⚗️ Settleable solids in water and wastewater — volume of sediment after 2 h in an Imhoff cone, PN-C-04559-03

Physicochemistry PN-72/C-04559/03

Overview

WHAT THE STANDARD COVERS. The scope from the PKN catalogue card, quoted in full: "The determination consists in establishing the volume of suspended solids that settle while a sample of water or wastewater stands for two hours in an lmhoff cone. This method is used to determine suspended solids contents above 0.05 ml/l that settle within 2 h of standing in an lmhoff cone." The spelling "lmhoff" (with the letter l) comes from the card; what is meant is the Imhoff cone — a conical vessel with a volume scale in its lower part.

STATUS (state of the card on 28 September 2026). The card carries the heading "Withdrawn" and the row "Date of withdrawal: 16-01-2006". There is no "Superseded by" field; "Supersedes: PN-C-04559:1955". Edition: published 29-11-1972, 1 page, PKN technical committee KT 119 (Water Quality — Basic Problems), ICS 13.060.60. This differs from sheet 02 of the same series (total, mineral and volatile suspended solids by the gravimetric method), which was withdrawn on 01-08-2002 and superseded by PN-EN 872:2002. The PKN search (29 September 2026) for "PN-C-04559" shows only PN-C-04559:1955 and sheets 01, 02 and 03 of 1972, and the three pages of results for "zawiesin" (suspended solids) contain no other standard on settleable solids in water or wastewater — we found no successor.

REGULATIONS: LIMIT VALUES AND A METHODOLOGY WITHOUT A STANDARD. The Regulation of the Minister of Construction of 14 July 2006 on the conditions for discharging wastewater into sewerage systems (consolidated text Journal of Laws 2016, item 1757, in force), Annex 2 ("Permissible values for other pollution indicators in industrial wastewater discharged into sewerage systems"), item 1: "Settleable solids" — 10 ml/l; § 16 requires the use of reference methodologies such as those in the regulations on discharging wastewater into waters or into the ground. Those regulations are the Regulation of the Minister of Maritime Economy and Inland Navigation of 12 July 2019 (Journal of Laws 2019, item 1311, in force): Annex 4 ("Highest permissible values of pollutants for industrial wastewater"), Table II, item 4 — "Settleable solids" 0.5 ml/l, with the scope-of-application column reading "Applies to all types of wastewater" and "Applies to all sectors"; Annex 12 ("Reference methodologies for the analysis of samples of wastewater and of rainwater or snowmelt water"), item 72 — "Settleable solids — volumetric method", with a dash in the standard column. For comparison, item 73 "Total suspended solids" in the same annex does have a standard: PN-EN 872. Conclusion for the laboratory: none of these regulations cites the withdrawn PN-C-04559-03, so its withdrawal does not conflict with the legal basis — the regulation requires a volumetric method, not this standard.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17 September 2026, read on 28 September 2026). All records of number 04559 with sheet 03: 18 entries at 17 laboratories. Forms: "PN-72/C-04559/03" — 11 laboratories (12 entries), "PN-72/C-04559.03" — 3 (AB 387, AB 1469, AB 1488), "PN-C-04559-03:1972" — 3 (AB 383, AB 901, AB 1226). The "Laboratories" tab searches for records BEGINNING with "PN-72/C-04559/03" and will show 11 laboratories in 12 entries; it will not show the other six. Test object: wastewater — all 17, of which eight also water. Technique: volumetric method — 16 laboratories; AB 418 writes "volumetric-sedimentation". AB 387 gives no measuring range; next to the standard number it has the note "(fixed scope)". Current scopes on the PCA website (read on 29 September 2026): all 18 entries stand in the valid issues with the same range as in the copy, and none is suspended — AB 1226 has items in its scope (issue 26 of 17 September 2026) suspended at its own request, but not this one.

RANGES AGAINST THE CARD AND THE REGULATIONS. All ranges given start above the card’s 0.05 ml/l: from 0.1 ml/l (AB 862), 0.2 (AB 300, AB 383, AB 1095, AB 1488) and 0.25 (AB 418), through 0.5 ml/l (eight laboratories), to 1.0 ml/l (AB 1469) — and AB 079 has two entries at two sites: in Gdynia from 1.0 and in Zgierz from 5 ml/l (PCA scope issue 71 of 15 May 2026). Upper limits: from 10 ml/l (AB 862) to 1000 ml/l (AB 383, AB 418). Against the 0.5 ml/l limit for industrial wastewater discharged into waters or into the ground: the ranges of AB 1469 (from 1.0) and both entries of AB 079 start above it, so a result "below the range" does not decide whether the wastewater meets the 0.5 ml/l requirement. The 10 ml/l limit for sewers lies within the ranges of all laboratories that give a range.

WHAT WE DO NOT GIVE. We did not have the text of the standard — PKN sells it (1 page). We do not give the capacity and dimensions of the cone, how it is filled and read, how bubbles and material on the walls are handled, the temperature or the precision.

Method principle

According to the card of the standard: a sample of water or wastewater is left for 2 hours in an Imhoff cone, and then the volume of the suspended solids that have settled in that time is read off; the result is in ml per litre of sample. The method covers contents above 0.05 ml/l. For industrial wastewater the result is compared with 10 ml/l (discharge into sewers, Journal of Laws 2016, item 1757) or 0.5 ml/l (discharge into waters or into the ground, Journal of Laws 2019, item 1311); both regulations require a "volumetric method" without naming a standard. We DO NOT GIVE the working details — we did not have the text of the standard.

Applications

• Industrial wastewater discharged into sewers — limit 10 ml/l (Journal of Laws 2016, item 1757, Annex 2, item 1)
• Industrial wastewater discharged into waters or into the ground — limit 0.5 ml/l, "Applies to all types of wastewater" (Journal of Laws 2019, item 1311, Annex 4, Table II, item 4)
• Monitoring of settling tanks and treatment plants — volume of the readily settling fraction of suspended solids in water and wastewater

Key parameters

Standard

Standard number

PN-C-04559-03:1972 (wersja polska)

Title (PL)

Woda i ścieki — Badania zawartości zawiesin — Oznaczanie zawiesin łatwoopadających metodą objętościową

Title (EN)

Water and wastewater — Tests for suspended solids content — Determination of settleable solids by the volumetric method

Step-by-step procedure

1. Status of the document

   PKN card: standard withdrawn on 16-01-2006, no successor (state of the card on 28 September 2026). The regulations require a "volumetric method" without a standard number — in the report the designation PN-C-04559-03:1972 is given as a description of how the test was performed.

2. Filling the cone

   The mixed sample of water or wastewater is poured into the Imhoff cone. Sample volume and procedure NOT GIVEN.

3. Sedimentation

   The sample is left in the cone for 2 hours (from the card).

4. Reading

   The volume of the settled solids is read on the graduation of the cone; result in ml/l.

5. Assessment

   For industrial wastewater, comparison with 10 ml/l (sewers) or 0.5 ml/l (waters and ground). A result "below the range" with a range starting at 1.0 ml/l does not decide compliance with 0.5 ml/l.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Wastewater may contain pathogenic microorganisms — work is done with gloves and goggles and with hygiene rules observed
• TECHNICAL NOTE: the regulations require a "volumetric method", not this standard — its withdrawal does not change the legal basis, but the working conditions must be described in the laboratory’s procedure

Frequently asked questions