Lamella Clarifier Design

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I want to design a lamella clarifier with the following specifics:

How can I best design the lamella clarifier?  

Will the suspended solids affect the design?

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9 Answers

  1. I need help for lamella design of following parameters.

    Flow 15000m3/day

    Rectangular Tank

    Length: 4.83 ft

    Width: 2.5 ft 

    This is a small waste water treatment plant

     

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  2. Aruna

    Why use a clarifer for this application?

    250ppm TSS is well within the application window for a textile media water filter and will have about 1/20th the foot print of a clarifier and probably wont need a coagulant.

    As a rule of thumb, if the TSS is 250ppm, a large proportion of the solids will be non settling!

  3. Dear Aruna,

    A  lamella clarifier  or  inclined plate settler  ( IPS ) is a type of settler designed to remove particulates from liquids. They are often employed in primary water treatment in place of conventional settling tanks They are used in industrial water treatment. Unlike conventional clarifiers they use a series of inclined plates. These inclined plates provide a large effective settling area for a small footprint. The inlet stream is stilled upon entry into the clarifier. Solid particles begin to settle on the plates and begin to accumulate in collection hoppers at the bottom of the clarifier unit. The sludge is drawn off at the bottom of the hoppers and the clarified liquid exits the unit at the top over a weir.

    There are a number of proprietary lamella clarifier designs. Inclined plates may be based on circular, hexagonal or rectangular tubes. Some possible design characteristics include:

    1. Tube or plate spacing of 50 mm.
    2. Tube or plate length 1–2 m.
    3. Plate pitches between 45° and 70° allow for self-cleaning, lower pitches require backwash.
    4. Minimum plate pitch 7°
    5. Typical loading rates are 5 to 10 m/h

     

    Lamella clarifiers can handle a maximum feed water concentration of 10000 mg/L of grease and 3000 mg/L of solids. Expected separation efficiencies for a typical unit are:

    90-99% removal of free oils and greases under standard operation conditions.

    20-40% removal of emulsified oils and greases with no chemical amendment.

    50-99% removal with the addition of chemical agent(s).

    Treated water has a turbidity of around 1-2 NTU.

    The Lamella Design Program uses four constraints to determine design values, the critical velocity of 10 m/day , the upward velocity at the bottom of the tank, the minimum space between the lamella and the predetermined length of the sedimentation tank. All of these constraints come together to determine the length of the lamella. The minimum spacing between the lamella was determine via laboratory experiments, at spacing closer than 2 cm failure occurred. The length of the sedimentation tank is set by the Sadimentation ProgrammeThe critical velocity is the rate at which a particle must fall to ensure that it settles out within the plate settlers. If the critical velocity is too large, flocs will not settle out, and will remain in the water sent through the distribution system. However, a small critical velocity comes at the expense of a large cross sectional tank area (so it is not practical to have an unnecessarily small critical velocity). The upward velocity at the bottom of the tank is important for sludge blanket formation, too high and the blanket will form too thin and will not capture particles, too slow and the blanket will either settle out instead of remaining suspended or the shear value in the blanket will be so high that flocs will get broken up in the blanket

    The program starts by determining the height needed for the launders above the lamella. This height needed for the launders is same as the depth of water needed above the lamella. This value is simply a function of leaving enough available head loss through the exit launder about the lamella to keep it properly submerged.

    1. Flow entry:

    The flow enters from both sides of the plate. Distribution and entry velocities are minimum to optimise the hydraulic flow regime, resulting in full plate utilisation, maximum efficiency and better effluent quality.

    2. Weir take-off: A weir launder provides an effective weir length. The weir has orifices on either side of each plate.

    3. Removable plates: Individual plates are easily removable even during operation, making the unit very simple to maintain without shutdown. The design offers flexibility to handle changes in influent characteristics.

    4. Hopper arrangement: Several options are available for sludge. The standard arrangement is a hopper bottom with a structural support frame. A second option is to mount the lamella clarifier on top of a thickener in order to achieve a higher solids concentration, while providing a large sludge volume.

