The ASCE manuals distinguish between clean-water and in-process oxygen transfer testing.
For clean water, ASCE/EWRI 2-22 primarily describes dynamic clean-water tests to determine oxygen transfer rate and oxygen transfer efficiency under defined conditions. In this approach, the water is first deoxygenated and the subsequent increase in dissolved oxygen concentration is evaluated over time. Both chemical deoxygenation and nitrogen sparging are recognized deoxygenation methods. In addition, the commentary describes a desorption method using oxygen supersaturation as a supplementary testing method.
For measurements under operating conditions, ASCE/EWRI 18-18 recommends three methods: the dynamic method, the off-gas method, and the inert-gas tracer method. In practice, the off-gas method has become particularly widespread because it can directly assess oxygen transfer under actual process conditions and provides highly meaningful information regarding alpha factors, energy efficiency, and real plant performance. However, in-process methods are intended as technical guidelines and not as compliance tests for aerators, since wastewater composition and process conditions significantly influence measurement accuracy.
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