⚖️ Suspended solids to PN-EN 872 — and the upper limit the standard does not give

Physical chemistry PN-EN 872

Overview

SCALE: THE SECOND MOST FREQUENTLY CITED STANDARD IN THE SCOPE DATABASE. Measurement of 22 Sep 2026: 340 entries at 251 laboratories; matching by the BEGINNING of the recorded string gives 338 entries at the same 251 laboratories — here the two figures are almost equal, because the standard nearly always stands alone in the citation.

STATUS (state of the PKN catalogue cards on 22 Sep 2026). PN-EN 872:2007 — POLISH VERSION, published 17 May 2007, 12 pages, ICS 13.060.30 and 13.060.60, technical body KT 119 (Water Quality — Fundamental Problems). The "Implements" field: EN 872:2005 [IDT]. The card carries no withdrawal note and no "Replaced by" line — the standard is CURRENT. Under "Additional elements" the card lists PN-EN 872:2007/Ap1:2007P, that is, the CORRIGENDUM in the Polish version; this is what appears in the scopes as the element "+Ap1:2007". THE TEXT OF THE CORRIGENDUM IS AVAILABLE FREE OF CHARGE — and it changes the result of the test. Beside the "Additional elements" field on the card there is a link to a PDF file (sklep.pkn.pl/fileuploader/download/download/?d=0&fileId=5909); direct download returns an error, but the file opens through the r.jina.ai reader. The corrigendum runs to two pages, was drawn up by KT 119 for Water Quality — Fundamental Problems, was approved on 10 August 2007, and its content is TWO points: • point 1 — editorial: in the Foreword, fifth paragraph, "Removal" is to read "Emptying"; • point 2 — SUBSTANTIVE: in 5.3, "150 °C" is to read "105 °C". The second point concerns the DRYING TEMPERATURE of the filter. A difference of forty-five degrees changes the mass: at 150 °C part of the material escapes that at 105 °C stays on the filter, and the mass of the filter is the entire result of this method. A laboratory working from the standard without the corrigendum dries at the wrong temperature — and that is why the element "+Ap1:2007" in a citation is not an ornament of the designation but an indication that the provider knows the corrected value. The link and the text of the corrigendum were checked on 22 Sep 2026.

THE CHAIN OF EDITIONS, AND A CHANGE VISIBLE IN THE SCOPE DESCRIPTION ITSELF: • PN-EN 872:2002 (Polish version, implementing EN 872:1996) — withdrawn 15 Jun 2005. Its scope description ends with the sentence: "The result presented may not include very finely divided or COLLOIDAL substances". • PN-EN 872:2005 (English and German versions, already implementing EN 872:2005) — withdrawn 17 May 2007. Here the scope description introduces a sentence about the INSTABILITY of samples. • PN-EN 872:2007 (Polish version of the same EN 872:2005) — the edition in force. Between the 2002 edition and the present one the emphasis of the warning therefore shifted: from "the result may not include colloidal substances" to "the suspended-solids content depends on storage time, transport and pH". Both warnings concern the same thing — that "suspended solids" is not a property of the sample independent of what happened to the sample after it was taken.

WHAT THE STANDARD STATES EXPRESSLY (from the scope description on the PKN card): a method for determining suspended solids in RAW WATER, WASTEWATER and TREATED WASTEWATER, using filtration through glass-fibre filters. THE LIMIT OF DETERMINATION IS 2 mg/l. NO UPPER LIMIT OF DETERMINATION IS SET. Water samples are not always stable, and therefore the suspended-solids content depends on storage time, the manner of transport, the pH value and other factors; results from unstable samples are to be interpreted with caution.

THE UPPER LIMIT — THE MOST IMPORTANT MATTER IN THIS ARTICLE. Since the standard sets no upper limit, every upper figure in an accreditation scope comes from VALIDATION AT THAT PARTICULAR LABORATORY. Measurement of 22 Sep 2026: 71 entries at 55 laboratories declare a measuring range, and the declared upper limits stretch from 30 mg/l to 15,000 mg/l — a FIVE-HUNDREDFOLD span. The commonest: 2.0–1000 mg/l (13 entries), 2.0–5000 (7), 2.0–2000 (6), 2.0–500 (5), 5.0–2000 (4), 5.0–6000 (3), 4.0–500 (3). A practical conclusion for the purchaser: for raw wastewater or diluted sludge the question "does the laboratory hold PN-EN 872" is not enough — one has to check the UPPER limit in its scope, because the difference between 500 and 15,000 mg/l decides whether the sample can be tested without dilution. The lower limit, in turn, may be HIGHER than in the standard: beside the commonest 2.0 mg/l (in line with the standard), the scopes carry 3.0, 4.0, 5.0 and 10.0 mg/l. A laboratory may declare a limit more cautious than the standard's — but that means it will not report a result below its own limit, even though the standard provides for the method down to 2 mg/l.

