Tube module settler vs lamella plate clarifier

A. What happens in a plain clarifier (with no lamella plates or tube modules) is this: the water flows into the bottom and out at the top, and you make it so big that even though the descent rate of the tiny floc particles is very slow, the rise rate of the water is even slower, so the particles settle to the bottom.

The theory behind both a tube settler and a lamella unit is very similar, with this change: Although the water rises as before and the particles settle as before, the water is flowing inside a tube or channel that is set at a 45 degree (or so) angle. The water will have to travel several feet from the entrance of the tube to the exit, but particles will only have to fall a couple of inches before they hit the bottom of the tube or plate and start agglomerating -- so the size can be greatly reduced.

The theory more or less works, as witness the countless lamella and tube settler clarifiers installed. So the thing really becomes a matter of convenient geometry. Tube modules less than two foot deep can fit into a round or rectangular tank in a reasonably small space whereas long lamella plates set at an angle must go into a funny shape tank which, viewed from the side is, instead of a rectangle like a building, a parallelogram slanted at the 45 degree (or so) angle.

All things being equal, and with enough room, I'd probably go with the lamella plate because the plates can have real mechanical integrity whereas the tube modules I am familiar with were usually flimsy thin plastic boxes. But finding installation height for a lamella settler can be tough. The lamella is all usable area because the tank walls and the plates are parallel. But the tube settler has dead area because any tubes near the wall are dead ends, so very small diameter tube settlers won't work -- they need to be fairly large diameter (or large rectangles) so the percentage of dead space is minimized (Picture a two-foot deep 45-degree tube module in a two-foot square tank: water could not flow at all because every tube would be a dead end with one end or the other running into the vertical walls of the tank.

A. Tube settlers are based on different theory that states that settling is dependent on settling area rather than detention time. We keep the angle of inclination of Tubes between 45 degree and 60 degree. since above 60 degree angle will cause them to be ineffective and below 45 degree angle will cause choking problems.
The equations for settling is simply derived from time- distance-speed relationship, which further calculates the distance required to settle the particle with and above a specific settling velocity.
Since the water is supplied through small channels the fluid attains least turbulence and thus keeps the control over flow pattern.

A. The advantages of tube settlers over plate settlers are numerous. 1. Tube settlers are self supporting block, plates need specific grooves with fixing mechanism. 2. Tube settler can be easily fitted into a circular/square/rectangular tank, plates are suitable for rectangular/square tank only. 3. Tube settler made of UV stabilised PVC are more economical than plates. 4. mechanical strength of TS block is more than plates. 5. TS block allows foot traffic. 6. Choking chances are less as compared to plates. 7. Efficiency is more than plates. 8. Provides higher settling area compared to plates.

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Hi, cousin Santanu.

If you present 8 advantages for tube modules and no advantages for its very widely implemented competition, people might dismiss your posting as product advocacy rather than a balanced technical presentation. Please consider the time-proven approach of "damning your competition through faint praise" :-)

Luck and Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 2, 2010

A. Hi Ted,
Sorry if you found my views appeared as a one-sided affair. Here are 8 advantages of plate settler. 1. Plates made of SS have longer life. 2. Plates can be removed from the slots for cleaning and packing them back into grooves. 3. Plates can be ordered as per design and delivered by the manufacturing company for ready to fit in. 4. Needs less storage space at site during installation. 5. FRP plates are easily available in the market. 6. FRP plates are comparable in price against Tube settler made of UPVC. 7. FRP plates have higher thickness than Tube settler. 8. FRP plates can be easily resized at site during installation.

Hope this satisfies .. :-) and helps the reader to take judicious decision ...

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September 3, 2010

Thanks, Santanu! Now, thanks to your extreme diligence, this page represents a thoughtful, balanced and very good answer to the question!

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi, Sourabh

Increasing the hydraulic radius means making the tubes larger in cross sectional area. From a practical standpoint this may make the tubes less subject to becoming blocked, and easier to clean out. The disadvantage is that a particle has further to fall before contacting the bottom of the tube, so the workable flow rate for the clarifier is theoretically reduced.

Regards,

Q. Dear Ted,
1. At the onset I would like to thank you for your reply. If you can give a mathematical relation that would be beneficial.
I would also like to ask if Reynolds number has something to bear with? if yes, your explanation will be thankful.

2. Regarding Shantanu, Paul I would also like to thank him for stating the advantages of tube settlers. But Ted I would also point out that you made us picture a two square foot tube settler, which was never required for such a small size and moreover the loss of area you pointed out shall be both in lamella plates and tube settlers provided they are inclined.
I would also like to have some major advantages of lamella clarifier.
Thanking you

A. Hi, Sourabh.

1. This website receives close to 200 inquiries a day, allowing me only 3 or 4 minutes to dispatch each inquiry. So I apologize that generally, when a question requires research or investigation into mathematical models like Reynolds number, etc., I have to rely on readers who may specialize in that field to answer it. Sorry.

