1. Land fills
2. Deep - well injection
3. Surface impoundments
Management of hazardous wastes
Hazardous wastes may remain dangerous for thousands of years. The hazardous waste include radioactive refuse, metallic compounds, organic solvents, acid asbestos, organic cyanides, pathological hospital wastes, disposable medical equipments and tools.
The following methods are adopted for the disposal of hazardous wastes.
1. Land fills : There are permanent storage facilities for military related liquid and radioactive waste materials in secured lands. High level radio active wastes are stored in deep underground storage.
Wastes are carefully contained to prevent cross - mixing of reactive substances. The land fill is capped with impervious clay to prevent infiltration and percolation of water through the fill. Fill bottom is lined and provided with drainage system to contain and remove any leakage that occurs. Monitoring the wells provides a final check.
2. Deep - well injection : It involves drilling a well into dry, porous material below groundwater. Hazardous waste liquids are pumped into the well. They are soaked into the porous material and made to remain isolated indefinitely. However fractures in the impermeable layer may permit the injected wastes to escape and contaminate ground water.
3. Surface impoundments : This method is used to dispose large amounts of water carrying relatively small amounts of chemical wastes. Surface impoundments are simple excavated depressions (ponds) into which liquid wastes are drained. Solid wastes settle and accumulate while water evaporates. If the pond bottom is well sealed and if evaporation equals input, wastes may be stored in the impoundment indefinitely.
4. Incineration : The hazardous biomedical wastes are usually disposed off by means of incineration. Human anatomical wastes, discarded medicines, toxic drugs, blood, pus, animal wastes, microbiological and biotechnological wastes etc are called Bio-medical wastes.
5. Bioremediation : This is another rapidly developing clean up technology. Cleaning the environment with biological options such as microbes and plants is called bioremediation. Some naturally occurring bacteria and other microorganisms have the capability to degrade or absorb or detoxify the wastes such as heavy metals. Many plant materials are successfully used as adsorbents for xenobiotics (phytoremediation). Genetically Engineered Microorganisms (GEMS) are currently produced in large scale to remove the hazardous radionuclides and heavy metals such as mercury, chromium, cadmium etc. Certain plants such as Gibberella fusarium were able to breakdown cyanide and reduce it to a non-toxic form. The bacteria Pseudomonas, nicknamed as 'super - bug' are capable of degrading variety of toxic compounds and also degrade oil.
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