heading
EnvironmentEN1ASet standards for quality of effluent discharges arising from wastewater services
Environment regulators translate national environmental standards and norms into established regulatory frameworks for water and sanitation services within their mandate.
They therefore transpose national environmental directives into policies, guidelines, and frameworks, with the objective of protecting the environment from noxious substances discharged through wastewater services. Most commonly, regulators outline a list of substances, along with permissible limits, allowed for municipal, industrial, or agricultural wastewater disposal.
Expected outcomes
- Environmental norms are properly integrated within water and sanitation sectors.
- Service operators’ contracts adequately reflect their environmental duties.
- Environmental protection is ensured through clearly defined effluent quality standards.
Examples
Colombia
In Colombia, Resolution No. 0631 of 2015 stipulates the maximum permissible parameters and limits in the dumping of wastewater into surface water bodies and public sewerage systems. This regulation changed a set of very limited parameters that had been established in 1984 and set forth the maximum permissible parameters.
The regulation also establishes parameters for active ingredients in pesticides in Toxicity Classes I-a, I-b and II, and the maximum permissible limits when dumping non-domestic wastewater (ARND) into the public sewerage system.
Mexico
In Mexico, Official Mexican Regulation NOM-002-ECOL-1996 establishes the maximum permissible contaminant limits allowed in wastewater discharged into the urban or municipal sewerage systems. The regulation establishes the maximum permissible contaminant limits allowed in wastewater discharged into the urban or municipal sewerage systems with the aim of preventing and controlling the contamination of water bodies and national resources as well as protecting the infrastructure of such systems and requires mandatory compliance from entities conducting such discharges.
Pursuant to the regulation, the maximum permissible contaminant limits in wastewater discharged into the urban or municipal sewerage systems should not exceed those indicated in the following table. In the case of grease and oils, it is the weighted average according to flow, based on results from analyses carried out on each of the individual samples.
| MAXIMUM PERMISSIBLE LIMITS | |||
| PARAMETERS
(milligrams per liter, unless otherwise specified) |
Monthly Average
|
Daily Average
|
Instantaneous |
| Grease and Oils | 50 | 75 | 100 |
| Sedimentable solids | 0.5 | 0.75 | 10 |
| Total cadmium | 0.5 | 0.75 | 1 |
| Total cyanide | 1 | 1.5 | 2 |
| Total copper | 10 | 15 | 20 |
| Hexavalent chromium | 0.5 | 0.75 | 1 |
| Total mercury | 0.01 | 0.015 | 0.02 |
| Total nickel | 4 | 6 | 8 |
| Total lead | 1 | 1.5 | 2 |
| Total zinc | 6 | 9 | 12 |
The maximum permissible limits are only reference values; if a value exceeds the reference value in the table, the entity responsible for the discharge is obliged to provide the competent authority with the daily and monthly averages, as well as the laboratory results of the corresponding analyses, in a timely manner and as required by local legal codes.
Tanzania
In Tanzania, wastewater effluent quality discharges should comply with the latest national standard (TZS 860:2006) on limits for municipal and industrial wastewaters. The standard prescribes permissible limits for municipal and industrial effluents discharged directly into water bodies, and its use promotes a consistent approach towards prevention of water pollution.
| Table 2a: Physical Components | ||
| Parameter | Limit | Test Method |
| BOD5 at 20°C | 30 mg/L | EMDC1 1173: Part 3 ± Five-day BOD Method |
| COD | 60 mg/L | EMDC1 1173: Part 4 ± Dichromate Digestion Method |
| Color | 300 TCU | ISO 7887: 1994, Water quality ± Examination and determination of color ± Section 3: Determination of true color using optical instruments |
| pH range | 6.5-8.5 | EMDC1 1173: Part 2 ± Electrometric Method |
| Temperature range | 20-35°C | See Annex A |
| Total Suspended Solids | 100 mg/L | EMDC1 1173: Part 1 ± Gravimetric Method |
| Turbidity | 300 NTU | APHA Standard Methods:2130 B. Nephelometric Method |
| Table 2d: Microbiological Components | ||
| Parameter | Limit | Test Method |
| Total Coliform Organisms | 10,000counts/100mL | ISO 6222: 1999, Microbiological methods |
Sample of permissible limits for municipal and industrial wastewaters (TZS 860:2006).
