A comparison of technologies for remediation of heavy metal contaminated soils

TLDR: In this article, a review of the current status of technology deployment and recommendations for future remediation research is presented. And the authors also elucidate and compare the available technologies that are currently being applied for remediation of heavy metal(loid) contaminated soils, as well as the economic aspect of soil remediation for different techniques.

About: This article is published in Journal of Geochemical Exploration.The article was published on 2017-11-01 and is currently open access. It has received 792 citations till now. The article focuses on the topics: Environmental remediation & Soil contamination.

Figures

Table 2 Accumulation of heavy metal(loid)s in edible parts exceeding permissible limits of vegetables and crops when cultivated on heavy metal(loid)s polluted soils.

Fig. 1. Comparison of different soil clean-up methods. Soil remediation methods can be broadly divided into three categories: physical, chemical and biological. Physical remediation methods include (1) soil replacement, (2) soil isolation, (3) vitrification, and (4) electrokinetic; biological methods generally include (5) phytostabilization, (6) phytoevaporation and (7) phytoextraction, and chemical methods contain (8) immobilization and (9) soil washing. However, biological and chemical methods can be applied jointly depending on the type ofmetal, soil, plant and chemical reagent. Moreover, the effectiveness of different phytoremediation techniques can be enhanced bymicrobial-, chelate- and genetic-assisted remediation.

Table 3 Some examples of hyperaccumulator plants accumulating high levels of heavy metal(loid)s in their above ground parts.

Frequently asked questions

Q1. What have the authors contributed in "A comparison of technologies for remediation of heavy metal contaminated soils" ?

This review summarizes the soil contamination by heavy metal ( loid ) s at a global scale, accumulation of heavy metal ( loid ) s in vegetables to toxic levels and their regulatory guidelines in soil. In this review, the authors also elucidate and compare the pool of available technologies that are currently being applied for remediation of heavymetal ( loid ) contaminated soils, as well as the economic aspect of soil remediation for different techniques. This review article includes an assessment of the contemporary status of technology deployment and recommendations for future remediation research. 

Q2. What are the future works mentioned in the paper "A comparison of technologies for remediation of heavy metal contaminated soils" ?

Through the introduction of foreign resistant genes, the possibility to create an ideal plant species for clean-up of heavy metal ( loid ) s contaminated soil is feasible. Several researchers have proposed that establishing ideal crop hyperaccumulator in the future can be an ideal choice due to its feasibility and applicability in the field of which current emphasis is scarce. Therefore, establishing an optimum soil + plant + microbes combination using transgenic technology can be a promising way in the future development. By mean of genetic engineering, ability of a plant to accumulate, translocate and detoxify heavy metal ( loid ) s can be significantly enhanced. 

Q3. What are the main methods used for producing electric and thermal energies from contaminated plant biomass?

Combustion and gasification are important approaches used for producing electric and thermal energies from contaminated plant biomass. 

Q4. What is the effect of organic amendments on metal bioavailability?

In addition to formation of stable complexes with metal ions, organic amendments can reduce metal bioavailability by increasing in surface charge (Gadd, 2000). 

Q5. What is the effect of adding compost on soil microbial diversity?

addition of compost significantly enhances microbial diversity via long-lasting buffering-effect on pH, and consequently allowing plants to germinate and accumulate more heavy metal(loid)s in roots (Valentín-Vargas et al., 2014). 

Q6. What are the common heavy metal(loid)s in soils?

The most common heavy metal(loid)s present in polluted soils are in order of Pb, Cr, As, Zn, Cd, Cu and Hg. Natural processes also contributes towards heavy metal(loid) contamination of soils. 

Q7. What are the main types of remediation methods?

Physical remediation methods (soil replacement and electrokinetic remediation) can completely remove heavy metal(loid)s from contaminated soil. 

Q8. How can chemo-assisted remediation reduce the time required for contaminated sites?

Chelates- and microbial-assisted as well as use of transgenic plant species can greatly reduce the time required for complete remediation of contaminated site. 

Q9. What is the main reason for the immobilization of heavy metal(loid)s in soil?

the immobilizing effect of organic amendments on heavy metal(loid)s at the initial stage of their application is important for remediation of contaminated sites. 

Q10. What is the key factor determining the success and practical application of soil clean-up technology?

In addition to societal and environmental acceptability aspects, cost involved is the key factor determining the success and practical application of remediation technology in the field conditions. 

Q11. What is the role of external magnetic fields in the removal of heavy metals from waste water?

introduction of external magnetic fields will greatly enhance mobility of magnetic NPs, thereby facilitating recycling of NPs used for treatment of waste water containing toxic heavy metal(loid)s (Zhang et al., 2010). 

Q12. What is the main reason why Portland cement is being used as a good metal retainer?

Ordinary Portland Cement (OPC) has been commonly used as a good metal retainer, and in the last few years, alternative binders are receiving growing attention. 

Q13. What is the reason for the lack of response in heavy metal(loid)s accumulation and tolerance?

The lack of response in heavymetal(loid)s accumulation and tolerance could be due to the fact that PC synthesis is also governed byGSHproduction. 

Q14. What is the effective and tested mobilizing agent for the remediation of metals?

Among the chelating agents, EDTA is considered the most effective and tested mobilizing amendment for the remediation of metals especially Pb (Shahid et al., 2014c). 

Q15. What is the main limitation for cleanup of heavy metal-polluted soils?

In case of phytoremediation, major limitation for cleanup of heavymetal-polluted soils is the long time period required to completely remediate the sites (Bhargava et al., 2012). 

Q16. What is the common type of heavy metal(loid)s in soil?

Heavy metal(loid)s occur naturally in Earth crust and are released into soil by various human activities, which have resulted in high heavy metal(loid) contents in soil to toxic levels. 

Q17. What are the main reasons why physical remediation methods are not applicable to agricultural areas?

Physical remediation methods are generally not applicable to agricultural areas owing to their destructive nature and lose of soil fertility. 

Q18. What are the key factors that affect the applicability and selection of remediation technologies?

This review revealed that cost involved, time required, long-term effectiveness, general acceptability, applicability to high metal andmultimetal contaminated sites are the key factors that affect the applicability and selection of remediation technologies. 

Q19. What is the main reason why chelate-assisted phytoextraction has not gained?

Chelate-assisted phytoextraction of heavy metal(loid)s from soil has not gained considerable acceptance because of its high leaching risk, relatively low efficiency and high cost. 

Q20. Why does chelate-assisted remediation have no long-term effectiveness?

due to low degradability and long persistence in environment, chelate-assisted remediation does not have long-term effectiveness.