2. The blocked area of tube-module clarifiers that I described is because tube modules are usually placed into round or rectangular tanks. There is always some blocked area, and it is almost insignificant in very large tanks but becomes ever more significant as ever smaller tanks are used. All of the lamella plate clarifiers that I have ever seen involve tanks with sloped sides rather than vertical sides (the tanks are the shape of a single tube of a tube module); they are more involved to build, but there is no blocked area.

A reply from Shantanu, offering the advantages of lamella plate settlers crossed in the mail and is printed above; I think it will satisfy your needs in that regard. Good luck.

Regards,

A. Hi, Prakashchandra.

My personal opinion is that the substantive difference is the physical shape rather than any functional characteristics :-)

They are used for the same purpose, both are widely and successfully employed. The lamella plate design, by having a longer fluid path for the same particle drop path, allows the same flow rate in a taller but smaller footprint. The tube settler is not tall and unwieldy. In brief, although there may be some differences in the fluid dynamics aspects, and I don't strongly disagree with the advantages/disadvantages previously presented, for me the physical shape of the tank is the most defining difference, and has usually been the chief selection criteria in the projects I've worked with. Just my opinion.

Regards,

A. Hi, Shiv.

Probably! You do need to make sure that the weirs are such that they will work properly at the higher flow rates; you need to be aware that higher flows means more turbulence; you need to make sure that the higher solids loading that will result from higher flow rate won't be a problem. i.e., that there is some room for sludge accumulation.

But, yes, that's the idea behind tube settlers; and yes, back in the distant past, I remember being involved in a project that did just exactly that.

Regards,

A. Hi cousin Dada. It's difficult to answer because the readers do not know the operational conditions, but it is possible that you had a very heavy sludge loading and did not remove the bottom sludge fast enough. Try to get the sludge pumped out if that is applicable. It is also possible to overdose the polyelectrolytes and thereby give the sludge too much "body", making it sticky and robust enough to block the tubes. Good luck.

Regards,

A. Having worked with Tubesettler technology for more than 50 months, have found that tube settlers are best performing when the solids loading are less (as in case of municipal wastewaters of industries with low sludge post treatments (less inert TSS in inlet and less yield). These have a hydraulic radius of 80 mm or even 60 mm for hexagonal chevron model which keeps the velocity of settling low through pipes and thus the Reynold's number.

When we are to handle large quantity of sludges we work with lamella plates spaces about 100 mm apart (spacing can even be different based on requirements and quantity of sludges generated).
There are no specific tools available, yet the calculations for finding tubesettler media and tank size are simple.
Having a tubesettler or lamella after an activated sludge system (suspended growth system) is not recommended, as the sludges have affinity to stick on the surface of the plates/tubes.

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August 2016

Thanks, Sourabh.

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi Achim. I tried to explain 10 years ago that from my perspective as an engineer packaging these units together as part of wastewater treatment systems, the most salient selection issue was usually just the shape of the tank: the lamella systems being rectangular and tall (sometimes a problem), but small in footprint; the tube settler style usually being round, short and squat, and consuming more real estate (sometimes a problem).

Each successfully served their function for me; each had periodic issues like blocked channels, sticky sludge, flotsam, insufficient sludge capacity, difficulty in determining sludge level, etc. It's not an opinion that I can put a superfine point on. They both worked, they both had similar periodic misfires.

Although others on this thread, such as Sourabh, seem to have suggested that they have done hydraulic analysis on tube settlers, and that the sides of the tubes affect such calculations, I haven't. Sorry; for me personally, such calculations would represent precision without accuracy.

Regards,

A. Hi Ninad. There is no question about the benefit of solids contact. Occasionally, conventional tube settlers and lamella settlers have the incoming wastewater enter below the sludge level; and recirculating a slipstream of sludge into the incoming wastewater is a common design feature. But I am personally unfamiliar with HRSCC; so I can't comment on its use in place of tube settling. As for cost differences, please simply get quotes for the correct capacity units ... it's possible that for smaller sizes one technology is cheaper and for larger sizes the other. Good luck.

Regards,

A. Hi Noel. I was introduced to Reynolds Number in my Fluid Dynamics course, but I'm out of school 50 years now and was never once was in a discipline which used Reynolds number calculations, so I'm too lazy to re-learn them now, sorry :-)

But in the tube settlers which I have seen, there were no "longest and shortest" tubes, there were only the long, functioning, tubes and the short blocked tubes (the flow blocked by the walls of the tank). Best of luck.

Regards,

A. Hi Mani. To my knowledge the inlet and outlet IDs have no effect on the rise rate calculation. Rather, I think you divide your 125 cubic meter / hour flow rate by the surface area of the clarifier in square meters and you have your rise rate in meters per hour. If the surface area of your clarifier is 125 square meters, the rise velocity is 1 meter per hour. Good luck.

Regards,

A. There are some good video tutorials for this topic online. One example that explains the differences between a tube and plate settler is here: https://youtu.be/z_N0e3UzVb4