🫧 BOD5 by the dilution and seeding method to PN-EN ISO 5815-1

Physical chemistry PN-EN ISO 5815-1

Overview

SCALE: THE THIRD MOST FREQUENTLY CITED STANDARD IN THE SCOPE DATABASE. Measurement of 22 Sep 2026: 277 entries at 210 laboratories; matching by the BEGINNING of the recorded string gives 269 entries at 203 laboratories — the "Laboratories" tab shows the second figure.

STATUS (state of the PKN card on 22 Sep 2026). PN-EN ISO 5815-1:2019-12 — published 19 Dec 2019, 36 pages, ICS 13.060.50, technical body KT 122 (Water Quality — Chemical Testing — Organic Substances). The "Implements" field: EN ISO 5815-1:2019 [IDT] and ISO 5815-1:2019 [IDT]. The "Replaces" field: PN-EN 1899-1:2002 — Polish version. The card carries no withdrawal note — the standard is CURRENT.

A CHANGE OF LANGUAGE VERSION AT A CHANGE OF STANDARD GENERATION. The predecessor PN-EN 1899-1:2002 was in the POLISH version. The standard in force, PN-EN ISO 5815-1:2019-12, was issued by PKN in the ENGLISH version. A laboratory that moved to the new document — and virtually the whole community did: 210 laboratories against the 3 that still cite PN-EN 1899-1 — works from an English text.

THIS STANDARD IS THE VERY DOCUMENT THAT STANDS AT THE END OF THE CHAIN OF THE WASTEWATER REGULATION. The regulation on substances particularly harmful to the aquatic environment (Dz.U. 2019 item 1311) points, for BOD5, to two standards: PN-EN 1899-1 and PN-EN 1899-2 (Annex 12, item 12). The card of the first of them (card status as of 23 Sep 2026) gives a withdrawal date of 19 Dec 2019 and names a successor: PN-EN ISO 5815-1:2019-12, English version. The withdrawal took place AFTER the regulation entered into force — but the act has its own rule for this. Explanatory note 2 under the table of Annex 12 reads: "If a standard indicated in the annex is replaced and withdrawn, the new standard from the Polish Standards shall be regarded as the recommended standard" (our translation). PN-EN 1899-1 was replaced and withdrawn, and its card names the successor — so, according to the act itself, PN-EN ISO 5815-1 is today the recommended standard in its place. The other standard of that item, PN-EN 1899-2, has not been withdrawn (card with no withdrawal date, read 23 Sep 2026) and remains indicated alongside it. A laboratory that applies PN-EN ISO 5815-1 applies the standard the act tells it to regard as recommended in place of PN-EN 1899-1. The rule works only for a REPLACED standard: for a standard withdrawn without a named successor the note has nothing to point to, and the withdrawn standard stays in the act. The register of legal acts (ELI, read 23 Sep 2026) lists no amending acts and no consolidated text for this regulation.

A SERIES THAT PARTED WAYS — AND WHY ITS TWO PARTS NOW BELONG TO DIFFERENT FAMILIES. The former PN-EN 1899 series had two parts: part 1 (dilution and seeding) and part 2 (UNDILUTED samples). Today: • part 1 has been replaced by PN-EN ISO 5815-1:2019-12 — a document of the ISO family, English version; • PN-EN 1899-2:2002 is still CURRENT (card with no withdrawal note, read 22 Sep 2026), Polish version, implements EN 1899-2:1998 and ISO 5815:1989 [MOD], and covers undiluted samples with a BOD from 0.5 to 6 mg/l of oxygen; • no counterpart "PN-EN ISO 5815-2" WAS FOUND in the Polish collection. A laboratory measuring BOD in clean waters and in wastewater therefore cites two documents from two different generations of standardisation — and that is how it looks in the scopes: two entries name both standards side by side.

SCOPE OF APPLICATION (from the scope description on the card): a method for all waters with a BOD from 1 mg/l to 6,000 mg/l, with particular application to wastewater, also useful in the analysis of natural waters. Above 6,000 mg/l O2 the method may be used, but particular care is needed in selecting samples for the successive dilution stages.

