Implications of Lower TSS content(< 50ppm) on Lamella performance

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Hi,

A Lamella designed for 100-200ppm TSS load is currently receiving Feed water with TSS < 50ppm including oxidised heavy metals.

Can the Lamella clarifier performance effectively for this low TSS or will there be any implication on its performance?

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4 Answers

  3. Hey Abilash Srinivasan . We are designing and selling lamella clarifier systems for over 10 years. A lower TSS level will generally have no effect on your settling performance. At the same time a high TSS level has only a small effect on the settling performance too. (Except the TSS level is so high that your media is clogging). Important for the design of lamella clarifier is the particle size, density and shape. As long as the settling velocity of the particle is bigger as the Flow Q divided by the projected surface area the particles will settle. This equation is also described in Hazens law of sedimentation and Stokes theorem of drag forces. Both is more explained here: 

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  4. The great thing about a Lamella is the amount of solids-contact surface area created by the inclined plates.  Regardless of your solids loading into the clarifier, those solids will still make contact with those plates and promote settling.  So, all other things being equal, I would not expect you to see a negative impact.

    That said, you have to make sure that you are effectively treating the solids to maximize settling capability.  A lower TSS water is typically harder to treat...  or at a minimum it will require a dosage adjustment to your coagulant / flocculant.  I would recommend running more frequent jar testing to ensure you are dosing your treatment chemicals at their optimum levels.  Depending upon the cause of the change in water quality, you may need to evalute different chemistries as well (if this change in water quality is going to stick around for a while).  To give you an example, I spent time with a particularly challenging raw water quality on the Texas Gulf Coast, and during heavy rain events the TSS level would drop from 70-ppm down to 20-ppm...  but the amount of color in the water would spike significantly because of the organics that would get flushed into the canal by the runoff.  These organics would significantly increase our demand for coagulant.  Because the organics were soluble, the resulting floc would be MUCH smaller than normal, and we would have to implement a flocculant feed in order to increase the size / weight of the floc and get good settling.  Just something to keep in mind - a positive change in water quality for one parameter can often be replaced by a negative change in that same water quality for another parameter!!

    The other thing to watch is your throughput, specifically the rise rate.  I have seen a number of instances where operations is getting "cleaner" incoming raw water and they view it as an opportunity to increase clarifier throughput...  and then they exceed the design rate for the equipment and it results in solids carryover and higher levels of effluent TSS.

    Regards - Jesse Stamp

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    2. Hi Jesse,

      Thanks for the detailed response. I was a bit sceptical about Lamella performance at lower solids loading. The operators claim that jar testing shows that there is a requirement to increase the document dose to 3ppm to ensure the outlet turbidity is good. I feel 3ppm flocculant dose is quite high and we require to change our flocculant dosing system. Alternatively I am considering Sludge recycling so that there is some sludge. Seeding which helps in settling of the solid particles. The Feed being treated is Mine water blended with various other water sources.

      Thanks.

      Abilash