{
  "url": "https://openlegislation.uk/eu-directive-1991-271/annex-I/division-D",
  "json_url": "https://openlegislation.uk/eu-directive-1991-271/annex-I/division-D.json",
  "legislation": "eudr/1991/271",
  "legislation_title": "Council Directive of 21 May 1991 concerning urban waste water treatment (91/271/EEC)",
  "legislation_url": "https://openlegislation.uk/eu-directive-1991-271",
  "path": "annex/I/division/D",
  "kind": "division",
  "number": "D",
  "heading": "Reference methods for monitoring and evaluation of results",
  "text": "Table 1:\nRequirements for discharges from urban waste water treatment plants subject to Articles 4 and 5 of the Directive. The values for concentration or for the percentage of reduction shall apply.\nReduction in relation to the load of the influent.\nThe parameter can be replaced by another parameter: total organic carbon (TOC) or total oxygen demand (TOD) if a relationship can be established between BOD5 and the substitute parameter.\nThis requirement is optional.\nParameters\nConcentration\nMinimum percentage of reduction\nReference method of measurement\nBiochemical oxygen demand (BOD5 at 20 °C) without nitrification\n25 mg/l O2\n70-90\n40 under Article 4 (2)\nHomogenized, unfiltered, undecanted sample. Determination of dissolved oxygen before and after five-day incubation at 20 °C ± 1 °C, in complete darkness. Addition of a nitrification inhibitor\nChemical oxygen demand (COD)\n125 mg/l O2\n75\nHomogenized, unfiltered, undecanted sample Potassium dichromate\nTotal suspended solids\n35 mg/l\n35 under Article 4 (2) (more than 10 000 p.e.)\n60 under Article 4 (2) (2 000-10 000 p.e.)\n90\n90 under Article 4 (2) (more than 10 000 p.e.)\n70 under Article 4 (2) (2 000-10 000 p.e.)\nFiltering of a representative sample through a 0,45 μm filter membrane. Drying at 105 °C and weighing\nCentrifuging of a representative sample (for at least five mins with mean acceleration of 2 800 to 3 200 g), drying at 105 °C and weighing\nAnalyses concerning discharges from lagooning shall be carried out on filtered samples; however, the concentration of total suspended solids in unfiltered water samples shall not exceed 150 mg/l.\nReduction in relation to the load of the influent.\nTotal nitrogen means the sum of total Kjeldahl nitrogen (organic and ammoniacal nitrogen) nitrate-nitrogen and nitrite-nitrogen.\nThese values for concentration are annual means as referred to in Annex I, paragraph D.4(c). However, the requirements for nitrogen may be checked using daily averages when it is proved, in accordance with Annex I, paragraph D.1, that the same level of protection is obtained. In this case, the daily average must not exceed 20 mg/l of total nitrogen for all the samples when the temperature from the effluent in the biological reactor is superior or equal to 12 °C. The conditions concerning temperature could be replaced by a limitation on the time of operation to take account of regional climatic conditions.\nParameters\nConcentration\nMinimum percentage of reduction\nReference method of measurement\nTotal phosphorus\n2 mg/l ( 10 000 — 100 000 p.e.)\n80\nMolecular absorption spectrophotometry\n1 mg/l (more than 100 000 p.e.)\nTotal nitrogen\n15 mg/l ( 10 000 - 100 000 p.e.)\n70-80\nMolecular absorption spectrophotometry\n10 mg/l (more than 100 000 p.e.)\nTable 3\nSeries of samples taken in any year\nMaximum permitted number of samples which fail to conform\n4-7\n1\n8-16\n2\n17-28\n3\n29-40\n4\n41-53\n5\n54-67\n6\n68-81\n7\n82-95\n8\n96-110\n9\n111-125\n10\n126-140\n11\n141-155\n12\n156-171\n13\n172-187\n14\n188-203\n15\n204-219\n16\n220-235\n17\n236-251\n18\n252-268\n19\n269-284\n20\n285-300\n21\n301-317\n22\n318-334\n23\n335-350\n24\n351-365\n25",
  "extent": "E+W+S+N.I.",
  "status": null,
  "version": "current",
  "annotations": [
    {
      "type": "F",
      "label": "F1",
      "text": "Substituted by Commission Directive 98/15/EC of 27 February 1998 amending Council Directive 91/271/EEC with respect to certain requirements established in Annex I thereof (Text with EEA relevance)."
    },
    {
      "type": "X",
      "label": "X1",
      "text": "Substituted by Corrigendum to Commission Directive 98/15/EC of 27 February 1998 amending Council Directive 91/271/EEC with respect to certain requirements established in Annex I thereof (Official Journal of the European Communities L 67 of 7 March 1998)."
    },
    {
      "type": "footnote",
      "label": "f1",
      "text": "Reduction in relation to the load of the influent."
    },
    {
      "type": "footnote",
      "label": "f2",
      "text": "The parameter can be replaced by another parameter: total organic carbon (TOC) or total oxygen demand (TOD) if a relationship can be established between BOD5 and the substitute parameter."
    },
    {
      "type": "footnote",
      "label": "f3",
      "text": "This requirement is optional."
    },
    {
      "type": "footnote",
      "label": "f4",
      "text": "Reduction in relation to the load of the influent."
    },
    {
      "type": "footnote",
      "label": "f5",
      "text": "Total nitrogen means the sum of total Kjeldahl nitrogen (organic and ammoniacal nitrogen) nitrate-nitrogen and nitrite-nitrogen."
    },
    {
      "type": "footnote",
      "label": "f6",
      "text": "These values for concentration are annual means as referred to in Annex I, paragraph D.4(c). However, the requirements for nitrogen may be checked using daily averages when it is proved, in accordance with Annex I, paragraph D.1, that the same level of protection is obtained. In this case, the daily average must not exceed 20 mg/l of total nitrogen for all the samples when the temperature from the effluent in the biological reactor is superior or equal to 12 °C. The conditions concerning temperature could be replaced by a limitation on the time of operation to take account of regional climatic conditions."
    }
  ],
  "outstanding_effects": [],
  "provenance": {
    "source": "legislation.gov.uk",
    "source_url": "https://www.legislation.gov.uk/eudr/1991/271/annex/I/division/D",
    "retrieved_at": "2026-11-01T15:23:25.830639+00:00"
  },
  "licence": "Open Government Licence v3.0",
  "licence_url": "https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/",
  "attribution": "Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives."
}