French to English Tech/Engineering Environment & Ecology Sewage treatment

Another term which has cropped up in this list of maintenance equipment and activities for a sewage treatment plant:

Local polymère zone humide
Niv. 28.10
(E27-20) Bâches 1,2 et 3 de maturation des polymères de boues digérées
(E27-25 ; E27-26 ; (E27-27)
3 agitateurs de 50 kg
*Mouilleurs* (boues digérées)

I've found this translated as "damper" but can't find it specifically in connection with sewage treatment. Does anyone know what these are called in this context?

Many thanks.