Water Treatment

This row of obsolete water treatment towers is one of the weirder corners in DC - not far from where we live. Covered in vines, trees sprouting from the roof. In the light of a setting sun they can look downright Tolkien-esque -- like a string of abandoned elvish castles. In addition to the towers, the green grass covers over extensive catacombs which housed the guts of the treatment process. Very epic.
From 1902 to 1985, McMillan Reservoir was one of the primary water treatment facilities in the city. Now it is largely abandoned and falling to bits. The city keeps trying to find a way to develop this (extremely valuable) mid-city property (a not uncontroversial plan of action). But no ground appears to have been broken yet.


I was curious about the purpose of the towers. Apparently the process used here was slow sand filtration, and so the towers basically stored the sand. But here's the weird thing about sand filtration: all of the purification work is done not by the sand, but by a thin layer of biological organisms (bacteria, protozoa, etc.) living on the top layer of the sand. To keep the filter working efficiently you have to continually maintain this crust of organisms. The somewhat bizarre term for this biofilm is schmutzdecke (German, naturally, for "dirt cover").


Learn something new every day.