Guidelines to Statutory Order on the Licensing of Waste Water Discharges 8. Emission limit values for certain substances discharged from public waste water systems8.1 Background 8.1 Background Part 8 of the Statutory Order establishes the national emission standards that apply to municipal water treatment plants. The national standards follow up on the Aquatic Environment Plan 1987 and implement the EU Directive on urban waste water treatment from 1991. The Aquatic Environment Plan To implement the Aquatic Environment Plan adopted by the Danish Folketing in 1987, emission limit values were fixed for the load of aerobic organic substances, total nitrogen and total phosphorus that may be discharged with effluent from public waste water systems. The limit values were first implemented for waste water systems representing more than 5,000 p.e., which had to complete the modifications necessary to improve their treatment quality by the end of 1992. However, a few systems were granted exemption from this time limit. Today, all waste water systems covered by the Aquatic Environment Plan have been modified to comply with the emission standards established in the Plan. The Urban Waste Water Treatment Directive The EU Directive on urban waste water treatment was implemented in Danish legislation by the previous statutory order on waste water management (Statutory Order no. 310 of 25 April 1994). In addition to the fixed emission standards established in the Aquatic Environment Plan, the Urban Waste Water Treatment Directive introduces the parameter ‘chemical oxygen demand (COD)’, in terms of which it defines a fixed emission standard for the load of aerobic organic substances discharged. This implies that it is not possible to stipulate higher limit values for aerobic organic substances measured as BOD5 (modified) and for COD, total nitrogen and total phosphorus in discharge licences, whereas lower limit values may be stipulated, always provided that this is in compliance with the quality objectives set in the regional plan for the receiving water body. These rules also apply to the revision of existing discharge licences, provided that it is estimated that the total load of the system whose licence is to be revised has increased to a level exceeding the capacity limits fixed in section 18 of the Statutory Order. 8.1.1 Determining the capacity of a municipal waste water system How to determine capacity Whether the rules regarding fixed emission standards are directly applicable to a given system depends on its capacity. The capacity is determined in terms of the volume of waste water that may be discharged from the catchment area of the waste water system concerned under a licence issued by the regional council. Pursuant to section 17 of the Statutory Order, the regional council must define the capacity of the system in the discharge licence. In determining the capacity of a given public waste water system, allowance should be made for the load represented by properties connected to the discharge pipe of the system and located within its catchment area, cf. section 28(3) of the Environmental Protection Act. To the extent that no capacity (expressed in p.e.) is specified for the catchment area identified in the current waste water plans, the capacity must be determined in accordance with section 17 of the Statutory Order on the basis of the definition of one p.e. given in section 4(5) of the Statutory Order, cf. Chap. 2 on definitions. 8.2 Waste water treatment plants subject to national emission standards Types of plant subject to emission standards In implementation of the EEC Urban Waste Water Treatment Directive, section 18(1) of the Statutory Order establishes a requirement for a reduction of the load of organic substances measured as BOD5 (modified) and COD in the effluent from waste water treatment plants having a minimum capacity of 2000 p.e. and discharging into fresh waters, watercourses and lakes. In continuation of the Aquatic Environment Plan, section 18(2) of the Statutory Order establishes requirements for a reduction of the total phosphorus load emitted by plants having an approved capacity of at least 5,000 p.e. In addition, plants in this category are required to reduce their effluent loads of BOD5 (mod.) and COD as from 1 January 1999 in accordance with the EEC Urban Waste Water Treatment Directive. Further in continuation of the Aquatic Environment Plan, section 18(3) of the Statutory Order provides that plants having a capacity of 15,000 p.e. or more are subject to certain requirements regarding a reduction of BOD5 (mod.), total nitrogen and total phosphorus. As from 1 January, 1999, this type of plant is also subject to requirements in respect of reduced COD levels in accordance with the Urban Waste Water Treatment Directive. Table 8.1 summarises the types of municipal treatment plant that are subject to the national emission standards. Table 8.1.
