Challenges of Recalcitrant Organic Contaminants
Discuss about the Remediation of Recalcitrant Organic Contaminants in Soil.
Remediation process is an important process which ensures that the cleanup of the soils is able to happen. Many of the organic chemical which are used on soils are recalcitrant and they have hazardous effects to the ground water and soils. When exposed to the soils, they are able to contaminate it and lead to changes in its original quantities. Remediation of the recalcitrant organic contaminants is an important process which is able to ensure that the original composition of the soil is maintained. Different processes have been developed in the aim of improving the remediation process for such organic contaminants (Zearley, & Summers, 2012). First, the recalcitrant contaminants are able to pose a great challenge on the changes on soil biological compositions. These contaminants are able to facilitate different biological changes in soil components. From various analysis, many of the recalcitrant organic contaminants and chemicals cannot serve as both carbon and energy sources for microbial growth. This is one of the major reason which prompts the need for the remediation of such contaminants in soils. Moreover, the remediation is able to ensure that the soil quality is improved. This paper will be able to look at the different methods which are used for the remediation of the recalcitrant organic contaminants which are found in soils. Moreover, this paper will be focusing on the remediation on Barangaroo, Sydney related to the recalcitrant organic contaminants.
The removal of the recalcitrant organic contaminants is important to ensure that the soil is able to retail its value and composition. Some of the recalcitrant organic contaminants are man-made and this is able to make their remediation process difficulty (McCann, Servos, & University of Waterloo, 2016). Most of the recalcitrant organic contaminants found in the soils are soluble. Separating these materials from the soil during the remediation process is not easy. Different methods have been improvised and with the increase of technology some of the suggested process have been able to make the process effective (Rai, Lee, Kailasa, Kwon, Tsang, Ok, & Kim, 2018 and Jasper, 2014). In addition, the remediation process of these contaminants is one of the most expensive affair and thus limits the methods which can be applied during the remediation of the soil (In He, In Wu, & Soil Science Society of America, 2015). Nevertheless, it has been found that the remediation processes of the recalcitrant organic contaminants are limited due to their solubility nature.
Methods of Remediation
One of the key method which is used for remediation of the soil from the recalcitrant organic contaminants is the soil washing. This method is able to use water in the removal of the contaminants from the soils. This process works by either by dissolving and suspending the contaminants in the wash solution (Agrawal, 2018). Moreover, this method is combined with the physical techniques in the remediation process. Separation is the key process which is used during the remediation of the recalcitrant organic contaminants in the soils. Most importantly, the major contaminants which are removed through this process include some heavy metals, fuels radionuclides as well as some key VOCs and pesticides. The method is usually a water base process which is used for scrubbing soil in order to remove the contaminants (Ceci et al., 2018). This is seen as one of the most inexpensive method for the removal of the recalcitrant organic contaminants in soils.
One of the key process for this process is through dissolving or suspension of the contaminants in the wash solution or water. The soil washing is able to rely on the factor that most of the recalcitrant organic contaminants are able to bid either physically or chemically with the fine particles. The introduction of key addictive is able to facilitate the biding process of the recalcitrant organic contaminants (Liang, et al., 2017). This method can be sustained through the control and manipulation of the pH level for a period is time. At the end of the wash, the level of the pH of the soil will return to the required level. This will be an indicator of the removal of the recalcitrant organic contaminants. After the washing, the soil and water are separated from the contaminants. The washwater is able to contain the contaminants while the soil is left at its initial condition and composition. This method is able to rely on the biding nature of the recalcitrant organic contaminants to the fine grained soils (Milavec, 2017 and In Prasad, 2018). The method facilitates the binding process of these contaminants and therefore leave the other key soil particles uncontaminated. The removal of the contaminated fines and washwater are then treated or disposed off leaving the soil without any contaminants. After the removal of the contaminants from the soil, the washed soil can be used to backfill the excavated sites and ensure that the contamination is controlled. Mostly, this method is used to control the level of contamination resulting from the recalcitrant organic contaminants on sites (Norris, 2018). This means that the method is mostly applied for a localized areas of contamination. The volume of the recalcitrant organic contaminants is controlled when this method is applied as a key remediation method for the soils.
Soil Washing Method
The major steps which are carried out during the soil washing include the Pretreatment process. This ensures that the treatment to ensure the separation of the contaminants and soil particles do happen. The bidding process of the contaminants to the fine particles is able to happen at this stale. The second key process of the soil washing is the separation process (Lawrinenko, 2016). This process involves the separation of both the contaminated fine particles and washwater from the main soil particles. The other step which is involved in this process is the coarse grained treatment. These are the main soil particles which the contaminants are removed from the soil. This is a key process which has to ensure that the soil does not have the contaminants. The next process which is carried out is the fine rain treatment. This is the removal of the binding recalcitrant organic contaminants from the fine grain soil particles. Nevertheless, this is not a key process and disposal of the contaminated fine grained soil particle is carried out. Next., the water washing also involves the process of water treatment (In Adhya, In Lal, In Mohapatra, In Paul, & In Das, 2018). The wash water is treated in order to conserve the environment and control any further contamination using the contaminated washwater. Lastly, the water washing is able to involve the residue management. The residue is able to compose of the contaminated fine soil particles and the recalcitrant organic contaminants. The contaminated washwater is also included in this part of the residue management process. This is also an important process which has to ensure further contamination of the soil does not happen during the disposal of the residue.
The water washing process has not yet been commercialized. The process is mostly used to remediation of localized areas where the soil can be excavated washed and then refilled again. Nevertheless, this is one of the most effective method for the recalcitrant organic contaminants. The method is cost effective and therefore important for onsite soil remediation process (In Luo, & In Du, 2018). Nevertheless, the method required a large area to set up for the treatment. In addition, this method is able to include some key additives during the washing process. The additives can be source of new contamination of soil.
Another method which is used for the remediation of the recalcitrant organic contaminants in soils if the ex situ thermal desorption. Under this method, the contaminated soil is heated in order to volatilize water and the recalcitrant organic contaminants. The method is able to utilize the carrier gas or use of vacuum system which is able to transport the volatilized water and the recalcitrant organic contaminants to the treatment systems (Oves, Zain, & Mi, 2018). Most importantly, this process is able to allow for the reuse of the soil after the remediation process. The low temperature desorption is an important method for the soil remediation which ensures that the recalcitrant organic contaminants are evaporated from the soil layers. This process is able to begin with the excavation of the contaminated soil or material in order to allow for the thermal disrober unit to treat the samples. The next step involves the removal of the large rocks and debris or they are crushed to reduce the sizes (In De, In Belkin & In Lima, 2018). This ensures that the heat will be able to pass through the particles easily. In addition, mechanical handling is also allowed when the moisture material is too high. Then the soil is fed into the TDU through the mechanical weigh belt and it is then heated between 350 and 450oC. this helps to volatilize the recalcitrant organic contaminants for effective removal through gas stream. Retention time of the material is usually allowed at 12 to 15 minutes.
Ex Situ Thermal Desorption Method
In conclusion, the water washing and the thermal desorption methods are critical methods which are used in the remediation of the recalcitrant organic contaminants. The two methods are cost effective and are able to result to better results of the soil. The methods are able to ensure that the soil refill can be done and able to control further contamination.
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