Tech Talk 48
- Do whatever is possible to allow fish feces to drop intact into the waste collection area or self-cleaning bottom with minimal breakage. Minimize the use of pumps, aerators and air diffusers wherever feces is present.
- Do not pump the waste prior to separation. Design for gravity flow (or siphon) into a sedimentation tank or basin. Splashing and turbulence can attach air bubbles and break apart solids. Feces and food particles smaller than 40 microns may not settle without chemical flocculent.
- Always locate the biofilter after the solids removal system. Solids provide carbon for heterotrophic bacteria, which can foul a biofilter and reduce its performance.
- Clean both the settling area and filters at least once a day, even if they contain little waste.
- If further filtration is required after sedimentation, pump the water to an affinity bead clarifier, particulate filter, or foam fractionator.
Here is a good sedimentation basin design: Wide inlet (to reduce velocity), a surface area of .7 to 1.4 ft² of basin per gpm flow (for feces with a specific gravity of 1.01 or greater), wide outlet weir (never a stand pipe), no baffles (which increase velocities), and a simple waste drain. A depth of just a few inches is enough for most designs.
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