7 Ways to Clean Dirt
November 01, 2016
GE Reports Canada
Human activity can sometimes wreak havoc in the environment, but thankfully there are many ways to clean up after ourselves. Scientists use a range of innovative processes to scrub soil and cleanse water.
Canadian scientist Kelcie Miller-Anderson, for example, experimented with mushrooms and other fungi on tailings ponds. This research led her to invent fungi-based mats that pull hydrocarbons from soil through a process known as mycoremediation. Her work was featured in the first episode of Decoding Genius, a podcast series exploring genius through six extraordinary young minds who are changing the world with their creations.
Apart from mycoremediation, numerous other technologies have been developed to assist in environmental remediation—the process of removing contaminants from soil and water—either in situ (on site) or ex situ (off site). From fungi to fescue, from heat to hydrogen peroxide, here are seven ways to clean the earth.
Excavated soil is fed through a portable thermal unit and blasted with heat at temperatures between 200 and 1,000 degrees Fahrenheit. The resulting gas vapors are then collected and destroyed in devices such as thermal oxidizers, or trucked to larger facilities offsite. This method is best used for shallow soil that is easily excavated and on sites with high pollutant concentrations.
Contaminants are chemically destroyed by pumping oxidants like hydrogen peroxide and chlorine into wells at different depths underground. These solutions spread out from the wells, destroying fuels, solvents and pesticides in the soil or groundwater. Chemical oxidation is best used on soils that are tough to access, such as underneath buildings.
Fungi, bacteria and other microbes use contaminants as a food and energy source—essentially, they eat pollutants—converting them into harmless end products. These tiny organisms rely on atmospheric oxygen (“aerobic”) to help them digest organic chemicals, like wood preservatives and hydrocarbons. Shallow soil is spray-irrigated, and injection wells are used for deeper soils. The area is often amended with oxygen, nutrients, and pH and temperature controls, to provide ideal feasting conditions for the microorganisms. Yum!
This process works much like aerobic bioremediation, but without oxygen. It’s used in soggy, saturated soils, like lake sediment, where oxygen is absent or in limited supply. In the absence of oxygen, microorganisms use other chemicals such as nitrate or sulfate to break down pollutants and release the energy they need to survive and grow. Tasty additives like molasses or vegetable oil can boost conditions for the organisms.
Co-solvent and Surfactant Flushing
In co-solvent flushing, soil is cleaned by pumping a mix of water and chemicals, such as alcohol or methanol, into the ground. There, the pollutants dissolve and are pumped back out. Surfactant flushing works the same way, delivering detergents and emulsifiers—both effective at breaking down oily compounds—to flush contaminants out of the soil. These methods work best in permeable soil through which groundwater flows easily, and where the soil beneath the permeable layer is impermeable, like clay.
Here, plants are used to purge pollutants from soil. Through their root systems, plants can absorb, metabolize, and transport contaminants from a site. An enormous range of plants can be used: trees, sunflowers, wheat, rice, and more. Phytoremediation is best used on sites with lower levels of pollution. These plants can clean up metals, solvents, crude oil, pesticides, explosives, and others.
Sequential and Hybrid Remediation
This strategy takes a mixed-media approach and combines various remediation methods. Using multiple technologies helps tackle plumes of mixed pollutants. In sequential treatment, chemical oxidation and chemical reduction are used one after the other, while the hybrid approach uses both chemical and biological strategies.