http://www.legislation.gov.uk/id/uksi/1994/2841/schedule/3

SCHEDULE 3

PART I REQUIREMENTS FOR DISCHARGES FROM TREATMENT PLANTS

5

The points of discharge of urban waste water shall be chosen, as far as possible, so as to minimise the effects on receiving waters.

TABLE 1 REQUIREMENTS FOR DISCHARGES FROM URBAN WASTE WATER TREATMENT PLANTS SUBJECT TO REGULATION 5(1) AND (2)

The values for concentration or for the percentage of reduction shall apply.

Parameters	Concentration	Minimum percentage of reduction {s001}	Reference method of measurement
Biochemical oxygen demand (BOD5 at 20°C without nitrification {s002}	25 mg/l O₂	70—90	Homogenized, unfiltered, undecanted sample. Determination of dissolved oxygen before and after five-day incubation at 20°+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
{s001} Reduction in relation to the load of the influent. {s002} 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.

Parameters

Concentration

Minimum percentage of reduction {s001}

Reference method of measurement

Biochemical oxygen demand (BOD5 at 20°C without nitrification {s002}

25 mg/l O₂

70—90

Homogenized, unfiltered, undecanted sample. Determination of dissolved oxygen before and after five-day incubation at 20°+1°C, in complete darkness. Addition of a nitrification inhibitor

Chemical oxygen demand (COD)

125 mg/l O₂

Homogenized, unfiltered, undecanted sample Potassium dichromate

{s001} Reduction in relation to the load of the influent.

{s002} 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.