Soil Remediation
Physical Remediation Technologies
Soil Vapor Extraction
Soil vapor extraction, an insitu technology, can be applied to contaminated soil unsaturated (vendose) zone. This technology is also called insitu soil venting, insitu volatilization or enhanced volatilization (Siddique, 2015).
Soil vapor extraction technology can effectively remove volatile organic contaminants, including gasoline, BETX (benzene, toluene, elthybenzene and xylene), PCE (tetrachloroethylene) and TCE (trichloroethylene) (Siddique, 2015). However, it is not suitable for remediation of heavy petroleum hydrocarbons since they heavy oils such as diesel and lubricating oils are not volatile. Based on soil texture, the applicability of soil vapor extraction declines as soil texture change from coarse (sand and gravel) to fine (clay or silt).
Multiphase Extraction
Multiphase extraction is also called dual phase extraction (DPE) or two phase extraction (TPE)(Siddique, 2015). This technology is applied to remove contaminants from both soil saturated (groundwater) and unsaturated zones.
Multiphase extraction can effectively remove halogenated volatile organic compounds, aromatic volatile organic compounds, total petroleum carbons, and floating products (Light Non Aqueous Phase Liquid) on the surface of groundwater.
Thermal Desorption
Thermal desorption technology extracts soil contaminates by heating the soil to a certain temperature in a thermal desorber. The applied high temperature allows vaporization and separation of the well site contaminants from the soil (Nelson Environmental, 2015). These vaporized contaminants are converted into carbon dioxide and water as the end products.
Thermal desorption is one of the fastest technologies to remove soil volatile and semi volatile organic compounds including gasoline, BETX (benzene, toluene, elthybenzene and xylene), chlorinated organic compounds, PAHs (polycyclic aromatic hydrocarbons) and herbicides (Qu, 2010).
Electro-kinetic Technology
Electro-kinetic technology is an insitu soil remediation technique that utilizes direct current to control migration of contaminants in the soil through electromigration, electroosmosis, and electrophoresis (Cameselle et al. 2013; Ghosh et al. 2011; Lee et al. 2014; Wei et al. 2016).
Electro-kinetic technologies are able to remove radioactive elements, toxic anions, petroleum hydrocarbons, ion-organic complexes, chlorinated organic compounds, and PAHs (polycyclic aromatic hydrocarbons), but most effective in removing metal contaminants (Qu, 2010). Electro-kinetic technologies are targeted to low permeable clay soils. Generally, ions in the clay soil have low mobility, however, the mobility is greatly enhanced under the electro-kinetic potential. The efficiency of electro-kinetic technologies in removing Hg, Ni, Mn, Zn, Pd, Cd, Cr, Co from kaolinite reaches 85% to 95% (Qu, 2010).
Chemical remediation
Soil Leaching and Washing
Soil leaching and washing technologies enhance cation exchange, dissolution and migration of contaminants in the soil matrix via application of soil amendments or chemical solvent. This technique can be applied insitu and exsitu.
Soil amendment
Inorganic calcium and magnesium soil amendments are effective in remediating soil salinity issue at well sites. Gypsum is the most common chemical substance applied to adjust soil physical and chemical properties affected by salt accumulation (Bischoff ect, 2017). Other soil effective amendments are limestone and magnesium carbonate. In addition, adding these amendments can improve soil structure, balance osmotic water potentials, and ionic potentials, and increase nutrient availability in the soil (Bischoff ect, 2017).
Soil solvent
Soil surfactants target on oil well produced organic and inorganic contaminants like heavy metals, petroleum hydrocarbons, drilling additives and herbicides that are strongly adsorbed on the soil particles.
Insitu Chemical Oxidation
Chemical oxidation remediation is an insitu technology involving applications of chemical oxidants into the contaminated soil and groundwater through injection wells. The injected oxidants oxidize target contaminants into environmental friendly end products such as water and carbon dioxide.
Insitu chemical oxidation technology is excellent in immediately remediating of organic pollutant in both soil saturated and unsaturated zones. For oil and gas recovery, it is effective in degrading petroleum hydrocarbon and herbicides that are highly resistant in soil. The most common chemical oxidants used for soil remediation are permanganate salts (NaMnO4, KMnO4), peroxide (H2O2), ozone (03), and persulfate salts (Na2S2O8, K2S2O8) (Siddque, 2015).
Biological Remediation
Bioremediation
Bioremediation technologies have been studied for decades and has provided abundant evidence that organic contaminant can be degraded by activities of microorganism under both aerobic and anaerobic conditions. It is important to know that Nature has the ability to digest contaminants in a positive way. To degrade petroleum hydrocarbons including BTEX (benzene, toluene, elthybenzene and xylene), gasoline and monoaromatic hydrocarbons, bioremediation can be achieved via oxidation reaction under aerobic conditions (soil unsaturated zone), and reduction reaction under anaerobic conditions (groundwater). Soil temperature, soil water content and soil pH play important roles in microorganism survivals, growth, reproduction and metabolism.
Phytoremediation
Phytoremediation can be defined as “the efficient use of plants to remove, detoxify or immobilize environmental contaminants in a growth matrix (soil, water or sediments) through the natural biological, chemical or physical activities and processes of the plants” (Peuke & Rennenberg, 2005). These processes require plants growing in a contaminated matrix for a required growth period in order to remove contaminants from the root zone or facilitate immobilization and detoxification of the pollutants (UNEP, 2002). Once remediation is completed, the plants can be harvested, processed and disposed of.
References:
Bischoff, B. Fowler, M. Guan, P. Jierui. Keating, R. McConnell, S. Peel, B. Reid, C. Renaud, J. Sommer, A. Thiele, C. Tremblay, H. Watkinson, N. Yuan, H. 2017. Renewed Solution. Reclamation Of A Dumping Ground And Three Well Sites
At Enoch Cree Nation. Renewable Resources 495, University of Alberta.
Cameselle C, Belhadj B, Akretche DE, Gouveia S (2013) Advances in electrokinetic remediation for the removal of organic contaminants in soils. INTECH Open Access Publisher
Nelson Environmental Limited. 2015. Nelson Environmental Limited. Thermal Desorption. Seminar Notes. The University of Alberta. September, 2015
Peuke, A& Rennenberg,H. 2005. US Natual Library of Medicine Nation Institutes of Health. Phytoremediation. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1369103/
Qu,X. 2010. Soil Environmental Science. Chapter 5. Soil Remediation Technologies. Qinghua University.
Siddique, T. 2015. Renewable Resources 482. Soil remediation. The University of Alberta. September, 2016.
UNEP. 2002. United Nations Environment Programme Division of Technology, Industry and Economics. Phytoremediation: An Environmentally Sound Technology for Pollution Prevention, Control and Remediation. An Introductory Guide To Decision- Makers. http://www.unep.or.jp/Ietc/Publications/Freshwater/FMS2/