minimal inputs and waste production.

The benefit of being able to harvest and sell a variety of crops is offered by aquaponics.

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Home aquariums and inland commercial aquariums are examples of RAS where the fish stocking density is relatively low and the water quality is closely monitored. Instead of generating food, these systems aim to display the fish.

However, to lessen the requirement for water exchange and to preserve water purity, biofilters and other methods of water treatment are still utilized.

Ammonia chemistry and removal techniques in RAS

Good water quality is essential to the development and growth of aquatic species.

The ammonia levels in the water are an important property.

Ammonia is highly soluble in water and originates from nitrogenous waste.

Fish and crabs expel ammonia through gill diffusion, cation exchange, and excretion of urine and feces.

Ammonia can also originate from decaying matter from uneaten feed or dead crabs that were not removed from the systems.

The more feed and crude protein there is, the more ammonia is produced.

Biofilters are the treatment equipment that removes ammonia in recirculating aquaculture systems.

The biofilters utilize microbes to clean up the excess ammonia in the water and convert them into Nitrite and Nitrate which are less harmful to mud crabs.

RAS water treatment processes

To preserve water quality in intensive fish farming operations, a range of treatment methods are used.

After exiting the fish-holding vessel, the water is cleaned for particles before entering a biofilter to convert ammonia.

Degassing and oxygenation follow, which is frequently followed by heating/cooling and sterilizing.

Solids removal

In addition to treating the liquid waste excreted by fish the solid waste must also be treated, this is done by concentrating and flushing the solids out of the system.

Removing solids reduces bacteria growth, oxygen demand, and the proliferation of disease.

The simplest method for removing solids is the creation of a settling basin where the relative velocity of the water is slow and particles can settle at the bottom of the tank where they are either flushed out or vacuumed out manually using a siphon.

Typical RAS solids removal methods include using a sand or particle filter where solids become lodged and can be periodically backflushed out of the filter, or using a mechanical drum filter where water is run over a rotating drum screen that is periodically cleaned by pressurized spray nozzles and the resulting slurry is treated or discharged.


The water system oxygenation is a crucial part to obtain high production densities.

Fish, like bacteria colonies in the biofilter, require oxygen to consume food and develop.

Dissolved oxygen levels can be increased through two methods, aeration and oxygenation.

PH control

All RAS PH must be closely watched and managed.

The bio filter’s initial stage of nitrification depletes alkalinity and lowers the system’s pH.

It’s essential to maintain the pH in a healthy range (5.0–9.0 for freshwater systems) to protect the well-being of the fish and the biofilter.

Usually, adding alkalinity in the form of lime (CaCO3) or sodium hydroxide regulates PH (NaOH).

Temperature control

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Each type of fish has a preferred temperature range between which it will suffer poor health impacts and eventually perish.

Submerged heaters, heat pumps, chillers and heat exchangers are used to regulate temperature.

To maintain a system at the ideal temperature for optimum fish output, all four can be used.


Disease outbreaks occur more readily when dealing with the high fish stocking densities typically employed in intensive RAS.

Outbreaks can be reduced by operating multiple independent systems with the same building and isolating water-to-water contact between systems by cleaning equipment and personnel that move between systems.

Also, the use of an Ultraviolet (UV) or ozone water treatment system reduces the number of free-floating viruses and bacteria in the system water.

These treatment systems reduce the disease loading that occurs on stressed fish and thus reduce the chance of an outbreak.

Maintaining water quality in RAS

Maintaining variables within ranges that encourage growth while limiting sickness in cultured animal is the fundamental concept of knowing water quality in RAS.

Various types of nitrogen may need to be measured daily or weekly, depending on the intensity of feeding, while dissolved oxygen is routinely measured frequently throughout the day and evening.

The fact that harmful nitrogen accumulation and aeration needs are based on feed amounts that are placed in the RAS and not the harvestable biomass is one of the rules that must be addressed when talking about water quality in RAS.

The simplest solution to avoid issues with any variable affecting water quality may be to simply interchange water by bringing in water that is oxygen- and nitrogen-free and dumping nutrient-rich trash and carbon dioxide into nearby waterways.

Temperature: When talking about water quality in RAS, the temperature is the most specific parameter to comprehend and control.

The more productive and financially feasible a RAS system can be, the nearer it comes to the optimal temperature for a cultured animal.

Oxygen and carbon dioxide: For fish and shrimp, oxygen levels are typically maintained at a level above 4 mg/L and higher for other more sensitive species.

Higher carbon dioxide levels make lower oxygen levels far more harmful because they prevent aquatic species from breathing normally.


[1] https://www.asc-aqua.org/explained-what-is-ras-aquaculture/

[2] https://thefishsite.com/articles/maintaining-water-quality-in-ras-the-essentials

[3] https://www.ras-aquaculture.com/post/ammonia-chemistry-and-removal-techniques-in-ras-aquaculture-technology

[4] https://www.watercom/drinking-water/potable-water-quality/article/16199196/aquaculture-boom-paves-way-for-133b-water-treatment-market-by-2030-research-finds

[5] https://www.sciencedirect.com/science/article/pii/S277242712100022X

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