The management and maintenance involved in keeping the aqueducts flowing is well described by Julius Frontinus, a general appointed by the emperor Nerva as water commissioner towards the end of the first century AD.  He described his work on the distribution system in De aquaeductu published at the end of the first century AD.  When first appointed he surveyed and mapped the entire water supply system.  He also meticulously investigated the many abuses, in particular unauthorised abstraction. Maintenance of the aqueducts was introduced with groups of specially trained workmen. Frontinus also tried to separate the supply so that only the best quality water was provided for drinking and cooking, while lesser quality water was only used for the fountains, baths and finally flushing of the sewers.

The composition of sewage has changed hugely since the time of Frontinus.   Eating patterns are vastly different and enormously variable.  Synthetic foodstuffs are present in unprecedented quantities as too are preservatives and colourants.

Sewage treatment the world over predominantly makes use of a combination of mechanical and biological treatment processes.  Although great improvements have been made since the early 1900’s, the unit treatment processes have not changed significantly.  We are still very dependent on naturally occurring bacteria to clean up after us.