SCH 3U- Detox for Contaminated Land Physical, chemical, and biological remediation methods

What is Contaminated Land? Environment Canada reports that there are tens of thousands of sites across Canada with hazardous substances. Some contamination occurred at a time before the harm of some chemicals was fully understood. Other contamination resulted from lax environmental laws and dumping of chemicals. Contaminated land is land containing hazardous substances that pose a threat to human health or the environment. These hazardous substances can be solid, liquid or gases. Once in the ground they can interact with groundwater and soil. Remediation is the process of decontaminating land or water so it can be safely used again.

Remediation vs. Total Cleanup Remediation of contaminated land is not the same as total cleanup. A total cleanup involves the complete removal of all hazardous materials. This is not always necessary to make the land useful again. It depends on the intended use of the land. Land that is going to be used for a playground needs far more extensive remediation than land used for a parking lot. The most appropriate and cost-effective strategy should be used to rehabilitate the land. The land could be: (1) A restricted site; (2) Covered (eg. With concrete); (3) Excavated and replaced with clean soil; (4) Treat the soil on or off site and use the cleaned soil.

Remediation of contaminants: Definition Remediation is the process of treating contaminated land or soil so that it is safe to use again.

Types of remediation: 1. Physical treatment may include flushing soil, filtering of water, etc. In soil flushing, large volumes of a fluid (such as water, acids, bases, solvents, detergents) are pumped through the soil to remove contaminants. Remediation companies must ensure that the flushing fluid does not enter the environment.

Types of remediation 2. Chemical remediation includes stabilization and solidification, oxidation and electrolysis. In stabilization and solidification, chemical rxn are used to convert the contaminant to a safe form and then a binding agent like cement immobilizes the contaminant.

Chemical Remediation In electrolysis, a power supply and electrical conductors (+ and - ) are inserted into the ground. Toxic metal ions can be removed when an electrical current is applied. The positive metal ions build up on the negative electrode and forms metals. The electrode with metal attached can later be safely removed.

Chemical Remediation Chemical oxidation uses chemical rxn to convert the contaminant into a less hazardous substance. Chemicals for this process are worked into the ground using large drills or augers. Liquids such as hydrogen peroxide can be injected into the ground under pressure.

Bioremediation Biological treatment (bioremediation) utilizes plants and micro-organisms to consume or absorb toxins from the environment. Usually more cost-effective and less disruptive than physical and chemical remediation, but often takes longer.

Bioremediation Some micro-organisms that occur naturally in soil can decompose things like oil and gasoline. Products are relatively harmless, but do include carbon dioxide (greenhouse gas). For some oil spills, chemical dispersants are sprayed onto the spill site to break up the oil into smaller droplets. This helps naturally occurring micro-organisms decompose the oil more quickly. Micro-organisms and sometimes oxygen can also be pumped into the ground, where they find and decompose contaminants.

Bioremediation Phytoremediation is a type of bioremediation that uses plants to decontaminate soil or water. Plants use their roots to draw up groundwater and its contaminants. Micro-organisms in the roots or plant itself break down contaminants. The plant will either utilize the products or release them to the atmosphere. Substances not degraded by plants such as metals, accumulate in the plant. Metals that the plants have trapped can be mined by harvesting and burning the plant. Metals are recovered from the ashes.

Examples of bioremediation: Microbes have been used for centuries to remediate wastewater (biol. treatment). Microbes can also degrade and detoxify a wide variety of synthetic organic compounds, metals, toxic elements, etc. Microbes used to degrade contaminants include bacteria, and fungi. Plants, animals, and mixed populations of different organisms can also be used .

Genetically-engineered microbes: Attempts have been made to genetically engineer microbes so that they degrade contaminants more efficiently and quickly. Microbes have been patented for this purpose (“superbug” to degrade oil spills). There is concern that these “unnatural” microbes may become pests in the environment.