- : Not subject to emission standards Emission standards are fixed according to capacity The approved capacity is the criterion that determines the emission standards to be met by a municipal waste water treatment plant. The capacity of a given plant is to be understood as the approved capacity defined in the discharge licence, cf. section 4(8) of the Statutory Order. In connection with the licensing of discharges from waste water treatment plants having a capacity of at least 5,000 p.e. in cases involving either the establishment of a new treatment plant or an increase of the approved capacity of an existing plant, compliance with the limit values applying to BOD5 (mod.), COD, total nitrogen and total phosphorus must be ensured, cf. section 18(4) of the Statutory Order. This provision does not apply to variations of discharge licences effected to update emission standards, or to minor adjustments of emission standards that do not entail major modification of the plant concerned. Similarly, variation of a discharge licence merely to stipulate a new monitoring method according to the current Danish Standard is not subject to the provisions of section 18(4). 8.3 National emission standards Section 19(1) of the Statutory Order lists the limit values for substances discharged from treatment plants subject to national emission standards. These limit values are shown in table 8.2 below. Effluent monitoring should be based on flow-weighted 24-hour samples. The samples are to be analysed according to current Danish standards and codes of practice: Table 8.2
The procedures for collecting and analysing effluent samples must conform with the rules laid down in Statutory Order No. 637 of 30 July 1997 on quality standards for environmental measurements by accredited laboratories, certified individuals, etc. 8.3.1 Monitoring procedure for treated effluent Under the provisions on municipal treatment plants laid down in the previous version of the Statutory Order, effluent monitoring was subject to Danish EPA’s Environmental Guidelines No. 42 of 11 January 1988 on national standards for discharges from municipal treatment plants into watercourses, lakes or the sea. These guidelines stipulate the use of the modified, more stringent procedure for control of the daily average discharge of waste water laid down in Dansk Ingeniørforening’s Code of Practice for water pollution control, 1st edition, May 1971. This has now been changed, cf. section 19(2) of the Statutory Order, to the Danish standard for effluent monitoring and statistical computation of effluent data from time to time in force. The current standard is DS 2399: Effluence control – Control computation of effluence data. This standard entered into force in April 1999, with effect from 1 January 2000, cf. section 19(2) of the Statutory Order. Monitoring should be based on measurement of daily discharge volumes. For this purpose, at least 12 samples should be collected at regular intervals throughout the inspection period (one year), cf. section 19(3) of the Statutory Order. According to section 19(4) of the Statutory Order, monitoring of treatment plants having an approved capacity of at least 50,000 p.e. must be based on a 12-month inspection period and a minimum of 24 24-hour samples taken at regular intervals throughout the year. For the purpose of monitoring ordinary waste water, it is recommended not to increase the number of samples significantly beyond one weekly sample without considering inspection based on random sampling. To verify whether the standard stipulated in the licence applying to the waste water treatment plant is met, the recorded, flow-weighted mean load should be less than or equal to the maximum concentration specified in the licence. 8.3.2 Minimum number of effluent samples Minimum number of samples for effluent monitoring Section 19(3 and 4) of the Statutory Order establishes the minimum number of samples to be taken for the purpose of monitoring effluent compliance with the parameters defined in section 18 of the Statutory Order and the corresponding limit values fixed in section 19(1) of the Statutory Order. Section 19(3) of the Statutory Order was inserted in connection with the adoption of the Aquatic Environment Plan, according to which it is the responsibility of the local council, in cooperation with the regional council, to provide the requisite data and plan a timetable for sample collection. Any similar measurements requested by the regional council in its capacity of supervisory authority will be used for monitoring purposes on a par with measurements made by the local council. Under the national monitoring program, most recently revised in 1998, the regional authorities have agreed to take responsibility for ensuring that a minimum number of samples, depending on the size of the plant, are collected. Section 19(4) of the Statutory Order implements requirements laid down in the EEC Urban Waste Water Directive. Local councils responsible for municipal treatment plants whose capacity equals or exceeds 15,000 p.e. must ensure that a total of 24 samples are taken. Any similar measurements requested by the regional council in its capacity of supervisory authority will be used for monitoring purposes on a par with measurements made by the local council. The national requirements applying to sampling of municipal treatment plant effluents are summarised in table 8.3. Table 8.3
Internal control: Sampling as stipulated in the discharge licence issued for the plant. The table summarises the requirements set out in section 19(3 and 4) of the Statutory Order and in the agreement on the effluent sampling to be carried out by the regional council as part of the monitoring programme adopted under the Aquatic Environment Plan, revised most recently in 1998 and at the same time renamed NOVA 2003. 8.4 Administrative provisions Generally, the provisions laid down in sections 18-19 of the Statutory Order do not imply a requirement to apply for a new discharge licence. However, in the case of any other changes to a waste water system, such as the establishment of a new outfall, or the stipulation of additional requirements in order to ensure appropriate verification of compliance with the Statutory Order, a new discharge licence will have to be obtained under section 28 of the Environmental Protection Act. 8.5 Supervision and enforcement According to section 52 of the Statutory Order, the regional council is responsible for supervising all municipal waste water effluents described in this chapter. The regional council must ensure that the treatment plants meet the national emission standards. In the case of non-compliance with the emission standards, the regional council must take enforcement action against such unlawful conduct under Part 9 of the Environmental Protection Act.
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