Headworks and Screening Practice Questions for Level 4 · Expert

1. Question 1

   Two parallel screen bays have separate upstream approaches and a common downstream channel. At peak flow, Bay 1 receives 65% of the flow and reaches its differential-level limit while Bay 2 remains below half its tested capacity. Both rakes operate normally. What is the best operating response?

   1. Increase both rake speeds
   2. Lower the common downstream channel
   3. Rebalance gates and verify bay loadings
   4. Raise Bay 1's differential-level limit
   Show the answer

   Answer: C. Rebalance gates and verify bay loadings

   The screen equipment is working, but the separate approaches are distributing flow unevenly. Rebalancing and verifying both loads uses available capacity without weakening protection.

2. Question 2

   A headworks upgrade will provide two duty screens, and either screen can pass peak flow. Both proposed screens discharge to one washer-compactor. If that unit fails, screenings accumulate at both screens within 30 minutes, and the plant has no safe manual-handling plan. Which design change best improves system redundancy?

   1. Provide an independent screenings-handling path that can serve either screen.
   2. Increase the drive rating on both screens while keeping the shared washer-compactor.
   3. Install finer openings on both screens to reduce rag loading in downstream pumps.
   4. Add upstream storage that delays flow for 30 minutes during compactor failure.
   Show the answer

   Answer: A. Provide an independent screenings-handling path that can serve either screen.

   The two screens are not truly redundant when one shared washer-compactor can disable both trains. An independent handling path removes that common failure point.

3. Question 3

   A plant is deciding whether its manually cleaned bypass rack provides adequate backup for two mechanical bar screens. The rack can pass peak flow when clean, but it reaches its allowable headloss in 20 minutes during storm debris loading. The response crew needs 45 minutes to arrive. Which evaluation should control the decision?

   1. Whether the rack has the same bar spacing and material as the mechanical screens.
   2. Whether average dry-weather flow can pass without exceeding its headloss limit.
   3. Whether the backup stays operable until the response crew arrives.
   4. Whether the rack costs less to maintain than a mechanical screen.
   Show the answer

   Answer: C. Whether the backup stays operable until the response crew arrives.

   Backup equipment must remain usable until help can arrive. A rack that reaches its headloss limit in 20 minutes cannot bridge a 45-minute response time.

4. Question 4

   Fine screens meet solids-capture requirements at normal flow but reach their verified hydraulic limit during short wet-weather peaks. Upstream coarse screens have spare capacity, and an existing equalization basin can receive coarse-screened flow and return it after the peak. Which operating strategy best protects the fine screens without bypassing treatment?

   1. Divert coarse-screened peak flow to equalization and meter it back through the fine screens after influent flow falls.
   2. Divert coarse-screened flow to equalization but return it through the fine screens during the same peak period.
   3. Store fine-screen effluent during the peak and meter it to downstream treatment afterward.
   4. Operate the equalization basin as pass-through storage and increase fine-screen cleaning frequency.
   Show the answer

   Answer: A. Divert coarse-screened peak flow to equalization and meter it back through the fine screens after influent flow falls.

   Storing coarse-screened peak flow reduces the hydraulic load reaching the fine screens. Returning it after influent flow falls preserves treatment without exceeding the verified screen limit.

5. Question 5

   A plant is selecting replacement panels for two drum microscreens. A 30-day trial shows that 40-micron panels improve capture by 8%, but cut peak hydraulic capacity by 25% and double wash-water use. The existing 100-micron panels meet downstream solids targets and wet-weather capacity. Which recommendation is best?

   1. Use 40-micron panels and increase wash frequency
   2. Retain 100-micron panels for verified plant capacity
   3. Put 40-micron panels on one drum and keep one 100-micron drum
   4. Use 40-micron panels during dry weather and change them before storms
   Show the answer

   Answer: B. Retain 100-micron panels for verified plant capacity

Operator Master has 5 Level 4 · Expert headworks and screening questions, free.

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