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2710 TESTS ON SLUDGES*

* Approved by Standard Methods Committee, 1997.

 

2710 C. Settled Sludge Volume

 

1. General Discussion

 

    The settled sludge volume of a biological suspension is useful in routine monitoring of biological processes. For activated sludge plant control, a 30-min settled sludge volume or the ratio of the 15-min to the 30-min settled sludge volume has been used to determine the returned-sludge flow rate and when to waste sludge. The 30-min settled sludge volume also is used to determine sludge volume index1 (Section 2710D).

    This method is inappropriate for dilute sludges because of the small volume of settled material. In such cases, use the volumetric test for settleable solids using an Imhoff cone (2540F). Results from 2540F are not comparable with those obtained with the procedure herein.

 

2. Apparatus

    a. Settling column: Use 1-L graduated cylinder equipped with a stirring mechanism consisting of one or more thin rods extending the length of the column and positioned within two rod diameters of the cylinder wall. Provide a stirrer able to rotate the stirring rods at no greater than 4 rpm (peripheral tip speed of approximately 1.3 cm/s). See Figure 2710:1.

    b. Stopwatch.

    c. Thermometer.

                               

 

 

3. Procedure

 

    Place 1.0 L sample in settling column and distribute solids by covering the top and inverting cylinder three times. Insert stirring rods, activate stirring mechanism, start the stop watch, and let suspension settle. Continue stirring throughout test. Maintain suspension temperature during test at that in the basin from which the sample was taken.

    Determine volume occupied by suspension at measured time intervals, e.g., 5, 10, 15, 20, 30, 45, and 60 min.

    Report settled sludge volume of the suspension in milliliters for an indicated time interval.

    Variations in suspension temperature, sampling and agitation methods, dimensions of settling column, and time between sampling and start of the determination significantly affect results.

 

4. Precision and Bias

 

    Bias is not applicable. The precision for this test has not been determined.

 

 

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5. Reference

  1. Dick, R.I. & P.A. VESILIND. 1969. The SVI-What is It? J. Water Pollut. Control Fed. 41:1285.

 

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