SS Enviro Engineers | Clarifier Mechanisms
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Clarifier Mechanisms

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S S Enviro clarifiers, which is a clarifier using peripheral influent/peripheral effluent design, is used for waste water activated sludge process.

It possesses such advantages as:

  •   Greater capacity
  •   Higher overflow rate
  •   Best hydraulic stability
  •   Maximum range of scum skimming
  •   Lower fabrication cost

Design Considerations:

Final clarifiers should be designed with rapid sludge withdrawal systems to inhibit the tendency of the sludge to become anaerobic if not removed quickly. The tanks should be sufficiently baffled to reduce velocities and to disperse the flow evenly to reduce short-circuiting.

Short-circuiting will tend to increase the solids losses over the clarifier weirs. Also, final clarifiers should include some type of surface skimming device to remove floating solids and scum. Final clarifiers should be designed with a hydraulic detention time from 2 – 2 hours.
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The three functions of S S Enviro clarifiers have been analyzed:

  •   Storage capacity that determines the sludge distribution between biological reactor and settler.
  •   The various flow configurations have been presented for both circular and rectangular settlers and the specific case of a circular secondary settler with radial flow was analyzed in detail for
  • Solid-liquid separation that has a direct effect on effluent quality sludge thickening important to control the sludge age the inlet structure with particular attention to the flocculation zone whose advantaged and drawbacks have been highlighted;
  •   The outlet structure with particular attention to the effects of the baffles on the effluent quality and on the clarifier performance; scum collection systems; sludge collection systems. Range of values for the classical design parameters like as hydraulic loading, hydraulic retention time, solid flux, hydraulic loading of the effluent weirs, recycle ratio have been identified.
  •   Finally, as alternative to traditional plant configurations and as possible solution to the problem represented by the huge areas occupied by secondary clarifiers membrane reactors have been considered.
  •   Other significant advantage of this technological alternative, besides the reduced space required, is the good effluent quality that does not depend on the activated sludge quality.
  •   The economic disadvantages make the application of membrane reactors suitable for specific situations as expensive land localization, when the permeate can be utilized in agriculture or when very high effluent quality is required.
  •   Gravitational settling is highly dependent on the particles’ properties such as size, density and permeability. Hence, flocculation and de-flocculation are essential to consider in the evaluation of the clarifier efficiency.
  •   Sludge Settleability Like MLSS, sludge settleability has a pro- found impact on clarifier design and operation. The density differential between the aeration basin floc (which contains greater than 75 percent water) and the surrounding water is small; therefore, flocculation is necessary for effective solids separation in the clarifier. Flocculation is the process by which particles aggregate into large r (up to 2 mm diameter) and heavier particles that settle readily. When this happens in biological systems, it is called bio flocculation.

Principle of the Process:

The mixed liquor of activated sludge enters S S Enviro clarifiers through the peripheral influent channel and is uniformly distributed by the orifices on the bottom of the channel. The settled sludge is discharged through the header and manifold. The scum in the basin is collected into the scum pit by scum blade and discharged, so is the scum in influent channel by the scum blade in influent channel.

Many cost analyses have been conducted of S S Enviro clarifiers and central feed secondary clarifier. If the two kinds of clarifiers have the same dimensions, the costs are basically the same considering all the expenses. But in the design of central feed clarifier, it is necessary to set an outside effluent channel and energy dissipation influent well making the cost advantage of S S Enviro clarifiers more obvious.

As S S Enviro clarifiers is designed for greater capacity and a higher overflow rate than a conventional center feed unit because of its inherent hydraulic efficiency. Increased efficiency means a smaller tank that result in cost saving on area and construction.

It is proved from the dye dispersion test in the actual installation that S S Enviro clarifiers eliminates short circuiting and makes full use of the entire tank so that its tank surface area is 50% less than that of a central feed clarifier. The diagram below shows the flow.

At respective 10, 20 and 40 minute intervals, the tank is checked after the water from the influent channel is dyed. Unlike S S Enviro clarifiers, center feed secondary clarifier causes turbulence as a result of high velocity of water inflow. Despite accurately installing the effluent channel and baffle, the turbulence causes short circuiting so as to decrease the effective capacity of the tank.

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The flow enters the S S Enviro clarifiers by means of an influent feed channel, which distributes the flow uniformly around the entire tank periphery. The width of the influent channel decreases in the direction of the flow to provide a uniform velocity in the channel. The influent is evenly distributed around the periphery of the tank. There are orifice tubes at the bottom of influent channel, the size and spacing of which are calculated by computer, controlling head loss to assure uniform distribution of water. The spacing of orifice tubes is designed to avoid solids deposition in the channel.

The mixed liquor enters the tank through orifice tubes and is deflected by the deflection baffle beneath the influent channel, eliminating spurt of water to assure complete and fast dispersion of the flow between the tank wall and the skirt baffle at influent area. The skirt baffle establishes a clean water area in the tank and the area of its surface controls the influent velocity at 1.5m/min. The inflow enters the tank from under the skirt baffle and flows outwards then upwards and finally returns to the effluent channel. During this course, solids uniformly settle out.


Technical Characteristics and Advantages:

Influent Channel

Varying width assures uniform water distribution and keeps flow rate constant to prevent solids from depositing in the channel. There are two modes of water distribution that are single direction and double direction.

Orifice Tubes

The size and spacing of orifice tubes are designed by computer to provide uniform flow rate and controlled head loss. Spurt of water and turbulence are eliminated and solids deposition in the channel is avoided.

Effluent Channel

It is designed to have a varying width based on the theory of hydraulics in order to accommodate to large volume of flow. Peripheral effluent reduces the probability of a short circuiting and makes the weir and channel easy to clean.

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Effluent Weir and Scum Baffle

The effluent weir has triangular-toothed top and the scum baffle can effectively prevent the scum from entering the effluent channel.

Skimming

Both the surface skimmer and the skimmer of influent channel are installed in A-Frame Support connected with the truss.

Scum Removal

The scum in influent channel is carried by water flow to the end of the raceway where a weir gate can be used to remove all influent channel scum to a pit just outside the clarifier wall.

Common Channel Wall

Cost of construction can be reduced, as there is a common wall between influent and effluent channels.

Deflection Baffle

Installed under the orifice tube, it eliminates spurt and turbulence to assure complete and fast dispersion of water flow.

Skirt Baffle at influent area

With its 1.5m height under water, the skirt baffle directs influent into the distribution area, controlling the flow rate under 1.5m/min at maximum flow in order to minimize agitation to the clean water area.

Maximum Area of Influence

It assures low flow rate at the inlet and helps with flocculation process.

Tow-Bro Header

It can effectively collect and remove activated sludge.

Discharge Outlet

When it is necessary to drain the mixed liquor from the clarifier for maintenance, the water above the header can be discharged through the nozzles of the header and the water under it can be removed from the outlet. Our Tow-Bro unitube sludge collector is the most ideal equipment for this kind of clarifier.

For an activated sludge process to achieve optimum plant efficiency the final clarification unit must effectively separate the biological solids from the mix liquor. If these solids are not separated properly and removed from the clarifier in a relatively short period of time, operating problems will result, causing an increased load on the receiving waters and a decline in plant efficiency. The most important function of the final clarifier is to maintain the wastewater quality produced by the preceding processes.