Is it possible to have greater Electric Conductivity (EC) value for Waste Water than Total Dissolved Solid (TDS)?

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Hello.

I am facing a problem with our waste water treatment setup. The TDS found in waste water is 1200 mg/l whereas the EC calculated for the same waste water is around 1600dS/m.

My experience says that EC has relation with TDS, which is EC = 0.67 x TDS.

In our factory we process waste water generated from Personal Care Cosmetics and Soaps .

I know that EC varies with temperature and ionic compounds, but what we are experiencing is confusing. So I need your advice. It is normal to have greater EC value for waste water than TDS ? If not, what could be the possible reasons behind it?

Thanks in advance.

Regards,

Forhad, Chemical Engineer, BUET.

 

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18 Answers

  1. Hello. I don't want to say that you're wrong, but my experience in water and wastewater analisys say that is the oposite (EC x 0,6~0,8 = TDS), and is been like that al along. I sugest you to take a look in the Standart methods (http://www.standardmethods.org/store/ProductView.cfm?ProductID=63), methods 2540 Solids and 2510 Conductivity/2520 Salinity (Method "B - Electrical Conductivity Method") for more information. Best Regards. Léo.

  4. Let me say that nearly all comments are correct except the coefficient in TDS = 0.64*EC is not true. Depending on the character of the water it may vary from 0.55 to 0.75. Here are referencesa to key works on this topic.


    Hem, J.D., 1989. Study and Interpretation of the Chemical Characteristics of Natural Water, U.G. Geological Survey, Water Supply Paper 2254

    This supercedes

    Hem, J.D., 1970. Study and Interpretation of the Chemical Characteristics of Natural Water, 2nd Ed, U.S. Geol. Survey, WSP 1473

    also

    Garrels, R.M. 1960. Mineral Equilibria at Low Temperature andf Pressure, Harper & Brothers, New York.

    and Garrels, R.M. and Christ, C., 1965. Minerals and Equilibria.

    The bible of water chemistry is


    Stumm, W. and Morgan, J. 1981, 2nd Ed.. Aquatic Chemistry, An Introduction Emphasizing Chemical Equilibria in Natural Waters, John Wiley and Sons, Inc., New York

    Also you might enjoy this fun book

    Barth, R.B., 2010. The Chemistry of Beer, 2nd Ed. Greene Publications, West Chester, Pennsylvania.


    Regarding to TDS it is generally taken to mean dissolved natural solutes and should not include miscible organic compounds that may show up when the water of a sample is completely evaporated.


    Garrels

    1 Comment

    1. I agree my friend... because that i propose the gravimetric method as a reference before the conductivity method... each water is diferent and have to be treated like that, as i think you're proposing. cya!

  5. Good afternoon Muhammad Forhadul.


    How are you today? My answer is Yes, It is. There are samples with TDS readings higher than the EC readings. I have to say that it is not very common and the reason may be because of the presence of organic compounds . Please allow me to explain myself. Basically, as you know, the conductivity is a measure of the ability of an aqueous solution to carry an electric current and it is depends on the ions (concentration, mobility and valence) and the temperature of the sample. It is important to note since this is a waste water sample the presence of organic compounds that do not dissociate in aqueous solution conduct a current very poorly.

    Now, base on the method for checking correctness of analyses (SM 1030 E #5 (*)) the radio of calculated TDS to conductivity should be between 0.55 and 0.7. (TDS/CON = 0.55-0.7). If the ratio is above 0.7, the higher ion sum is suspect, it is recommend to re-analyze the sample, now if the ratio falls bellow 0.55 the lower ion sum is suspect, it is recommend to re-analyze the sample. We ran and re-ran for many years samples with a ratio up to 2. These are waste water samples with high concentration of molasses. On the other hand, I should mentioned, since I have very limited information about your data, analysis, sample collections, holding times, calculations, instruments, calibrations etc it is very difficult to determine if there is an issue with the data (either accuracy or precision). I will be more than happy to help you. If you have any questions please let me know. Thanks for sharing your experience with us.


    *Standard Methods for the examination of Water and Wastewater 21st Edition, 2005 D. Eaton Andrew, S. Clesceri Lenore, W. Rice Eugene and E. Greenberg Arnold.

  7. Dear People,

    Please note that the relationship between TDS and EC is

    TDS=0.64EC

    This means EC is always greated than the TDS. There is a slight effect of temperature on relationship. That is why we always make the measyrement at 25 degree celcius.

  10. Mohammed, if your waste water contains organic matter - i.e. effluent, decaying matter, we find that use of our natural mineral mix treats large ponds with a high EC value. We need a detention period of 48-72 for all solids to drop to sludge level - offering clean water to EPA regulations for irrigation purposes. In addition : Odor is vastly reduced, mosquito larva is killed and we achieve efficient treatment of 7 waterborne diseases (E-coli/Cholera & Typhoid)

  11. FACTORS AFFECTING THE CONDUCTIVITY OF ELECTROLYTIC SOLUTION

     1)   INTERIONIC INTERACTION: – Greater the inter-ionic interactions lesser will be the conductivity of the solutions.

    2)   SOLVATION OF IONS :- Greater the salvation of ions of an electrolyte lesser will be the electrical conductivity of the solution

    3)   VISCOSITY OF THE SOLVENT: – Greater the viscosity of the solvent   lesser will be the conductivity of the solution.

    4)    TEMPERATURE: – Conductivity of an electrolytic solution increases with the increase in temperature. This is due to increase in ionic mobility.

    5)   CONCENTRATION: – With the increase in concentration the conductivity of the solution decreases.

  13. Calculated TDS is aEC where EC in electrical conductivity and a is a constant that is between 0.55 and 0.7 5 so, 0.67. You have the formulabackwards. The authority is Hem, J.D, 1989, Study and Interpretation of the Chemical Characteristics of Natural Water, U.S. Geological Survey Water Supply Paper 2254 p. 67. Try abebooks.comorgotoUSGS.gov/Publications

  14. Normally TDS is smaller than EC and both measures are in close connection but to have a relationship you need more information considering that they are using different techniques and they measure different things.. It can and often happen that relationship can be fixed by testing in field and it will be applied only for your case.

  15. 1. TDS (mg/l) = k*EC(µs/cm); k=0.60-0.70


    2. Try and use the gravimetric method and instrumental analysis;

    3. Check for things like:


    TS (mg/l) = TSS (mg/l) + TDS (mg/l);

    4. You could also do a comprehensive test and check for ionic balance .

    5.Best wishes!!!

    1 Comment

  17. There is no standar relation between EC / TDS. Conductivity is the facility of electrons to move in a standard distance (1 cm), and it is relative to the dissolved ions and the ionic strengh of these ions. As higher the ion strengh as the conductivity will be higher fr the same ion concentration. So, high ionnic strengh ions like sodium chloride will give much higher conductivity than low ion strengh ions like Calcium carbonate in the same ionic concentration.

    For a certain water quality you have to find the relation between EC/TDS by measuring the real TDS by total evaporation of the sample at 105oC.

    1 Comment

    1. I have also to make clear that TDS has a specified clearly value (i.e. x mg/lt), instead of Conductivity, which's value is also temperature dependant, as the ions "speed" is higher as temperature rises. The relation between Conductivity/ΔΤ is also no standard (usually 1-2,5%/°C), depending also from the ions type (MW, ionic strenght etc.). So, concerning Conductivity, you have always to mention the temperature measured, in order to be certain.

  18. The TDS value is ALWAYS smaller that the EC value and the relationship is : TDS = 0,578 x EC

    1 Comment

    1. I would suggest to calibrate your EC and check temperature of your solution, it could affect your EC