1、BRITISH STANDARD BS ISO 15705:2002 BS 6068-2.80:2002 Water quality Determination of the chemical oxygen demand index (ST-COD) Small-scale sealed-tube method ICS 13.060.50 BS ISO 15705:2002 This British Standard, having been prepared under the direction of the Health and Environment Sector Policy and
2、 Strategy Committee, was published under the authority of the Standards Policy and Strategy Committee on 10 December 2002 BSI 10 December 2002 ISBN 0 580 40924 4 National foreword This British Standard reproduces verbatim ISO 15705:2002 and implements it as the UK national standard. The UK participa
3、tion in its preparation was entrusted by Technical Committee EH/3, Water quality, to Subcommittee EH/3/2, Physical, chemical and biochemicals, which has the responsibility to: A list of organizations represented on this subcommittee can be obtained on request to its secretary. This is one of a serie
4、s of standards on water quality, others of which have been, or will be, published as Sections of BS 6068. The various Sections of BS 6068 are comprised within Parts 1 to 7, which, together with Part 0, are listed below. Part 0 Introduction Part 1 Glossary Part 2 Physical, chemical and biochemical me
5、thods Part 3 Radiological methods Part 4 Microbiological methods Part 5 Biological methods Part 6 Sampling Part 7 Precision and accuracy NOTE. The tests described in this British Standard should only be carried out by suitably qualified persons with an appropriate level of chemical expertise. Standa
6、rd chemical procedures should be followed throughout. Cross-references The British Standards which implement international publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” f
7、acility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligat
8、ions. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of
9、pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii to v, a blank page, pages 1 to 18, an inside back cover and a back cover. The BSI copyright date displayed in this document indicates when the document was last issued. Amendments issued since publicatio
10、n Amd. No. Date Comments Reference number ISO 15705:2002(E)INTERNATIONAL STANDARD ISO 15705 First edition 2002-11-15 Water quality Determination of the chemical oxygen demand index (ST-COD) Small-scale sealed-tube method Qualit de leau Dtermination de lindice de demande chimique en oxygne (ST-DCO) M
11、thode petite chelle en tube ferm BSISO15705:2002BSISO15705:2002iiIS:50751 O2002(E) I SO 2002 All irthgs ersedevr iiiContents Page Foreword iv Introduction. v 1 Scope 1 2 Normative references 1 3 Terms and definitions. 2 4 Principle . 2 5 Interferences 2 6 Reagents 2 7 Apparatus. 5 8 Sample collectio
12、n and preservation 6 9 Preparation of tubes and instrument set-up 6 10 Analytical procedure for measurement of samples 7 11 Calculation of results 8 12 Expression of results 9 13 Test report 9 14 Precision 9 Annex A (informative) Comparison between the COD method according to ISO 6060 and the method
13、 described in this International Standard 10 Annex B (informative) Hazards 11 Annex C (informative) Information on the use of commercial small-scale ST-COD test kits utilizing photometric detection. 12 Annex D (informative) Low-range sealed-tube photometric method (up to 150 mg/l) 13 Annex E (inform
14、ative) Low-range sealed-tube titrimetric method (up to 150 mg/l) 14 Annex F (informative) Screening test for samples with high chloride concentrations. 15 Annex G (informative) Precision data. 16 Bibliography 18 BSISO15705:2002iiiIS:50751 O2002(E) vi I SO 2002 All irthgs ersedevrForeword ISO (the In
15、ternational Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee h
16、as been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical
17、 standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodi
18、es for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for id
19、entifying any or all such patent rights. ISO 15705 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2, Physical, chemical and biochemical methods. Annexes A to G of this International Standard are for information only. BSISO15705:2002ivIS:50751 O2002(E) I SO 2002 All ir
