ABSTRACT
Ever since mankind has mobilised into large towns and urban areas they have been concerned with the effective and safe disposal of liquid and solid wastes generated by domestic and/or commercial activities. Normally, the untreated liquid wastes were discharged into a stream, river or the ocean, but as population densities have increased this option has become increasingly unviable. Consequently, treatment systems were introduced to remove soluble as well as suspended organic matter from the sewage resulting in the production of sludge containing about 1 to 2% by weight dry solids. Conventionally this material was then disposed off either to agricultural land or to holding basins where it could be dried to a solid cake. This happy situation could not be continued mainly for two reasons; firstly, as treatment processes became more widely adopted, the sheer volume of sludge production increased dramatically while, at the same time, the availability of traditional disposal routes became limited. Secondly modem industrial civilization has resulted in a number of hazardous and highly toxic materials finding their way into sewage sludge, thus making it unsuitable for conventional methods of disposal.
