(a) What is sewage?

(b) Describe regulations controlling sewage discharge according to MARPO.

(c) Sketch biological sewage treatment plant.

(d) Describe above plant and explain its working principle.

(e) Explain how it is maintained to obtain it maximum efficiency.

(a) Sewage means:

  • Drainage and wastes from toilets and urinals and WC.
  • All drainage from medical premises.
  • Drainage from spaces containing living animals,
  • Other waste water mixed with above drainage.

(b) Regulations controlling sewage discharge

Ships over 400 GT and above; and less than 400GT with more than 15 persons.

1. Within 3 nautical miles from the nearest land.

2. More than 3 nautical miles from nearest land, comminuted and disinfected by an approved system discharged.

3. More than 12 nautical miles from the nearest land, sewage stored in holding tanks discharged at a moderate rate when ship is en route and proceeding at not less than 4 knots. Rate of discharge approved by Administration.

4. The ship has in operation an approved and certified sewage treatment plant.

5. The effluent shall not produce visible floating solids nor cause discoloration of the surrounding water.


(d) Working principle

  • System shown has four compartments.
  • Sewage enters into primary collection tank passing through a coarse screen, then flows into aeration tank.
  • In aeration tank, sewage is retained for about 24 hours thoroughly mixed and aerated by aerators located at bottom of tank.
  • Aerobic bacteria and microorganisms break down organic wastes and produce new bacteria cells and organisms.
  • Rotary blowers supply air (oxygen) for bacteria and micro organisms.
  • Mixed replaced by incoming sewage into settling tank.
  • In hopper of settling tank, all solids are formed as activated sludge at bottom and returned back to aeration tank by air lift.
  • Clean effluent flows into chlorination tank for disinfection.
  • Disinfection is carried out with a solution of calcium or sodium hypochlorite.
  • Discharge of effluent is controlled by float switches connected to discharge pump.

(e) To obtain the maximum efficiency of sewage plant,

1. Do not place near risk of explosion area.

2. Do not make hot work on the plant, to prevent damage of internal Epoxy coating and external corrosion resistance coating.

3. Regularly check effectiveness of disinfection by coliform count

4. Every 2 to 3 months remove sludge and send to shore or incinerate.

5. At sea, only cleaning the plant carried out every 6 months

6. Regular dose disinfecting agent, such as calcium hypo chloride.

(a) Who issued the IOPP certificate and validity of certificate?

(b) As a senior engineer explain the procedure for checking IOPP certificate when sign on?

(c) As a senior engineer how do you prepare for IOPP survey?

(a) IOPP certificate

International convention for oil pollution prevention

  • Issue by administration
  • Validity is 5 years.

(b) Checking Procedure

1. Check Validity of certificate

2. Check ORB records are up to date recording

3. Visual inspection of O.W.S and bilge pump and their capacity.

4. Check 15-ppm alarm and automatic stopping device are to be checked.

5. Check O.W.S spare filter element (at least one number)

6. Check Waste oil tanks and capacity

7. Compare fuel consumption and sludge formation

8. Check Incinerator capacity and workability.

(c) IOPP Survey preparations:

1. Check Validity of the IOPP Certificate

2. Maintain ORB up to date recording chronologically and attached receipt of sludge disposal to shore facility

3. OWS in good order, all pressure gauge and sensors are in good order, its piping free from oil leaks. O.W.S overboard valve locked in closed position

4. Check and kept 15ppm Alarm for ODM, Automatic Stopping Device

5. OWS spare filter onboard.

6. OWS operation procedure and piping diagram post near plant.

7. USCG Notice posted near OWS and bilge pumping-out station. Also post warning signboard ‘Don’t start OWS without CE permission’

8. Check function of high level alarms of sludge tank, waste oil tank and bilge holding tank

9. Calculate sludge formation, compared with 1 % of voyage fuel consumption.

10. Incinerating time, incinerated waste oil amount, remainder of waste oil in waste oil tank should be reasonable.

11. Kept Incinerator ready for demonstration, such as heating of waste oil tank.

Alarms control and functional test should be done prior to the survey

(a) List the information which must be entered in the Oil record book when pumping out bilges?

(b) How oil bilges find its way into the engine room bilge?

(c) How long should be kept oil record book and garbage record book onboard?

(a) Oil record book entries

After pumping out bilges, the following information are recorded in ORB


There are several ways oil can be found in machinery space bilge.

  • Over flowing of purifiers, dirty oil tank and sludge tank.
  • Leaking fuel oil and lube oil pump’s gland packing, Leaking oil pipes, joints and filters, Leaking crank case cover joint.
  • Mishandling of trays and pans containing oil.
  • In the engine room, main engine and all auxiliaries are provided with proper arrangements such as trays and gutters for possible leakage of oil. There would not be any oil flowing to the machinery space bilges.


  • Oil record book shall be kept 3 years from last entry date and
  • Garbage record book shall be kept 2 years from last entry date.

(a) Sketch a line diagram of pumping out bilges with marinfloc system which is used on board.

(b) Describe above including dosing, flocculation, filtration and control of discharge.


