Landfills, heavy metal contamination

The Ecolotree buffer uses phytoremediation, or plant processes, for environmental remediation purposes. Ecolotree buffers can be used to reduce the migration of subsurface water and surface runoff, while also acting as an in situ remediation technique for both organic and heavy-metal contaminants, including benzene, toluene, ethylbenzene, and xylene (BTEX) chlorinated solvents ammunition wastes and excess nutrients in soil or water. The technology is commercially available and has been used at landfill and waste treatment sites. 

Although USs may volatilize heavy-metal contaminants, the metals are not broken down or destroyed, and ash that contains excessive levels of heavy metals must be stabilized to meet toxicity characteristic leaching procedure (TCLP) prior to being disposed of in a landfill. 

Bisdom E. B. A., Boekestein A., Curmi P., Legas P., Letsch A. C., Loch J. P. G., Nauta R., and Wells C. B. (1983) Submicroscopy and chemistry of heavy metal contaminated precipitates from column experiments simulating conditions in a soil beneath a landfill. Geoderma 30, 1-20. 

Landfill leachate is a potential source of heavy metal contamination and a popular horror story in newspapers. Landfills concentrate wastes, the wastes are not always mixed thoroughly with soil, and soils have limits in their capacity to react. Landfills... 

Water supplies are closely monitored for heavy metals, because they tend to be very toxic. Major sources of heavy metal contamination include landfills, industries, agriculture, mining, and old water distribution systems. 

The automobile is also an indirect source of another heavy metal contaminant, chromium. Chromium compounds (such as Cr04 ) are used in chrome plating for bumpers and grills. This plating also requires the use of the cyanide ion (CN), another major pollutant. These contaminants used to be discharged directly into streams, but now they re either pretreated to reduce to a less-toxic form or precipitated (formed into a solid) and disposed of in landfills. 

In-situ immobilization is used to convert wastes to insoluble forms that will not leach from the disposal site. Heavy metal contaminants including lead, cadmium, zinc, and mercury, can be immobilized by chemical precipitation as the sulfides by treatment with gaseous H2S or alkaline Na2S solution. Disadvantages include the high toxicity of H2S and the contamination potential of soluble sulfide. Although precipitated metal sulfides should remain as solids in the anaerobic conditions of a landfill, unintentional exposure to air can result in oxidation of the sulfide and remobilization of the metals as soluble sulfate salts. 

The evaluation of risk has underlined the possible adverse effects both on human health after the exposure to drinking water contaminated by landfill leachate and on small rodents and aquatic species at the hypothesized condition for humans, the estimated toxic effects of the raw leachate are mainly due to the levels of ammonia and cadmium and carcinogenic effects are induced by arsenic first and then by PCBs and PCDD/Fs while ecological potential risk is mainly attributable to the concentration of inorganic compounds, in particular ammonia for small rodents, cadmium, ammonia, and heavy metals for fishes. 

Sorption can significantly diminish the mobility of certain dissolved components in solution, especially those present in minor amounts. Sorption, for example, may retard the spread of radionuclides near a radioactive waste repository or the migration of contaminants away from a polluting landfill (see Chapters 21 and 32). In acid mine drainages, ferric oxide sorbs heavy metals from surface water, helping limit their downstream movement (see Chapter 31). A geochemical model useful in investigating such cases must provide an accurate assessment of the effects of surface reactions. 

Landfill leachate is an important point pollution source to water body, which contains DOM with a large number of unknown molecules that actively involve in biogeochemical and environmental processes (Chin et al. 1997). DOM not only plays an important role in freshwater systems for the mobility of toxic heavy metals and other pollutants but also may itself be a groundwater contaminant (Christensen etal. 1998). 

Insoluble Fe(OH)2 is formed which precipitates soluble and insoluble inorganic and organic pollutants from the solution. The mechanism for removing contaminants from wastewater is not yet fully understood [312,317-319]. The process has proved itself to be highly effective in the removal of the color and heavy metals. Disadvantage The iron sludge must be dumped (landfills are scarce) or dried, pelleted and sintered for disposal in iron mills (very costly). 

Dioxins, furans and heavy metals can be released as air borne pollutants in the ash, which needs to be landfilled with special care (i.e. mixed with cement) due to a danger of ground water contamination. 

Many old landfills were located on permeable ground, where leachates were allowed to percolate and attenuate through the porous material. Table 16.1 shows that the leachates percolating out of landfill sites contain significant concentrations of nutrients, heavy metals and organics this uncontrolled means of landfilling has resulted in the contamination of aquifers at many landfill sites around the world [45]. 

The Chemical Stabilization Technology (CHEM-STA ) is a proprietary contaminant immobilization mechanism for treating soils, sludges, and ashes contaminated with toxic heavy metals and hydrocarbons. The three-step process can be applied either in situ or ex situ to form stable and insoluble chemical compounds. Treated wastes are usually acceptable for landfill disposal. This technology is commercially available from Environmental Solutions, Inc. (ESI). According to the vendor, CHEM-STA has the following advantages ... 

Comparing the BA heavy metal concentration according to the Swiss legislation for waste materials (TVA 1990) and the guidelines for non-contaminated and tolerable disposable materials (BUWAL 1999) it is evident that today s BA do not fullfil either threshold values for so called inert landfill type nor the limits for disposable materials allowed for re-use (Table 3). In comparison to naturally occurring rocks, the measured concentrations in, for example, Cu, Zn, and Pb are even orders of magnitude higher. 

Traditional landfill presents several disadvantages since the space available for landfill has become scarce. In addition, municipal waste has to be transported over increasing distances with associated wastage of energy [3]. Leachates from unprepared landfills may contain hazardous levels of substances such as ammonium salts, heavy metals and organic chemical waste that may contaminate the air, soil and ground water [4] and thus may affect crops and secondary animals and man [3, 4, 5, 6, 7]. 

Micro-foam, or colloidal gas aphrons have also been reportedly used for soil flushing in contaminated-site remediation [494—498], These also have been adapted from processes developed for enhanced oil recovery (see Section 11.2.2.2). A recent review of surfactant-enhanced soil remediation [530] lists various classes of biosurfactants, some of which have been used in enhanced oil recovery, and discusses their performance on removing different type of hydrocarbons, as well as the removal of metal contaminants such as copper and zinc. In the latter area, the application of heavy metal ion complexing surfactants to remediation of landfill and mine leachate, is showing promise [541]. 

Sewage treatment and many on-site facilities produce biosolids (sewage sludge). These may be used as a soil conditioner in agriculture or for other purposes, such as land reclamation. Biosolids that are not used for these purposes are disposed of in various ways, including by landfill. In some circumstances, the disposal of biosolids may give rise to leaching, particularly of nitrates. Where biosolids are heavily contaminated with industrial waste, such as heavy metals, these contaminants may also need to be considered. 

During the last few decades extensive attention has been paid to the hazards arising from contamination of the environment by arsenic. Decontamination of heavy metals in the soil and water around industrial plants has been a challenge for a long time. The use of microorganisms for the recovery of metals from waste streams (Joshi et al, 2008 Patel et al, 2006,2007 Maeaskie and Dean, 1990), as well as the employment of plants for landfill application (Tripathi et al., 2007), has received increasing attention. Recent developments and improvements have resulted in the construction of bioreactors (Oehmen et al, 2006) that have a smaller footprint, and treat the metals more effectively. Many studies have demonstrated primary removal mechanisms for the metals by arsenate-reducing bacteria, which transform arsenate to arsenite (Cohen, 2006 Afkar et al, 2003 Mukhopadhyay et al, 2002). Plants have been... 

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