The disposal of solid waste should be part of an integrated waste management plan.The method of collection, processing, resource recovery and the final disposal should be synchronized to achieve a common objective.
An integrated waste management strategy includes three main components : source reduction, recycling and disposal. Source reduction can be done by using less material when making a product, reusing products on site, designing products well, and using smart packaging to reduce their size and quantity. Recycling is the reuse of some components of waste that may have some economic value. Disposal of solid waste is done most commonly through a sanitary landfill or through incineration.
A modern sanitary landfill is a depression in an impermeable soil layer that is lined with an impermeable membrane. The three characteristics of a municipal sanitary landfill that distinguish it from an open dump are:
- Solid waste is placed in a suitably selected and prepared landfill site in a carefully prescribed manner
- The waste material is spread out and compacted with appropriate heavy machinery
- The waste is covered each day with a layer of compacted soil.
The problems with older landfills are usually associated with ground water pollution. Pollutants seeping out from the bottom of a sanitary landfill very often percolate down to the groundwater aquifer, no matter how thick the underlying soil layer. So today, suitable bottom-liners and leach collection systems along with the installation of monitoring systems to detect ground water pollution are used.The organic material in the buried solid waste will decompose due to the action of micro organisms.
At first the waste decomposes aerobically until the oxygen that was present in the freshly placed fill is used up by aerobic microorganisms. Then the anaerobes take over, producing methane, which is poisonous and highly explosive when mixed with air in concentrations between 5 and 15%.
The movement of the gas can be controlled by providing impermeable barriers in the landfill. A venting system to collect the blocked gas and vent it to the surface, where it can be safely diluted and dispersed in to the atmosphere, is thus a necessary component of the design of sanitary landfills.
Incineration is the process of burning municipal solid waste in a properly designed furnace under suitable temperature and operating conditions. Incineration is a chemical process in which the combustible portion of the waste is combined with oxygen forming carbon dioxide and water, which are released in to the atmosphere.This chemical reaction, called oxidation, results in the release of heat. For complete oxidation, the waste must be mixed with appropriate volumes of air at a temperature of about 815 degree Celsius for about one hour.
Landfills vs. Incineration
The landfill operation is a biological method of waste treatment.Although land-filling is an economic alternative for solid waste disposal, it has become increasingly difficult to find suitable land-filling sites that are within economic hauling distance, and very often citizens do not want landfills in their vicinity. Another reason is that no matter how well engineered the design and operation may be, there is always the danger of some environmental damage in the form of leakage.
Incineration can reduce the municipal solid waste by about 90% in volume and 75% in weight and make the product stable. The risks of incineration, however, are air quality problems and toxicity and disposal of the fly and bottom ash produced during the incineration process. Fly-ash consist of finely divided particulate matter, including cinders, mineral dust and soot. Most of the incinerator ash is bottom-ash while the reminder is fly-ash. The possible presence of heavy metals in incinerator ash is harmful.
Thus toxic products and materials containing heavy metals should be segregated. Extensive air pollution control equipment, high level technical supervision and skilled employees for proper operation and maintenance are required.
So while sanitary landfills and incinerators have their own advantages and disadvantages, the most effective method of sold waste management is source reduction and recycling.