Fact sheet: Ultraviolet treatment

From: Public Services and Procurement Canada

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Ultra-violet (UV) oxidation, also called advanced oxidation, is an ex situ treatment that destroys groundwater contaminants. The contaminated groundwater is pumped, mixed with one or two oxidizing agents and passed under ultraviolet light. Ozone and/or hydrogen peroxide are often the oxidizing agents used to accelerate contaminant decomposition. Oxidation can either be direct, using an oxidizing agent, or combined with ultraviolet radiation. This technology is principally used for volatile and semi-volatile compounds, but can also be applied to pesticide and explosives degradation. The principal advantage of this technique is the destructive nature of the reaction.


Implementation of the technology

Groundwater extraction devices (wells, trenches, permeable drains or other) are used to collect contaminated groundwater that is conveyed to the treatment system, treated and discarded.

The implementation of a UV treatment system may include:

  • Mobilization, access to the site and temporary facilities.
  • Installation of a discharge system (evacuation to existing pipes, new surface water outlets, reinjection, infiltration field or infiltration basin).
  • The construction of wells, collection trenches or the installation of permeable drains.
  • The installation of pumps and supply lines (often underground or in trenches designed for freezing and protected from traffic).
  • Installation of a treatment system (may require a small building or container)
  • installation of a gaseous emissions treatment system.

Materials and Storage

  • This technology is implemented using traditional methods and equipment that are commonly available for well construction and installation.
  • Processing units can be built on-site or pre-assembled and transported in shipping containers, trailers or pallets.
  • Treatment equipment requires the installation of a power source and may require the use of maintenance products.
  • Treatment systems vary and may include the use of oxidants, biological substrates, adsorbents and/or different agents.
  • Construction and landscaping generally have minimal impact and require little on-site storage.

Residues and Discharges

The implementation of the system could lead to the management of contaminated soils resulting from drilling or excavation activities. In this case, these soils must be removed off-site.

Treatment systems can generate large quantities of solids (inert salts), liquid and gaseous discharges.

Generally, treated groundwater meets the applicable criteria and doesn’t pose a high risk when discharged. Treated water that contains by-products or excess reactive agents, as well as unacceptable pH levels can be a source of danger for downstream receptors. Monitoring of the water quality is required.

Recommended analyses for detailed characterization

Chemical analysis

  • pH
  • Alkalinity
  • Metals concentrations
  • Contaminant concentrations present in the following phases:
    • dissolved
  • Total organic carbon
  • Redox potential
  • Total dissolved solid
  • Iron and iron bacteria

Physical analysis

  • Temperature
  • Suspended solids concentrations
  • Presence of non-aqueous phase liquids (NAPLs)
  • Turbidity

Recommended trials for detailed characterization

Chemical trials

  • Evaluation of the matrix oxidant demand


On-site treatment trials will establish the efficiency of the technology and the parameters that influence the treatment time and cost (e.g. residence time, pump flow rate, requirements for pre-treatment, etc.).

Other information recommended for detailed characterization

Phase II

  • The flow of water to be treated


Treatment trials on site will establish the efficiency of the technology and the parameters that influence the treatment time and cost (example: residence time, pump flow rate, requirement for pre-treatment, etc.).


  • UV oxidation is applicable to dissolved phase.
  • UV oxidation is efficient to treat many types of organic compounds.

Applications to sites in northern regions

The extraction and treatment of groundwater is not always appropriate in remote areas that do not have access to public services or to local labour that can monitor and maintain equipment. During the installation of extraction points (wells, trenches or drains), deep freezing of the soil and seasonal changes in soil conditions will have to be considered. Treatment equipment should be designed considering the possibility of long periods without any intervention of the system operator.

