REMEDIATION TECHNIQUES FOR HEAVY METAL-CONTAMINATED SOILS

Posted: August 25th, 2021

REMEDIATION TECHNIQUES FOR HEAVY METAL-CONTAMINATED SOILS

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Remediation Techniques for Heavy Metal-Contaminated Soils

General Overview

            Pollution is a common subject in the modern age where climate change and global warming are drastically affecting humanity. Heavy metal pollution of soils is among the environmental issues that have been on the limelight in recent years. This is particularly so because of the increased threat that heavy metals pose to animals, human beings, and the quality and safety of agricultural products (Selvi et al. 2019). Heavy metals such as mercury, chromium, arsenic, cadmium, and lead are not suitable for living organisms and human beings, especially when they are in large amounts (Jaishankar et al. 2014). Unfortunately, heavy metals enter the soil through natural and anthropogenic processes and cause biological toxicity. Some of the sources of heavy metal soil pollution include metal mining, wastewater, manure and biosolids, fertilizers, and pesticides (Wuana &Okieimen 2011). The toxicity can reach human beings thanks to the rules of nature such as accumulation through the food chain (Li et al. 2019). Therefore, it is paramount for humanity to remediate polluted soils. Important to note, there are numerous soil remediation methods available to people. Most of the remediation techniques make use of physical, biological, thermal, and chemicalremedy methods to cleanse contaminated soils. Unfortunately, many of the conventional approaches are plagued with issues such as high chemical cost, long operation time, treatment failure, secondary pollution, soil degradation, and large energy consumption (Xu et al. 2019). This research proposal aims to shine a light on the different ex-situ remediation techniques and suggest the most appropriate method. This topic is relevant to the environmentalists and in general, the disciplineof environmental science as it advances the principle of sustainability.

Literature Review

            The subject of heavy metal contamination of soil has attracted the attention of many scholars and environmentalists. As a result, there are numerous literature resources that address the issue of heavy metal pollution of soil and the various methods of soil remediation. Zwolak, Sarzyńska, Szpyrka & Stawarczyk (2019) acknowledge that the accumulation of heavy metals in the soil has a detrimental effect on the safety of vegetables. The authors continue to assert that road traffic, industrial pollutants, mineral fertilizers, and plant protection products comprise some of the sources of heavy metal soil contamination. Yang et al. (2018) conducted a study and came to the conclusion that arsenic, lead, and cadmium pose a bigger risk than people imagine. They also determined that heavy metal pollution of soils affects children more than adults. Many other authors confess that polluted soils need to be cleansed to ensure sustainability. In this spirit, Liu, Li, Song & Guo (2018) undertook research through which they ascertain that over 20 million hectares of earth’s soils are contaminated by heavy metals. Notably, the concentration of heavy metals in the soil exceeds the regulatory levels. Liu, Li, Song & Guo (2018) outline several ex-situ remediation techniques that have been employed in various contaminated sites including immobilization,vitrification, landfilling, stabilization, surface capping, extraction, bioremediation, and phytoremediation. Three broad categories of remediation technologies are immobilization, containment, and treatment technologies.

Damian (2018) defines immobilization as the remediation process of decreasing bioavailability of heavy metals in soil by introducing immobilizing agents. Clay, reported cement, microbes, phosphates, and organic amendments are some of the amendments used to restrain heavy metals. Biological treatments are held in high regard when it comes to rectifying environmental issues as they are sustainable, unlike the chemical processes(Damian 2018). These interventions introduce tolerant plants and microorganisms into contaminated soils with the aim of decreasing toxicity. Phytoremediation and bioleaching are the most common biological techniques that cost between $50 and $90 per squaremeter to implement (Damian 2018). Biological agents such as bacteria oxidize the heavy metals making their segregation easier(Damian 2018). Biological treatments require elongated periods of time to get rid of heavy metals efficiently. The chemical method of soil washing is suitable for remedying highly contaminated soils. Chemical additives are introduced into polluted soil and mixed so that the product is clean soil(Damian 2018). This method is associated with a high washing efficiency when done correctly. On the other hand, soil washing requires large amounts of water and some soils often necessitate further treatments.Due to the limitations of individual soil remediation techniques, researchers have resolved to adopt combined approaches where diverse technologies are merged(Selvi et al. 2019). By combining the advantages of several techniques, integrated remediation methods become more efficient (Selvi et al. 2019). Most of the existing research projects focus on individual soil remediation methods. Nevertheless, a resource by Selvi et al. (2019) summarizes the various integrated methods of soil remediation including chemical biological, electro-kinetic microbial, electrokinetic phytoremediation, and phytobial soil rehabilitation approaches. Evidently, the list of methods applicable to rehabilitating heavy metal-polluted soil is endless. Arriving at the best remediation technique requires laboratory studies to determine both the nature of heavy metal pollutants and the extent of pollution.

Key Research Questions

            There is no denying that the amount of heavy metals in many parts of the world is alarming. Since soils are essential for agriculture and human existence, remediation of heavy metal polluted soils is essential (Rai et al. 2019). While most quarters agree on this suggestion, there is less information pointing to a favorite remediation technique. Environmentalists are spoilt for choice when it comes to the methods of removing heavy metals from soils. The choice of remedial method depends on factors such as the intended usage of the site, the degree of contamination, and the availability of other cost-effective/ innovative techniques. While there are many soil remediation tactics, they can be categorized under three major groups namely immobilization, containment, and treatment technologies. Soil washing, vapor extraction, chemical extraction, chemical oxidation, dehalogenation, thermal desorption, biomediation, incineration, and phytoremediation are some of the methods of soil remediation (Rodríguez, Gómez, Blazquez & Tarazona 2014). Choosing one among the many techniques can be a daunting task. This research project’s key research questions are inspired by the need to choose the most suitable method of soil remediation. In particular, this research aims to answer the following questions.

