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denitrification

Definition

The biochemical reduction of nitrate via the intermediate nitrite to molecular (gaseous) nitrogen and carbon dioxide through microbiological activity. This process occurs most efficiently in oxygen-deficient environments (e.g. below 0.5 mg/L). The bacterial groups involved are generally called denitrifiers. In aquaculture, denitrification becomes a necessary treatment process in recycling systems with little or no water exchange because of the rapid nitrate accumultion derived from effective biological nitrification in biofilters. Denitrification can also occur in settling tanks, suspended solid traps and water storage tanks where sludge (i.e., waste food and faeces) accumulates and causes oxygen depletion when allowed to settle for too long. This may also happen at other locations within an aquaculture system where water flow is slow and sludge accumulates. If the carbon source for effective denitrification is too low at such places, denitrification will be incomplete, leading to the release of dangerously high amounts of toxic nitrite. Therefore, the accumulation of organic sludge should be avoided in intensive aquaculture through appropriate system design.

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