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WASTE. Waste. An increase in the world population and consumption has led to a rapid growth in the quantity of solid waste which needs to be disposed. Treating and disposing of all this material, without harming the environment, is a serious global issue. .
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Waste • An increase in the world population and consumption has led to a rapid growth in the quantity of solid waste which needs to be disposed. • Treating and disposing of all this material, without harming the environment, is a serious global issue.
The simplest way to deal with the waste is open dumping. It is inexpensive and convenient for the dumper, but is not generally suitable as it causes air and ground water pollution and encourages rodents and insects which can be a health hazard.
Recycling • Ideally materials should be reused so that no waste is produced, however recycling is an option. • It reduces: • The use of raw materials • Energy costs • The level of pollution • The need of land for waste disposal • The main challenge is the separation and purification of the materials.
METALS • Recycling metal saves the Earth’s reserves of the ores and reduces energy costs • Aluminum from drink cans is worth recycling because of its resistance to corrosion and the high cost of the initial extraction process. • Steels can be easily separated from other metals by the use of magnets and other metals can be separated by their differences in density. • Recycled metals are used as alloys, which reduces the need to purify the metal completely.
GLASS • The fragility of glass is an advantage in recycling because it can be easily broken into small pieces. • Recycling of glass can reduce energy costs and the need for sandstone and limestone quarries. • As glass is not degraded during the recycling process it can be recycled many times.
PLASTICS • The used plastics are heated in absence of air when they split up into their monomers in a process known as pyrolysis. • Thermoplastics can be melted down and remolded. If recycling is to be successful and self-sustainable, the cost of recycling must be less than that needed to produce new materials. • Mixtures of plastics are much weaker than the individual plastics so the recycled product is often lower quality than the original and has a limited range of uses.
PAPER • It makes up a significant proportion of our domestic waste. • It can be composted but does not generally decompose in landfill sites. • Recycled paper has a reduced strength as cellulose fibres are damaged during the repulping and so is used for low grade products such as cardboard and newspapers.
Waste Disposal • Landfill • The purpose is to bury the waste in such a way that it will be isolated from groundwater, will be kept dry and will not be in contact with air. • The type of material dumped must be controlled to prevent chemical toxins leaching into local groundwater.
Organic Matter is decomposed by anaerobic bacteria to produce methane, which can be collected and used as a fuel, and hydrogen sulfide and organic acids. • The use of non-biodegradable plastics poses additional problems as they are not broken down by bacteria.
Waste Disposal Cont. • Incineration • Waste can be burned. This produces waste of a more uniform composition and reduces the bulk as most of the organic waste is converted into gases. • The carbon dioxide produced is a greenhouse gas and carbon monoxide produced during incomplete combustion of plastics is poisonous.
Nuclear Waste • The radioisotopes which are used in research laboratories and for treating patients in hospitals are classified as low level waste. • The spent fuel rods from nuclear power stations are high level waste. • The time taken for the radioactivity to fall to half its initial value is called its half life.
Low Level Waste • As the decay process produces heat energy, low level waste is stored in cooling ponds of water until the activity has fallen to safe levels. • Low activity and short half-life • The water is then passed through an ion exchange resin, which removes the isotopes responsible for the activity, and diluted before being released into the sea.
Low Level Waste • Other methods of disposal include keeping the waste in steel containers inside concrete-lined vaults.
High Level Waste Products formed from nuclear reactors can maintain dangerously high levels of radioactivity for thousands of years. Waste disposal presents a formidable problem because daughter products from the decay process may themselves act as parents for other nuclear reactions.
The site selected for the disposal must safely contain the material for a very long period of time and prevent it from entering the underground water supply.
There is always the problem that land masses may move and the radioactive material escape, the waste is buried in remote places that are geologically stable.
Disposal of Nuclear Waste Advantages of incinerating waste: Reduces volume/stable odour-free residue/ source of energy Disadvantage expensive to build and operate/can form dioxins/toxic gases/requires energy/adds to greenhouse effect
