Wherever people live there is sewage. The advanced civilisations
in the Middle East and China already acknowledged the problem of
waste water treatment and built drainage systems in order to
lead dirty water out of their cities. The construction of the
vast sewerage network in ancient Rome with its central element,
the cloaca maxima, was state of the art in the fifth century BC
and the peak of sewage treatment in antiquity. With the decline
of the Roman Empire, however, this knowledge was lost. In the
Middle Ages, cities literally drowned in human waste. The common
practice of simply disposing of household refuse in the streets
repeatedly caused raging epidemics. The Industrial Revolution in
the 19th century exacerbated the waste water problem – not only
because the rapidly growing towns produced previously unheard-of
quantities of waste water but also because, for the first time
in human history, this sewage contained large amounts of toxic
residue from industrial processes. In the metropolitan area of
the R