RECORDING THE CORRIGENDUM — FOURTEEN FORMS OF ONE DESIGNATION. The same standard appears in the scopes as: "PN-EN 872:2007+Ap1:2007" (273 entries), "PN-EN 872:2007 + Ap1:2007" (24), "PN-EN 872:2007 | PN-EN 872:2007/Ap1:2007" (9), "PN-EN 872:2007+ Ap1:2007" (6), "PN-EN 872:2007+Ap.1:2007" (5), "PN-EN 872:2007 +Ap1:2007" (4), "PN-EN 872" without the year (4), "PN-EN 872:2007" without the corrigendum (2) and others — FOURTEEN different forms in all. Six entries do not mention the corrigendum at all. The differences come down to spaces before and after the "+" sign, the full stop in "Ap.1" and the recording of the corrigendum as a separate document after a vertical bar. A search key matching the exact character string — for example "PN-EN 872:2007+Ap1:2007" — misses 67 entries out of 340, that is, every fifth.

WHAT THE SCOPES SHOW. The methodology is almost always "Suspended solids" (264 entries), less often with the range and technique added ("Gravimetric method"). Test objects: water and wastewater in various wordings (86 + 39 + 13), wastewater alone (68), water alone (15), rain and meltwater (9). This is the basic method of a wastewater treatment plant — suspended solids are one of the indicators for which a water-law permit sets limit values.

WHAT THIS ARTICLE DOES NOT SETTLE. We have neither the text of the standard nor the text of corrigendum Ap1 — CEN does not release sample extracts the way ISO does. Everything above comes from the scope descriptions on three PKN catalogue cards and from measurement on the accreditation scopes. We therefore do not know: the diameter and type of filter, the drying temperature and time, the sample volume, the manner of preparing the filter, or the content of the corrigendum. Those data have to be taken from the standard itself.

Method principle

A measured volume of the sample is filtered through a glass-fibre (borosilicate) filter. The solids retained on the filter, together with the filter, are dried under defined conditions and weighed; the mass of suspended solids is determined as the difference between the mass of the filter after and before filtration, and the result is referred to the volume of the filtered sample. The result covers only what the filter retains — very fine particles and colloidal substances may pass through the filter and will not be reported.

Applications

• Control of raw and treated wastewater — suspended solids are an indicator in water-law permits
• Testing of surface waters and of raw water before treatment
• Rain and meltwater discharged from paved surfaces
• Control of settling-tank operation and assessment of the effectiveness of mechanical treatment
• Reading an accreditation scope in which the upper limit of determination comes from the laboratory, not from the standard

Key parameters

Standard

Standard number

PN-EN 872:2007 + Ap1:2007 (wersja polska; wprowadza EN 872:2005 [IDT])

Title (PL)

Jakość wody — Oznaczanie zawiesin — Metoda przez filtrację przez sączki z włókna szklanego

Title (EN)

Water quality — Determination of suspended solids — Method by filtration through glass fibre filters

Step-by-step procedure

1. Checking whether the sample falls within the PROVIDER's range

   The standard gives only the lower limit (2 mg/l) and sets no upper one. What decides is therefore the range in the laboratory's accreditation scope — in the scope database the upper limits run from 30 to 15,000 mg/l. For raw wastewater, check this BEFORE placing the order.

2. Sampling and transport

   A STEP FROM THE STANDARD'S WARNING: the suspended-solids content depends on storage time, the manner of transport and pH. The longer the sample waits, the more the result describes the history of the sample rather than the state of the effluent at the moment of sampling.

3. Preparing and weighing the filter

   The glass-fibre filter is prepared and weighed before filtration. The conditions of preparation (rinsing, drying) are given by the standard — we do not have its text, so we do not state them here.

4. Filtering a measured volume of sample

   The volume is chosen so that the mass of retained solids falls within the weighing range and so that the filter does not clog. For samples rich in solids the volume has to be smaller — and it is that, alongside validation, which decides the practical upper limit.

5. Drying at 105 °C, cooling and weighing

   A STEP CHANGED BY THE CORRIGENDUM: clause 5.3 of the standard gave 150 °C, and corrigendum Ap1:2007 replaced that value with 105 °C. The filter with the solids is therefore dried at 105 °C, cooled in a desiccator and weighed. The mass of suspended solids is the difference between the mass of the filter after and before filtration — which is why the drying temperature is not a detail here but a quantity bearing directly on the result.

6. Calculating and reporting the result

   The result is referred to the volume of the filtered sample and reported in mg/l. A result below the laboratory's limit of determination is reported as less than that limit — and the limit may be higher than the standard's 2 mg/l.

7. Recording the citation together with the corrigendum

   The citation should include the corrigendum, in the form matching the accreditation scope. In the scopes the same standard appears in fourteen forms — mixing them makes it harder to check a test report against the scope.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The upper limit of the range in an accreditation scope does NOT come from the standard — the standard does not set one. Comparing laboratories "by the standard" says nothing about how concentrated a sample each of them will test
• A laboratory's lower limit may be higher than the standard's 2 mg/l — "below the limit" means different things at different providers
• The result covers only what the filter retained; very finely divided and colloidal substances may pass through and will not be reported
• The suspended-solids content changes with storage time, the manner of transport and pH — a result from an unstable sample has to be interpreted with caution
• A citation without the "+Ap1:2007" element omits the corrigendum that changes the DRYING TEMPERATURE from 150 °C to 105 °C — a quantity bearing directly on the mass and on the result; in the accreditation scopes six entries do not mention it
• Drying at 150 °C (the value in the standard BEFORE the corrigendum) gives a different mass than at 105 °C — at the higher temperature part of the material escapes
• Searching for this standard on an exact character string misses every fifth entry — there are fourteen forms of the recorded string

Frequently asked questions