# Council Directive of 21 May 1991 concerning urban waste water treatment (91/271/EEC), Division D: Reference methods for monitoring and evaluation of results

Extent: E+W+S+N.I.

Table 1:
Requirements 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.
Reduction in relation to the load of the influent.
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.
This requirement is optional.
Parameters
Concentration
Minimum percentage of reduction
Reference method of measurement
Biochemical oxygen demand (BOD5 at 20 °C) without nitrification
25 mg/l O2
70-90
40 under Article 4 (2)
Homogenized, 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
Chemical oxygen demand (COD)
125 mg/l O2
75
Homogenized, unfiltered, undecanted sample Potassium dichromate
Total suspended solids
35 mg/l
35 under Article 4 (2) (more than 10 000 p.e.)
60 under Article 4 (2) (2 000-10 000 p.e.)
90
90 under Article 4 (2) (more than 10 000 p.e.)
70 under Article 4 (2) (2 000-10 000 p.e.)
Filtering of a representative sample through a 0,45 μm filter membrane. Drying at 105 °C and weighing
Centrifuging 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
Analyses 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.
Reduction in relation to the load of the influent.
Total nitrogen means the sum of total Kjeldahl nitrogen (organic and ammoniacal nitrogen) nitrate-nitrogen and nitrite-nitrogen.
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.
Parameters
Concentration
Minimum percentage of reduction
Reference method of measurement
Total phosphorus
2 mg/l ( 10 000 — 100 000 p.e.)
80
Molecular absorption spectrophotometry
1 mg/l (more than 100 000 p.e.)
Total nitrogen
15 mg/l ( 10 000 - 100 000 p.e.)
70-80
Molecular absorption spectrophotometry
10 mg/l (more than 100 000 p.e.)
Table 3
Series of samples taken in any year
Maximum permitted number of samples which fail to conform
4-7
1
8-16
2
17-28
3
29-40
4
41-53
5
54-67
6
68-81
7
82-95
8
96-110
9
111-125
10
126-140
11
141-155
12
156-171
13
172-187
14
188-203
15
204-219
16
220-235
17
236-251
18
252-268
19
269-284
20
285-300
21
301-317
22
318-334
23
335-350
24
351-365
25

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Source: https://www.legislation.gov.uk/eudr/1991/271/annex/I/division/D (the official version)
Page: https://openlegislation.uk/eu-directive-1991-271/annex-I/division-D
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.