Thickening or densification is generally the first stage the sludge coming from water treatment is submitted to, in order to reduce the moisture of the sludge itself. Thickening allows for a limited reduction of the humidity; after the treatment, the sludge still shows a water content of approx. 95%.
In such conditions, the sludge behaves like a liquid and can still be pumped through conventional equipment. The reduction of humidity – even if small – involves a remarkable reduction in the volume of the material to be processed and – subsequently – remarkable reduction in sizing in the following stages and – therefore – significant savings in the investment and service costs of the sludge treatment and disposal plants.
Such treatment exploits the differences in the specific weight of the materials the sludge consists of. Such difference in the specific weight can be either natural or induced.
The floating materials generated by thickening are pumped back to the primary treatment, whilst the thickened sludge is pumped upstream the primary clarifier of the water line for further treatment. Depending upon the position with respect to the sludge stabilizing treatment, you can have
- Preliminary thickening
The gravity thickeners generally consist of circular tanks with reversed truncated cone bottom.
Within the tanks, the sludge thickens by gravity effect, thus reducing their volumes by three to four times. Our machinery equips the tank with a bottom scraping system, a system of rotating combs hinged to the center, which mechanically collects the set sludge and conveys it to the collection hopper. The scraper is provided with pegs that break the sludge crust, thus freeing the water.
- The machinery consists of a fast geared motor unit of the epicycloidal type coupled to a helical worm gear motor c/w torque limiting device that preserves the mechanics from any accidental excessive operating torque.
- The drive is mounted on a lantern unit attached to a bridge on the tank centerline. The double arm scraping system is handled by a center tubular shaft directly coupled to the drive unit. The shaft is suspended in axis to the rotation unit and is driven at the bases by a bushing support. The two supporting arms are of the trellis type and carry in the extrados the segmental blades, provided with neoprene shoes, whilst the thickening pegs are carried in the intrados. The center collection hopper is equipped with purposely-allocated blades to facilitate the extraction of the sludge.
- The standard supplied machine includes a stilling cylinder, supply piping and overflow edges with the accessories required for its correct installation.