Domestic refuse includes paper, cardboard, metals, glass, food matter, ashes, plastics, wood, and other substances discarded from homes. It also includes old furniture, household appliances, and other items. Increasing amounts of paper, cardboard, plastics, glass, and other types of packaging are concomitants of improved standards of living. At the same time, the increasing use of gas, oil, and electricity for heating and cooking has resulted in a decline in the ash content of solid wastes. Thus, the proportion of paper and paper products in domestic refuse has already reached more than 50% in some countries, and this trend will continue.
Commercial refuse includes the wastes discarded by markets, shops, restaurants, offices, and similar businesses. Such refuse is growing in importance not only as a result of increasing business activity, but also because there are few opportunities to deal with it on-site.
Industrial refuse comprises a very wide variety of wastes ranging from comparatively inert materials such as calcium carbonate to highly toxic and explosive compounds. Other examples are trimmings and scrap from manufacture, sludges and slag from industrial processes, and wastes from the food processing industry. Wastes produced in large quantities by mining and some other operations are usually treated by the respective industries themselves. The natural growth and diversity of industry generally, together with rapid technological developments, have resulted in substantial increases not only in the volume of industrial wastes, but also in their complexity.
Agricultural wastes include wastes arising from the production and processing of food and other crops and from the raising and slaughtering of livestock. In many areas the practice of agriculture near urban areas is resulting in the need to consider this type of waste, which is growing in volume, as part of the general urban waste-disposal problem.
General community waste includes demolition and construction debris, street refuse, discarded motor vehicles, and refuse arising from community services such as hospitals, abattoirs, transport systems, parks, canals and harbours. Special handling is required for potentially dangerous wastes such as those from hospitals, international ports and airports, and firms using radioactive materials. As in the other classifications, the volume of material arising from these sources is increasing.
The above data show representative waste contributions in highly developed urban centres in industrialized countries with relatively high standards of living. Although the figures for other areas are lower at present, they can be expected to approach these figures in time. In developing countries, the amounts of solid wastes may well be very small percentages of the figures given. However, the data do not adequately reflect the additional solid wastes produced by agricultural and large industrial operations, nor do they take into account the solid pollutants increasingly being separated from gaseous and liquid wastes by improved treatment processes developed to comply with stricter environmental standards.