     

    Regards,

    Prem Baboo

    1 Comment

    1. Dear Sir, Thank you for an elaborate answer. 

      Commented on by

  4. Dear Aruna,

    I worked out my own program that works very well. The theory behind it is the following:

    - The flow of water along the lamellas has to be laminar, and I suggest a prudent Re number of less than 500. According to the profile of velocity in laminar flow, the velocity of the water is zero at the Surface of the lamellas. Hence the upflowing water is not sustaining the solids deposited on the Surface of the lamellas and the solids can slip downwards by gravity.

    - The velocity of sedimentation of the solid particles is a function of the solid density and of the particle sizes. Normally the density of the solids is assumed 2,2 (sand). The particles size can be either analyzed or referred to statistics applicable for simila water. A typical statistic data is that 90% weight is of particles sized more than 30 microns.  The velocity can be calculated with the Stokes law (easy found in Internet)

    -  The hold-up time inside the lamellas packing should be long enough the ensure that the particles (example larger than 30 microns) have time sufficient to sink from any part of water inside two lamellas down to the lamellas underneath, according to the calculated velocity

     

    Please write to me privately to get a copy of my program

    3 Comments

    2. How could I ​get a copy of ​your program? ​

      Commented on by

  5. Hi Aruna, You can assume suitable overflow rate based on the characteristics of the water/wastewater. The normal range is 24-36 m3/day/m2. You can divide your flow rate by this overflow rate to get the plan area of your lamella clarifier. You can assume depth of clarifier in the range of 2 to 3 m. Include some allowance for sludge storage. The lamela tubes should be fitted in the tank with some inclination. They will provide more surface area for settlement of suspended solids and remove the suspended solids efficiently. A company Prachi Services Inc has developed softwares for a) Design of water treatment plant b) Design of sewage/effluent treatment plant c) Design of advanced wastewater treatment plant ..etc. You can visit their website www.worldenviro.com  if you want to purchase one.

     

  6. Before doing any thing, a jat test is needed to carry out . Based on the test result, then you can design a clarifier. Because a diffrent source of wastewater, will have dirrferent characteristic and settleability.

    With the jar test result and follows the procedure of text book to design a lamella clarifier.

  7. Designing a lamella clarifier requires many calculations that would start with chemical precipitation chemistry for the specific wastewater. For instance if you want to remove Cu, a simple pH adjustment to 8.5 will do the job, if the Cu is not chelated. However, if your wastewater contains Cr+6, then you need to reduce that to Cr+3 by adding Na2S2O5.  Otherword, you need to create insoluble precipitates, followed by either natural or synthetic organic polyelectrolytes, which would adsorb onto the particulate surface, to accelerate particle aggregation. Depending upon your wastewater characteristics, the chemistry part of the design may also require other coagulants like PAC or FeCl3. 

    Then you need to do particles dynamics and separation design calculations. This would give you inlet, outlet and settling zone parameters. Then under the settling zone you need to design the discreet particle, flocculant, hindered and compression settling zones, which would include inclined plates as a minimum. 

    Therefore, to design a lamella clarifier is not something that can be done on a short message. The better way is to just purchase one as we have gone through number of modifications to get our clarifiers to perform properly (http://www.solutionsrecovery.com/wastewater-treatment-products/chemical-precipitation-water-treatment/).

     

  8. Hi Aruna,

    Is the flow rate that you have mentioned the peak flow or the average flow that you will be expecting? What is the application?

    The suspended solids content will affect the design and, depending on your desired effluent quality, may or may not require the addition of chemical dosing to enhance the settlement in the Lamella.

    We provide Lamella separators and would be happy to assist you with the correct sizing and specification. If you can let me know where the project is, I will be able to put the relevant member of our technical team in contact with you.

    Regards,

    Mark

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  9. What is the industry of the wastewater?Do you make jar test for the project?

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