Reducing The Waste Stream

Toxic wastes are harmful or fatal when ingested or absorbed, or leach toxic chemicals into the soil or groundwater when disposed of on land. Examples include wastes that contain high concentrations of heavy metals, such as cadmium, lead, or mercury.

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Certain compounds are exempt from regulation of hazardous waste if they are accumulated in less than 1kg (2.2 lbs) of commercial chemicals or 100kg of contaminated soil, water or debris.

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Even larger amounts (1000kg) are exempt when stored at an approved waste treatment facility for the purpose of being beneficially used, recycled, reclaimed, detoxified or destroyed.

MANAGEMENT OF HAZARDOUS WASTE

Hazardous waste is ignitable, corrosive, or reactive (explosive). Waste that exceeds certain amounts of toxic chemicals is considered hazardous. The USEPA defined 500 specific wastes as hazardous. These include heavy metals like lead and mercury, radioactive substances including highly toxic radionuclides like plutonium-239, or organic chemicals with toxic properties, like the heavily chlorinated hydrocarbon DDT (McCarthy, 2001).

Hazardous waste management is a rapidly developing industry full of experimentation and innovation. This innovation is being driven by the need for effective and economical processes for reclaiming, treating, or destroying wastes rather than landfilling them without treatment. A hierarchy of general waste management options can be constructed. The most desirable option is source reduction through process modification (Combs 1989; Blackman, 2001).

Hazardous waste management options and priorities

•Source reduction (process modification)

•Separation and volume reduction

•Exchange / sale as raw materials

•Energy recovery

•Treatment

•Source ultimate disposal (landfill)

Source: Combs (1989); Blackman, (2001).

In situ biodegradation or biological treatment of industrial wastewaters is usually accomplished in bioreactors and can effectively remove organic pollutants in wastewaters having low-to-moderate concentrations of simple organic compounds and lower concentrations of complex organics. The biota are generally less effective in attacking mineral or heavy metal constituents, but in carefully controlled conditions, can be usefully employed (Alexander, 1999 ; Blackman, 2001 ).

Physical treatment processes

gas cleaning

•mechanical collection

•electrostatic precipitation

•fabric filter

•wet scrubbing

liquid-solids separation

•centrifugation

•clarification

•coagulation

•filtration

•flocculation

•flotation

•foaming

•sedimentation

•thickening

removal of specific components

•adsorption

•crystallization

•dialysis

•distillation

•electrodialysis

•evaporation

•leaching

•reverse osmosis

•solvent extraction

•stripping

Chemical treatment processes

•absorption

•chemical oxidation

•chemical reduction

•wed oxidation

•ion exchange

•neutralization

•chemical fixation and solidification

•dehalogenation

Biological treatment processes

•aerobic systems

•anaerobic systems

•activated sludge

•spray irrigation

•tricking filters

•waste stabilization ponds

•rotating bio contactors

Thermal treatment processes

•incIrenation

•pyrolysis

•vitrification