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May 2011, Vol. 23, No.5

Certification Quiz

Test your knowledge of solids processing and management

    True or False Questions:
  1. Liquid ferric chloride will not freeze; therefore, it can be stored in bulk outdoors.
  2. The purpose of sludge thickening is to decrease the volume of sludge and increase efficiencies of downstream processes.
  3. The thickening mechanism of a rotary-drum thickener is similar to a gravity-belt thickener, because the separated solids are retained on a filter screen while the filtrate is allowed to drain away.

    4. Multiple Choice Questions:

  4. Which choice below lists two typical thickening tests? 

    5. A. Sludge density index and settleable solids.
    B. Sludge volume index and total suspended solids.
    C. Solids capture and total dissolved solids.
    D. Settled sludge volume and sludge volume index.

  5. An ideal pump for a solids dewatering process will produce a steady, uniform flow rate with little or no shear. With these parameters in mind, which biosolids pump would not be appropriate for supplying biosolids to a mechanical dewatering device? 

    6. A. Diaphragm pump.
    B. Progressive cavity pump.
    C. Rotary lobe pump.
    D. Double disc pump.

  6. How biosolids are handled before dewatering will have a significant effect on their dewaterability and the chemical dosage needed. Which of the following will have the most beneficial effect on the dewaterability and chemical dosage?

    7. A. Produce more primary solids by maximizing suspended solids removal.
    B. Store biosolids in an aerated tank before processing.
    C. Operate anaerobic digesters with sufficient detention time to meet volatile-solids-reduction requirements for Class B biosolids.
    D. Process alum sludge from the water treatment plant at the wastewater treatment plant.

  7. A primary sludge pump ran continuously for 24 hours and delivered 1090 m3 (288,000 gal). What is the capacity of the pump? 

    8. A. 22,700 L/h (100 gal/min).
    B. 45 m3/h (200 gal/min).
    C. 114 m3/h (500 gal/min).
    D. 225 m3/h (1000 gal/min).

  8. An anaerobic digester currently uses a gas-mixing system. The chief plant operator would like to convert the digester to a pumped mixing system using centrifugal, nonclog pumps. It is desired to “turn the digester over” every 20 minutes. The digester has a volume of 3800 m3 (1 million gal). What is the capacity of the pump needed?

    9. A. 3400 m3/h (15,000 gal/min).
    B. 5700 m3/h (25,000 gal/min).
    C. 11,400 m3/h (50,000 gal/min).
    D. 17,000 m3/h (75,000 gal/min).

Questions excerpted from the Operation of Municipal Wastewater Treatment Plants Study Guide, published in 2007 by the Water Environment Federation (Alexandria, Va.). 

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