The paper reviews the current methods of sludge technology, and compares them with those discussed by Ashton in 1904. The paper also plots the development of some of the current technology over the last century, particularly those methods of treatment which were mentioned by Ashton but were not in existence at the time.
The 1990s have been a most interesting era, and have probably seen more changes in sludge technology than any other decade this century. The most significant impact will be due to the cessation of the sea disposal route which, at the beginning of the 1990s, was used for about 30% of the total sludge production in England and Wales and approximately 76% of the total sludge produced in Scotland.