5.(a) State the MARPOL Annex number which deals with the disposal of sewage.(1)
(b) With reference to the Annex stated in part (a), state the rules for EACH of the following:
(i) when the sewage is untreated;(2)
(ii) when the sewage is comminuted and disinfected.(2)
(c) Explain why the final discharge from an approved sewage treatment plant is chlorinated before discharge.(2)
(d) Explain how chlorination is carried out and monitored.(2)
(e) State the correct chlorine content of the final discharge.(1)
MARPOL – Sewage Regulations
(a) MARPOL Annex number: Annex IV. (1 mark)
(b) Rules for discharge under Annex IV:
(i) Untreated sewage (2 marks)
- Discharge permitted 12 nautical miles or more from the nearest land.
- Must be carried out while the ship is en route, at a moderate rate, and not instantaneously.
(ii) Comminuted and disinfected sewage (2 marks)
- Discharge permitted 3 nautical miles or more from the nearest land.
- Must also be carried out while the ship is en route.
(c) Chlorination of final discharge (2 marks)
- Chlorination ensures that harmful bacteria and pathogens are destroyed before sewage enters the sea.
- Protects marine life and reduces health risks to coastal populations.
(d) How chlorination is carried out and monitored (2 marks)
- Carried out by dosing sewage effluent with calcium hypochlorite or chlorine solution in a dosing chamber.
- Monitored by chlorine test kits or meters to check residual chlorine levels in the discharge.
(e) Correct chlorine content of final discharge (1 mark)
- Not more than 0.5 ppm (parts per million) free chlorine.