2540 SOLIDS*

* Approved by Standard Methods Committee, 1997.


2540 F. Settleable Solids


1. General Discussion


    Settleable solids in surface and saline waters as well as domestic and industrial wastes may be determined and reported on either a volume (mL/L) or a weight (mg/L) basis.


2. Apparatus


    The volumetric test requires only an Imhoff cone. The gravimetric test requires all the apparatus listed in Section 2540D.2 and a glass vessel with a minimum diameter of 9 cm.


3. Procedure


    a. Volumetric: Fill an Imhoff cone to the 1-L mark with a well-mixed sample. Settle for 45 min, gently agitate sample near the sides of the cone with a rod or by spinning, settle 15 min longer, and record volume of settleable solids in the cone as milliliters per liter. If the settled matter contains pockets of liquid between large settled particles, estimate volume of these and subtract from volume of settled solids. The practical lower limit of measurement depends on sample composition and generally is in the range of 0.1 to 1.0 mL/L. Where a separation of settleable and floating materials occurs, do not estimate the floating material as settleable matter. Replicates usually are not required.

    Where biological or chemical floc is present, the gravimetric method (3b) is preferred.

    b. Gravimetric:

     1) Determine total suspended solids as in Section 2540D.

    2) Pour a well-mixed sample into a glass vessel of not less than 9 cm diam using not less than 1 L and sufficient sample to give a depth of 20 cm. Alternatively use a glass vessel of greater diameter and a larger volume of sample. Let stand quiescent for 1 h and, without disturbing the settled or floating material, siphon 250 mL from center of container at a point halfway between the surface of the settled material and the liquid surface. Determine total suspended solids (milligrams per liter) of this supernatant liquor (Section 2540D). These are the nonsettleable solids.


4. Calculation


mg settleable solids/L = mg total suspended solids/L - mg nonsettleable solids/L


5. Precision and Bias


Precision and bias data are not now available.


6. Bibliography


FISCHER, A.J. & G.E. SYMONS. 1944. The determination of settleable sewage solids by weight. Water Sewage Works 91:37.






Standard Methods for the Examination of Water and Wastewater. 20th Ed. American Public Health Association, American Water Works Association, Water Environment Federation.