BS EN ISO 9509:2006

Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
5 Reagents and materials
6 Apparatus
7 Procedure
8 Calculation and expression of results
9 Validity of results
10 Precision
11 Test report
Annex A (normative) Determination of the nitrifying
        activity of an activated sludge
Annex B (normative) Example for preparation of the test
Annex C (informative) Apparatus for culturing nitrifying
        activated sludge
Bibliography

States a method for assessing the short-term inhibitory effect of waters, wastewaters or test substances on nitrifying bacteria in activated sludge.

This International Standard specifies a method for assessing the short-term inhibitory effect of waters, waste waters or test substances on nitrifying bacteria in activated sludge. The inhibitory effect is estimated over an exposure period of usually 3h or up to 24h with weakly nitrifying sludge.

The method is applicable to nitrifying activated sludge derived from domestic and synthetic sewage and also to sludges from industrial and mixed domestic and industrial waste waters.

The nitrifying activity of the sludge is verified by testing in the presence and absence of a specific inhibitor (e.g. N-allylthiourea; see AnnexA). If the nitrification rate is within a suitable range for the test, i.e. 2mg of nitrogen per gram of suspended solid and hour to 6,5mg of nitrogen per gram of suspended solids and hour, the sludge may be used directly. If not, adjustments are necessary (see Clause9).

The method is applicable to water-soluble, non-volatile chemicals, and to waste waters

Sludges from different sources respond differently to a given concentration of an inhibitor mainly due to reaction between the inhibitor and components of the sludge. This results in a partial neutralisation of the toxic effect. Also, since the test lasts only hours, any inhibitory effects may diminish or increase over a longer period, e.g. in the continuous activated sludge system (see ISO5667-16).