Hazardous Waste Heavy Metal

According to the technology developer, the technology treats petroleum-contaminated soils, hazardous wastes, heavy metals, polychlorinated biphenyls (PCBs), semivolatUe organic compounds (SVOCs), volatile organic compounds (VOCs), polynuclear aromatic hydrocarbons (PAHs), and pesticides. 

Two major divisions of biochemical metabolism that operate on hazardous waste species are oxic processes, which use molecular O2 as an oxygen somce, and anoxic processes, which make use of another oxidant. For example, when sulfate ion acts as an oxidant (electron receptor), the transformation sol" H2S occurs. (This has the benefit of providing sulfide, which precipitates insoluble metal sulfides in the presence of hazardous waste heavy metals.) Because molecular oxygen does not penetrate to such depths, anoxic processes predominate in the deep sediments, as shown in Figure 15.6. 

Second, not all chemical wastes that contain hazardous substances are deemed to be hazardous. EPA considers wastes that contain certain hazardous substances (heavy metals and organic compounds, including carcinogens and noncarcinogens) not to be hazardous if the leachability of the substances from the waste form is limited. This characterization of waste as nonhazardous is based on EPA s judgment that potential risks to humans resulting from disposal of the waste would not exceed acceptable levels. 

Solidification with cement generally is accomplished with a Portland cement and other additives. The quantity of cement can be varied according to the amount of moisture in the waste. Heavy metal cations in the waste form insoluble carbonates and hydroxides at the high pH of the mixture. The surface of the hardened mass can be coated with asphalt or other material to reduce leaching of hazardous components. If the waste is mixed with anhydrous cement and water there is the possibility of ions incorporation in the cement structure during the hydrolysis process. Heavy metal ions could bind with the cement by the process of chemisorption, precipitation, surface adsorption,... 

When antifreeze becomes unsuitable for use, either because of depletion of inhibitors, presence of corrosion products or corrosive ions, or degradation of the fluid, recycling and reuse of the antifreeze, rather than disposal, may be considered. Although ethylene glycol is readily biodegraded in typical municipal waste treatment faciHties, antifreeze disposal becomes problematic because the coolant may contain hazardous quantities of heavy metals picked up from the cooling system. Recycling may be economically preferred over coolant disposal and reduces the concern for environmental impact. 

The only components in a coating powder which might cause the waste to be classified as hazardous are certain heavy-metal pigments sometimes used as colorants. Lead- (qv) and cadmium-based pigments (qv) are seldom used, however, and other potentially hazardous elements such as barium, nickel, and chromium are usually in the form of highly insoluble materials that seldom cause of the spent powder to be characterized as a hazardous waste (86). 

NOTE - Petrochemical plants also generate significant amounts of solid wastes and sludges, some of which may be considered hazardous because of the presence of toxic organics and heavy metals. Spent caustic and other hazardous wastes may be generated in significant quantities examples are distillation residues associated with units handling acetaldehyde, acetonitrile, benzyl chloride, carbon tetrachloride, cumene, phthallic anhydride, nitrobenzene, methyl ethyl pyridine, toluene diisocyanate, trichloroethane, trichloroethylene, perchloro-ethylene, aniline, chlorobenzenes, dimethyl hydrazine, ethylene dibromide, toluenediamine, epichlorohydrin, ethyl chloride, ethylene dichloride, and vinyl chloride. 

Demirbas, A., Heavy metal adsorption onto agro-based waste materials A review, Journal of Hazardous Material, 157, 220-229, 2008. 

Pohland, F.G. and Gould, J.P., Containment of Heavy Metals in Landfills with Leachate Recycle, Proc. 7th Annual Symposium Disposal of Hazardous Waste, EPA 600/g-81-002a, pp. 171-189, 1981. 

The only means by which inorganic wastes can be rendered nonhazardous are dilution, isolation (as in deep-well injection), in some cases changes in oxidation state, and neutralization. Acidic wastes made up one-fifth of the injected waste volume and involved one-third of the injection wells in 1983. Most of the volume was from inorganic acids (hydrochloric, sulfuric, and nitric). Acid-base characteristics and neutralization were discussed in detail earlier, so the remainder of this section will focus on heavy metals and other hazardous inorganics (selenium and cyanide). 

Recycling and Disposal of Hazardous Solid Wastes Containing Heavy Metals and Other Toxic Substances... 

Heavy metals have the potential to enter the water supply from the leachate or runoff from landfills. It is estimated that nonrecycled lead-acid batteries produce about 65% of the lead in the municipal waste stream. When burned, some heavy metals such as mercury may vaporize and escape into the air, and cadmium and lead may end up in the ash, making the ash a hazardous material for disposal. 

To reduce the amount of waste, start with pollution prevention. Starting with pollution prevention leads to less or no leftover waste that could potentially become hazardous wastes. The use of rechargeable batteries results in a longer life span and use fewer batteries. However, rechargeable batteries still do contain heavy metals such as nickel-cadmium. When disposing of rechargeable batteries, recycle them if possible. 

The expense of proper disposal leads to the shipment of large amounts of e-waste to China, India, Pakistan, Nigeria, and other developing countries. Shipment is often through middlemen, and under tariff classifications that make quantities difficult to assess. There, despite the intents of national regulations and hazardous waste laws, most e-waste is treated as general refuse, or crudely processed, perhaps by burning or acid baths, to recover only a few materials of value. Harm to the environment, workers, and area residents is inevitable, often from release of dioxins, furans, and heavy metals. 

Zhao G, Zhou H, Wang Z (2010) Concentrations of selected heavy metals in food from four e-waste disassembly localities and daily intake by local residents. J Environ Sci Health A Tox Hazard Subst Environ Eng 45(7) 824-835. doi 10.1080/10934521003709016... 

METLCAP A process for encapsulating hazardous heavy metal wastes in a proprietary type of cement. Developed and offered by Environmental Remediation Technology, Cleveland, OH. 

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