From: Public Services and Procurement Canada
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:
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 implementation of an ex situ adsorption system may include:
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.).
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.
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.
None.
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.
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.
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.
Following the remediation work, the adsorbent materials must be adequately treated and disposed of.
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.
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.
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.
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:
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).
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
Air/steam—by-products
Runoff
Groundwater—displacement
Groundwater—chemical/ geochemical mobilization
Groundwater—by-product
Accident/Failure—damage to public services
Accident/Failure—leak or spill
Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions.
Other—Liquid emission (point source)
Source monitoring, integrate the collection and treatment of liquid emission in the design, if applicable.
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
