Fact sheet: Adsorption—ex situ

From: Public Services and Procurement Canada

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Description

The ex situ adsorption technology allows the treatment of contaminated liquid and gaseous effluents. This technology does not destroy contaminants but reduces the concentration of contaminants present. It often represents a complementary technology, in a global restoration treatment (ex situ or in situ) and is then used as a polishing technology.

The liquid or gaseous effluent is pumped and transported through a system containing an adsorbent material. Upon contact, the contaminants are retained, while the liquid or gaseous effluent continues to flow. When the adsorbent material becomes saturated, it is replaced. The treated liquid or gaseous effluent is then analyzed for discharge concentrations of contaminants before being returned to the environment.

This technology can be used for the treatment of effluents from municipal, industrial and hazardous waste.

There are several types of adsorbent material, the most used being active ingredients, organic materials and resins. The most common adsorbent is granulated activated carbon. Other natural and synthetic adsorbents include activated alumina, lignin sponges, sorption clays and synthetic resins.

Source:

Implementation of the technology

The implementation of ex situ adsorption requires the establishment of a suitable system for the treatment of liquid or gaseous effluents. The choice of the unit to be put in place and the type of adsorbent depend both on the type of effluent to be treated, the type of contaminant as well as other elements of the treatment train preceding the ex situ adsorption.

They are among the main factors to consider when sizing the following elements:

  • The circulation system of effluents on the adsorbent.
  • Size and number of beds of adsorbent materials.
  • The adsorbent replacement/regeneration method.
  • The usage time of the adsorbent and its frequency of change or regeneration.

The implementation of an ex situ adsorption system may include:

  • Mobilization and access to the site.
  • Installation and connection to the existing system, if necessary, of the treatment unit (may require the construction of a building or container).
  • Establishment of reservoirs for the recovery of liquid effluents resulting from treatment.
  • Disposal equipment for treated liquids (for disposal).

Since ex situ adsorption is often complementary to other stages of a series of treatments, other implementation steps specific to these technologies will also need to be considered, for example, the installation of pretreatment equipment (bag filter, settling tank, etc.).

Materials and Storage

The work required for the implementation of this technology generally has little impact and requires few materials on the site. Clean adsorbents and waste materials such as used sorbents can be stored at the site during treatment.

Other materials or storage related to other technologies in the treatment series may also be on-site.

Residues and Discharges

The adsorbent materials used and the accumulated solids must be transported off site, usually in batches.

Following treatment, treated groundwater should meet the discharge criteria and should not pose a high risk when discharged.

Discharges of gaseous effluents are treated during the process, and emissions of vapours are minimal.

The treatment system can generate significant amounts of liquid and gaseous residues, but the management, storage and disposal of process residues are part of the efficient operation of the system.

Recommended analyses for detailed characterization

Chemical analysis

  • pH
  • Contaminant concentrations present in the following phases:
    • dissolved
    • gaseous
  • Contaminant concentrations in the air
  • Metal concentrations in water

Physical analysis

  • Temperature
  • Gas effluent humidity
  • Suspended solids concentrations
  • Contaminant physical characteristics including:
    • viscosity
    • density
    • solubility
    • vapour pressure
    • etc.

Recommended trials for detailed characterization

None.

Other information recommended for detailed characterization

Phase III

  • The volume of water or gaseous effluent to be treated
  • Circulating water flow to be treated

Notes:

Laboratory trials are recommended to verify adsorbent material efficiency for the target organic compound at an appropriate concentration, or to select the most efficient adsorbent material.

Applications

  • Efficient for contaminated groundwater and gas emissions
  • Especially efficient for organic compounds
  • Efficient for reducing concentrations of certain heavy metals

Applications to sites in northern regions

Groundwater treatment is not always appropriate in northern areas that do not have access to utilities or local labour to operate and maintain the system. The system must be adapted to the climate and consider factors such as deep freeze and frost heave.

In addition, remote sites require greater mobilization, resulting in higher on-site monitoring costs. Equipment availability is limited and work windows are relatively short.

