Until the introduction of the fine bubble aeration, the alpha factor was hardly known, because this factor of 0.93 had always been neglected with surface aeration. Later on, this comparison factor between pure water and sewage water became an increasing problem for the fine bubble aeration process.
Initially it was calculated with an alpha factor of 0.80 for bubble aeration, but a value of 0.65, which can dramatically fluctuate, quickly became a standard in the literature. Because most pressure elements lose 2 – 3 % per year of effectiveness, most offices calculate today using an alpha factor between 0.50 until 0.60.