Coverage density is the ratio between the total effective off-gassing surface area of all aeration elements and the basin floor area and is expressed as:
CD [%] = (Effective off-gassing surface area of all aerators [m²]) / (Basin floor area [m²])
An “optimal” coverage density is not derived from a fixed guideline value but from the process design of the specific basin.
In practice, it is determined iteratively. First, oxygen demand, basin geometry, submergence depth, and load scenarios are defined. Then the number and arrangement of aerators are selected so that uniform air release and adequate mixing are achieved under minimum, average, and maximum oxygen demand conditions without dead zones or sludge accumulation. Too low a coverage density leads to high aerator loading and reduced efficiency. Excessively high coverage density may adversely affect mixing. Therefore, the decisive factors are the combination of coverage density, air loading, aerator spacing, and basin mixing characteristics.
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