Catalogue

Plants, equipment and machines for water treatment

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Clariflocculators-clarifiers, Settlers, Flotators

The water clarification process in a civil or industrial sewage treatment plant can be found many times in a treatment process. Typically, there is a primary settlement upstream the biological treatment and a secondary settlement downstream the biological treatment. A primary perfectly operating clarifier allows an about 25% – 30% reduction of the polluting load in terms of COD and BOD5 at biological treatments inlet. Even more important are the secondary clarifiers, whose efficiency depends on quantity of total suspended solids in the outlet waters. A perfectly working biological treatment, if combined to an inefficient secondary settlement, produces outlet water of a very bad quality.
For the sizing of the clarifier, besides the surface load and the hydraulic retention time, it is necessary to consider many other important factors such as the retention time of sludge on the sedimentation tank bottom (especially if it is desired to minimize the risk of rising), the efficiency of removal of the floating materials (very important as regards foaming and/or rising), the water height in the sedimentation tank (in order to minimize the negative effects caused by the bulking), etc. The right selection of the clarifier will allow good results even in the presence of biological treatment failure such as those mentioned above. The wide range of products and sizes offered by SERECO allows to make the best choice.
In particular, regarding the sludge extraction from the circular sedimentation tanks the selection can be made between scraping systems of radial, diametral type or of a type with a length equal to 1+1/3 of the sedimentation tank radius and suction systems of radial, diametral type or of a type with a length equal to 1+1/3 of the sedimentation tank. It is useless to say that, the peripheral speed of the traveling girder being the same, a diametral sludge recovery system allows a sludge retention time in the sedimentation tank which is half the time of a radial system and that a suction system further reduces the sludge retention time in the tank with respect to that of a scraping system.
The direction of rotation of the scraping or suction bridges is such that the effect of the Coriolis force on the centripetal sludge motion and centrifugal clarified water motion must be considered. In particular, in the Northern Hemisphere the recommended direction of rotation of clarifier bridges is anticlockwise while in the Southern Hemisphere is clockwise (it is however possible to supply clarifier bridges with direction of rotation different from the standard one).
If it is desired to have a more effective removal of the floating materials, besides selecting the mobile girder type (the diametric one has double efficiency with respect to the radial one), the scum box length might be modified or two scum boxes might be installed in a diametric position with respect to the clarifier (further efficiency doubling). In any circular type of clarifiers it is possible to install the channel cleaning system consisting of sliding brushes or a rotating brush. Moreover any types of circular clarifier can be provided with current baffles which maximize the sedimentation efficiency with an adequate guide of the fluid threads.
The wide range of SERECO products also allows to select bridges that, rather than the peripheral control, are supplied with wholly central drive. The central drive bridges (even of big size, up to a 60 m diameter) are supported by means of the central slewing ring and driven by a sturdy gear motor connected to the slewing ring. This way, the clarifier volume is free from any mechanical part in motion and makes, for example, the installation of lamellar packs possible in its inside; furthermore the maintenance on the clarifier concrete wall, necessary in peripheral drive bridge in correspondence of the traction trolleys, is avoided, and it is noticeably reduced the general maintenance due to the lower quantity of mechanical parts.
As support of the settlement in the chemical-physical treatment processes, it is possible to select clariflocculators (with central or peripheral control) having, as an integral part, a turbine of adequate profile or several electric agitators gate type which allow the mixing with reagents, coagulation flocculation and final clarification processes inside the same tank. In this units, the dimensions of the central deflector are such as to ensure an adequate flocculation time.
Available on the catalogue there also is the equipment necessary for the clarification on rectangular tanks, in particular backward and forward traveling bridges with a sludge scraping or suction recovery system on the bottom, floating recovery system of scraping type, or settlement systems with chain scrapers.
The range of SERECO products also comprises an effective dissolved air flotation system (DAF) available in many sizes and with different characteristics.
It is finally possible to prefer lamellar pack clarification systems, very interesting for their compactness and efficiency, much used for the primary or tertiary sedimentation processes. They carry out the countercurrent clarification that, according to the long experience of SERECO, has proven more effective; this is also confirmed by the specific technical literature.
Any models are available in carbon steel protected with hot dip galvanization, stainless steel or aluminum. SERECO has directly experienced and therefore recommends the installation of clarifiers having the surfaced parts (such as the mobile girder) in aluminium and the underwater parts in stainless steel. To this criterion, lightness, sturdiness and resistance to corrosion will be joined. The higher initial investment will be amortized in a very few years thanks to the reduced maintenance expenses.
SERECO, always aiming at the environmental protection, at making progresses in the research & development field, also thanks to the minimization of the electric power consumption of its equipment, is in a position to supply, on specific request, clariflocculators, dissolved air flotation units or clarifiers fed by solar energy with the installation of photovoltaic panels. In fact it is expected that due to its increasing efficiency and life, its lower and lower installation cost, the photovoltaic panel system can be a valid alternative, especially where the electric power procurement is a problem or in isolate places and/or in places far from the city network.

Clariflocculators-clarifiers, Settlers, Flotators

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