The disposal of solid waste to landfill is a waste management strategy common
to many countries worldwide. Despite an increasing emphasis on alternative options,
solid waste disposal to landfill retains an important role in Europe. In many
other areas of the world, the more "sophisticated¿ strategies have little applicability
and basic landfilling is more common. Leachate is the liquor that is collected
at the base of landfills after rainwater has entered the emplaced waste materials
and leached out contaminants. Depending on the nature and age of the wastes,
the characteristics of the leachate will change. The leachates from landfilling
domestic wastes, which are more likely to be of a biodegradable nature, are
discussed in this article.
Leachates can be classed as acetogenic or methanogenic depending on the state
of degradation of the waste materials in the landfill. Leachate from "young¿
wastes is characterized by high chemical oxygen demand (COD) and biological
oxygen demand (BOD) values, and by high ratios of BOD to COD. Methanogenic leachates
are derived from older landfills where extensive degradation of organic materials
in the wastes has occurred. End products of methanogenesis in the landfill are
methane and carbon dioxide. Leachate is categorized by lower COD values, very
much lower BOD values, and lower BOD to COD ratios.