1) Primary sedimentation
Influent municipal wastewater flow, after a coarse screening through a mechanically cleaned bar screen, is settled in a rectangular tank with a capacity of about 900m3. A travelling-bridge-type collector equipped with scraper blades removes continuously settled solids, which are subsequently discharged.
3) Secondary sedimentation
The aerated mixed liquor outcoming from the biological oxidation process, is a dispersion of activated sludge in purified water. Simply exploiting the gravity force, it is possible to separate these two phases, which are poured into the sedimentation stage, where no chemicals are added and the spontaneous settling of sludge occours.
After a first degasation step, the mixed liquor is distributed between 4 rectangular tanks of about 900m3 each and equipped with chain-and-flight solids collectors. In these tanks gravity sedimentation of the biological sludge take place. The clarified stream flow outcomes from each tank by the effluent channel, whereas settled sludge is scraped to solid hoppers by the chain and flights collector, at the same time .
Treated wastewater is continuously monitored by the internal laboratory and, on the basis of specific analysis and results, it can be addressed to two different stages:
- denitrification step of the industrial wastewater section
- clariflocculation step of the industrial wastewater section
Settled activated sludge are mainly returned to the biological oxidation step, while excess sludge is discharged together with the primary sludge into a thickening tank, or it is returned to the second biological oxidation of the industrail wastewater treatment section.