Transcript Slide 1
Landfills and Biodegradation Are Degradable Products the Means to Extend Landfill Space Landfills and Biodegradation How do modern landfills protect the environment? • The purpose of solid waste management is to remove wastes from living areas in a way that protects human health and the environment. Landfills fulfill this mission by sealing wastes away from the surrounding environment preventing the pollution of groundwater, the elimination of noxious emissions and the attraction of vermin. • By sealing in wastes, landfills also control biodegradation. Biodegradation in a landfill results in the emission of methane, a potent greenhouse gas and if uncontrolled biodegradation also creates a toxic sludge or leachate that could pollute groundwater. Landfills and Biodegradation Landfills and Biodegradation Landfills and Biodegradation How do modern landfills protect the environment? • Modern landfills are tombs that try to “mummify” waste. Many materials that one would expect to degrade do so only very slowly “Garbageologists” identify the strata of their excavations by reading the newspapers at the particular level. 35 year old papers have been found as have 10 year old carrots and 15 year old corn. • The degradation that does occur in a landfill is anaerobic ie. it is occurring in the absence of oxygen and one of the major products of such degradation is the production of methane which as a GHG is 23 times more potent than carbon dioxide. 10% – 14% of Canada’s GHG emissions are thought to come from landfills. Landfills and Biodegradation How do modern landfills protect the environment? • In modern landfills attempts are made to capture methane however capture is far from 100%. • Degradation also produces noxious juices (leachates) that have to be trapped and treated before discharge to the environment. Lead, cadmium, mercury and even dioxins can be found in landfill leachate. Many plants and vegetables adsorb heavy metals during growth and these tend to be concentrated in a landfill. • The ideal materials for landfills are totally inert residues that will not degrade. Landfills and Biodegradation • The ideal materials for landfills are totally inert residues that will not degrade. • This is reflected in a number of regulatory initiatives being undertaken in Europe. • Europe’s Landfill Directive states that by 2010, the amount of biodegradable waste going to landfill must be 75% of the amount disposed in 1995. By 2013 this is to be reduced to 50% and by 2020 to 35%. • The U.K.’s Landfill Allowance Trading Scheme has just gone into effect. It is designed to help the U.K. reach the terms of the European directive. Disposal authorities that exceed the limit set by the landfill allowances that they hold will be fined £ 150/t • Germany is mandating that no materials containing more than 2% carbon are to be landfilled. Biodegradable Plastics When discussing wastes the comment is often made that plastics are not biodegradable and if they were then all our problems with lack of landfill space would be solved even though plastics are but 8% of municipal waste. We have already noted that a landfilll is not a bioreactor. They are designed to be tombs in which biological decay is controlled. Plastics can be created to be biodegradable and photo degradable also. Biodegradable polymers are simply another class of polymers. The raw materials for them can be based on oil and gas or they can be derived from naturally grown crops such as corn. The processes used to produce biodegradable plastics can be normal chemical processes or they can be biochemical such as fermentation. Biodegradable Plastics There have been a number of biodegradable plastic products that have been around for a long time, eg. Medical sutures, pins, implants and tissue regeneration membranes. These usually have been expensive materials. New technologies now permit the manufacture of biodegradable resins on a large scale. They are still more expensive than the common commodity plastics but are finding niche markets where they contribute high value in use. These opportunities include the medical market but have branched out into more commonplace hygiene products such as diapers, agricultural products such as seeding strips, mulches etc and composting bags. Biodegradable Plastics The markets for biodegradeable products will continue to grow as will the range of plastics making up the field. Biodegradeable plastics will not however provide a panacea for all that ails waste management. Biodegradeable plastics derived from “natural sources” such as corn will not end the debate between synthetic and natural or renewable and nonrenewable resources. Recent life cycle analyses have shown that there are very heavy env. burdens associated with the growing of monocultures and the the transformation of crops into other products can be very energy intensive. Often we forget that paper derived from trees does not drop from the tree like leaves. Landfills and Biodegradation Waste Management of Plastics Plastics contribute much environmental good by virtue of their light weight. The packaging of 1000 litres of soft drinks requires 24 kilograms of PET. It requires 999 kilograms of glass. Many plastic containers are recyclable, getting them back is difficult. Over 95% of Canadians have access to plastics recycling, yet the recovery of PET bottles is only 48% and the recovery of HDPE bottles is about 37%. EPIC is working to encourage the public to participate to a greater degree in recycling. We believe that plastics should be recycled when this can be carried out in an economically and environmentally sustainable way. Should we haul soft drink containers from the Yukon to North Carolina when they could be gasified locally with other waste to provide a clean fuel to heat a school or public building Waste Management of Plastics With the exception of some oxy degradable species plastics that end up in a landfill are inert. They do not release greenhouse gases nor do they produce toxic leachates. However, the landfill is not the place for plastic residues. The burying of plastics is tantamount to burying energy. HDPE is essentially frozen natural gas in terms of its energy content (intrinsic energy). The intrinsic energy of plastics can be captured in safe and efficient ways. The very efficient energy from waste plants in Denmark and Sweden incorporate plastics in their waste because of their calorific value. The blast furnaces of Germany use plastics to reduce their demand for coke which requires a dirty process for its production. Waste Management of Plastics The manufacturers of cement are constantly seeking high energy materials to lessen their dependence on coal and natural gas. The high temperatures of a cement kiln coupled with modern emission controls effectively eliminates organic materials. Modern “advanced thermal technologies” such as gasification can convert plastics into carbon monoxide and hydrogen. These two compounds can be used to produce many new chemical species or the hydrogen could be used as the fuel in fuel cells. EPIC has carried out significant studies involving the gasification of plastic residues and has the data to back up the claims of the benefits of the technology. The management of any waste requires an integrated approach using a variety of technologies so that the system is economically and environmentally sustainable.