(b) Marinfloc Emulsion Breaker Bilge Water Cleaning System

  • Preheater- when feed pump is running bilge water passes the pre-heater (raises 50 ~ 60˚C) enters into oil de-scaler tank.
  • De-scaler tank- If free oil presents, flow from top of the tank to sludge tank.
  • Water flow from bottom of the tank into circulation tank by circulation pump (under 3 to 4 bars)
  • Circulation tank- At top of circulation tank, water sprays of sprinkle, feeding of compressed air effects to dissolve air into water.
  • Flocculation tank-The aerated water continuously discharged to the flocculation tank.
  • Between circulation tank and flocculation tank, flocculent chemicals injected by dosage pump, high amount of dissolved air fall out as micro bubbles in the tank due to pressure different
  • Flocculent chemical break the bonding formations in the emulsified water and collect pollutants such as oil into flocks.
  • Enrich with air, flocks float to the surface of the tank form the foam removed by drain pump to sludge tank.
  • PID regulator control water inlet valve of flocculation tank and rate of chemical dosage
  • Polishing tank- water from flocculation tank by running discharge pump to 3-filter steps, remove remaining flocks and discoloration
  • Sample water from outlet of filter steps flow through 15 PPM monitor
  • If less than 15 ppm, solenoid valve is opened and water pass through the 3-way valve to overboard.
  • If not, solenoid valve is opened and water return back to bilge water tank.
  • If system is stopped for more than 5 hours, 3 filter steps back-flushed for cleaning.
  • Pre-heater is maintained 65˚C for the back-flush water.

(a) State the regulation regarding the oily bilge disposal.

(b) Sketch Oily Water Separator.

(c) How to maintain to get optimum performance.


  • MARPOL 73/78 Annex (I) is international regulation for prevention of pollution by oil from ship.
  • According to this regulation it is prohibited oil, oily water or machinery space bilge water discharging except following conditions
  • Special Areas: for Annex: I. Mediterranean Sea, Baltic Sea, Black Sea, Red Sea, all gulf Areas and Antarctic Area


  • The sketch shown is combined system of oily water separator and filter.
  • For preliminary separation, consists of Turbulo type separator
  • Filtering unit for stopping dirt and coalescence
  • The plant enables degree of purity less than 15ppm of oil content at discharge.
  • Fit ODM unit, alarm control unit, automatic stopping device. Relief valve, manual drain valve, test cock for safety.
  • Heater is provided for good separation effect.

(c) To maintain OWS optimum performance, the followings should be done.

1. Every before operation teat alarm and control system as Saturday routine

2. Every after-operation O.W.S flushed with clean F.W.

3. Clean regularly ODM sensor and sample water glass tube

4. Clean or renew coalescer or filtering elements as per maker’s instruction.

5. Check any leakage and rectified at once.

6. While operation, Oil mixture temperature to be maintained about 55˚ for good separation.

7. Avoid the operation with following agents. It may impair the operation of equipment.

(i) Oil from compressor drains

(ii) Boiler washing agents

(iii) cooling water treatment, such as, anti-corrosive oil

(iv) Detergents for cleaning bilge.

(a) What are the international regulations regarding disposal of garbage into sea?

(b) What requirements to be provided onboard to solve the garbage disposal problem?

(c) How will you organize your E/R crew to control the disposal of garbage into sea?

(a) MARPOL Annex V sets regulatory requirements regarding the disposal of garbage from ships.

According to this Annex, shipboard generated garbage is grouped into following categories: (1) Plastic (2) Food wastes (3) Domestic wastes (4) Cooking oil (5) Incinerator ashes (6) Operational wastes (7) Cargo residues (8) Animal carcasses (9) Fishing gear

NM= Nautical miles from the nearest land (1) not harmful to marine environment
(a) Trade within special area (b) no reception facilities available

(b) To solve the garbage disposal problem, the following requirements are provided onboard

  • Every ship of overall length12 m or more display garbage disposal placards to notify the crew and passengers.
  • Placard written with both flag state language and English.
  • Every ship of 400 GT and above which is certified to carry (15) person or more, following equipment and accessories provided.

1. Comminuter or grinder

2. A screen with openings not greater than 25mm

3. Incinerator

4. Garbage compactor

5. Garbage bag

6. Collection Drum

7. Garbage management plan, state procedures for collecting, storing, processing and disposing of garbage

8. Garbage record book

(c) To control the garbage disposal into sea, Senior Engineer should organize the E/R crew as follows

(1) Give instructions to the E/R crew regarding garbage disposal regulations and to minimize garbage generated onboard.

(2) Ensure that they clearly understood the garbage’s placards and procedures of collecting, storing, processing, disposing of garbage and using of equipment fitted onboard.

(3) Place marked-containers in E/R workshop and other working spaces to keep segregated garbage. Do not dispose any garbage without C.E permission

(4) Incinerate sludge, waste oil and oily rags properly. Ashes keep onboard and dispose to shore reception facilities when available.

(5) Incineration of Oil residue recorded in Oil record book properly.

(6) Incineration or Landing ashore of garbage recorded in Garbage record book properly.