June 2011, Vol. 23, No.6
Test your knowledge of filtration
True or False Questions:
- Filtration is typically a tertiary treatment located downstream of secondary processes.
- The traditional media for tertiary filters at wastewater treatment plants is synthetic fiber.
- A well-run granular-bed filter typically requires between 7% and 10% of its influent flow volume for backwashing.
- Continuous filters can filter and backwash at the same time.
- All filters require chemical addition.
Multiple Choice Questions:
When filtering effluent from sedimentation basins with a total suspended solids concentration of 3 to 5 mg/L, what concentration of total suspended solids can be expected in the effluent from a sand filter?
A. Virtually zero
B. 0.1 to 0.5 mg/L
C. 1 to 2 mg/L
D. 2 to 2.5 mg/L
For conventional filters, what is the typical range of backwash duration?
A. 1 to 2 minutes
B. 5 to 8 minutes
C. 12 to 15 minutes
D. About 20 minutes
Given a filtration step with three filters, each filtering 200 L/s (3170 gal/min), that requires one 9-minute, 400-L/s (6340-gal/min) backwash per filter daily, calculate the percentage of backwash water.
What are the primary parameters used to monitor filter performance?
A. Influent flow rate and backwash percentage
B. Effluent flow rate and chemical addition rate
C. Backwash duration and flow rate
D. Effluent turbidity and filter head loss
Click here to show or hide the answer key
Questions developed by Steve Spicer and reviewed by the Operations forum Editorial Advisory Board and the Association of Boards of Certification (Ankeny, Iowa) Validation and Examination Committee.
Water Environment Federation (2008). Operation of Municipal Wastewater Treatment Plants; Manual of Practice No. 11, Sixth Ed. Alexandria, Va.: Water Environment Federation.
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