Exam Question
(a) Sketch and describe a biological sewage treatment system. (6)
(b) How does the biological Sewage Treatment Plant work? (6)
(c) What is understood by the term BOD? What are the factors that affect BOD? (4)
Class 4 (4th Engineer)
MEKG
📅 Dec 2025
Reference Answer
### (a) Sketch and Description of a Biological Sewage Treatment System
A biological sewage treatment system, specifically the extended aeration activated sludge type commonly found on ships, is a multi-stage process designed to treat raw sewage to a standard acceptable for discharge overboard as per MARPOL Annex IV regulations. The system primarily utilizes aerobic bacteria to decompose organic waste into harmless substances.
**(i) System Components:**
A typical plant consists of four main compartments integrated into a single unit:
A biological sewage treatment system, specifically the extended aeration activated sludge type commonly found on ships, is a multi-stage process designed to treat raw sewage to a standard acceptable for discharge overboard as per MARPOL Annex IV regulations. The system primarily utilizes aerobic bacteria to decompose organic waste into harmless substances.
**(i) System Components:**
A typical plant consists of four main compartments integrated into a single unit:
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