E: Besides the mechanical cleaning, the biological treatment stage is an essential part in
treating waste water. Many substances can be degraded by microbial activity and this
may be enhanced in WWT by adaptation. Biodegradability is a key parameter in finding
target substances. The more a substance is persistent, the higher is the possibility that
the substance could be released from a WWTP and persist in the environment.
Biodegradation is a complex process and may not be described by a single physico-
chemical parameter. In this scheme the parameter ready biodegradability is used to
decide whether the substance needs to be examined more closely or whether it is seen
as not target.\\
The following parameter apply:\\
• Ready biodegradability (mineralisation of test item), test guideline OECD 301 a-f,
OECD 310. A substance is readily biodegradable, if ≥ 60 % O 2 depletion or CO 2
development (pass level) is achieved an the 10-days-window is fulfilled.
According to the test result, ready biodegradability is a yes/no decision and more a
“classification” than a statement about the degradation behaviour. If the test criteria are
narrowly missed, it is not possible to conclude on a “possible” or “inherent”
degradability.\\
Any other biodegradability classification (e.g. inherently biodegradable, partly or non-
biodegradable, degradation half-life dt 50 (disappearance of 50% of the test item in 40
days in surface water) requires expert judgement for interpretation.

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