RAS Projects

RAS Projects

Recirculatory Aqua culture System (RAS) Need of the Hour

recirculatory aqua

What is RAS?

  • Recirculation aquaculture is essentially a technology for farming fish or other aquatic organisms by reusing the water in the production.
  • The technology is based on the use of mechanical and biological filters, and the method can in principles be used for any species grown in aquaculture such as Fish, Shrimps, Prawns.
  • Recirculation can be carried out at different intensities depending on how much water is recirculated or re-used. Seen from an environmental point of view, the limited amount of water used in recirculation is of course beneficial as water has become a limited resource in many regions.
  • Recirculation aquaculture can therefore be considered a most environmentally friendly way of producing fish at a commercially viable level.
  • Controlling parameters such as water temperature, oxygen levels, or daylight for that matter, gives stable and optimal conditions for the fish & Shrimp, which again gives less stress and better growth.

Why Water To Be Recirculate?

  • Seen from an environmental point of view, the limited amount of water used in recirculation is of course beneficial as water has become a limited resource in many regions.
  • Also, the limited use of water makes it much easier and cheaper to remove the nutrients excreted from the fish as the volume of discharged water is much lower than that discharged from a traditional fish farm.
  • Recirculation aquaculture can therefore be considered a most environmentally friendly way of producing fish at a commercially viable level. The nutrients from the farmed fish can be used as fertilizer on agricultural farming land or as a basis for biogas production.

What to Be Controlled in RAS?


Controlled Aspects in RAS From Nature

  • Earth
  • Water
  • Energy
  • Air
  • Space

Surveillance of Fish

  • Eating feed and using oxygen results in fish growth and excretion of waste products, such as carbon dioxide, ammonia and faeces.
  • Surveillance fish

Maximising the Fish/Prawn Performance

Combination of many factors

  • Temperature
  • pH Levels
  • Dissolved Oxygen
  • Water hardness
  • Ammonia Levels
  • Fish Size
  • Seed Density & Distribution
  • Water Levels & Feed

How will be water consumption in RAS?

Type of system Consumption of new water per kg fish produced per year Consumption of new water per cubic meter per hour Consumption of newwater per day of total system water volume Degree of recirculation at system vol. recycled one time per hour
Pond Culture 30 m3 1 712 m3/h 1 028 % 0 %
Bio Flock 3 m3 171 m3/h 103 % 75.3%
RAS intensive 1 m3 57 m3/h 34 % 95.6 %
RAS super intensive 0.3 m3 17 m3/h 6 % 99.6 %

Difference Between In RAS & Bio-Floc

  • RAS systems require a biological filter to process ammonia into nitrite, then nitrate.
  • Biofloc is used as a biological filter for some species. It is extraordinarily cheep to run as a system but can kill the fish when it is not managed properly.
Biofloc Clear-water RAS
Survival (%) 69±0.6 (68-70) 78±4.3 (70-85)
Individual weight (g) 11.1±0.2 (10.8-11.3)a 11.6±0.3 (11.1-12.2)b
Growth rate (g/week-1) 1.4±0.0 (1.4-1.4) 1.5±0.0 (1.4-1.5)
FCR 1.8±0.1 (1.7-1.8)a 1.3±0.1 (1.3-1.6)b
Biomass produced (kg/m3) 1.7±0.0 (1.6-1.8)a 2.0±0.1 (1.9-2.2)b

Recirculation Aqua Culture….

  • In a recirculation system it is necessary to treat the water continuously to remove the waste products excreted by the fish, and to add oxygen to keep the fish/ Prawn alive and well.
  • From the outlet of the fish tanks the water flows to a mechanical filter and further on to a biological filter before it is aerated and stripped of carbon dioxide and returned to the fish tanks.
  • Several other facilities can be added, such as oxygenation with pure oxygen, ultraviolet light or ozone disinfection, automatic pH regulation, heat exchanging, denitrification, etc. depending on the exact requirements.

RAS Development……

Temperature Sensors


The environment in the fish rearing tank must meet the needs of the fish, both in respect of water quality and tank design. Choosing the right tank design, such as size and shape, water depth, self-cleaning ability, etc. can have a considerable impact on the performance of the species reared.
Temperature Sensors

Circular tank, D-ended raceway, and raceway type.

Tank properties Circular tank D-ended raceway Raceway type
Self-cleaning effect 5 4 3
Low residence time of particles 5 4 3
Oxygen control and regulation 5 5 4
Space utilization 2 4 5

Mechanical Filter

  • Mechanical filtration of the outlet water from the fish tanks has proven to be the only practical solution for removal of the organic waste products.
  • RTiTS drumfilter is by far the most commonly used type of microscreen, and the design ensures the gentle removal of particles.

RTiTS Drum Filter

  • The Total body is made with SS-103
  • In-built Drive System
  • Easy To Clean
  • Safety Cover At Top
filter tank

Function Of Drum Filter

  • Water to be filtered enters the drum.
  • The water is filtered through the drum’s filter elements. The difference in water level inside/outside the drum is the driving force for the filtration.
  • Solids are trapped on the filter elements and lifted to the backwash area by the rotation of the drum.
  • Water from rinse nozzles is sprayed from the outside of the filter elements. The rejected organic material is washed out of the filter elements into the sludge tray.
  • The sludge flows together with water by gravity out of the filter escaping the fish farm for external waste water treatment

Bio - Filtration

The efficiency of biofiltration depends primarily on:

  • The water temperature in the system.
  • The pH level in the system.

Temperature Effect

  • To reach an acceptable nitrification rate, water temperatures should be kept within 10 to 35 °C (optimum around 30 °C) and pH levels between 7 and 8.
  • The water temperature will most often depend on the species reared and is as such not adjusted to reach the most optimal nitrification rate, but to give optimal levels for fish growth. Regulation of pH in relation to biofilter efficiency is however important as lower pH level reduces the efficiency of the biofilter

pH Effect

Thermocouples with ceramic protection tube

  • The Production of CO₂ from the fish & from the Bio-Logical activity of the Bio-filter.
  • The Acid Produced from Nitrification Process.


  • The nitrifying process produces acid (H+) and the pH level falls. In order to stabilize the pH, a base must be added. For this purpose lime or sodium hydroxide (NaOH) or another base needs to be added to the water.
  • Fish excretes a mixture of ammonia and ammonium (Total Ammonia Nitrate (TAN) = ammonium (NH₄+) + ammonia (NH₃)) where ammonia constitutes the main part of the excretion. The amount of ammonia in the water depends however on the pH level as can be seen in below slide, which shows the equilibrium between ammonia (NH₄+ ) and ammonium (NH ₃)

How Bio-Filter Works?

  • Biofilters are typically constructed using plastic media giving a high surface area per m3 of biofilter. The bacteria will grow as a thin film on the media thereby occupying an extremely large surface area.
  • The aim of a well-designed biofilter is to reach as high a surface area as possible per m3 without packing the biofilter so tight that it will get clogged with organic matter under operation.
  • It is therefore important to have a high percentage of free space for the water to pass through and to have a good overall flow through the biofilter together with a sufficient back-wash procedure. Such back-wash procedures must be carried out at sufficient intervals once a week or month depending on the load on the filter.
  • The biofilter is shunted while the washing procedure takes place, and the dirty water in the filter is drained off and discharged before the biofilter is connected to the system again.
Temperature Sensors


  • The aeration process of the water, which is the same physical process as degassing or stripping, will add some oxygen to the water through simple exchange between the gases in the water and the gases in the air depending on the saturation level of the oxygen in the water.
  • The equilibrium of oxygen in water is 100% saturation. When the water has been through the fish tanks, the oxygen content has been lowered, typically down to 70%, and the content is reduced further in the biofilter.
  • Aeration of this water will typically bring the saturation up to around 90%, in some systems 100% can be reached.
  • Oxygen saturation higher than 100% in the inlet water to the fish tanks is however often preferred in order to have sufficient oxygen available for a high and stable fish growth. Saturation levels above 100% call for a system using pure oxygen.
Temperature Sensors

Ultra–Violet Treatment

  • UV disinfection works by applying light in wavelengths that destroy DNA in biological organisms.
  • In aquaculture pathogenic bacteria and one-celled organisms are targeted. The treatment has been used for medical purposes for decades and does not impact the fish as UV treatment of the water is applied outside the fish production area.
  • The best control is achieved when effective mechanical filtration is combined with a thorough biofiltration to effectively remove organic matter from the process water, thus making the UV radiation work efficiently.
  • In order to control bacteria and viruses the water needs to be treated with roughly 2 000 to 10 000 µWs/cm2 to kill 90% of the organisms, fungi will need 10 000 to 100 000 and small parasites 50 000 to 200 000 µWs/cm2.
filter tank


  • The use of dry feed(Float Feed) is safe and also has the advantage of being designed to meet the exact biological needs of the fish.
  • Dry feed is delivered in different pellet sizes suitable for any fish stage, and the ingredients in dry fish feed can be combined to develop special feeds for fry, brood stock, grow-out, etc.
  • In a recirculation system, a high utilization rate of the feed is beneficial as this will minimize the amount of excretion products thus lowering the impact on the water treatment system.
filter tank

Feed Conversion Rate

What Is FCR(Feed Conversion Ratio)?

  • The Feed Conversion Rate (FCR), describing how many kilos of feed you use for every kilo

Feed conversion & Growth

Temperature Sensors

Working of Auto Feeders

  • The Automatic Feeders will Maintain the FCR, since it delivers the feed at correct time & correct quantity with Punctuality as controller designs! So the fish will alerts at that particular time takes the feed!
  • For the prawns this automatic feeders will delivers the feed whenever it needs by sesing the sounds releasing by prawns..

Working of controller

  • CPU gets actual Temp , pH, DO, CO2,Water Levels, NH3
  • Display .. Shows the actual conditions in the tank
  • Relays… get command from CPU to operate. As per the programme.
  • Relays gives signals to operate various equipment like Motors, Valves, Pumps, Blowers and Filters and many more ….
  • CPU can connect to Internet via another unit .

Controller capacity / model

  • Basically depends upon how many functions it can handle
  • This will depend on no. of relays it has ..
  • How the recirculation can be achieved
  • In packets of water treatment like Mechanical treatment, Bio-logical treatment or Oxygenation etc,.precisely
  • How much data it can hold
  • Communication with laptop / internet..
  • Most important .. What you need and what your work force / staff can handle .

Evikon Précised Controller

  • Graphic touchscreen
  • Two independent RS232/RS485 interfaces
  • Linux operating system
Temperature Sensors

How Controller Works?

  • For each function need a relay.
  • Relay will operate the control circuit contactor to operate the equipment like Pump, Valve, Blower, heater
  • Controller needs to be programmed to get Recirculation requirement achieved which depends on

Aim of the controller…

  • To give maximum performance from seed..
  • To keep Fish at required comfort level..
  • To maintain require water parameters..
  • To perform Water Treatments…
  • To adopt environmental conditions & to save Environment from pollution