No. 0377 Sewage Treatment Systems

Q1: Which of these is considered as being ‘grey water’?
A: Drainage from the galley sink

Q2: If there is a smell of ‘sewage’ in toilets or bathrooms of the accommodation, why should this be investigated immediately? Select the ONE best answer:
A: Because it could mean that toxic gases are being released into the accommodation

Q3: What are the products from the “aerobic” breakdown of sewage?
A: Water, carbon di-oxide and an inert residue

Q4: Which of these is defined as ‘sewage’ under MARPOL?
A: Drainage from the dispensary or sick bay

Q5: What are the products from the ‘anaerobic’ breakdown of sewage?
A: Water, carbon di-oxide, hydrogen sulphide, methane and an inert residue

Q6: Your ship is just over 3 miles from land, and not in a special area. Under MARPOL Annex IV regulations, what is the minimum treatment required before sewage can be released at a moderate rate?
A: It must have been comminuted and disinfected

Q7: Under MARPOL Annex IV, how fast must the ship be moving before it can discharge sewage that has been treated in an ‘approved’ sewage treatment plant?
A: There is no requirement for the vessel to be moving if an approved sewage treatment plant is used

Q8: When more than 12 miles from land, under MARPOL Annex IV, how fast must the ship be moving before it can discharge untreated sewage?
A: The ship must be ‘en-route’ and travelling at a speed of at least 4 knots

Q9: When more than 3 miles from land, under MARPOL Annex IV, how fast must the ship be moving before it can discharge sewage that has been only comminuted and disinfected?
A: The ship must be ‘en-route’ and travelling at a speed of at least 4 knots

Q10: Why are ‘vacuum’ sewage systems used?
A: They reduce water consumption and require a smaller holding tank

Q11: Under MARPOL Annex IV regulations, how far must a ship be from land before untreated sewage can be released at a moderate rate?
A: At least 12 miles, and the ship must be en-route

Q12: Which parts of a sewage storage or treatment system need to be ventilated to remove CO2 and other gases?
A: Anywhere that sewage is stored or treated

Q13: Some types of aerobic sewage plants have sections of clear piping just above the tank. What are these for?
A: So that operators can check that the air-lifts are working

Q14: Why do the IMO place a limit on the amount of residual Chlorine for type approval of a sewage treatment system?
A: To reduce the harmful effects of putting Chlorine into the sea

Q15: What are coliform bacteria, and why do we measure how many there are in treated sewage?
A: They are the bacteria present in the human intestine and how many are left in treated sewage gives us a guide to how effective treatment has been

Q16: A sample of treated sewage has a high ‘Biochemical Oxygen Demand’. What does this mean?
A: That the sewage treatment is incomplete

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