Solid WasteSolid waste is a general term for all discarded materials other than fluids. Solid wastes, including some HAZARDOUS WASTES, are by-products of industrial, MINING and agricultural operations as well as being the garbage and sewage produced by society. The first 3 categories of wastes involve special disposal techniques which are, or should be, integral parts of the operation that produces them. The by-products of human activities become more and more a problem as concentrations of population increase; in Canada, they are largely the responsibility of the municipalities. Municipalities must cope with 2 general categories of solid waste: garbage and sewage sludge.
GarbageMost Canadian communities probably produce domestic, commercial and urban industrial waste at a rate near the North American average of 2.5 kg per person per day, with considerable seasonal variation. This high rate is attributed to North American affluence, with a preoccupation with exploitation of virgin RESOURCES and a high level of subsidization of garbage disposal. The disposal of this volume of garbage is expensive; costs average $40 per person per year. Traditional open garbage dumps are now generally illegal because they attract large mammals, rodents and birds which may be hazards to health and safety. If properly operated, sanitary landfills reduce POLLUTION problems (air and groundwater contamination, odour, litter). Garbage collection and disposal is generally a local government responsibility, whether carried out by municipal employees or by private contractors. Federal and provincial laws relate to health, clean air and water supply.
Solid-waste management should adhere to 3 priorities: to reduce the volume of waste generated, through control of packaging and emphasis on durability and repairability as design criteria for products; to direct the recycling of materials through separation at source (business or home), where volumes of garbage and population densities allow; to provide economic incentives to reduce waste and to encourage recycling and the use of recycled products.
Any concentration of humans will eventually encounter problems with disposal of human wastes. On average, each human adult produces approximately 0.5 L of urine per day and 115 g of feces. Safe return of body wastes to the ecosystem maintains the natural cycles of nutrients and moisture. However, population concentrations soon create problems which lead to disease, pollution of natural systems and a generally offensive environment.
The development of sewage handling and treatment technologies has reduced or eliminated sewage-related diseases and has made our cities much more pleasant places to live in (see WATER TREATMENT; WATER-BORNE DISEASE). Most communities dump their treated or untreated sewage into bodies of water, creating special WATER POLLUTION problems, including the incorporation of toxic materials and disease-causing organisms, and the accelerated growth of unwanted vegetation and algae. Many towns now use sewage lagoons, large-scale equivalents of the septic tanks used in less densely populated areas. Composting toilets are a dry alternative to septic tanks.
Where more sophisticated primary, secondary and tertiary sewage-treatment plants are used, sewage sludge is generated. The city of Calgary leads Canada in sludge utilization by disposing of the liquid sludge in a safe, odourless way by injecting it as fertilizer into agricultural land. Otherwise the sludge is incinerated or disposed of in landfills.
Another solution to water pollution problems from sewage is land disposal where soil conditions are suitable. This practice is followed throughout the world, especially in countries which cannot afford the loss of the valuable nutrients. In Canada some ecologists advocate using sewage for fertilizer. Where soils are suitable, especially on the prairies, use of liquid effluent in farm IRRIGATION eliminates the water pollution problem and provides water and nutrients for crops.