Effluent discharge limits in Angola
Angola’s water-quality regulation establishes national emission-limit values for wastewater discharged to water or soil, and it makes a discharge licence central to the regime. A public sewer connection is not a workaround: industrial clients need the network operator’s authorisation and must respect the parameters written into the discharge licence.
Angola’s national wastewater emission limits in Annex VI to Presidential Decree No. 261/11 include BOD₅ 40 mg/L, COD 150 mg/L, total suspended solids 60 mg/L, total nitrogen 15 mg/L, total phosphorus 3 mg/L, pH 6.0–9.0, oils and mineral hydrocarbons 15 mg/L, and detergents 2 mg/L.
The values are monthly averages. A representative 24-hour daily sample may not exceed twice the monthly average. The Ministry responsible for environment issues the discharge licence; an industrial discharge to a public sanitation system also requires authorisation by its operating entity.
Annex VI: national emission limits for wastewater discharge
Presidential Decree No. 261/11 approved the Regulation on Water Quality. Chapter III covers protection of water against pollution from wastewater discharge and Annex VI gives the Valores Limites de Emissão (VLE). The regulation prohibits using deliberate dilution as a substitute for treatment.
| Parameter | Emission limit | Relevance to a flotation plant |
|---|---|---|
| pH | 6.0–9.0 monthly average | Final pH control is required after coagulant dosing. The daily value may lie within 5.0–10.0. |
| Temperature | Maximum increase of 3 °C in receiving water | Hot discharge needs equalisation/cooling; evaluate 30 m downstream as specified. |
| BOD₅ at 20 °C | 40 mg O₂/L | Requires biological treatment for soluble organic load. |
| COD | 150 mg O₂/L | DAF removes particulate COD but not most dissolved organics. |
| Total suspended solids | 60 mg/L | A stable DAF should achieve this with a good safety margin on high-FOG effluent. |
| Total nitrogen | 15 mg N/L | Needs nitrification/denitrification where ammonia or organic nitrogen is high. |
| Total phosphorus | 3 mg P/L | Iron coagulant at the DAF can be an efficient phosphorus-removal step. |
| Aluminium | 10 mg/L | Monitor residual aluminium when alum or PAC is used. |
| Total iron | 2 mg/L | Important constraint on high ferric dosing; final pH and solids capture matter. |
| Total manganese | 2 mg/L | Relevant to mining and industrial groundwater streams. |
| Mineral oils | 15 mg/L | Free-oil separation followed by DAF is the normal treatment sequence. |
| Detergents (sodium lauryl sulphate) | 2 mg/L | Source control is crucial because surfactants interfere with flotation and biology. |
| Total cyanide | 0.5 mg/L | Dedicated destruction process; segregate from acid streams. |
| Sulphides | 1.0 mg/L | Iron dosing can precipitate sulphide but upstream H₂S safety must be controlled. |
How the limits are averaged
The VLE is a monthly average: the arithmetic mean of daily averages for the operating days in a month. The daily value comes from a representative wastewater sample taken over 24 hours, composed to reflect the discharge regime. The daily sample may not exceed twice the monthly average. That is a meaningful operational requirement: a plant that has one severe production-day upset every week is unlikely to comply even if the monthly grab-sample average looks acceptable.
For DAF systems, use an effluent flow meter, a final composite-sampler location after the last treatment stage, and recorded pH/chemical dose/float removal. Equalisation converts batch cleaning and production shocks into a treatable feed; it is often the difference between compliance and a series of 24-hour failures.
Licence and public sewer connection
Article 13 of the water-quality regulation requires a licence from the Ministry responsible for environment for wastewater discharge to water or soil; the licence fixes the applicable discharge standards. It also makes deliberate pre-discharge dilution unlawful. The authority can prohibit the discharge and revoke the licence after a non-compliance is not corrected.
For discharge to a public sanitation system, the 2023 public water and wastewater service regulation requires industrial clients to obtain the corresponding authorisation from the operating entity and comply with the parameters defined in the discharge licence. The operator may sample, require emergency retention capacity, and require industrial pre-treatment. Do not assume that the national outfall values are automatically acceptable to the network.
What this means for DAF design in Angola
- DAF is strong on oils, solids and phosphorus. The 15 mg/L mineral-oil and 60 mg/L TSS objectives are normal flotation duties; 3 mg/L phosphorus is practical with iron dosing.
- COD 150 mg/L and BOD₅ 40 mg/L are usually a biological-treatment requirement. A DAF protects the biological stage by taking out the particulate fraction first.
- Iron residual can become a design constraint. At 2 mg/L total iron, high ferric doses need strong pH control, adequate flocculation and dependable solids capture. Consider jar testing both iron and aluminium chemistry.
- Do the nitrogen balance early. DAF does not remove dissolved ammonia. A 15 mg/L total-nitrogen target needs biological design where food, abattoir or domestic load is significant.
- Design for the 24-hour rule. Size equalisation and chemical storage around production cycles, not average flow alone.
Source and verification
| Instrument | Presidential Decree No. 261/11 of 6 October 2011 approving the Regulation on Water Quality |
| Schedule used | Annex VI — Emission Limit Values for Wastewater Discharge |
| Licence authority | Ministry responsible for environment, with water-resource and other competent bodies |
| Public-service regulation | Presidential Decree No. 129/23 of 30 May 2023, regulating collection of wastewater by public systems |
| Sources | Presidential Decree 261/11 — legal text · Presidential Decree 129/23 — public wastewater service regulation |
| Checked | 7 August 2026 |
Frequently asked questions
What are Angola’s COD and BOD limits for wastewater discharge?
Annex VI to Presidential Decree 261/11 sets COD 150 mg/L and BOD₅ 40 mg/L as monthly average emission limits. A representative 24-hour daily sample may not exceed twice the monthly average.
What is the suspended-solids limit in Angola?
60 mg/L total suspended solids. This is normally achievable by a correctly sized and operated DAF on high-solids industrial effluent, provided chemical conditioning and sludge removal are stable.
Does an industrial site need a discharge licence in Angola?
Yes. Article 13 requires a licence for wastewater discharge to water or soil. The licence sets the applicable standards. Industrial discharge to a public sanitation system also requires authorisation by the system’s operating entity.
Can a DAF meet Angola’s wastewater limits by itself?
It can often meet mineral oil, suspended solids and phosphorus targets. It does not remove dissolved COD or nitrogen sufficiently to guarantee 150 mg/L COD, 40 mg/L BOD₅ and 15 mg/L total nitrogen on a typical high-strength organic stream; biological treatment is normally required after flotation.