Method and system for purging off-flavor compounds from farm-raised fish
A depuration process is employed for removing off-flavor contaminants from fish through an advanced oxidation process. Before the fish is harvested, the fish is transferred to a depuration tank or zone containing water. Off-flavor compounds leach from the tissue of the fish into the water in the depuration tank or zone. The water in the depuration tank or zone is circulated through an advanced oxidation reactor that, through an oxidation process, reduces the concentration of the off-flavor contaminants in the water.
1. A method of oxidizing geosmin or 2-methylisobornel (MIB) compounds in aquatic organisms raised in a recirculating aquaculture system (RAS), comprising:
before harvesting the aquatic organisms, transferring the aquatic organisms from a grow-out area in the RAS to a depuration zone or tank containing water;
ceasing to feed the aquatic organisms after the aquatic organisms have been transferred to the depuration zone or tank;
circulating the water from the depuration zone or tank to a degassing and oxygenation unit and degassing the water and supplying oxygen to the water, after which the water is returned to the depuration zone or tank;
circulating the water from the depuration zone or tank to and through a flowthrough reactor containing a UV light source, a first electrode having a titanium dioxide catalyst associated therewith and a second electrode, and back to the depuration zone or tank and in the process generating a water current in the depuration zone or tank;
a. oxidizing and reducing the geosmin and MIB compounds in the water passing through the reactor by a photo electrocatalytic process comprising: irradiating the titanium dioxide catalyst with UV light emitted from the UV light source in the reactor, causing UV radiation to be absorbed by the titanium dioxide catalyst which creates negative charged free electrons and positively charged electron holes in the surface of the titanium dioxide catalyst;
b. applying a voltage across the first and second electrodes;
c. contacting the geosmin and MIB compounds flowing through the reactor with the titanium dioxide catalyst which results in the oxidation of the geosmin and MIB compounds due to the positively charged electron holes in the surface of the titanium dioxide catalyst pulling electrons from the geosmin and MIB compounds;
d. reacting the positively charged electron holes with the water passing through the reactor to form hydroxyl radicals;
e. reacting the hydroxyl radicals produced by the reactor with the geosmin and MIB compounds which reduces the concentration of the geosmin and MIB compounds in the water through an oxidation process;
whereby by oxidizing the geosmin and MIB compounds in the water passing through the reactor, a geosmin or MIB concentration gradient is maintained between the aquatic organisms and the water in the depuration zone or tank, which in turn results in a mass transfer of geosmin or MIB from the tissue of the aquatic organisms into the water.
2. The method of claim 1 wherein there is provided a plurality of reactors disposed in parallel relationship through which water from the depuration zone or tank is circulated through.
3. The method of claim 1 wherein each reactor includes an elongated chamber having a water inlet on one end portion and a water outlet on the opposite end portion.
4. The method of claim 1 including mixing hydrogen peroxide with the water, resulting in the hydrogen peroxide reacting with UV light from the UV light source to form additional hydroxyl radicals.
5. The method of claim 1 further including injecting an oxidant into the water upstream of the reactor.
6. The method of claim 5 wherein the oxidant is taken from the group consisting of hydrogen peroxide, chlorine dioxide, ozone, and Fenton's reagents.