1.2.1. Conventional Remediation Methods

Excavation and dredging

This technique involves removing contaminated soil or other materials from a polluted site. The most common form of soil remediation process is excavation. This can be as simple as hauling the soil away and replacing it with uncontaminated soil, or it might involve more complex processes such as aeration. This depends on the contaminant.

Dredging is the physical removal of contaminated sediments from freshwater or marine water in order to reduce risks to human health and the environment. Dredging depends on environmental conditions (the hardness and quantity of material to be dredged, site exposure, the method of disposal, etc.), contaminant types and the degree of contamination of sediments. Releases of contaminants associated with dredging can occur in particulate, dissolved or volatile fractions, each characterised by differing transport and/or exposure pathways. Different types of dredging equipment and techniques are employed to achieve the required project outcomes in the most efficient way.

Soil vapor extraction

Soil vapor extraction (SVE) technology uses vacuum pumps to create a movement of air in the soil matrix that remove the contaminant, which is distributed through all the soil phases. The extracted vapours are then treated and discharged to the atmosphere or re-injected into the subsurface if permitted. SVE is more commonly used remedial approach for removal of contamination from the soils when excavation is not feasible due to presence of some physical barriers (building, tree, etc.), or where the extent of soil contamination is extensive. The contaminanted soil and groundwater can be purified at the same time by SVE technique.

Solidification or stabilization

This technique involves mixing of a contaminated media with a specific binder in order to convert hazardous constituents into less soluble, mobile or toxic forms by incorporating waste into a solidified matrix. This technology is currently being used to treat a wide variety of wastes from different industries, such as sludge from the tannery and from the wastewater treatment plants of electroplating and metal finishing industries. These wastes usually contain heavy metals, organics and soluble salts.

Soil washing

This process refers to ex situ or in situ techniques that employ physical and/or chemical procedures to extract metals contaminants from soils. Soil washing procedure is mostly suitable for granular soils with less clay content and contaminated with inorganic pollutants (heavy metal). Soil washing is one of the few permanent treatment alternatives to remove metal contaminants from soils. If the contaminants are organic, it is necessary to remove organic pollutants and then certain solvents or surfactants are used as washing agents.

Air sparging

In this technique air is injected through a contaminanted site. This injected air helps to flush (bubble) the contaminants up into the unsaturated zone where a vapor extraction system is usually implemented in conjunction with air sparging to remove the generated vapor phase contamination. Air Sparging is an in situ remedial method that is used to reduce lighter molecule constituents (benzene, ethylbenzene, toluene and xylene) from petroleum products like gasoline from the saturated soil zone. Air sparging is a cost-effective, time-efficient system for the remediation of volatile and/or biodegradable contaminants.

Pump and treat

This technique involves pumping contaminated ground water out of the ground and purifying it before returning it to the ground. Besides, pump and treat (PAT) is able to provide a vital alternative with fast response time, high reliability and adaptability. PAT has been widely used in groundwater remediation and aquatic restoration due to its excellence in pollutants removal and contaminants migration control.

Chemical oxidation

Chemical oxidation aims to mineralize the pollutants to CO₂, water (H₂O) and inorganics, or at least to transform them into harmless or biodegradable products. Chemical oxidization process has been used for decades in the waste-water industry for the treatment of carbon-containing compounds, such as petroleum hydrocarbons and chlorinated solvents, and numerous other contaminants.

Incineration

Incineration is a thermal treatment (high temperature) process for destroying hazardous waste materials.   Incineration of waste materials converts the waste into ash, flue gas, and heat. The ash is mostly formed by the inorganic constituents of the waste, and may take the form of solid lumps or particulate carried by the flue gas. The flue gases must be cleaned of gaseous and particulate pollutants before they are dispersed into the atmosphere.