What is Bivalve Depuration?
February 19, 2016
The Process of Purifying all Bivalves including Mussels, Oysters and Scallops is called Bivalve Depuration.
Todd Fisheries Technology Manufacture the Best Bivalve Depuration Systems in UK.
Any bivalve which is farmed or caught in less than A class waters must be purified. This ensures they are clean and fit for human consumption. We would recommend that all bivalves are depurated. All bivalves are filter feeders. They eat the phytoplankton. If there are any germs, bacteria or viruses in the water these can be concentrated in their gut. To ensure that anything harmful to humans is purged from the bivalves gut they are placed in a purification system.
The seawater in the purification tank passes through a Ultra Violet Steriliser. This damages the cells of the bacteria so that they cannot reproduce. The UV kills off germs and viruses e.g. e coli and fungal cells. The bivalves are held in trays in the tank for 42 hours. The flow rate of the water ensures that as the bivalves feed and produce waste this is passed through the UV enough times to denature the bacteria. Todd Fish systems include a flow rate meter to ensure the flow rate is optimised to provide efficient purification. We also add a larger UV than required e.g. on our 90Kg capacity unit we have a 55 watt UV Steriliser but the minimum requirement is only at 25 watts.
In the UK there has been lots of testing on depuration systems. Seafish set the standards which all systems need to pass. All Todd Fisheries Technology depuration systems are based on the Seafish Small Scale Shallow Tray Standard System. Before an operator can depurate bivalves they have to pass a challenge test. The local council Environmental Health Officer along with a representative from the Government e.g. Marine Scotland will test the system. They will contaminate a batch of shellfish and take samples at the start and end of the depuration cycle. These samples are analysed to ensure all bacteria are within safe levels. Once licensed the operator can sell their shellfish.
Operators need to keep records for each cycle of depuration and the lifespan of the UV bulb. Todd Fish systems include an hour run meter as an easy way to keep track of the bulb which needs replaced every 4000 hours (about every 6 months).
If you want any more advice give Keith a call on Tel. 01383 820685 (during office hours).
Seafish datasheet: http://www.seafish.org/media/Publications/datasheet_95_34_ft.pdf