The waste waters involved in the industrial processing are collected into a pit (A) and are conveyed to the decanter by a suitable pump, which works automatically through level probes. In the flocculant station (B) a solution of water and flocculant is prepared, and is subsequently injected into the pipe feeding the decanter (C). The flocculant acts on the solid particles increasing their settling speed. Once the waste water has entered into the decanter, the clean water rises towards the top of the silo and overflows into the clean water collection tank (H), from which it can be sent back to the machines. The mud accumulates at the bottom of the decanter and is extracted by a pneumatic group (D), which discharges it into the homogenizing tank (E). The tank is equipped with an agitator for preventing the settlement of the solids. A double speed centrifugal pump (F) takes the mud out of the tank and feeds the filterpress (G). The chamber-type filterpress squeezes out the residual water still retained in the mud and discharges the dry mud below its structure.