A SENTENCE THE STANDARD SAYS ABOUT ITSELF — AND WHICH APPEARS AT NO OTHER INDICATOR. From the scope description: the results obtained are the effect of the SUM of biochemical and chemical processes involving living organisms, which run REPRODUCIBLY ONLY OCCASIONALLY; those processes do not have the strict and unambiguous character of a single, precisely defined chemical process — yet the results supply information serving to assess water quality. This is a warning written into the very definition of the indicator: BOD is not the concentration of a substance but a measure of how much oxygen micro-organisms consumed under defined conditions and in a defined time. Two laboratories may perform the determination correctly and obtain results differing more than in a chemical determination — and neither of them is at fault.

SUPPRESSION OF NITRIFICATION — PART OF THE DEFINITION, NOT AN OPTION. The title of the standard names the addition of ALLYLTHIOUREA (ATU), and the scope speaks of suppressing the nitrification process. Without that addition, part of the oxygen consumed would fall to the oxidation of ammonium nitrogen by nitrifying bacteria and the result would be inflated relative to what the indicator is meant to describe (the breakdown of organic substances). A result determined without suppression of nitrification is not a result under this standard.

FIVE DAYS OR SEVEN — THE STANDARD PROVIDES FOR BOTH PERIODS. The scope names both 5-day and 7-day incubation; Polish practice and legislation operate with BOD5. The abbreviation in the test report (BOD5 or BOD7) is therefore part of the result, not an ornament: it is the same method, but a different incubation time and a different number.

WHAT THE SCOPES SHOW. The methodology is "Biochemical oxygen demand" in at least eight wordings differing in the abbreviation alone and in the sign before it: without the abbreviation (98 entries), "- BZT5" with a hyphen (56), "– BZT5" with an en dash (22), "− BZT5" with a minus sign (13), with no sign (8), "(BZT5)" (7), "-BZT5" without a space (3), "BZT5, BZT 2+5" (3). Some scopes add the range and the technique, for example "Range: (3.0 – 6000) mg/l O2 Electrochemical method" (5 entries) or "(3 – 3000) mg/l O2" (3). The technique may be electrochemical or optical — the title of the standard does not settle this, whereas the test report and the accreditation scope do. Test objects: water and wastewater in various wordings (84 + 41 + 15 + 10) and wastewater alone (83) — this is the basic indicator of a treatment plant and a condition in water-law permits.

FORMS OF THE RECORDED STRING. Beside the main form "PN-EN ISO 5815-1:2019-12" (252 entries), the scopes carry: "PN-EN ISO 5815-1:2019" without the month (6), "P N-EN ISO 5815-1:2019-12" with the PN element broken up (3), "PN-EN-ISO 5815-1:2019-12" with a superfluous hyphen (2), "PN-EN ISO 5815-1:2019:12" with a colon instead of a hyphen before the month (2) and "PN ISO 5815-1:2019" without the EN element (1). A search on the exact character string misses more than a dozen entries.

WHAT THIS MEANS FOR SOMEONE SEARCHING — THREE NUMBERS, THREE DIFFERENT QUESTIONS. Matching by the BEGINNING of the value, i.e. the way the "Laboratories" tab on this page searches: 269 entries / 203 laboratories. The full designation "PN-EN ISO 5815-1" ANYWHERE in the value: 270 / 204 — the only addition is the one row in which the standard stands after PN-EN 12566-3. The CORE "5815-1" alone, i.e. ignoring how the prefix was written: 277 / 210 — and only this definition covers the spaced-out "P N-EN", the superfluous hyphen and the form without the EN element. The difference between the first and the third number is SEVEN entries at SIX laboratories, and it lies entirely in the way the prefix was written, not in the content of the test. Anyone counting "how many laboratories have BOD5 according to 5815-1" will therefore get 203, 204 or 210 depending on what they asked — and each of these numbers is true.

CORRECTION TO THE PREVIOUS WORDING OF THIS ENTRY (23.09.2026): it said "252 entries" for the main form and "six forms of writing the standard". The first number is not reproduced by any method of counting known today — the exact string gives 254; the new number stands here together with the method of counting. The second was a selection of six forms differing in the designation, not the number of all forms, and it read like the latter.

WHAT THIS ARTICLE DOES NOT SETTLE. We do not have the text of the standard — the description of the method comes from the scope description on the PKN catalogue card. We therefore do not know: the composition of the dilution water, the requirements for the seeding material, the dose of allylthiourea, the incubation conditions (temperature, darkness), the requirements for blanks or the validity criteria of the determination (minimum oxygen depletion and minimum residual oxygen concentration). Those data have to be taken from the standard.