Treatment type

Treatment type
Treatment typeApplies or Does not apply
In situ
Does not apply
Ex situ
Does not exist
Does not exist
Dissolved contamination
Free Phase
Does not exist
Residual contamination
Does not exist
Does not exist

State of technology

State of technology
State of technologyExist or Does not exist
Does not exist

Target contaminants

Target contaminantsApplies, Does not apply or With restrictions
Aliphatic chlorinated hydrocarbons
Does not apply
Monocyclic aromatic hydrocarbons
Non metalic inorganic compounds
Does not apply
Petroleum hydrocarbons
Phenolic compounds
Policyclic aromatic hydrocarbons
Polychlorinated biphenyls

Treatment time

Treatment time
Treatment timeApplies or Does not apply
Less than 1 year
1 to 3 years
3 to 5 years
More than 5 years
Does not apply

Long-term considerations (following remediation work)

Long-term considerations are related to pumping and treatment technology and not for the UV treatment technology as such.

Secondary by-products and/or metabolites

The secondary products formed by the UV treatment are carbon dioxide, water and inorganic salts. Certain volatile organic compounds, such as trichloroethane, may not be completely destroyed by UV treatment and are volatilized. In this case, gas emissions from the UV treatment system must be collected and treated.

Limitations and Undesirable Effects of the Technology

  • High water turbidity restricts the use of the UV technique by limiting UV light penetration.
  • Water to be treated should not contain high concentrations of inorganic compounds.
  • Presence of free phase product can cause fouling of the light source.
  • The treatment requires a significant amount of energy.
  • Treatment management can be difficult because of fluctuations in contaminant concentrations.
  • UV treatment may enhance the volatilization of certain organic compounds such as trichloroethane.
  • Specially trained staff are required for the application of this technology.

Complementary technologies that improve treatment effectiveness

Groundwater pretreatment may be required to improve the efficiency of this technology, and may include:

  • Water filtration to reduce turbidity.
  • Pre-treatment to remove metals may be required prior to use of this technology.
  • Separation of free phase products from groundwater, if any.

Required secondary treatments

In the presence of certain volatile organic compounds such as trichloroethane, produced gas vapours must be collected and treated.

Application examples

In 1998, UV oxidation was used at the Bofors Nobel Superfund site, Michigan, to treat groundwater contaminated with volatile and semi-volatile organic compounds. The treatment was combined with activated carbon filtration, pH adjustment and air stripping techniques.

More information is available at the following websites:


This technology has been successfully applied in the remediation of contaminated sites with volatile or semi-volatile organic compounds.

The application of UV treatment on explosives is recent and more limited. Tests conducted by the USA Army Environmental Center have shown this technology to be 99.9% effective in destroying common explosives in groundwater (CPEO, 1998).

Measures to improve sustainability or promote ecological remediation

  • Optimization of facilities and pumping equipment.
  • Optimization of the pumping rate to reduce energy consumption (pumping and water treatment systems).

Optimization of the calendar to promote the sharing of resources and reduce the number of days of mobilization.

Use of renewable energy and energy-efficient equipment.

Potential impacts of the application of the technology on human health

Main Exposure Mechanisms

Applies or Doesn’t Apply

Monitoring and Mitigation


Doesn’t apply (minor during mobilization and construction)


Atmospheric/Steam Emissions—Point Sources or Chimneys

Applies (in certain cases)

Emissions monitoring (choice of parameters, types of samples and type of intervention [source, risk or local requirements])

Atmospheric/Steam Emissions—Non-point Sources

Doesn’t apply



Doesn’t apply



Doesn’t apply



Doesn’t apply


Groundwater—chemical/ geochemical mobilization

Doesn’t apply




Groundwater quality monitoring

Accident/Failure—damage to public services


File checks and obtaining pre-excavation or drilling permits, development of excavation or drilling procedures and emergency response

Accident/Failure—leak or spill


Risk assessment, elaboration of accident and emergency response plans, monitoring and inspection of hazardous conditions

Accident/Failure—fire or explosion


Risk assessment, elaboration of accident and emergency response plans, monitoring and inspection of hazardous conditions

Other—Handling contaminated soils or other Solids


Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions


Author and update

Composed by : Serge Delisle, Eng. M.Sc., National Research Council

Updated by : Karine Drouin, M.Sc., National Research Council

Updated Date : February 12, 2013

Latest update provided by : Nathalie Arel, P.Eng., M.Sc., Christian Gosselin, P.Eng., M.Eng. and Sylvain Hains, P.Eng., M.Sc., Golder Associés Ltée

Updated Date : March 22, 2019