Research question 1: What are the various methods used to remediate soil polluted by heavy metals and how do these methods compare?

Research question 2: Which is the most appropriate method of rehabilitating heavy metal polluted soil and why?

Methodology

            This research project is heavily dependent on the existing literature. Therefore, secondary data analysis is the research method that will be employed in the quest to investigate the set research questions. This study is a success only if it highlights the various methods used to rehabilitate heavy metal-polluted soil, examines how these approaches compare and determines the most appropriate technique of the discussed. Fortunately, there is enough literature to explore these areas conclusively. Considering the nature of this project, much of the data explored is qualitative. Thus, there is no need for laboratory experiments or questionnaires. The decision to go with secondary data analysis is guided by the benefits such as cost-effectiveness and ease of accessing relevant sources (Crossman 2018). More to the point, tapping into the available information makes things easier for a rather technical subject. While there is the option to collect first-hand data, there is no need to duplicate information that is already available (Crossman 2018). It should be noted that the main purpose of this research is to evaluate the many methods of remediating heavy metal-contaminated soil and pick the most appropriate. While most resources are available for free, the researcher will spend considerable time evaluating them to determine their validity and credibility. Overall, only credible academic papers will shape this study.

Results

            After a comprehensive evaluation of available research studies, this project aims to put into context the common methods of soil remediation applicable to the removal of heavy metals. The intended outcomes must therefore highlight not only the soil rehabilitation methods, but also how they work and compare to each other. This research also targets to determine which remediation approach towers above the others as regards appropriateness and efficiency. This finding would be of great use as it would help turnaround the worsening state of affairs in the area of soil sustainability. As things stand, the accumulation of heavy metals in the soil poses a great danger to the environment and other living things that depend on it.

Timescale

            This research paper will be prepared and organized in sections. The important sections including abstract, introduction, literature review, methodology, results, discussion, and conclusion. The table below indicates the various tasks that go into this study and the deadlines for their completion.

Tasks/ Sections	Date of completion
Preliminary research work	20/8/2019
Preparing and organizing the paper to include abstract, introduction, literature review, methodology, results, discussion, and conclusion sections.	25/8/2019

Bibliography

Crossman, A. (2018, December 29). How to use secondary data in social science research. ThoughtCo. Available at: https://www.thoughtco.com/secondary-analysis-3026573. [Accessed 11 Aug. 2019].

Damian, G. E. (2018). New approaches regarding remediation techniques of heavy metal contaminated soils from mining areas. Studia Universitatis Babeș-Bolyai Ambientum, 63(1), pp.15-31.

Jaishankar, M., Tseten, T., Anbalagan, N., Mathew, B. B., & Beeregowda, K. N. (2014). Toxicity, mechanism and health effects of some heavy metals. Interdisciplinary Toxicology, 7(2), pp.60-72.

Li, C., Zhou, K., Qin, W., Tian, C., Qi, M., Yan, X., & Han, W. (2019). A review on heavy metals contamination in soil: Effects, sources, and remediation techniques. Soil and Sediment Contamination: An International Journal, 28(4), pp.380-394.

Liu, L., Li, W., Song, W., & Guo, M. (2018). Remediation techniques for heavy metal-contaminated soils: Principles and applicability. Science of the Total Environment, 633, pp.206-219.

Rai, P. K., Lee, S. S., Zhang, M., Tsang, Y. F., & Kim, K. (2019). Heavy metals in food crops: Health risks, fate, mechanisms, and management. Environment International, 125, pp.365-385.

Rodríguez, F., Gómez, G., Blazquez, A., & Tarazona, J. (2014). Soil pollution remediation. In Anderson, B., Peyster, A. D., Gad, S. C., Hakkinen, P. B., Kamrin, M., Locey, B., Mehendale, H. M., Pope, C., & Shugart, L. Encyclopedia of Toxicology (3rd ed., pp.344-355). Amsterdam: Elsevier.

Selvi, A., Rajasekar, A., Theerthagiri, J., Ananthaselvam, A., Sathishkumar, K., Madhavan, J., & Rahman, P. K. (2019). Integrated remediation processes toward heavy metal removal/recovery from various environments – A review. Frontiers in Environmental Science, 7(66), pp.1-15.

Wuana, R. A., & Okieimen, F. E. (2011). Heavy metals in contaminated soils: A review of sources, chemistry, risks and best available strategies for remediation. ISRN Ecology, 2011, pp.1-20.

Xu, J., Liu, C., Hsu, P., Zhao, J., Wu, T., Tang, J., … Cui, Y. (2019). Remediation of heavy metal contaminated soil by asymmetrical alternating current electrochemistry. Nature Communications, 10(1), pp.1-8.

Yang, Q., Li, Z., Lu, X., Duan, Q., Huang, L., & Bi, J. (2018). A review of soil heavy metal pollution from industrial and agricultural regions in China: Pollution and risk assessment. Science of The Total Environment, 642, pp.690-700.

Zwolak, A., Sarzyńska, M., Szpyrka, E., & Stawarczyk, K. (2019). Sources of soil pollution by heavy metals and their accumulation in vegetables: A review. Water, Air, & Soil Pollution, 230(7), pp.1-9.