July 2007, Vol. 19, No.7
Test Your Knowledge of Headworks Treatment
True or False Questions:
- Screening presses and vacuum containers are used at wastewater treatment plants to remove the liquid from the screenings before transport to reduce excess water, volume, and weight.
- The spacing between the bars in bar screens is typically 0.25 to 0.5 in. (6.35 to 12.7 mm).
- The chains used in chain-driven bar screens tend to stretch from wear.
- The basic components of wastewater grit material consists of such materials as sand, cinders, rocks, coffee grounds, cigarette filter tips, and other relatively nonputrescible organic and inorganic substances.
- Grit classifiers remove organics from the grit.
Multiple Choice Questions:
Hand-cleaned grit chambers are typically used in what size plants?
A. Large plants with flows greater than 11 mgd.
B. Medium-sized plants with flows between 6 and 10 mgd.
C. Small plants with flows generally between 3 and 5 mgd.
D. The smallest plants with flows generally less than 1 mgd.
Aerated grit chambers provide a period of wastewater detention to trap grit through air-induced rotation of the wastewater at approximately what speed?
A. 1 ft/s (0.3 m/s).
B. 3 ft/s (0.9 m/s).
C. 5 ft/s (1.5 m/s).
D. 7 ft/s (2.1 m/s).
Calculate the monthly screenings disposal cost for a 10-mgd wastewater treatment plant. Assume that on a typical day, 1.2 yd3, 2.3 yd3, and 0.7 yd3 of compacted screenings were removed during the first, second, and third shifts, respectively. The plant pays $35 to dump each 12-ft-long, 4-ft-wide, 5-ft-high container at the landfill.
A. $66 per month.
B. $147 per month.
C. $380 per month.
D. $515 per month.
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Questions were developed by Steve Spicer and reviewed by the Association of Boards of Certification (Ames, Iowa) Validation and Examination Committee.
Water Environment Federation (2007). Operation of Municipal Wastewater Treatment Plants; Manual of Practice No. 11, Fifth Ed. Alexandria, Va.: Water Environment Federation.