Waste is defined as any substance, solid, liquid or gaseous that remains as residue or an incidental by-product of the processing of a substance or for which no use can be found by the organism or system that produces it.
According to United Nation Environmental Program (UNEP), Wastes are substances or objects, which are disposed of or are intended to be disposed of or required to be disposed of by provision of national laws.
The World Health Organization refers to waste as something, which the owner no longer wants at a given time and space and which has no current or perceived market value. However, what one regards as waste may not be totally useless as much can be recycled to produce new products.
Waste includes all items that people no longer have any use for, which they either intend to get rid of or have already discarded. Many items can be considered as waste e.g., household rubbish, sewage sludge, wastes from manufacturing activities, packaging items, discarded cars, garden waste, old paint containers etc.
Waste can be photodegradable, e.g. broken down by sunlight after a time like plastic, non-bio- degradable, e.g. steel, biodegradable e.g. broken down by bacteria on exposure, like organic matter.
Examples of waste include household waste, industrial (which often contain toxic chemicals), medical waste (which may contain organism that cause disease) and nuclear waste (which is radioactive).
Waste Generation
Every human activity generates waste but it is the accumulation of wastes that constitute environmental health hazards. Waste generation occurs through domestic, commercial, industrial, agricultural and other social activities.
The composition of the various wastes that are generated include but not limited to: Household waste – 85%; Commercial waste – 8%; sewage Sludge – 3.5%; Industrial Waste – 1.6%; Agricultural waste – 1.1%; Mini waste – 0.5%; and Hazardous waste – 0.3%.
Domestically, human activities such as environmental sanitation, food preparation, consumption of packaged foods, laundry, washing of utensils, discharge of unwanted household items or unserviceable household equipment and old furnishing all lead to huge volume of waste.
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Activities like retailing and distributive trade, small, medium and large-scale industrial operations also bring about the generation of both solid and liquid waste. On-farm operation and in-farm gate activities are usually characterized by waste generation.
Typical examples include timber and wood-processing industry, which generate large quantities of waste in form of sawdust and shavings.
Waste generation and disposal is a growing problem worldwide and is directly connected to industrial development and population growth. Wastes, both from domestic and commercial sources have grown significantly over the past decade.
Currently, as a result of industrialization and rapid population growth in many cities and towns, wastes are generated faster than they are collected, transported and disposed. It is difficult to quantify the volume of waste generated from each households, but merely from observation, it shows that the generation of waste amounts to millions of tons.
It has been observed that about 75% of the total wastes generated each month are mainly from the urban centers (Nnamani, 2000).
Several researchers have studied the volume of waste generated some cities; for example, Maclaren International Ltd (1970) estimated this volume at 182.900 tones. The study concluded by Haskoning and Konsadem Associates (1994) estimated the per capita rate at 0.6kg/day, with a density of 300kg/m3.
Effect of Waste on Environment
The world’s accelerated economic development in recent decades has led to a rapid urbanization and an uncontrolled population growth in urban centers.
Changes in the consumption patterns of the urban dwellers have resulted in an excessive generation and disposal of waste. Disposing of waste has huge environmental impacts and can cause serious problems.
Landfill is the most widely employed for waste disposal worldwide. The dumps do not have bottom liners to prevent the seepage of leachate. During degradation process, one tone of land filled waste generates about 0.2m3 of leachate, depending on the type of waste and seasonal climate.
This wastewater primarily results from the degradation of the organic portion of the waste in combination with percolating rainwater and moisture that leaches out organic and inorganic constituents through the waste layer in the landfill.
A landfill site may still produce leachate with a high concentration of NH3-N for over 50 years after filling operations have ceased.
If not properly treated, leachate seeping from a landfill can enter the underlying groundwater, posing potentially serious hazards to the environment and to public health.
For this reason, the generation of leachate has become a worldwide environmental concern in recent years.
Also, the dumps do not have a top cover or other preventive measures to reduce methane emission into the atmosphere. Methane and carbon dioxide are two major gases produced from the decomposition of the organic waste in the landfill. Methane gas has a 21-fold global warming potential as compared to carbon dioxide.
According to the Intergovernmental Panel on Climate Change, such emissions contribute to 18% of the total methane emissions to the atmosphere, ranging from 9 to 70 mega tones annually.
Therefore, landfills have been implicated as the largest source of atmospheric methane in the world, leading to a natural phenomenon called “global warming” (Hansen, 2005). Due to global warming, changing temperature and rainfall patterns will bring a variety of pressure upon plant and animal life.
If temperature rises as projected, one-third of species will be lost from their habitat, either by moving elsewhere or by becoming extinct (Hansen, 2005).
Incinerating waste also causes problems, because plastics tend to produce toxic substances, such as dioxins, when they are burnt. Gases from incineration may cause air pollution and contribute to acid rain, while the ash from incinerators may contain heavy metals and other toxins.
In addition, there are a substantial number of uncontrolled disposal sites that contain hazardous wastes and that could present serious environmental or public health problems. For example, municipal waste sludge and incinerator ash can contain toxic heavy metals such as lead, cadmium, mercury, and other toxic materials.
Heavy metals such as chromium and lead have been long contaminants of soil. Chromium (IV) was found to cause throat and lung cancer, shortened lifespan, reproductive problems and lower fertility.
Lead causes plumbism (lead poisoning), anemia, effects on the intestines and central nervous system. Also in children (generally having a less well-developed blood brain barrier than adults), Pb causes behavioral changes; decreased intelligence, brain damage and even death have been observed.
Other heavy metals such as copper, mercury, and selenium, get into water from many sources including industries, exhaust pipes, mines, and even natural soil (Encarter, 2007).
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Nitrates, which are commonly associated with fertilizers and agricultural waste runoff, can seep into groundwater. Well water contaminated with nitrates is hazardous to humans, particularly the infants, as it results in oxygen depletion in the blood.
Once ingested into the human body, nitrate is converted into compound known as nitrosoamines, which are known carcinogens. Moreover, nitrates could be chemically reduced in the body of infant humans to nitrites, which reduces the oxygen carrying capacity of hemoglobin.
The current WHO public health standard for safe drinking water requires that nitrates levels in drinking water should be less than 50 mgl-1. When nitrate level in drinking water exceeds this standard, costly measures have to be taken to make water safe for drinking.
Nitrates in the agricultural waste runoffs also contaminate surface water, which leads to Eutrophication thereby killing aquatic life.
In conclusion, considering the consequence of excessive waste generation worldwide, an integrated management plan and its implementation need to be undertaken consistently.
The outcomes of the scheme may provide inputs for local government and relevant stakeholders to formulate and implement integrated waste management in a holistic manner.
These strategies may provide a policy framework to accomplish the target of reducing waste generation worldwide by 1% annually. This will facilitate ways to achieve an environmental sustainability, one of the UN Millennium Development Goals (MDG) in 2015.