Waste

Waste, rubbish or materials that are not needed and are economically unusable without further processing. It may be in liquid, gas, or solid form and originate from a wide range of human operations, such as industry, commerce, transport, agriculture, medicine, and domestic activities. Waste may be classified in many different ways, such as according to its origin (for example, domestic, industrial, commercial, clinical, construction, nuclear, agricultural) or its properties (for example, inert, toxic, inflammable). Without suitable treatment such waste becomes a source of contamination of the environment at large, leading to air pollution (such as acid rain or traffic pollution), water pollution, and oil pollution.

The amount of waste produced by human activities is increasing in most parts of the world, accompanied by problems of disposal. In developing countries waste-disposal facilities are minimal, but substantial quantities are diverted for recycling. Waste disposal operations in the developed world are becoming increasingly sophisticated with specialist companies and facilities. The United Kingdom produces 500 million tonnes of waste per year, this consisting of mineral (27 per cent), agricultural (40 per cent), industrial (20 per cent), and municipal (4 per cent) wastes, sewage sludge (7 per cent), and dredged spoil (2 per cent). Most UK solid waste disposal is done through landfill in 4,000 licensed sites. Suitable locations for landfill are becoming increasingly difficult to find and disposal of waste by this method has potential environmental problems, such as leaching of toxins into groundwater and generation of explosive methane gas (which may also contribute to the greenhouse effect). Combustible wastes can be incinerated, but the process is expensive, may result in air pollution, and has a low level of public acceptability. Highly specialized incinerators are used to burn hazardous wastes and eliminate their toxic properties; they produce a solid residue which is landfilled, but the volume is much reduced and it is inert. Sewage disposal in the United Kingdom used to see much sewage sludge being dumped at sea, but in 1998 this was banned, and anaerobic digestion (in which waste decomposes in an enclosed chamber) and incineration are now the common alternatives. Certain wastes represent special hazards and require appropriate treatment, for example, clinical waste which may be contaminated with pathogens (and is incinerated), and nuclear waste for which highly engineered burial facilities are required. Many countries are now adopting policies to encourage waste minimization, which consists of a hierarchy of management options ranging from cessation of waste production (the most favoured), reuse, recycling, combustion for fuel and disposal by landfill, and so on, to incineration (the least favoured). In order to encourage waste minimization the UK government introduced a tax in 1996 of £7 per tonne on landfill for many wastes (£2 per tonne for chemically inert waste). Together with other strategies, such as encouragement of recycling centres and domestic composting of organic matter, it is likely that there will be a substantial move away from traditional waste-disposal practices. Indeed, the UK government has set a target for 2015 by when 33 per cent of household waste will be recycled.