Aerosol emissions from wastewater treatment plants

A WWTP is supposed to be a source of gaseous and aerosol emissions into air. Within the PerFORM WATER 2030 project, a study to evaluate and quantify the components of the air emissions deriving from the different compartments of a plant has been performed. In this way, an estimation of the distribution of the residue contaminant (mass balance) in the different matrices - water, sludge, air – involved in a WWTP has been derived.

Does a WWTP produce air emissions?

What are the air emissions from a WWTP?

What does the air emissions study mean inside the PerFORM WATER 2030 project?

How air emissions are measured?

Why is it important to know the air emissions at a WWTP?

Is it possible to limit the air emissions of a WWTP?


Does a WWTP produce air emissions?

A WWTP is a potential source of contaminant into the air in gaseous and aerosolized form. These emissions can derive directly from the wastewater entering the plant or from the purification processes, in the form of reaction products or treatment matrices. The main section involved in the aeriform emissions are:

  • Sewer collector and lifting station

  • Biological oxidation tanks

  • Sludge line

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What are the air emissions from a WWTP?

The air emissions from a WWTP are:

  • Greenhouse gases (CH4, N2O): these gases represent degradation products and by-products of the treated wastewater and are emitted mainly by the biological oxidation tanks and the sludge line. In addition to the listed gases, the most significant emission of WWTPs is CO2. Although the latter is supposed to be of biogenic origin and thus not counted among greenhouse gases, the current study carries out its quantification to better understand the purification processes.

  • Volatile organic substances (VOCs): these compounds are present in the wastewater entering the plant or are produced during the purification process and are emitted mainly from the sewage collection area entering the plant and from the oxidation tanks. Some of those substances can be a cause for the perception of bad smells nearby the plant.

  • Particulate Matter: micrometric particles (PM10) emitted mainly by the oxidation tanks and the sludge line. These particles can represent condensation nuclei on which organic / inorganic pollutants can concentrate, with potential harmful-allergenic characteristics

  • Bioaerosol: airborne microorganisms of pathogenic and non-pathogenic nature. This component comes from the wastewater entering the plant and from the biological treatment processes. The emissions of this component are mainly concentrated in the sewer collector and lifting station and from the oxidation tanks.


What does the air emissions study mean inside the PerFORM WATER 2030 project?

The study of air emissions in the PerFORM Water 2030 project means to provide an integrated/holistic evaluation of the overall wastewater treatment process and in particular:

  1. Wastewater characterization across every section of the water line

  2. Sludge characterization across every section of the sludge line

  3. Analysis of gaseous and aerosol emissions in different points of the plant

  4. Collection of the operational parameters of the WWTP

The study involves the execution of analytical campaigns every 2-3 months for the duration of the project with sampling of the matrices: water, sludge and air.

Monitoring and reduction of emissions from wastewater biological treatment

Project details


How air emissions are measured?

Within the PerFORM WATER 2030 study, air emissions are measured with specific instrumentation for each analysed compound.

1. Greenhouse gas: emissions analysis from oxidation tanks with a flow chamber and portable gas chromatograph. Continuous analysis for 24-48 hours every 2-3 months.

1. Greenhouse gas
Emissions analysis from oxidation tanks with a flow chamber and portable gas chromatograph.
Continuous analysis for 24-48 hours every 2-3 months.

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2. VOC: sampling by canister in different points of the plant, in continuous for 4 hours every 2-3 months. Instrumental laboratory analysis.

2. VOC
Sampling by canister in different points of the plant, in continuous for 4 hours every 2-3 months.
Instrumental laboratory analysis.

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3. Particulate matter: sampling in different points of the plant by means of a Dekati impactor, continuously for 2-3 weeks. Metals and micro-polluting organic substances (Fragrances) laboratory instrumental analysis.

3. Particulate matter
Sampling in different points of the plant by means of a Dekati impactor, continuously for 2-3 weeks.
Metals and micro-polluting organic substances (Fragrances) laboratory instrumental analysis.

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4. Bioaerosol: instantaneous sampling by impact sampler at eye-level and at 5 meters height, along the treatment line and at the plant boundaries, every 2-3 months. Analysis of Total Bacterial Counts at 22°C and 36°C, of Fungi (Molds), of total coliforms, of enterococci and of E.coli.

4. Bioaerosol
Instantaneous sampling by impact sampler at eye-level and at 5 meters height, along the treatment line and at the plant boundaries, every 2-3 months.
Analysis of Total Bacterial Counts at 22°C and 36°C, of Fungi (Molds), of total coliforms, of enterococci and of E.coli.

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Why is it important to know the air emissions at a WWTP?

The air emissions study at a WWTP is important because it allows to:

  • Evaluate the overall environmental impact (ecological footprint) of a WWTP in relation to the urban / rural context in which it is inserted

  • Improve the knowledge of the different purification processes efficiency

  • Set up plant or process modifications to optimize the purification sectors and reduce the environmental impact of the WWTP

  • Characterize the quality of the air inside the plant and evaluate any prevention and protection measure for the health and safety of workers


Is it possible to limit the air emissions of a WWTP?

Reducing of air emissions from a WWTP is possible and the main strategies are:

  • Reduction of turbulence zones in the water treatment and in the sludge treatment lines

  • Coverage of the points most subject to aerosolization/gaseous emission (collection compartment, oxidation tanks, sludge dewatering areas)

  • Collection and treatment of gaseous emissions from covered compartments or confined spaces

  • In biological oxidation tanks, use of highly efficient oxygen transfer aeration systems or pure oxygen systems or cover the tanks to reduce the gases and aerosols escape, and reduction of alternate cycle processes (on/off of the oxygenation system) to minimize the production of N2O


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