ISO 9888 pdf download.Water quality — Evaluation of ultimate aerobic biodegradability of organic compounds in aqueous medium — Static test (Zahn-Wellens method)
1 Scope
This International Standard specifies a method for the evaluation in aqueous medium of the ultimate biodegradability and, as additional information, the primary biodegradability and the total elimination from water, of organic compounds at a given concentration by aerobic microorganisms. The conditions described in this International Standard normally correspond to optimal conditions for allowing the maximum value of biodegradation to occur with the chosen inoculum in the test time. These conditions may even be more favourable than in full-scale wastewater treatment plants, especially if their hydraulic retention time, sludge age or the adaptation of the activated sludge is not optimal. The method applies to organic compounds which are a) water-soluble at the concentration used under the test conditions and not expected to be transformed to insoluble metabolites if biodegradation and not elimination only shall be determined; b) nonvolatile, or which have a negligible vapour pressure under the test conditions; c) not lost by foaming from the test solution; d) not inhibitory to the test microorganisms at the concentration chosen for the test. Inhibitory effects can be determined using a suitable test method (e.g. see ISO 81 92). If the test compound is toxic, the test concentration must be lowered, or a pre-exposed inoculum can be used. This International Standard is also applicable to the measurement of biodegradation and elimination of dissolved organic compounds in wastewater (also called “test compound” in the method). NOTE If more information is required to predict the behaviour of test compounds or wastewater in a treatment plant, a simulation test (e.g. the activated sludge simulation test ISO 1 1 733) should be performed. For appropriate use of this method and for alternative biodegradation methods, see ISO 1 5462.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 6060:1 989, Water quality — Determination of the chemical oxygen demand . ISO 8245, Water quality — Guidelines for the determination of total organic carbon (TOC) and dissolved organic carbon (DOC).
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply. 3.1 ultimate aerobic biodegradation breakdown of a chemical compound or organic matter by microorganisms in the presence of oxygen to carbon dioxide, water and mineral salts of any other elements present (mineralization) and the production of new biomass 3.2 primary biodegradation structural change (transformation) of a chemical compound by microorganisms resulting in the loss of a specific property 3.3 activated sludge biomass produced in the aerobic treatment of wastewater by the growth of bacteria and other microorganisms in the presence of dissolved oxygen 3.4 concentration of suspended solids of an activated sludge amount of solids obtained by filtration or centrifugation of a known volume of activated sludge and drying at about 1 05 ° C to constant mass 3.5 total organic carbon TOC all that carbon present in organic matter which is dissolved and suspended in the water 3.6 dissolved organic carbon DOC that part of the organic carbon in the water which cannot be removed by specified phase separation NOTE Phase separation may be specified for example by centrifugation at 40 000 m◊s –2 for 1 5 min or by membrane filtration using membranes with pores of 0,2 µm to 0,45 µm diameter. 3.7 chemical oxygen demand COD mass concentration of oxygen equivalent to the amount of a specified oxidant consumed by a chemical compound or organic matter when a water sample is treated with that oxidant under defined conditions NOTE COD is expressed in this case as milligrams oxygen consumed per milligram or gram of test compound. 3.8 lag phase time from the start of a test until adaptation and/or selection of the degrading microorganisms are achieved and the biodegradation degree of a chemical compound or organic matter has increased to about 1 0 % of the maximum level of biodegradation NOTE Lag phase is recorded in days.