The object of this volume is to discuss the various aspects of one particular form of water treatment - the "biological filtration" or "slow sand filtration" process. This system of water purification has been in continuous use since the beginning of the nineteenth century, and has proved effective under widely differing circumstances.
HUISMAN, L. WOOD, W.E. (1974): Slow Sand Filtration. Geneva: World Health Organisation (WHO) URL [Accessed: 06.02.2012]