How Do You TREATMENT OF SLOPS AND OILY WATER On Ship

 TREATMENT OF SLOPS AND OILY WATER

  • Oil or oily mixtures, which cannot be discharged in compliance with, shall be retained on board or discharged to reception facilities or loaded on top (where permitted by the terms of the relevant contract of carriage of cargo),  
  • Decanting of separated water from slop tanks to sea, shall only take place provided all the conditions required by MARPOL Annex I are complied with.
  • The time required for oil and water to separate in the slop tanks depends on the motion of the vessel as well as on the type and density of previous cargo. Under favourable conditions a few hours may be sufficient, but generally 24 hours or more should be allowed. Discharge from the slop tanks must cease well before the interface is reached to avoid discharge of any oil in water emulsion overboard.
  • Before starting to decant the content of the slop tanks, an accurate interface and ullage reading, using an oil/water interface detector, shall be taken to determine the depth of the oil layer.
  • Although every effort should be made to remove as much water as possible from the slop tank, the prime objective shall be to prevent oily water reaching the sea. Extreme care is therefore necessary, and a close check shall be kept on the overboard discharge.
  • Agitation of the content of the slop tanks shall be kept to a minimum to avoid drawing oil into the suction when the oil/water interface approaches the top of the structural members in the tank bottom. Pumping rates shall be strictly controlled.

Decanting Slop Tanks

1) Slop lines to be used for decanting slop tanks shall be flushed as follows using the slop pump:

  • Open valves in the slop tank leveling line in order to avoid overflow of the slop tanks.
  • Operate pump at moderate rate with suction from slop tanks, to flush the slop main line (over the deck) into dedicated slop tank. 
  • Switch on the oil discharge control and monitoring system (ODMCS) in accordance with the Operating Instructions. Set ODMCS (diverting valves) in manual mode.
  • Continue pumping at moderate rate with suction from a slop tank, flush the overboard line into dedicated slop tank until the ODMCS shows acceptable oil content values for discharge overboard.
Read:  Waste And Sewage Water Disposal On Ship

2) Set ODMCS diverting valves in auto. Open the overboard valve and pump down the slop tanks using the appropriate pump at slow speed until water depth of about 20 percent of the tank depth is reached.

3) Stop the appropriate pump, then take an oil/water interface and ullage reading and recalculate the remaining water depth.

4) Resume pumping of the slop tanks very carefully until a pre-determined water depth is reached, which for the particular size and construction of the slop tank, is known not to give rise to discharge of oil. The pumping rate shall be slowed further as the predetermined water depth is approached.

5) Observe the trend of the ODMCS reading carefully.

6) If oil should appear before the predetermined water depth is reached, stop pumping.

7) Should this occur, further settling of the slop tanks contents should be allowed for as long as possible before repeating the steps given above.

8) Any decanting beyond this limit shall be carried out with extreme care and by strictly observing the ODMCS reading. When the trend of the monitor reading indicates that the interface is being entrained, the discharge shall be stopped immediately.


Final Line and Pump Flush

After decanting of the slop tanks has been completed, the lines and pump used will contain traces of oil. This line must therefore be thoroughly flushed from sea into the dedicated slop tank, or while the ship is still more than 50 nautical miles from the nearest land and outside a special area, thoroughly flushed from sea to sea ensuring that the permitted instantaneous rate of discharge of oil and the permitted total quantity of oil discharged are not exceeded.


Retention of Slops

  1. After decanting of the water content in the slop tank the oil residues may be retained in the slop tank or be transferred to a cargo tank for load on top, depending upon the compatibility with the next cargo. If preferred or required the remaining slop shall be discharged to a reception facility.
  2. If slop is to be retained on board, the slop tanks shall be inerted (oxygen content 8% or less by volume) with a positive tank pressure of at least 100 mm Wg. All purge pipe covers and P/V valves are to be properly closed and secured.
  3. Retention of slops may be subject to local Port State regulations, when carrying dry bulk cargoes on OBOs.
Read: PRODUCED WATER/ OILY WATER TREATMENT & DISPOSAL


Engine Room Bilge Water

  1. Bilge water from the engine room shall be separated / filtered through the oily water separator or filtering equipment, ensuring an oil content of 15 PPM or less, prior to discharge overboard.
  2. Oil residues shall be transferred to the sludge tank(s) for later on board incineration or transfer to reception facilities. 
  3. Oily water separator equipment shall be operated in accordance with the Maker's instructions.


Precautions related treatment of Slops and Oily Water

  1. When retaining slops on board regular inspections shall be made to detect any leakages from the slop tank(s).
  2. Vessel's fixed gas detection system shall be fully operational and continuously in service.
  3. Inert gas pressure and O2 content in the inerted tanks shall be monitored continuously.  Prior to discharge of oily water to sea an oil/water interface detector shall be used to determine the depth of the oil layer.
  4. Any discharge of slops, oily water or dirty ballast shall be monitored by a recently calibrated oil discharge monitor, with the alarm reading properly set for the correct value.
  5. The oil discharge control and monitoring system readings shall be observed throughout the operation.
  6. Where applicable, prior to intake of ballast water in the cargo tanks the Chief Officer shall ensure through inspections, that the dedicated clean ballast tanks, pumps and piping system are clean and gas-free as required.


Documentation, Filing and Verification

  • Positions and times for commencement and completion of discharge shall be entered in the deck and engine log book as appropriate.
  • No separate filing is required is requires by this procedure. 
  • Verification of this procedure shall be done during Master’s Review, Internal and External Audits 

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