Between Landfill and Inceneration
The placement of solid waste in landfills is the probably the oldest and definitely the most prevalent form of ultimate garbage disposal. From the outset, it must be recognized that many “landfills” are nothing more than open, sometimes controlled, dumps. The difference between landfills and dumps is the level of engineering, planning, and administration involved. Open dumps are characterized by the lack of engineering measures, no leachate management, no consideration of landfill gas management, and few, if any, operational measures such as registration of users, control of the number of “tipping fronts” or compaction of waste. In an examination of landfills throughout the developing world in 1997-1998, Johannessen (1999) found varying amounts of planning and engineering in MSW dumping; among the various regions visited, African nations (with the exception of South Africa) had the fewest engineered landfills, with most nations practicing open dumping for waste disposal; waste managers in Asian and Latin American nations were more likely to be aware of environmental effects of improper landfill design and were much more likely to design and implement some control measures, however limited in scope. ‘Sanitary’ landfills, on the other hand, are sites where waste is allowed to decompose into biologically and chemically inert materials in a setting isolated from the environment. Cointreau (1982) outlined four features that must be present in order for a landfill to be considered sanitary :
- Full or partial hydrogeological isolation through the use of liners to prevent leachate infiltration into the soil and groundwater; collection and treatment infrastructure should be used where leachate is expected to be generated
- Formal engineering preparations with an examination of geological and hydrological features and related environmental impact analysis, waste tipping plan and final site restoration plan
- Permanent control, with trained and equipped staff to supervise construction and use
- Planned waste emplacement and covering, with waste and soil placed in compacted layers as well as daily and final soil cover to reduce water infiltration and reduce odors and pests
Other practical and social considerations must be addressed when planning landfills, especially in the context of developing nations and their problems as outlined above. One of the most important is the siting of landfills in proximity to urban areas. Naturally, there are few people who would be excited by having a landfill in their backyard, however it is important to realize that landfills must be located within a reasonable distance to population concentrations along a good road system. If they are located too far from collection points and transfer stations, waste transport could become prohibitively expensive due to the distance the waste is transported. In the poorest of nations, development agencies may finance all or part of landfill construction. However if it is sited far from the urban area, without regard to the ability of the government to transport waste with its limited finances, scattered unregulated dumping will become financially attractive once again.
It is obvious that a proper, engineered landfill is more expensive to design, implement and maintain. This is naturally the main constraint in developing countries, and therefore landfill construction is a focus of development assistance by the World Bank and many other aid organizations. Although the costs may be defrayed and technical assistance given, in the long term it will be the responsibility of local and national governments to ensure proper waste disposal is a practical and viable option.
Another option for waste reduction and disposal is incineration. Incineration should not be considered a ‘disposal’ option, since following incineration there is still some quantity of ash to be disposed of (probably in a landfill), as well as the dispersal of some ash and constituent chemicals into the atmosphere. It should instead be considered more in terms of its waste-reduction potential, which can be 80-95% in terms of waste volume (Rand, et al 2000). This appears to be an extremely attractive option, however, with occasional exceptions, incineration is an inappropriate technology for most low-income countries. Above all, the high financial start-up and operational capital required to implement incineration facilities is a major barrier to successful adoption in developing countries (Rand et al 2000, UNEP 1996). A large portion of that cost is the environmental hazard mitigation components, including emissions “scrubbers”; use of best available technology in the United States can cost as much as 35% of the overall project cost (Rand et al 2000).
Financially and practically, incineration seems at present a promising option for few countries; however small island nations are perhaps a category where such technology may be practical. With their smaller land mass, island nations often have less land available to them for landfilling, and even in the event land is available, environmental considerations may not reveal these sites to be viable options. Further, in nations with islands scattered about, transportation of waste to select centralized sanitary landfills, instead of open dumps on each island, could be prohibitively expensive and time consuming. Being surrounded by open water increases the attractiveness of ocean dumping. Most developed nations have abandoned this practice out of environmental concerns, however environmental regulations may not outlaw this practice in some poorer nations. Reduction by incineration, along with sanitary disposal of the residue, would therefore be a useful alternative to traditional disposal methods, and have proven useful in nations such as Bermuda and the British Virgin Islands (Lettsome 1998).
There are two widely used varieties of incineration plant as described by UNEP (1996), mass-burn and modular. A third, fluidized-bed incineration is used widely in Japan. Mass-burn systems are the most versatile, accepting almost any common municipal solid waste save for large single items such as refrigerators and furniture. Waste is dumped from trucks onto either a tipping floor or a conveyor belt, which then conveys the waste to the incineration chamber. Common facilities use two or three incineration chambers, providing a capacity of between 100 and 3000 tons per day; modular incinerator units, on the other hand, can usually only process between 5 and 120 tons MSW per day per unit, although multiple units are often used at any one site. The process of incineration is somewhat different, utilizing two combustion chambers; gasses generated in the first chamber are more completely combusted in the second, providing the primary environmental pollution control.
Negative environmental consequences of incineration mostly revolve around airborne emissions. Certainly, incinerators should not be located where prevailing wind patterns would carry emissions over densely settled areas. The use of emissions reduction technology, although expensive, should be mandatory in any new construction. Incineration volatilizes many compounds potentially harmful to human health: metals (especially lead and mercury), organics (dioxins), acid gases (sulfur dioxide and hydrogen chloride), nitrogen oxides, as well as carbon monoxide and dust (UNEP 1996).