Treatment type

Treatment typeApplies or Does not apply
In situ
Does not apply
Ex situ
Applies
Biological
Does not exist
Chemical
Does not exist
Control
Does not exist
Dissolved contamination
Applies
Free Phase
Does not exist
Physical
Applies
Residual contamination
Does not exist
Resorption
Applies
Thermal
Does not exist

State of technology

State of technologyExist or Does not exist
Testing
Does not exist
Commercialization
Exist

Target contaminants

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


Notes:

Adsorbent material must be selected as a function of contaminants present in the effluent to be treated (liquid or gaseous). Each chemical compound has an adsorption isotherm specific to the adsorbent material. It is important to consider these absorption isotherms for the choice of adsorbent material. For example, in general, small molecules, such as vinyl chloride, are more difficult to adsorb than others with a larger molar mass.

Treatment time

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

Long-term considerations (following remediation work)

Following the remediation work, the adsorbent materials must be adequately treated and disposed of.

Secondary by-products and/or metabolites

The ex situ adsorption process is non-destructive and does not produce secondary reaction sub-products. However, the treated liquid and gaseous effluent must be analyzed before being disposed to control the residual contaminant concentrations and make sure they meet the discharge standards.

Limitations and Undesirable Effects of the Technology

  • The adsorbent material must be reactivated or changed periodically.
  • Natural organic matter, bacteria, dust and metals can obstruct the adsorbent material, and reduce performance of the system, which increases the maintenance time and costs.
  • High humidity in the gas effluent can saturate the adsorbent material.
  • The presence of free phase may require pretreatment before filtration in the adsorbent material.
  • Water-soluble compounds and small molecules are not well adsorbed.
  • The presence of absorbable contaminants in high concentration can lead to frequent replacement of the adsorbent unit.
  • Trace compounds may require a significant residence time in the adsorbent material.
  • Treatment costs can be high depending on other treatment technologies that are combined with ex situ adsorption (e.g., groundwater pumping).
  • In the case of unusual or emerging contaminants, or complex contamination (e.g., inorganic/organic contaminants), a laboratory treatability study (for adsorption) may be required.

The main advantage of the technology is that the duration of treatment is generally shorter, and that the uniformity of treatment is better ensured because of the possibility of continuous monitoring and mixing of groundwater. The treatment, however, requires groundwater pumping, resulting in increased costs and time allocated to the installation of equipment.

Complementary technologies that improve treatment effectiveness

  • A dust removal or dehumidification system for the gaseous effluent can be installed upstream of the adsorbent material if required.
  • Pre-filtration or decantation of suspended solids in water is often required to prevent premature clogging of the adsorbent material.

Required secondary treatments

When saturated and at its disposal, the adsorbent material containing the contaminants must be treated using techniques such as thermal treatment and incineration. In some cases, it can be recovered and recycled.

Application examples

Ex situ adsorption technology is well documented and several private companies offer adsorption systems that are suitable for various kinds of contaminated site situations.

The following website provides an application example:

Performance

According to the Canadian Petroleum Products Institute (CPPI, 1994), carbon adsorption is particularly efficient for the elimination of hydrocarbons present at low concentrations (up to 1,000 µg/L), with a removal efficiency of up to 99% (CSMWG, 2005).

Measures to improve sustainability or promote ecological remediation

  • Optimizing the size of the circulation unit.
  • Optimization of the calendar to promote the sharing of resources and reduce the number of days of mobilization.
  • Use of renewable energy and low-energy equipment.
  • Optimizing circulation flow to reduce energy consumption.
  • Optimization of water and gas treatment processes to reduce waste and non-durable goods (activated carbon).
  • Regeneration and reuse of the adsorbent material.

Potential impacts of the application of the technology on human health

Main Exposure Mechanisms

Applies or Does Not Apply

Monitoring and Mitigation

Dust

Does not apply

N/A

Atmospheric/Steam Emissions—Point Sources or Chimneys

Applies

Source monitoring, integrate the collection and treatment of off gases in the design, if applicable.

Atmospheric/Steam Emissions—Non-point Sources

Does not apply

N/A

Air/steam—by-products

Does not apply

N/A

Runoff

Does not apply

N/A

Groundwater—displacement

Does not apply

N/A

Groundwater—chemical/ geochemical mobilization

Does not apply

N/A

Groundwater—by-product

Does not apply

N/A

Accident/Failure—damage to public services

Does not apply

N/A

Accident/Failure—leak or spill

Does not apply

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

Other—Liquid emission (point source)

Applies

Source monitoring, integrate the collection and treatment of liquid emission in the design, if applicable.

References

Author and update

Composed by : Mahaut Ricciardi-Rigault, M.Sc., MCEBR

Updated by : Magalie Turgeon, National Research Council

Updated Date : August 24, 2017

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

Date Modified: