Dear Hamed,

The concept of RAS (for Recirculating Aquaculture System) is to reuse a volume of water by a continuous treatment allowing the supply of aquaculture species.

Due to its design and components, the RAS facility supports high nutrient intake; it ensures a high growth rate and a high stocking density, compatible with the economic profitability of the production.

The Kaldnes® RAS semi-closed loop system with aeration and particulate removal system is designed to maximize production while reducing pollution and water consumption.

Particle removal: particle separation is ensured by Hydrotech drum filters, which are recognized worldwide for their efficiency, designed specifically for aquaculture applications and whose introduction on the market dates back more than 25 years.

Biological treatment: AnoxKaldnes ™ MBBR (Moving Bed Biofilm Reactor) is a continuous biological treatment process for the removal of carbon and / or nitrogen pollution using biomass on a support in suspension. Its compactness and operation without backwashing make it a solution that ideally meets the needs of the aquaculture sector.

With my best regards

Bachir ACHOUR

Dear Bachir Achour ,

Thanks for the information. Do you mean RAS dose not need UV or Ozone systems?

Biological treatment without backwash is interesting! I checked some different designation for biofilters; all of them had backwash in bio filter chambers.

Dear Hamed,

Yes, it is useless to use UV or ozone.

Regards

Bachir ACHOUR

Bachir Achour

Dear Bachir,

But the inlet water from natural resources may contain contamination as hazardous bacteria or viruses!

Dear Hamed,

Ultraviolet treatment can be used to kill bacteria and viruses in water coming from breeding ponds.

Principle drawing of a recirculation system : The basic water treatment system consists of mechanical filtration, biological treatment and aeration/ stripping. Further installations, such as oxygen enrichment or UV disinfection, can be added depending on the requirements.

Regards

Bachir ACHOUR

Bachir Achour

You are right. Therefore, return to the question please. My question was about disinfection part of system: UV? Ozone? or both?

Dear Hamed,

When necessary, UV is preferably used. This is the most common method used in RAS. The ozone-based purification system requires a large investment initially. Ozone production consumes energy and the system is quite complex.

Regards

Bachir ACHOUR

Dear Bachir Achour ,

Thanks for the information.

I agree@ Bachir Achour for your answer.

I will not recommend ozone, because you will face different influential factors like ozone concentration, time etc although to decrease the ozone concentration is it self a issue.

Please read

Dar et al 2019 (ozonation of pentabromophenol....)

Salmon aquaculture facilities in Norway successfully use low level ozonation to treat the recirculated water. It may be combined with flotation to remove suspended solids that are a major cause of problems.

One research project to start with ran in 2013-2014:

http://www.razone.no/

Afzal Ahmed Dar , Ralf Hornung , Bachir Achour , Omar Ali Al-Khashman :

Thanks for the answers. I think this is a challenged subject. In a big RAS aquaculture farm, it is an important question what kind of water treatment is adequate. A system designed by Norwegian companies have a rate of 22 m3 intake. Water come from coastal well, remain in 600m3 reservoir for 24 h, pomp to refinery after UV, and enter the system. But if do not use of ozone, in recirculating system how to remove or reduce fine and colloidal solid (parts that not remove by drum filters)? how to remove dissolved organic compounds? and how to remove nitrite when and organic loadings on the biofilter increase?

(Nitrite can accumulate as production intensifies and organic loadings on the biofilter increase. Bacteria that process ammonia into nitrite (Nitrosomonas spp) operates more efficiently under high organic loadings than bacteria that process nitrite to nitrate (Nitrobacter) and levels of nitrite rise accordingly)

From what I remember, you are on the right track: the very fine and colloidal solids are the major source of problems as they are not removed by the drum filters. They make up a large portion of the total load of organics and detrimental substances. They also act as carriers for microorganisms/pathogens.

One idea was to use let ozone trigger microflocculation of the collodial particels which then may be removed by flotation. The pilot tests were promising, however I do not know whether large scale testing have been conducted by now.