GENERAL INFORMATION:
The efficiency of aeration systems can be measured by different methods. The standard clean water reaeration test is the best known test. This test is also preferred by some engineers because of its reproducibility.

DMT is not opposed to the clean water test, but has the following comments:
•    An aeration system is designed for the aeration of activated sludge, not clean water.
•    The result of the clean water reaeration test can be used to judge and compare the efficiency in real life conditions of aeration systems of identical design. This means that in surface aeration direct drive aerators should never be compared to low speed gearbox driven aerators. Surface aeration should never be compared to fine bubble diffused air systems according to the clean water test.
•    All correction factors, used to calculate the difference between the oxygenation capacity of an aeration system in clean water and in activated sludge are determined in the liquid phase of the activated sludge and are still not reflecting the real conditions because they do not consider the transfer of that liquid phase to the micro-organisms themselves that are assembled in flocs.

The oxygen transfer rate in real life conditions can be determined by the steady state test according to the Anderson method. The fact that this measurement is performed in activated sludge and that the oxygen uptake is brought into account is the major advantage of this test. The fact that this measurement does not always produce the same result is because the steady state condition was not achieved or due to eventual openings in the walls, etc...

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