20、thgs ersedevr vIntroduction The chemical oxygen demand, ST-COD value, of water as determined by this dichromate method can be considered as an estimate of the theoretical oxygen demand, i.e. the amount of oxygen consumed in total chemical oxidation of the organic constituents present in the water. T
21、he degree to which the test results approach the theoretical value depends primarily on how complete the oxidation is. The ST-COD test is an empirical test and the effects of any oxidizing or reducing agents are included in the result. Under the conditions of the test, many organic compounds and mos
22、t inorganic reducing agents are oxidized to between 90 % and 100 %. For waters that contain these compounds, such as sewage, industrial waste and other polluted waters, the ST-COD value is a realistic measure of the theoretical oxygen demand. However, for waters that contain large quantities of othe
23、r substances that are difficult to oxidize under the conditions of the test, such as nitrogenous and heterocyclic compounds (e.g. pyridine and aliphatic and aromatic hydrocarbons), the ST-COD value is a poor measure of the theoretical oxygen demand. This may be the case for some industrial effluents
24、. The significance of an ST-COD value thus depends on the composition of the water studied. This should be borne in mind when judging results obtained by the method specified in this International Standard. Detailed testing has shown good comparison between this method and the method of ISO 6060. Ho
25、wever, it should not be assumed that this method is comparable in all cases to that of ISO 6060 without testing, particularly when there is a problem in obtaining a 2 ml representative sample (e.g. samples with high content of suspended solids). BSISO15705:2002vINTENRATIONAL TSANDADR IS:50751 O2002(
26、E)I SO 2002 All irthgs ersedevr 1Water quality Determination of the chemical oxygen demand index (ST-COD) Small-scale sealed-tube method WARNING Persons using this standard should be familiar with normal laboratory practice. This standard does not purport to address all of the safety problems, if an
27、y, associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and to ensure compliance with any national regulatory conditions. 1 Scope This International Standard specifies a method for the determination of the chemical oxygen demand (ST-COD)
28、using the sealed tube method. The test is empirical and is applicable to any aqueous sample, which includes all sewage and waste waters. The method is applicable to undiluted samples having ST-COD values up to 1 000 mg/l and a chloride concentration not exceeding 1 000 mg/l. Samples with higher ST-C
29、OD values require predilution. For samples with a low COD, the precision of the measurement will be reduced and the detection limit will be poorer. Samples with a high chloride concentration will need to be prediluted to give a chloride concentration of approximately 1 000 mg/l or less before analys
30、is. The method oxidizes almost all types of organic compounds and most inorganic reducing agents. It has a detection limit (4,65 times the within-batch standard deviation of a blank or very low standard) of 6 mg/l for photometric detection at 600 nm, and 15 mg/l for titrimetric detection as reported
31、 by one laboratory comparing the photometric and titrimetric techniques using a commercial test kit with a range up to 1 000 mg/l. The titrimetric part of this International Standard is applicable to samples exhibiting an atypical colour or turbidity after the digestion stage. NOTE A comparison betw
32、een the full-scale method (ISO 6060) and the method of this International Standard is given in annex A. A discussion of possible hazards is given in annex B. Information on commercial small-scale test kits is given in annex C. The method can be used over a reduced range (see annexes D and E). For ch
33、ecking the chloride concentration, see annex F. 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 publi
34、cations 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 ap
35、plies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 3696:1987, Water for analytical laboratory use Specification and test methods ISO 5667-3:1994, Water quality Sampling Part 3: Guidance on the preservation and handling of samples BSISO15705:20021IS:50751
