Refining filtration

THE most significant difference between Mowi’s Inchmore hatchery and its Lochailort facility, which opened in 2013, is the filtration system.

Inchmore has a two-stage form of biofiltration that removes the need for cleaning biofilters, a system fine-tuned by Mowi freshwater manager John Richmond, who also oversaw construction of the Lochailort plant.

At Inchmore, in the primary filtration stage, a series of Faivre drum filters, with 26 micron screens, remove solids from the water.

From here, the water is fed into submerged tanks for treatment with biomedia, before being pumped into biotowers, where plastic media captures any particulates, and bacteria breaks down ammonia.

The tertiary filtration involves ozone injection to disinfect the water, which then goes back to the tanks and continues to recirculate.

Manager Matthew Paget said: ‘We worked out how much we feed, how much ammonia the fish will produce, how much CO2 they will produce, and from that we can calculate how much surface area of biofilm we need, what drum filter screens, what flow do we need to meet the demand of the fish, what flow can go through those drum filter screens, what pumps we need to produce that flow.

‘So it’s all worked out with the farmers. It works from sales – what do they need, what do we need to produce, and what do we need to build to produce that. All farming works from the top down.’