Landfill Leachate: Growing Concerns to Aquatic Environment
Landfill is one of the most widely employed methods for the disposal of solid waste (SW) around the world. After being landfilled (Figure 1), the refuse decomposes through a series of combined physico-chemical and biological processes, which may take a period of more than 50 years.
Figure 1. Open dumps for Solid Waste
During the degradation process, one tonne of landfilled solid waste generates about 0.2 m3 of highly contaminated wastewater, called "leachate" (Figure 2), depending on the type of waste and seasonal climate. This wastewater primarily results from the degradation of the organic portion of the waste in combination with percolating rainwater and moisture that leaches out organic and inorganic constituents through the waste layer in the landfill. Depending on the rainfall conditions, the color of leachate varies from black to brown.
Figure 2. Generation of Landfill Leachate
The common features of raw leachate from landfills are its high concentrations of ammoniacal nitrogen (NH3-N) (2,000-5,000 mg/L) and moderately high strength of recalcitrant compounds (as reflected by its COD value) (5,000-20,000 mg/L), as well as a low ratio of BOD5 /COD of less than 0.1 (Kurniawan et al., 2006a). Of the toxic pollutants that are present in landfill leachate, NH3-N, resulting from the decomposition process of organic nitrogen, has been identified not only as a major long-term pollutant (Kurniawan et al., 2006b), but also as the primary cause of acute toxicity [10]. Because NH3-N is stable under anaerobic conditions, it typically accumulates in the leachate. With a concentration of higher than 100 mg/L, untreated NH3-N is highly toxic to aquatic organisms(Kurniawan et al., 2006c).
If allowed to migrate, the contaminant released from a landfill would also pose potentially serious threats to the surrounding soil and the underlying groundwater. Since groundwater is the major source of drinking water worldwide, in recent years, the risk of groundwater pollution has become one of the most important environmental concerns, particularly in developing countries, where most of the landfills have been built without any sound engineering design such as engineered liners and leachate interception and collection system.
Unless properly treated, leachate that seeps from a landfill can infiltrate and contaminate the underlying groundwater. Once the leachate escapes to the groundwater, it is difficult and costly to controll and clean it up, thus posing serious hazards to living organisms and public health in the long-term. In most cases, it is extremely complicated to restore the contaminated groundwater to its former state. For this reason, the risk of groundwater pollution due to leachate seepage has become a major environmental concern worldwide in recent years.
Further reading
Kurniawan, T.A. et al. (2006a). Degradation of recalcitrant compounds from stabilized landfill leachate using a combination of ozone- GAC adsorption treatment. Journal of Hazardous Material 137(1): 443- 455.
Kurniawan et al. (2006b). Physico-chemical treatments for removal of recalcitrant contaminants from landfill leachate. Journal of Hazardous Material 129(1-3): 80-100.
Kurniawan et al. (2006c).Radicals-catalyzed oxidation for degradation of recalcitrant compounds from landfill leachate. Chemical Engineering Journal 125(1): 35-57.
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