Wastewater treatment

The fourth entry is o tanque de arejamento, and the noun inside it rests on a verb that Portuguese uses without a second thought. Arejar is built straight on o ar, and it runs from the domestic to the technical without changing shape: arejar o quarto is to open a window, arejar a roupa is to hang washing out, arejar as ideias is to get some fresh air into your head, and o tanque de arejamento is the basin where blowers drive air into sewage for the bacteria to live on. English cannot follow that with one word. We have « to air », the old native verb, and it has stayed indoors: we air a room, we air the bedding, we air a grievance or a view. It will not go into a treatment works. For that we reach for the Latinate « to aerate », and with it « aeration » and « the aeration tank ». The division is worth fixing early, because « an airing tank » is not English, and neither is aerating a bedroom.