Dewatering Based on Sludge Rheology

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How efficient ​is using ​sludge rheology ​(deformation ​and sludge flow)​ to calculate ​the ​dose of ​polyelectrolytes ​for sludge ​dewatering? ​

Theoretically, ​this makes ​sense but I ​have my doubts ​regarding ​actual plant ​conditions. ​since there are ​so many ​parameters that ​affect this ​method. ​

How do I make ​the best ​approximation ​for these ​calculations?​

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8 Answers

  1. Removal the cost of chemical from the dewatering system is currently very effective..

    1 Comment

    1. Thank you for all your insightful comments. The Jar tests are very well-known because it is always used by poly suppliers to test various Poly brands or to get the proper dosage at commissioning stage. Normally the dosing of poly, example 4kgPoly/TonDS would be established with tests and this would be inserted in the control philosophy to give a certain Poly dose per hour. This Poly dose is related to Solids Load as you know.

      Above and beyond the jar tests, Studies have started here in SA focusing on Sludge Rheology to further decrease or Optimize Poly usage. Technology has also been marketed here in South Africa based on this Rheology concept

      As many said, various parameters influence the behaviour of sludge which I agree on.

      But as sludge enters the dewatering section on its way to the dewatering device, it's viscosity is determined by a measuring device. The whole idea is to relate sludge viscosity to Poly dose.

      I wanted to know whether someone has tested this theory and was it any fruitful with respect to actually minimizing poly consumption.

  3. Dear Ghoewylah, 

    Factors that affect the selection of the type and dosage of the polyelectrolyte are the source, properties of solids and the type of mixing and dewatering devices to be used. Important solids properties are concentration, age, pH, alkalinity. Source of sludge to be dewatered, like primary sludge, waste activated sludge, digested sludge have various requirements. Alkalinity and pH also affect the performance of conditioning agent. Th method of dewatering is also important for selection of conditioning agent and polymers are typically used for centrifugation and belt filter presses.

    As my colleagues wrote, the dosage should be determined in laboratory. The simplest is the widely used jar tests with different dosage of polyelectrolyte. Beside this Buchner funnel test for determination of specific sludge resistance could be used.

    In general, the type of sludge has the greatest impact on the quantity of chemicals required.

    Typical levels of chemicals (Wastewater Engineering Treatment and Reuse – Metcalf & Eddy are given hereafter

    Type of sludge

    Belt filter press,

    kg/t dry solids

    Solid bowl

    Centrifuge,

    kg/t dry solids

    Primary

    1-4

    1-2.5

    Primary and waste activated

    2-8

    2-5

    Waste activated

    4-10

    5-8

    Anaerobically digested primary

    2-5

    3-5

    Anaerobically digested primary and air waste activated

    1.5-8.5

    2-5

     

    However dosage could vary considerably depending on the molecular weight of polymer, ionic strength, activity level.

    Therefore It is always good to consult polyelectrolyte manufacturers for more information on polymer applicability.

  4. Dear Ghoewyiah,

    Activated sludge flow rheology is a very complicated phenomenon. Studies related to activated sludge tend to classify sludge as non-Newtonian fluid. Until now, several theories have been built to describe the complex behavior of activated sludge with varying degrees of success. sludge with solids concentrations above about 2% exhibit non-Newtonian behavior, i.e., the sludge apparent viscosity changes with the shear rate (flow velocity).Sludge rheological properties play a fundamental role in determining its performance in pipes, tanks or reactors. However, the relative information on high-solids sludge is very rareincrease of solid particles concentration in the liquid leads to arising from the strength of the system, which means that below certain value of shear stress the system will behave like a solid, but above this value will flow with variable viscosity depending on the shear velocity. The variability of viscosity is the result of structure

    changes proceeding in the sludge during the flow. Thickening of sludge increases its viscosity and causes more difficulties in the pump and hydraulic transport as the resultThe rheological characteristics of digested sludge are severely temperature dependent. An effect of temperature on rheological properties of digested sludge is partially irreversibleThe rheology of digested sludge affects the flow hydrodynamics, dewaterability, and the polymer consumption in wastewater treatment plants. The rheological characteristics of digested sludge are highly dependent on changes in total solid concentration, temperature, and polymer doseFor the high-solids sludge with TS 6%, 8%, 10% and 12%, their viscosities increased by 5.0, 9.1, 25.7and 24.9 times, respectively, when sludge organic content increased from 28% to 53%, and decreased by 36.5%, 49.5%, 54.0% and 65.4%, respectively, when sludge temperature rose from 9 ºC to 55 ºC. 

    Please find attached herewith usefull articles,

  5. Hello

    first of all you have to confirmed the dosage level,how many ppm you have to dose, in lab you can analyses jar test which gives exact dosage level.
    for eg:0.1ppm for 1 liter of waste water, if add more poly the sludge will get flout never settle down.

    for eg: in lab analyses that 0.2 ppm for 1 hour you have set poly for your flow rate of waste water.

    LPH=LITER PER HOUR FOR EX:FOR 10M3

    PPM*FLOW RATE OF WASTE WATER/% OF CHEMICAL*10 = 200

    % OF CHEMICAL IS 0.1

     

    THEN

    YOUR LPH IS 200  FOR 1 HOUR TO 10 M3

    AND NOW CHECK THE FLOW IS CORRECT.

    LPH=200, 200/3600*1000*5SEC = 2.77 ML OF POLY YOU GET.

  7. Obtain a Sludge Judge and reach down into the layer about a inch or two above the "Sludge storage layer" ( and usually about 2 feet about the solid bottom) and get a sample of this level and send it to a lab to get the assay of the sludge plus the total solids.  This will tell you approximately how much liquid you will have to get out of the sludge.  There are a few minerals like Silica or a polymer that will imporve the drainage with out having to squeeze out   as much water.  A big savings in costly electrical power.

  8. Hello,

    Sludge rheology is very complex and usually not used as a theoritical point of view for sludge dewatering operation optimization.

    The best is to conduct on site trials with a floculation test (different polymers @ different quantity) to assess the floculation and the floc resistance. According to the trials, the best poly @ best quantity will be chosen.

    The trials results will be different if you assess biological / primary / mixed sludge. 

    Following that, you can optimize the poly quantity at full scale level when using your dewatering device, especially with centrifuges with which you can play with the torque and liquid ring level.

    At full scale level, the polymer preparation, injection point and injection concentration is also very important.

    A first ratio that can be used to benchmark the results is :  8 to 10 kg of active matter of polymer per ton of dry solids treated.

     

    Regards