Getting RAS right – Warden Biomedia

Filter media optimises treatment for Norwegian fish farm

AN onshore fish farm in Norway has introduced a new type of filter media to reduce the size of the MBBR (moving bed biofilm reactor) systems required in its water treatment process.

Norwegian water treatment company Sterner focuses on recirculation aquaculture systems (RAS) for fish farming.

Over the last year, the company has constructed a RAS treatment plant for an onshore fish farm owned by fishing and aquaculture specialist Eidesvik Settesfisk.

The RAS plant comprises two 15m fish breeding tanks, each with a water volume of 780m3; a water treatment system; a feeding system; an energy system for temperature control and a plant for the treatment and handling of sludge.

The water treatment system integrates two-step particle separation, an MBBR for removal of total ammoniacal nitrogen (TAN) and a two-step carbon dioxide removal process.

Warden Biomedia’s Bioflo filter media was selected for use in the MBBR because Sterner wanted to reduce the volume of the planned reactor.

By replacing the standard biofilm carriers, which have a specific surface area of 650m²/m³, with a higher surface area media, the rate of oxidation of TAN into nitrate nitrogen (NO3-N) could be optimised.

Nitrifying biofilms are thin and the bacteria grow slowly, so the risk of the media clogging up is low. Having a high protected surface area is desirable to ensure high biomass concentrations.

It was decided that Bioflo, which has a 10.5mm width and a protected surface area of 800m²/m³, was the most suitable filter media from Warden’s range for this application.

Bioflo is a durable, rugged and highly efficient media designed to provide a large protected surface area for the biofilm and optimal conditions for bacteria culture growth.

The media’s large apertures allow waste water to pass freely, which helps maintain a thin and healthy biofilm.

It is ideal for use in biological reactor technologies such as MBBR, RAS and integrated fixed film activated sludge (IFAS) systems.

When compared to conventional filter media, Bioflo reduces the necessary MBBR tank volume and size, lowering civil engineering costs.
Sterner and Eidesvik Settefisk both say they are pleased with the results of the installation.

Sverre Amrani, technical sales manager at Sterner, said: ‘Selecting the right media is never an easy task. With Warden’s extensive knowledge of, and expertise in, filter media, we were able to select the most appropriate media for this plant. With their help we have been able to meet our targets.\’

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