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In Malaysia, most of the wastes are disposed in landfills and as such landfills play an
upmost environmental role. Landfills release a wide range of chemicals resulting from
waste degradation in the form of leachate, gas and particulate matter (PM) (Koshy et al., 2007). High rates of organic and inorganic pollutants are contained in leachate. It may become
a potential environmental hazard which threatens the soil, surface water and groundwater
if not handled carefully. Therefore, landfill leachate is known to be an important and
serious environmental problem by societies nowadays (Tauchert et al., 2006; and Atmaca, 2009). Landfill leachate is frequently treated by using biological treatment system. However,
they are not efficient enough to degrade high molecular weight fractions. Most of the
Asian countries, for example Malaysia, have high level of precipitation, hot and humid
climates throughout the year due to the tropical monsoon (Kho, 2005; and Latifah et al., 2009). Through the combination of physicochemical and biological processes, the refuse
was decomposed. By definition, leachate is contaminated wastewater produced in the process
of decomposition when rainwater percolates through the waste layers in landfill
(Kurniawan et al., 2006). Currently, lot of scientific literature shows that the accumulation and
depository of leachates are jeopardizing the surface and groundwater (Renou et al., 2008). It is imperative to remove the Chemical Oxygen Demand (COD), Biological Oxygen
Demand (BOD) and ammonium nitrogen from the leachate before discharging it into water
reservoirs (Castrillón et al., 2010).
Among all the treatment processes, sonolysis has been identified as one of the
physical treatment methods which is potential in treating environmental pollutants today
(Mason, 1992; and Goskonda et al., 2002). Sonolysis can be applied to a broad range of
organic pollutants in aqueous systems, including a complex mixture of chemicals in waste
streams (Catallo and Junk, 1995). There are two ways that an ultrasound can react with the
aqueous solution: physical and chemical processes. Physically, the ultrasonic waves can clean
the surface of solid particle, reduce the size of the particle and increase mass
transfer. Chemically, when ultrasonic waves are irradiated into an aqueous solution, cavitation
occurs which can react with pollutants (Rae et al., 2005; Yano et al., 2005; and Li et
al., 2008). The chemical effects due to cavitation lead to the formation of high temperatures and
pressures in excess of 5000 K and 500 atm (Thompson and Doraiswamy, 1999). There are
increasing efforts on the application of sonication technology towards the destruction of pollutants
in industrial wastewater. To our knowledge, so far, there are few reports on the usage
of ultrasound on the reduction of COD on landfill leachate. |
