Page 97 - Bluebook Sereco english

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Clariflocculators – Clarifiers -

Settlers – Flotators

• DAF • PRTPC1
• PRATP • PRTPC2
• PRATPD • PRVR
• PRCC • PRVA
• PRCCC1 • RC
• PRTP • SGSBR
• PRTPD • CPL

The water clarification process in a civil or industrial allow good results even in the presence of biological
sewage treatment plant can be found many times in a treatment failure such as those mentioned above. The
treatment process. Typically, there is a primary settle- wide range of products and sizes offered by SERECO
ment upstream the biological treatment and a sec- allows to make the best choice.
ondary settlement downstream the biological treat- In particular, regarding the sludge extraction from the
ment. A primary perfectly operating clarifier allows an circular sedimentation tanks the selection can be made
about 25% – 30% reduction of the polluting load in between scraping systems of radial, diametral type or
terms of COD and BOD5 at biological treatments inlet. of a type with a length equal to 1+1/3 of the sedi-
Even more important are the secondary clarifiers, mentation tank radius and suction systems of radial,
whose efficiency depends on quantity of total sus- diametral type or of a type with a length equal to 1+1/3
pended solids in the outlet waters. A perfectly working of the sedimentation tank. It is useless to say that, the
biological treatment, if combined to an inefficient sec- peripheral speed of the traveling girder being the same,
ondary settlement, produces outlet water of a very bad a diametral sludge recovery system allows a sludge
quality. For the sizing of the clarifier, besides the sur- retention time in the sedimentation tank which is half
face load and the hydraulic retention time, it is neces- the time of a radial system and that a suction system
sary to consider many other important factors such as further reduces the sludge retention time in the tank
the retention time of sludge on the sedimentation tank with respect to that of a scraping system.
bottom (especially if it is desired to minimize the risk The direction of rotation of the scraping or suction
of rising), the efficiency of removal of the floating bridges is such that the effect of the Coriolis force on
materials (very important as regards foaming and/or the centripetal sludge motion and centrifugal clarified
rising), the water height in the sedimentation tank (in water motion must be considered. In particular, in the
order to minimize the negative effects caused by the Northern Hemisphere the recommended direction of
bulking), etc. The right selection of the clarifier will rotation of clarifier bridges is anticlockwise while in the