One such system is known as the
slow sand filter, in which not the sand itself, but a
complex biological film that grows naturally on the
surface of the sand, is used to filter the water.
Thai Waterworks
Museum
Thai Waterworks
Museum
Whereas the
sand used in filtering process was dredged from the Kwae
River in
Kanchanaburi
(fig.),
the water itself was pumped into the plant from the
upstream
Chao Phraya
River nearby.