Waste

Waste can be loosely defined as any material that is considered to be of no further use to the owner and is, hence, discarded. However, most discarded waste can be reused or recycled, one of the principles of most waste management philosophies. What may be of no further use to one person and regarded as waste to be dumped, may be of use to the next person, and is the basis of the rag picking trade, the sifting through of refuse at landfills for recovery and resale, a very fundamental historical waste management practice still functioning in many countries, often conducted on a highly organised commercial basis.

Waste is generated universally and is a direct consequence of all human activities. Wastes are generally classified into solid, liquid and gaseous. Gaseous waste is normally vented to the atmosphere, either with or without treatment depending on composition and the specific regulations of the country involved. Liquid wastes are commonly discharged into sewers or rivers, which in many countries is subject to legislation governing treatment before discharge.
In many parts of the world such legislation either does not exist or is not sufficiently implemented, and liquid wastes are discharged into water bodies or allowed to infiltrate into the ground. Indiscriminant disposal of liquid wastes pose a major pollution threat to both surface and groundwater.
Solid wastes are mainly disposed of to landfill, because landfill is the simplest, cheapest and most cost-effective method of disposing of waste (Barrett and Lawler, 1995). In most low- to medium-income developing nations, almost 100 per cent of generated waste goes to landfill. Even in many developed countries, most solid waste is landfilled. For instance, within the European Union, although policies of reduction, reuse, and diversion from landfill are strongly promoted, more than half