Technologies
A 2007 study by the Goddard Institute of Space Studies and the Earth Engineering Center of Columbia University noted that the amount of waste generated in a particular nation followed closely the consumption of energy in that nation. On this basis, they estimated that the global generation of wastes will be doubled by the year 2030. In the US-EPA “hierarchy” of waste management, the first priority is waste reduction followed by recycling, composting, combustion with energy recovery (waste-to-energy or WTE), and finally landfilling.
On the average, U.S. citizens generate twice as much municipal solid wastes (MSW) (about 1.2 metric tons per capita) as Europeans and Japanese who have nearly the same standard of living. It is interesting to note that the per capita consumption of energy in the U.S. is also twice as much as that in Japan. Therefore, there is a lot of room for waste and energy reduction in this country. However, the goal of “zero waste” is unattainable. This has been demonstrated by the most environmentally conscious nations, such as Japan, where every possible effort has been made to promote recycling and yet they combust or gasify about 0.35 metric tons per capita.
Recycling is the next best thing to do after waste reduction and in the U.S. has reached the average of 20% of the MSW.
Currently Accepted Hierarchy of Waste Management
Composting - both aerobic and anaerobic - is the next step in the hierarchy of waste management. It is practical only for source-separated organics: otherwise, much of the compost product is not usable as a soil conditioner and ends up in landfills. About 9% of the U.S. MSW is composted; most of it consists of source-separated yard wastes that are composted in open windrows, in covered aerated static piles (Gore-Tex cover system) and in in-vessel reactors such as the Bedminster rotary kiln.
Of the post-recycling and post-composting wastes of the world’s urban population, an estimated 200 million tons of municipal solid wastes are processed in waste-to-energy (WTE) plants that recover some of the energy content of wastes in the form of electricity or heat. Of the U.S. MSW, about 7% is processed in 87 WTE plants that in total recover about 15 million kilowatt-hours of electricity. Detailed information on WTE is provided in the web page of the WTERT Council.
Landfilling
The bulk of the global urban MSW, over 800 million tons, is landfilled. Eventually, only inorganic, non-recyclable materials will be landfilled in most nations, as already is the case in Japan, Switzerland, Denmark, the Netherlands and some other nations. However, until there is sufficient global WTE capacity, there is much to be done with existing and new landfills. In particular, it is necessary for developing nations like China and India to follow the leading example of U.S. in constructing sanitary landfills that prevent liquid effluents from contaminating ground and surface waters and also reduce methane and other gaseous emissions to the atmosphere.
Not all landfills are the same. Modern landfills require a serious investment and effort to collect landfill gas (LFG) and use it to generate energy, thus reducing GHG impacts and use of fossil fuels. Therefore, the Earth Engineering Center has proposed the expansion of the hierarchy of waste management so as to clearly differentiate between better and worse types of landfills. The expanded hierarchy of waste management is the figure below. Uncontrolled landfilling is a major anthropogenic source of methane, which is the second most important of the greenhouse gases affecting climate change. The only two options for decreasing the emissions of methane in landfill gas (LFG), corresponding presently to 850 million tons of carbon dioxide, are replacing landfilling by thermal treatment of MSW and, also,increasing LFG capture in the interim period. The U.S. is the world’s largest landfiller with about 23% of the total MSW landfilled. However, it is also leading in the capture of landfill methane which is estimated at about 60% of the global methane recovery from landfills. The potential for reducing global LF methane emissions is discussed in this SUR paper presented at GWMS 2008.
The tonnages of MSW generated, recycled/composted, treated by WTE, and landfilled in the fifty states of the U.S. in 2004 (BioCycle/Columbia National Survey) are shown on this Waste Map.
Expanded Hierarchy of Waste Management