ISO 9509:2006 PDF

Scope: 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 3 h or up to 24 h 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. A/-allylthiourea; see Annex A). If the nitrification rate is within a suitable range for the test, i.e. 2 mg of nitrogen per gram of suspended solid and hour to 6,5 mg of nitrogen per gram of suspended solids and hour, the sludge may be used directly. If not, adjustments are necessary (see Clause 9). 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 ISO 5667-16).

ISO 9509:2006 Referenced Document

ISO 11733 Water quality - Determination of the elimination and biodegradability of organic compounds in an aqueous medium - Activated sludge simulation test
ISO 6777 Water quality; Determination of nitrite; Molecular absorption spectrometric method
ISO 7150-1 Water quality; Determination of ammonium; Part 1 : Manual spectrometric method

2006 ISO 9509:2006 Water quality - Toxicity test for assessing the inhibition of nitrification of activated sludge microorganisms
1989 ISO 9509:1989 Water quality; method for assessing the inhibition of nitrification of activated sludge micro-organisms by chemicals and waste waters