Method principle

The sample is diluted with water of known oxygen content and — where necessary — seeded with micro-organisms, allylthiourea is added to suppress nitrification, and the incubation vessels are then filled and left for 5 or 7 days at a defined temperature with no access of light. The dissolved-oxygen concentration is determined at the start and at the end of incubation; the difference, converted through the dilution factor and reduced by the depletion in the blank, gives the biochemical oxygen demand. The result corresponds to the sum of biochemical and chemical processes taking place with the participation of living organisms, not to the concentration of a single substance.

Applications

• Control of raw and treated wastewater — BOD5 is an indicator in water-law permits and in treatment-plant reporting
• Assessment of surface-water quality and of the effectiveness of biological treatment
• Testing for the purposes of the regulation on substances particularly harmful to the aquatic environment
• Control of the biological process at a treatment plant — loading with organic matter
• Reading an accreditation scope in which the oxygen-measurement technique (electrochemical or optical) stands beside the standard

Key parameters

Standard

Standard number

PN-EN ISO 5815-1:2019-12 (wersja ANGIELSKA; wprowadza EN ISO 5815-1:2019 [IDT] i ISO 5815-1:2019 [IDT])

Title (PL)

Jakość wody — Oznaczanie biochemicznego zapotrzebowania tlenu po n dniach (BZTn) — Część 1: Metoda rozcieńczania i zaszczepiania z dodatkiem allilotiomocznika

Title (EN)

Water quality — Determination of biochemical oxygen demand after n days (BODn) — Part 1: Dilution and seeding method with allylthiourea addition

Step-by-step procedure

1. Estimating the expected BOD and selecting the dilutions

   Whether the result will be valid at all depends on this: with too little dilution the oxygen will be consumed entirely, with too much the depletion will be too small. The method covers a BOD from 1 to 6,000 mg/l; above 6,000 mg/l O2 the standard requires particular care in selecting samples for the successive dilutions.

2. Preparing the dilution water and the seed

   The dilution water must be saturated with oxygen and contain mineral additions; a seed is used where the sample contains no microflora of its own capable of breakdown. The details are given by the standard.

3. Adding allylthiourea

   ATU suppresses nitrification. This is not an optional step — it is in the title of the standard; without it the result also covers the oxygen consumed in oxidising ammonium nitrogen.

4. Filling the vessels and measuring the initial oxygen

   The vessels are filled without an air bubble; the dissolved-oxygen concentration is determined at the start. Blanks are prepared in parallel.

5. Incubation for 5 or 7 days

   At a defined temperature, with no access of light. The choice of period (BOD5 or BOD7) is part of the determination and must appear in the test report.

6. Measuring the final oxygen and calculating

   The difference in oxygen concentrations is converted through the dilution factor and corrected for the blank. The validity criteria of the determination (minimum depletion and minimum residual oxygen concentration after incubation) are given by the standard — we do not have its text, so we do not state them here.

7. Reporting the result

   State the indicator together with the incubation period (BOD5 or BOD7), the oxygen-measurement technique where the accreditation scope names it, and the standard in the form matching the scope. For testing under the regulation Dz.U. 2019 item 1311: the act names PN-EN 1899-1 and PN-EN 1899-2, and its explanatory note 2 requires the replacing standard to be regarded as recommended when a named standard has been replaced and withdrawn — in place of PN-EN 1899-1 today PN-EN ISO 5815-1; PN-EN 1899-2 has not been withdrawn.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• BOD is not the concentration of a substance — it is a measure of the oxygen consumed by micro-organisms under defined conditions; the standard itself states that these processes run reproducibly only occasionally
• A determination without suppression of nitrification (without ATU) gives an inflated result and is not a result under this standard
• BOD5 and BOD7 are different numbers from the same method — omitting the incubation period makes the result ambiguous
• The result depends on the choice of dilution: complete consumption of the oxygen, or too small a depletion, invalidates the determination
• The standard in force exists in the Polish collection in English only — a working translation is the laboratory's own responsibility
• The wastewater regulation points to the standards PN-EN 1899-1 and PN-EN 1899-2; for the first, replaced and withdrawn, the act itself requires the replacing standard to be regarded as recommended (explanatory note 2 to Annex 12) — for regulated testing one has to read the notes under the table as well, not only its rows

Training and video materials

• BOD5 Test Procedure — Hach (Source: Hach)
• BOD Measurement with OxiTop — Xylem/WTW (Source: WTW)

Frequently asked questions