China 
Africa 
Explore chapters and articles related to this topic
Carbon Nanostructures and Their Application to Water Purification
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
These are characterized, in addition to the heaviness, by the low water solubility: the two physical properties mean that when released into the environment, in sufficient quantities, they can move through the soil and water until they meet a sufficiently resistant layer that will prevent, and they further vertical mass movement and allow it to accumulate. Depending on the nature of their release, the movement beneath the land surface can be quite complex, as the liquid follows the path that includes the least resistance. For example, homogeneous soils often have small differences in stratification that lead the DNAPLs to flow and then descend several times, to create a complex of vertical and horizontal clusters. Both the residuals of dense liquids in the non-aqueous phase in the soils, and the accumulations, over time become sources of contamination of groundwater and vapors from the ground. An example of DNAPL are halogenated hydrocarbons and chlorinated solvents.1
Contaminant Fate and Behavior Assessment
Published in Kofi Asante-Duah, Management of Contaminated Site Problems, 2019
Classically, DNAPLs form when chlorinated solvents percolate through a soil column and migrate downward through an aquifer until they encounter an impermeable clay or mudstone aquitard. Indeed, when DNAPLs are released into the subsurface, they tend to rapidly migrate downward toward the bottom of an aquifer. The DNAPL initially conforms to the surface of the aquitard to form a network of pools and interlacing strings. As the solvent continues to move independently of the groundwater, it begins to form dendritic branching patterns in microporous zones throughout the aquitard surface and inside the soil column. Over a period of time, the DNAPL can diffuse into impermeable layers, resulting in distributed source terms that are extremely difficult to remove or access. These source terms in the aquitard slowly migrate and dissolve or disperse into the aquifer. In addition to directly contaminating large quantities of groundwater, the DNAPL constituents also degrade slowly to form other hazardous substances, such as vinyl chloride, which can threaten human health and inhibit land reuse. On the whole, DNAPLs characteristically have great penetration capability in the subsurface because of their relatively low solubility, high density, and low viscosity (Yong et al., 1992). In fact, the relatively high density of these liquids provides a driving force that can carry contamination deep into aquifer systems that may exist at depth—and as such DNAPL tends to be of very great concern, where they exist.
Investigation of the influence of particle size on the migration of DNAPL in unsaturated sand
Published in Noor Amila Wan Abdullah Zawawi, Engineering Challenges for Sustainable Future, 2016
M.Y.D. Alazaiza, S.K. Ngien, M.M. Bob, S.A. Kamaruddin
Non-aqueous phase liquids (NAPLs) have a low solubility in water and occur in the subsurface as a separate phase and are considered as one of the most spread hazardous chemical (Newell et al., 1995). Theses NAPLs can be resulted from leakage of underground storage tanks and huge pipelines. NAPLs are classified into two types based on its density: the first type is light non-aqueous phase liquid (LNAPL) which has density less than water and the second type which is termed dense non-aqueous phase liquid (DNAPL) is denser than water. LNAPL include many hydrocarbon fuel components, for instance, toluene, benzene, xylenes (BTEX) and ethyl benzene. Tetrachloroethylene (PCE) and trichloroethylene (TCE) are examples of DNAPL materials (Newell et al., 1995). NAPL migration in the subsurface system depends on its relative density. When LNAPL enter the subsurface system, it will pass through unsaturated soil and migrate downward due to gravity and float on the surface of water table (Morris et al., 2003) resulting in deterioration of groundwater quality. On the other hand, DNAPL will pass through unsaturated zone and continue its downward migration under the effect of gravity until it reaches the saturated zone (Soga et al., 2004).
Morphological effect of dichloromethane on alfalfa (Medicago sativa) cultivated in soil amended with fertilizer manures
Published in International Journal of Phytoremediation, 2021
Sana Dardouri, Asma Jedidi, Sabrine Mejri, Sabrine Hattab, Jalila Sghaier
As a remedy for DNAPL pollution, many techniques were employed, including adsorption processes, air stripping and surfactant-enhanced dissolution (Khachikian and Harmon 2000; Huang et al. 2011). However, during the last decade, phytoremediation has been rapidly developing as a potential “green technology” for the cost-effective removal of DNAPL from soils and waters (Gerhardt et al. 2009; Cruz et al. 2014; Moccia et al. 2017). Several plants species have been tested for the DNAPL remediation, such as poplars (Gordon et al. 1998; Shang and Gordon 2002), Zea mays (Moccia et al. 2017), tobacco (Shang et al. 2001), fruit trees (Chard et al. 2006; Doucette et al. 2007), leguminous trees (Doty et al. 2007) and grass-like alfalfa (Zhang et al. 2013).