36、 O2002(E) 2 I SO 2002 All irthgs ersedevr3 Term and definition For the purposes of this International Standard, the following term and definition applies. 3.1 chemical oxygen demand ST-COD mass concentration of oxygen equivalent to the amount of dichromate consumed by dissolved and suspended matter
37、when a water sample is treated under the conditions specified in this International Standard NOTE 1 Adapted from ISO 6060. NOTE 2 1 mol of dichromate (Cr 2 O 7 2 ) is equivalent to 3 mol of oxygen (O). 4 Principle 4.1 Samples are oxidized in a standard manner by digesting with sulfuric acid and pota
38、ssium dichromate in the presence of silver sulfate and mercury(II) sulfate. Silver acts as a catalyst to oxidize the more refractory organic matter. Mercury reduces the interference caused by the presence of chloride ions. The amount of dichromate used in the oxidation of the sample is determined by
39、 measuring the absorbance of the Cr(III) formed at a wavelength of 600 nm 20 nm for a range up to 1 000 mg/l. Absorbance measurements are made in the digestion tube, which acts as a cuvette, and are converted to an ST-COD value. 4.2 For the reduced calibration range up to 150 mg/l, an alternative wa
40、velength 440 nm 20 nm may be used (see annexes D and E). For a further reduced calibration range up to 50 mg/l, an alternative wavelength of 348 nm 15 nm may be used. At 348 nm and 440 nm, the absorbance of the remaining chromium(VI) is measured. 4.3 For turbid and atypically coloured digested sampl
41、es, titration with standardized ammonium iron(II) sulfate is used. 5 Interferences 5.1 High concentrations of chloride give a positive bias caused by the oxidation of chloride ions to chlorine. The interference from chloride ions is reduced but not totally eliminated by the addition of mercury(II) s
42、ulfate. This binds the chloride ions as a soluble chloromercurate(II) complex. 5.2 Manganese can give a positive bias using photometric detection at 600 nm. Using a 0 mg/l to 1 000 mg/l commercial test kit, duplicate analysis of a 500 mg/l manganese solution (as sulfate) gave ST-COD results of 1 080
43、 mg/l and 1 086 mg/l and of a 50 mg/l manganese solution gave ST-COD results of 121 mg/l and 121 mg/l. The effect is much less with lower range (0 mg/l to 150 mg/l) kits at 440 nm (5.1). At this wavelength the interference is expressed as a negative bias. For a 0 mg/l to 150 mg/l commercial test kit
44、, duplicate analysis of a 500 mg/l manganese solution (as sulfate) gave ST-COD results of 7 mg/l and 8 mg/l. See also note in C.6. 5.3 Many aromatic hydrocarbons and pyridine are not oxidized to any appreciable extent. Some volatile organic substances may escape the oxidation by evaporating. 5.4 Amm
45、onium ions are not oxidized (organic nitrogen is normally converted to ammonium ions). 6 Reagents 6.1 Water, complying with ISO 3696:1987, Grade 3. BSISO15705:20022IS:50751 O2002(E) I SO 2002 All irthgs ersedevr 36.2 ST-COD sealed tubes Whenever possible it is recommended to use ST-COD sealed tubes
46、purchased ready for use. This minimizes the handling of toxic chemicals by laboratory staff. Commercial tubes can be purchased covering different analytical ranges (e.g. up to 50 mg/l, 160 mg/l, 1 000 mg/l or 1 500 mg/l). If tubes cannot be purchased already prepared, then prepare them within the la
47、boratory as described in 6.7, for an analytical range of up to 1 000 mg/l. In this instance the user shall ascertain the reproducibility of optical transmission of the tubes or transfer the contents after digestion to a glass cuvette of 10 mm optical path length. The ST-COD concentration range of co
48、mmercial tubes will be specified by the manufacturer and shall not be exceeded. If this occurs, the sample should be suitably diluted to within the specified concentration range. It is essential that the purchased sealed tubes contain mercury(II) sulfate for suppression of chloride interference. See
49、 note in C.6. 6.3 Standard reference solution of potassium dichromate, c(K 2 Cr 2 O 7 ) = 0,10 mol/l (range up to 1 000 mg/l ST-COD). Dissolve 29,418 g 0,005 g of potassium dichromate (dried at 105 C for 2 h 10 min) in about 600 ml of water in a beaker. Carefully add 160 ml of concentrated sulfuric acid (6.4.1) with stirring. Allow to cool and make up to 1 000 ml in a graduated flask. The solution is stable for 6 months. 6.4 Sulfuric ac
