The great increase in the production of wastes is causing storage, collection, and transport difficulties as well as problems of treatment and final disposal. Present methods of refuse management and disposal are dumping, controlled tipping or sanitary land-fill, recycling, incineration, composting, and discharge into the sea. Large world-wide variations in conditions relating to storage and collection of solid waste can render a method that is optimum for one country totally unsuitable for another. Examples of such variations are the nature and density of the wastes, access to properties, economic conditions, and climate. In some developing countries, collection methods are unsuitable because they involve excessively laborious and unsanitary handling of the wastes. The best methods of collection in less developed countries may involve handcarts or animal-drawn carts, and agricultural tractors pulling trailers. Dumping, which is widely practised, is an unsanitary method that creates public health hazards, nuisance, and severe pollution of the environment. Disposal of refuse at sea, some distance from shore, is practised by some large seaside communities.
Landfilling, the traditional disposal route, is still the cheapest option, but sites are becoming scarcer, and disposal costs are mounting as environmental protection standards are raised. Sanitary land-fill or controlled tipping is an acceptable method in suitable locations, if the possibility of pollution of surface water and ground water is eliminated. In some cases refuse is mechanically reduced in volume, or incinerated before being deposited in a tip or land-fill. In many cases it is difficult to find suitable land in or near urban areas. In congested areas, the absence of the substantial areas of land required for this operation has forced the adoption of other systems.
Incineration is used successfully in several of the industrialized countries, particularly in larger cities. This method reduces the volume of domestic refuse eventually to be disposed of, usually by tipping, to about 15-20% of the original. In many older plants, however, devices for removing pollutants from the exhaust gases are inadequate to comply with present air pollution standards or those likely to be established. The increasing quantities of bulky waste such as old furniture and other household equipment, also create problems in most existing incinerators; a few installations have incorporated special equipment for breaking up such large items before incineration.
There are many ways in which components of solid waste that have some value can be recycled. But such separation of the wastes must be controlled if health hazards, degradation of the environment and impairment of disposal operations, are to be avoided. Recycling the clean, reusable portion of municipal solid waste is a favoured option for reducing the amount of waste going to landfill, and is currently attracting a lot of public attention. Estimates suggest that as much as 50% of all domestic waste could perhaps be recycled, although few are achieving even a quarter of that amount at present. Food wastes can be fed to animals; metals can be recovered and remelted, and paper can be repulped. Glass and plastics may also be removed. In some countries solid wastes have a fuel value that can be utilized. Alternately, methane gas can be withdrawn from well-engineered landfill sites and used as fuel. Composting of domestic refuse, sometimes together with sewage sludge and other organic wastes such as market refuse and agricultural waste, has been adopted in several countries. In many cases the fraction of domestic refuse that can be suitably incorporated in compost is decreasing, resulting in increasing quantities of material (up to 50% in some cases) that must be dealt with in other ways. In addition, there is some anxiety that municipal compost might have certain toxic properties, and many large composting schemes involving heavy machinery have failed because of the high cost of producing the compost, or an insufficient market.
Municipal waste in OECD countries showed an increase in volume of 11.6 percent between 1985 and 1990, due principally to the growth of consumption coupled with the amount of packaging material.
The collection and transportation of solid wastes are very costly and may account for up to 80% of the total cost of solid wastes disposal, which in turn may absorb as much as 0.5% of the gross national product. Efficient methods are therefore vital and several unconventional systems are being developed. Current proposals for managing packaging waste in the EEC/EU favour reusable container and recycling over turning waste into energy through incineration.
In Northern Africa, at least 20 per cent and as much as 80 per cent of urban solid wastes are disposed of by dumping in open spaces. Rapid urbanization in Lagos increased solid waste generation sixfold to about 3.7 million tonnes a year in 1990, plus another half a million tonnes of largely untreated industrial waste because 90 per cent of the industries in Nigeria lack pollution control facilities (IMO 1995). The 1.3 million inhabitants of Lusaka produce 1 400 tonnes of solid waste daily, of which 90 per cent is not collected because the local authority has too few staff, funds and equipment.
Solid wastes are not being made full use of as potential resource materials. In the developing countries, fermentable organic matter forms a high proportion of domestic wastes and could readily be transformed into a compost, which in many countries would be a valuable soil conditioner and a minor source of plant nutrients. In the industrialized countries the improper management of solid wastes can lead to loss of valuable mineral resources such as copper, lead, tin, zinc, aluminium, iron, and crude oil. When a nation's reserve of one or more of these mineral resources has declined to the extent that practically all of its needs are imported from other parts of the world, it does not make economic sense for that nation to use these materials to produce items that are used briefly and then discarded and lost in a buried mass of heterogeneous materials.