United Kingdom
In the UK, the EU Urban Wastewater Treatment Directive was transposed in 1991 into UK law through the Urban Wastewater Treatment Regulations (1994). They detail the following standards for discharges from wastewater treatment plants.
- Discharges from urban wastewater treatment plants subject to treatment in accordance with regulation 5(1) and (2) shall, subject to paragraphs 4 and 5 of Part II of this Schedule, meet the requirements shown in Table 1.
- Discharges from urban waste water treatment plants to those sensitive areas which are subject to eutrophication as identified in sub-paragraph (a) of Part I of Schedule 1 shall, subject to paragraphs 4 and 5 of Part II of this Schedule, also meet the requirements in Table 2.
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TABLE 1 REQUIREMENTS FOR DISCHARGES FROM URBAN WASTE WATER TREATMENT PLANTS SUBJECT TO REGULATE 5(1) AND (2) The values for concentration or for the percentage of reduction shall apply. |
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|
Parameters |
Concentration |
Minimum percentage of reduction1 |
Reference method of measurement |
| Biochemical oxygen demand (BOD5 at 20°C without nitrification2) | 25mg/I 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 oxyzen demand(COD) | 125 mg/I O2 | 75 | Homogenized, unfiltered, undecanted sample Potassium dichromate |
|
1. Reduction in relation to the load of the influent. 2. 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. |
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TABLE 2 REQUIREMENTS FOR DISCHARGES FROM URBAN WASTE WATER TREATMENT PLANTS TO SENSITIVE AREAS WHICH ARE SUBJECT TO EUTROPHICATION AS IDENTIFIED IN SUB-PARAGRAPH(a) OF PART I OF SCHEDULE 1 One or both parameters may be applied depending on the local situation. The values for concentrattion or for the percentage of reduction shall apply. |
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|
Parameters |
Concentration |
Minimum percentage of reduction1 |
Reference method of measurement |
| Total phosphorus | 2 mg/l P (10,000-100,000 p.e.) 1 mg/l P (more than 100,000 p.e.) | 80 | Molecular absorption spectrophotometry |
| Total nitrogen2 | 15 mg/l N (10,000-100,000 p.e.) 10 mg/l N (more than 100,000 p.e.) | 70-80 | Molecular absorption spectrophotometry |
|
1. Reduction in relation to the load of the influent. 2. Total nitrogen means; thee sum of total Kjeldahl-nitrogen (organic N +NH3), nitrate(NO3)-nitrogen and nitrite(NO2)-nitrogen. |
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Links
Colombia: Maximum permissible limits in dumping
https://www.minambiente.gov.co/wp-content/uploads/2021/11/resolucion-631-de-2015.pdf
Mexico: Maximum permissible limits
https://www.profepa.gob.mx/innovaportal/file/3295/1/nom-002-semarnat-1996.pdf
Tanzania: Water and Wastewater Quality Monitoring Guidelines for Water Utilities
UK: The Urban Waste Water Treatment (England and Wales) Regulations 1994
https://www.legislation.gov.uk/uksi/1994/2841/schedule/3/made
Internal capacities needed and the role of partners
Establishing wastewater effluent quality standards requires a blend of technical and legal expertise, including an understanding of the current level of wastewater treatment, laboratory testing capacity, and the ambient water quality status of receiving water bodies and their relative ecological vulnerability.
Development partners and environmental civil society groups are well placed to provide technical support governments and regulators through capacity and knowledge building workshops, and could potentially help support a national review and mapping of existing evidence of ambient water quality and ecological status, upon which regulators could designate ecologically sensitive receiving water bodies and plan further ecological surveys if needed.