Maintenance of preliminary treatment units: Grit chambers in sewage treatment plants are typically cleaned at what interval under routine operation?

Introduction / Context:
Grit chambers remove sand and silt that would otherwise abrade pumps and reduce tank volumes. Regular cleaning is essential to maintain capture efficiency and prevent odors. This question reinforces typical maintenance frequencies used in many municipal plants.

Given Data / Assumptions:

• Municipal grit chamber with manual or mechanical cleaning.
• Average loading conditions without extraordinary storm events.

Concept / Approach:
The cleaning frequency depends on grit load, chamber volume, and equipment. Weekly (about 7 days) is a common baseline for manual-cleaned units, with more frequent removal during high-inflow seasons. Mechanized systems may operate daily, but the question asks typical interval under routine operation.

Step-by-Step Solution:
Consider routine municipal practice and typical grit accumulation rates.Select the commonly cited weekly interval.

Verification / Alternative check:
O&M manuals often suggest scheduled weekly removal, with adjustments based on observed accumulation and odor complaints.

Why Other Options Are Wrong:
2–5 days: Possible for heavy loads, but not the typical baseline.12–14 days: Risk of excessive accumulation and odor if left that long under normal loads.

Common Pitfalls:

• Ignoring seasonality (storms increase grit inflow).
• Assuming mechanized removal schedules apply universally to manual systems.

Final Answer:
7 days