boues déshydratées

CONT: [...] le liquide interstitiel séparé des boues essorées est très chargé, constituant, après recyclage en tête de station, une surcharge importante de celle-ci.

CONT: ... interstitial liquid separated from the dewatered sludge is heavily polluted and, after being recycled to the head of the plant, constitutes a heavy overload.
OBS: The term ""sludge"" is considered to be an uncountable noun. However, it is often found in the plural form (sludges), particularly when speaking of different types of sludge.