Tertiary Wastewater Treatment
In tertiary wastewater treatment, the water has gone through a first stage of sedimentation and/or flotation that has removed a large part of the suspended solids as well as part of the organic matter by mechanical means. It has also had a biological treatment that removes dissolved organic matter and pathogenic microorganisms in the secondary treatment stage.
When treated wastewater will be discharged into natural or reused water bodies, additional treatments are necessary to comply with the legally permissible limits that regulate the quality of treated water.
In Mexico, the Official Mexican Standard NOM-001-SEMARNAT establishes the limits of permissible contaminants when wastewater is discharged into receiving bodies owned by the country.
Tertiary treatment of wastewater with activated carbon
Activated carbon is a type of carbon that has had its porosity increased resulting in a larger surface area compared to non-activated carbon. It can be produced from coconut shell, wood or mineral origin. Its activation process can be thermal or chemical. Activated carbon for tertiary wastewater treatment can be applied in granular or powdered form.
Activated carbon is able to improve the color, odor and taste of water in general.
One indicator of wastewater quality is COD (Chemical Oxygen Demand), the result of which can give an estimate of the oxidizable organic pollutants still present in the water after primary and secondary treatment.
Carbon due to its chemical structure of covalent character usually seeks to satisfy the electromagnetic imbalance with other molecules of covalent character. This results in a low-intensity bond (London force) between the carbon and the approaching fluid molecules. This phenomenon is called adsorption.
The organic molecules that affect COD levels are covalent in nature, so the activated carbon will adsorb them, resulting in a lower COD level and improving the overall quality of the wastewater, making it suitable for discharge into natural water bodies.
Now, speaking of color, the use of activated carbon in tertiary wastewater treatment can be useful when the color is due to the presence of organic compounds, since activated carbon does not efficiently adsorb inorganic compounds.
Turning to wastewater toxicity, activated carbon is widely used as an antidote by adsorbing toxic organic compounds.
If fats and oils are present, additional technologies and treatments will be required to eliminate free or emulsified oil, even if they are organic compounds, since they interfere with the adsorption capacity of the activated carbon by impregnating and blocking it.
Biological activated carbon in tertiary wastewater treatment
Biodegradable organic molecules that could not be degraded in the biological treatment will be adsorbed by the activated carbon specifically when applied in granular form. This accumulation of biodegradable organic molecules attracts bacteria that will settle on the surface of the activated carbon and feed on the organic molecules. This phenomenon is known as biological activated carbon . This type of carbon is also useful for the tertiary treatment of wastewater, since there is a concentration of organic pollutants in the wastewater.
The bacteria will generate carbon dioxide, methane, water as well as assist in the generation of more bacteria. The bacteria by consuming the adsorbed organic molecules allow the carbon to have free surface area to adsorb more organic pollutants which will again serve as food for the bacteria.
In addition, Carbotecnia can help you comply with NOM-001-SEMARNAT-2021, which establishes the maximum permissible limits of pollutants in wastewater discharges into receiving water bodies owned by the nation. The use of biological activated carbon in tertiary treatment is an effective solution to ensure that discharges meet the standards established by these regulations, ensuring environmental protection and compliance with current legislation.
Activated carbon to comply with NOM-001-SEMARNAT-2021 in Mexican territory.
As mentioned above, NOM-001-SEMARNAT establishes the permissible limits for wastewater to be reintroduced into the environment when discharged into receiving bodies owned by the nation.
NOM-001-SEMARMAT-2021 is an update of the standard that became applicable in Mexican territory on April 3, 2023.
Among its modifications we find:
- Limiting the COD (Chemical Oxygen Demand) value instead of limiting the BOD (Biochemical Oxygen Demand) value.
- Added a limit to the true color not present in the previous version.
- A water toxicity limit not present in the previous version was added.
When the value of these parameters is caused by organic compounds, biological activated carbon is a very competitive option for compliance in tertiary wastewater treatment.
If you need tertiary wastewater compliance, contact us to help you.
More information on the update of NOM-001-SEMARNAT and its permissible limits can be found in this article: Activated carbon for compliance with the new limits allowed by NOM-001-SEMARNAT-2021
(True color and acute toxicity limits will be applicable on March 12, 2026.)
More information:
Activated carbon filters for drinking water – Filtrashop
NOM-001-SEMARNAT-2021, which establishes pollutant limits for wastewater discharges, is published.
